Doping and charge transport processes in organic and hybrid materials for energy applications

Resume : Experimentally, we observe that the electrical conductivity of a large number of organic semiconductors shows a maximum: The conductivity decreases at high doping levels. This behaviour is commonly attributed to changes in the microstructure as a consequence of doping. However, experimentally we find that even when using vapour doping, where there are no observable changes in the microstructure, this behaviour persists. A more thorough understanding of this maximum in conductivity could help unlock a class of materials with conductivities higher than currently possible. In this contribution, we use a kinetic Monte-Carlo model to study the transport properties in the presence of dopants and including both carrier-carrier and carrier-dopant interactions. In particular, we can simulate up to the relatively high doping densities that are experimentally relevant even though numerically challenging. We find that the density of states (DOS) of such systems shows a pseudo-gap at the Fermi level due to Coulomb interactions between the charge carriers. Such Coulomb gaps are a manifestation of the carrier-carrier interactions and have been predicted to exist in hopping systems, but are usually washed out at anything other than very low temperatures. This has profound implications for electrical conductivity as the pseudo-gap limits charge carrier transport at high doping densities.

Resume : This study focuses on the doping mechanism in highly oriented sequentially doped thin films of regioregular poly(3-hexylthiophene) (P3HT). Rubbing P3HT at temperatures in the 150-200°C range imparts high crystallinity (> 50%) and in-plane alignment (dichroic ratio > 15) to the films.[1] They can be doped with F4TCNQ, F6TCNNQ, FeCl3, Mo(tdf-COCF3)3 in orthogonal solvents while preserving in-plane orientation. The films become highly conducting and display enhanced transport and thermoelectric (TE) properties along the chain direction. [2] To what extent does the doping method/dopant geometry/electron affinity affect the structure of P3HT and the resulting TE film properties? In this study, we used TEM and Polarized UV-Vis-NIR spectroscopy to evidence the ordering of dopant molecules. Different intercalation mechanisms are highlighted for the four dopants. Doping with F4TCNQ results in a re-organization of polymer chains in individual ?-stacks in the smectic-like phase of P3HT and a disordering of successive ?-stacks in the semi-crystalline phase. Surprisingly, the larger F6TCNNQ molecules intercalate in a more ordered fashion than F4TCNQ. FeCl3 and Mo(tdf-COCF3)3 dope both crystalline and amorphous phases leading to large conductivities beyond 400 S/cm parallel to rubbing. Large power factors up to 0.125 mW.K-1.m-2 are observed for films doped with Mo(tdf-COCF3)3. [1] A. Hamidi-Sakr et al. Adv. Funct. Mater. 1700173 (2017) [2] V. Untilova et al. Macromolecules, submitted (2020).

Resume : Semiconducting organic materials have attracted increasing interest as thermoelectric (TE) converters in the recent years due to their potentially low fabrication costs and non-toxicity. One tool to control the performance of such organic TEs is the introduction of structural anisotropy via control of the molecular orientation of the polymer backbones. Such highly oriented conducting polymer films can show considerable increases in the electrical conductivity along the direction of orientation, while the influence on the Seebeck coefficient is less clear. Here, we use kinetic Monte Carlo (MC) simulations to study the impact of anisotropy on the thermoelectric properties of disordered organic semiconductors. We find that variable-range hopping (VRH) can consistently describe charge and energy transport in both the parallel and the perpendicular direction, which contrasts with the interpretation drawn from experiments on ordered PBTTT [1]. Furthermore, we clarify why some materials show a simultaneous enhancement in conductivity and thermopower in the direction of orientation, while for others the Seebeck coefficient remains largely unaffected. By analyzing the effect of the parameters affecting the length scales and the structural order of the system we demonstrate under which conditions structural anisotropy is a suitable strategy to enhance the conductivity and thermopower simultaneously. [1] Vijayakumar, V.; Zhong, Y.; Untilova, V.; Bahri, M.; Herrmann, L.; Biniek, L.; Leclerc, N.; Brinkmann, M. Bringing Conducting Polymers to High Order: Toward Conductivities beyond 105 S cm?1 and Thermoelectric Power Factors of 2 mW m?1 K?2. Adv. Energy Mater. 2019, 9, 1900266.

Resume : Charge transport in semiconductors is a crucial process that defines efficiency for optoelectronic devices such as solar cells and light-emitting diodes. Semiconducting organic–inorganic metal halide perovskites (PVSK) have recently been the focus of intense research, motivated largely by the rapid rise in efficiency of next-generation solar cells based on these materials. However, understanding the physical processes which govern charge transport within PVSK materials and ultimately the device performance is still on an relatively early stage of development. One problem, many groups are facing is the rather poor reproducibility of cell fabrication. To get deeper insight, we introduce a novel experimental technique derived from photo-EMF induced by running grating (RG) technique to study the photophysical properties of PVSK materials. This initial experimental investigation of RG photo-EMF was performed in at 633 nm wavelength. We confirm that MAPbI3 can be described as bipolar photoconductor with extremely short dielectric relaxation times flowed by slow processes in photoconductivity relaxation for both types of carriers. The RG Technique allows to determine a number of crucial material parameters such as the electron and hole photoconductivity relaxation time, the ambipolar diffusion length, and the minority carriers drift mobility. We have determined these parameters for a series of samples with different processing conditions – allowing us to draw crucial structure-property relations. Thus, the general features of the photoconductivity mechanism in PVSK semiconductors will be discussed.

Resume : The charge-transfer (CT) states that form at the interface between the electron-donor (D) and electron-acceptor (A) materials have a crucial role in exciton-dissociation, charge- separation and charge-recombination processes in organic electronic devices. Here, we will assess the current understanding of CT states and describe how factors such as the geometry of the D-A interface, electronic polarization, disorder and the extent of electron delocalization influence the radiative and non-radiative decay processes. We will first outline the theoretical and experimental approaches that are used to characterize these states. New features of the CT states, which emerge from the recent development of organic solar cells based on non-fullerene acceptors and development of organic light emitting diodes based on neutral-radical emitters will be then discussed.

Resume : Recent years have seen a considerable development in the field of organic solar cells with efficiencies exceeding 16%. The charge transport in the active layer is generally understood to occur by a hopping mechanism for which many models have been proposed. From an application perspective, the extended Gaussian disorder model (eGDM) [1], which assumes nearest neighbor hopping (nnH) in a Gaussian density of states, has by far been most successful, and typically works well for p-type materials. We find it gives an inconsistent description for typical electron-only devices, significantly underestimating disorder. Here we propose a more physical analytical variable range hopping (VRH) model which allows a consistent extraction of the hopping parameters from quasi steady state experiments, in particular T-dependent SCLC. The model has been calibrated by direct comparison to kinetic Monte Carlo simulations. It is tested for various material combinations, ranging from the highly studied TQ1: PCBM system (PCE ? 6%) to high-performance non-fullerene binary and ternary systems such as PM6:Y6 (PCE ? 16%). While for some materials a nnH model can still be applied, the major advantage of our model is that it provides a consistent description of all investigated material systems and can predict if nnH could be used alternatively. We inferred that the main difference between p- and n-type transport lies in the significantly larger localization radius of the latter, while all other parameters (disorder, attempt rates etc.) being comparable for holes and electrons. We also find a critical ratio of aNN/? (mean intersite distance:localization radius) of about three, below which hopping to non-nearest neighbors becomes important around room temperature and the eGDM cannot be used for parameter extraction. Typical (Gaussian) disorder values in the range 45?120 meV are found, without any clear correlation with photovoltaic performance, when the same active layer is used in an organic solar cell. Reference 1) Pasveer, W. F.; Cottaar, J.; Tanase, C.; Coehoorn, R.; Bobbert, P. A.; Blom, P. W. M.; de Leeuw, D. M.; and Michels, M. A. J. Unified Description of Charge-Carrier Mobilities in Disordered Semiconducting Polymers. Phys. Rev. Lett. 2005, 94, 206601. 2) Melianas, A.; Etzold, F.; Savenije, T. J.; Laquai, F.; Inganas, O.; & Kemerink, M. Photo-generated carriers lose energy during extraction from polymer-fullerene solar cells. Nat. Commun. 2015 6:8778.

Resume : Metal halide perovskites are remarkable thin film semiconductors with numerous favorable properties that are optimal for photovoltaic and light emission applications[1]. These characteristics include high absorption coefficients, long charge carrier lifetimes and a tunable bandgap. We have previously shown that the luminescence efficiency and charge carrier recombination behavior in mixed halide perovskites is significantly altered by the cation alloy employed during fabrication via facile solution processing[2]. The addition of alkali metal cations provides passivation of sub-bandgap defect states and also stabilizes an energetic landscape that facilitates photodoped carrier accumulation, leading to enhanced optoelectronic performance. Our current work aims to further unveil the influence of microscopic compositional variations on local photoinduced carrier accumulation in (CsMAFA)PbIxBr3-x perovskite films. We combine Femtosecond Transient Absorption Microscopy with nanoscale X-ray Fluorescence and Atomic Force Microscopy to track carrier diffusion and recombination across a heterogenous chemical and morphological landscape. We find that the complex interplay of local carrier recombination and diffusion will have important ramifications for solar cell and LED device performance. [1] Stranks, S. D. & Snaith, H. Nature Nanotech 10, 391-402 (2015) [2] Feldmann, S., Macpherson S. et al. Nat Photonics (2019) doi:10.1038/s41566-019-0546-8

Resume : It was aimed to study the photocatalytic activity of polyaniline (Pani)/iron doped titanium dioxide (Fe-TiO2) composites for the degradation of methylene blue under UV light irradiation. For this purpose, TiO2 nanoparticles were doped with iron ions (Fe) and the doped photocatalyst nanoparticles were introduced into Pani by using an in situ polymerization technique. Pani composites, including 10, 20 and 30 wt.% Fe-TiO2 and undoped TiO2, were prepared via this technique. FTIR, XRD, SEM, EDX and UV?Vis spectroscopies were utilized to characterize the photocatalyst and the composites. According to SEM images, both Fe-TiO2 and TiO2 nanoparticles in aggregated form were distributed homogeneously within Pani matrix. UV-Vis spectroscopy revealed that the band gap of TiO2 widened to 3.18 eV with iron doping and Pani extended the absorption of TiO2 nanoparticles to the visible light region. When compared with undoped TiO2 and its composites, Fe-TiO2 and Pani/Fe-TiO2 exhibited improved photocatalytic activity under UVC light irradiation. Doping the photocatalyst with iron ions might improve the photocatalytic activity through hindering the recombination of the photoinduced charge carriers on TiO2 nanoparticles. The highest dye removal value (28%) was obtained with Pani composite, containing 30 wt.% Fe-TiO2 nanoparticles. In addition, the discoloration rate of the model dye, methylene blue, for the composite sample was 0.0025 min-1.

Resume : Electrochemical supercapacitive properties of polyaniline (PANI)/cobalt hydroxide (Co(OH)2)-nickel hydroxide (Ni(OH)2) nanocomposite (NC) electrode materials, synthesized potentiostatically via an electrochemical deposition method, are explored and compared with PANI and Co(OH)2-Ni(OH)2 electrode materials. From the surface analysis, an amorphous PANI, NCs and Co(OH)2-Ni(OH)2 are entirely different from one another. The PANI surface demonstrates nanofibrous morphology, NCs exhibits nanofiber-platelet morphology and Co(OH)2-Ni(OH)2 endows platelet-type surface morphology. The electrochemical properties of the PANI, NCs and Co(OH)2-Ni(OH)2 electrode materials are obtained from the cyclic-voltammetry and galvanostatic charge-discharge measurements. The specific capacitances of PANI, NCs and Co(OH)2-Ni(OH)2 measured at a sweep rate of 10 mV/s in a 1.0 M NaOH electrolyte are found to be 0.59, 50.0-74.1 and 312.5 F/g, respectively. The retention values of PANI, NCs and Co(OH)2-Ni(OH)2 obtained at the same scan rate for 1000 cycles are 25.8, 70.5?57 and 42.4%, respectively. This work clearly illustrates the reasons for a weak electrochemical performance of PANI and its composites with Co(OH)2?Ni(OH)2 in alkaline electrolyte over Co(OH)2-Ni(OH)2 electrode material. Keywords: Electrochemical supercapacitor; Electrochemical deposition; Polyaniline; Nanofibers; Nanoplatelets; Nanocomposites ?Corresponding authors at: Guangdong Technion-Israel Institute of Technology, Shantou, Guangdong Province, China (V.V. Jadhav). E-mail addresses: vijaykumar.jadhav@gtiit.edu.cn (V.V. Jadhav)

Resume : Metal?organic frameworks (MOFs) are promising porous precursors for the construction of various functional materials for high-performance electrochemical energy storage and conversion. Herein we report several facile methods to rational design of novel nanoarrays on flexible carbon cloth substrate. One example is hollow NiCo2O4 nanoarrays obtained from a two-dimensional (2D) cobalt-based MOF, which is synthesized via a solution reaction with an additional annealing treatment. The as-obtained NiCo2O4 nanostructure arrays can provide rich reaction sites and short ion diffusion path. When evaluated as a flexible electrode material for supercapacitor, the as-fabricated NiCo2O4 nanowall electrode shows remarkable electrochemical performance with excellent rate capability and long cycle life. In addition, the hollow NiCo2O4 nanowall electrode exhibits promising electrocatalytic activity for oxygen evolution reaction (OER). Another example is hollow Co3O4 nanospheres embedded in nitrogen-doped carbon nanowall arrays on flexible carbon cloth (NC-Co3O4/CC). The hierarchical structure is facilely derived from a metal-organic framework (MOF) precursor. A carbon onion coating constrains the Kirkendall effect to promote the conversion of the Co nanoparticles into irregular hollow oxide nanospheres with a fine scale nanograin structure, which enables promising catalytic properties toward both OER and ORR. The integrated NC-Co3O4/CC can be used as an additive-free air-cathode for flexible all-solid-state zinc-air batteries, which presents high open circuit potential (1.44 V), high capacity (387.2 mAh g-1, based on the total mass of Zn and catalysts), excellent cycling stability and mechanical flexibility, significantly outperforming Pt and Ir-based zinc-air batteries. Our work provides good examples of rational design of hollow nanostructured arrays with high electrochemical performance and mechanical flexibility, holding great potential for future flexible multi-functional electronic devices.

Resume : A cobalt-phosphate (Co-Pi) catalyst having octahedral CoO6 molecular units as reaction sites is a key component in photoelectrochemical (PEC) water oxidation systems, but its limited adsorption sites for oxygen-evolving intermediates (*OH, *OOH), slow charge transfer rates, and fast degradation of reaction sites are yet to be overcome. Here, we report that Co-Pi nanoparticle with low-coordinated Co ions and doped nitrogen atoms could be decorated on hematite nanorod arrays to form N-CoPi/Hematite composites. Moreover, the local atomic configuration and bond distance studies show that trivalent Co3+ states are partially reduced through nitrogen radicals in the plasma to low-coordinated bivalent Co2+ states playing as the facile adsorption sites of oxygen-evolving intermediates due to the decreased activation barrier for water oxidation. Electron transport is also reinforced by nitrogen species due to the formation of hybridizing N 2p orbitals that give the acceptor levels in the bandgap. As a result, both the incident photon-to-electron conversion efficiency and also the charge transfer resistance on N-CoPi/Hematite outperform those on a bare hematite by about three folds. Furthermore, N-CoPi/hematite gives high activity retention over 90% after the long operation of water oxidation, supporting that the reaction sites on N-CoPi do not degrade during the successive water oxidation.

Resume : We have proposed new catalyst that satisfies not only catalytic activity and price but also stability of the catalyst that can be adapted in an extreme environment for the production of high purity hydrogen through water-splitting reaction. To meet all three considerations, we prepared the catalyst through a simple pyrolysis process after the newly introduced soaking method using porous metal-organic framework (MOF). The nanoparticles of tetragonal zirconia (t-ZrO2) are formed from MOF having a homogeneous structure, while oxygen vacancy help form metal nanoparticles and Metal single atoms (Me1) during the pyrolysis process. It was confirmed that Me1-ZrO2/C catalyst was very stable due to electronic metal-support interaction (EMSI) between the bottom layer of metal and the top surface of ZrO2 even after HPS and ADT experiments. Above all, Me1-ZrO2/C catalyst will contribute to commercialization because it has catalytic activity per unit mass which is about four times higher than the previously reported papers and commercial catalysts.

Resume : The problem of efficiently obtaining of hydrogen through photocatalytic water splitting is one of the most promising areas of renewable energy. Semiconductor TiO2 with photocatalytic activity in the ultraviolet region only is one of the most common materials for this process. For efficient light utilization, the fabrication of g-C3N4/TiO2 composite material has attracted much attention. However, both pristine g-C3N4 and g-C3N4/TiO2 composite exhibits photoactivity in blue region of visible spectrum only. It is found that the doping of carbon nitride by oxygen significantly improves its photocatalytic properties. Therefore, to improve the photocatalytic activity of semiconductor photocatalyst, the coupling O-doped g-C3N4 (O-g-C3N4) with anatase TiO2 is a good strategy. New composite material O-g-C3N4/TiO2 was synthesized by gas phase method under the special reactionary conditions of the pyrolysis of melamine. Deposition of O-g-C3N4 (~5% O) on the anatase nanopowder particles is confirmed by XRD, IR, XPS, SEM methods. It is found by UV-Vis-DRS method, that O-g-C3N4/TiO2 photosensitivity is observed in the significant part of the visible light region and the band gaps of product is determined to be less than 2.38 eV. Constructing heterojunction structures of TiO2 and O-g-C3N4 may be used as a cost-effective way to avoid the drawbacks of each component and realize a synergic effect for boosting the photocatalytic activity for hydrogen evolution.

Resume : Improving devices incorporating solution-processed halide perovskite nanocrystals demands a better understanding of charge transport in this emerging new class of semiconductor nanomaterials. Here we perform a systematic study on CsPbBr3 nanocrystal-based field effect transistors to develop a model for charge transport that is applicable to versatile device architectures. Using temperature and electric-field dependent transient response characterizations we demonstrate electronic current is the dominant current passing through the NC films under dark condition. Unlike a galvanostatic polarization condition in perovskite bulk films, the electronic current is found to be significantly augmented when the ion migration is gradually awakened at T > 240 K, underpinning a mobile-ion-induced doping modification mechanism. At T < 240 K the electronic transport can be readily decoupled from the ionic transport in CsPbBr3 NCs, leading to a clean unipolar transport characteristic in a p-type mode featuring well-defined linear and saturation regime. We use the physical insights from our model to elucidate the heterovalent impurity doping effect on the charge transport in halide perovskite NCs.

Resume : For spatial-limited applications such as portable electronics and wearable electronics, energy storage platforms require high power densities, high level of efficiency, lightness and flexibility. In terms of manufacturing and safety for flexible energy storages, solid-state materials as both separator and electrolyte are preferred instead of use of liquid electrolytes. Gel polymer electrolytes (GPEs) can act as both separator and electrolytes without the leakage of liquid electrolytes. However, there are challenges associated with the wettability at the electrolyte/electrode interface and the ionic conductivity of the polymer-based electrolytes. Here, good interface formation between electrodes and GPE is significant for high-performance energy storages. We prepare GPEs consisting of ethylene glycol-containing acrylate monomers (PEGMA and ETPTA) with a lithium salt solution by UV irradiation. Ionic conductivity and mechanical strength are changed by varying the composition of PEGMA and ETPTA as well as the content of lithium salt solution in the polymer. The GPEs with highly ion conductivity is impregnated into carbon nanomaterials-based electrodes which can enhance electrolyte-accessible surface area of electrodes. The GPEs with large mechanical stability can be used as both separator and electrolyte, providing flexible solid-state energy storage devices. This strategy holds significant promise as a platform to design high-performance carbon nanomaterial-based electrodes for energy storages.

Resume : To respond with the increasing need for high power and energy, required for the promising next-generation applications ranging from portable electronics and transportations, there are the rapid advances in the field of microporous carbon materials as high performance electrodes for energy storage. Herein, hierarchy-structured porous carbon with both considerable surface area and high electrical conductivity is set by the solution casting of intrinsically microporous precursor (polymer of intrinsic microporosity, PIM-1), that made of non-solvent induced phase separation (NIPs) process and subsequent carbonization, for use in supercapacitor electrodes. PIM-1 is a polymer with a large fractional free-volume with a high intrinsic surface area (~2100 m2 g-1). Hierarchical nanostructured porous electrodes show high electrical conductivity (~150 S cm-1), high specific capacitances in three- or two-electrode systems, and an outstanding specific energy. The PIM-1 that has interconnection in three dimensions and ordered pore channel is important for increasing supercapacitors performance. The important attributes of the hierarchy porous structure are its ability to improve overall reaction kinetics through pathways that was provided for efficient ion and electron transportation and facilitate electrolyte infiltration into the electrode while supercapacitor is charged/discharged.

Resume : The barrier in the development of energetic material is the material design and performance improvement based on it. Currently, creative design and preparation of novel nitrogen-rich compounds are significant for new generation of green energetic materials. At the present work, organic heterocyclic hybrid pyrazol-triazole was constructed, synthesized and applied as building blocks in the development of versatile thermally stable high-energy materials. All derivatives were fully characterized by vibrational infraredspectroscopy (IR), multinuclear NMR (1H, 13C)spectroscopy, elemental analysis, differential scanning calorimetry (DSC), impact and friction-sensitivity test. Additionally, the structures of4-8 and 10-13 were further confirmed by single-crystal X-ray diffraction and their crystal packing characteristics were thoroughlyanalyzed. Compound 2 not only enchanced physical properties of its ionic derivatives obviously, but also showed good detonation performance(D: 9075 m s-1) exceeding that of RDX, excellent insensitivity(IS>80J, FS>360N) comparable to that of TATB and superior thermal stability(331oC) to that of HNS. Meanwhile, we developed its salts and other derivatives as green energetic material alternatives based on this novel nitrogen-rich framework. Its ionic salts (compounds 4-14) also exhibit reasonable properties, such as good experimental densities (1.75 g cm-3-2.10 g cm-3), high thermal stability(174oC-289oC), good safety properties, excellent detionation performance (Dv: 7745 m s-1-8952 m s-1, P: 23.8 GPa-30.6 GPa), suggesting this new pyrazol-triazole hybrid is beneficial for improving their physical performance. According to the theoretical analysis of Hirshfeld surface and fingerprint plots, this phenomennon can be explained by their intensive N?O???H and N?H???N hydrogen-bond interactions. Worth noting that with assembly of heterocyclic anions into this new cation, these salts also exhibited impactful ?-? interactions in their molecular crystals, such as compound 10 presenting very promising performance for considerable candidate for RDX. Compound 14 also indicated its potential as a secondary explosive,which presented superior physical performance to those of RDX. This design and synthetic strategies broaden our knowledge of ionic energetic materials, which can effectively elongate the scope to study structure-property relationships of next-generation green energetic materials. Overally, this work is helpful for accelerating the discovery of insensitive, thermostable and high-energy green organic and hybrid materials in energy applications.

Resume : Organic-inorganic hybrid perovskites (OHP), described by ABX3 (A = organic cation, B = metal cation, X = halogen anion) has attracted much attention as a candidate material for future solar-cell applications with easy-fabrication, low-cost, and high-efficiency. The materials are some of the best candidate materials for solar-cell applications. It looks like it is now going towards optimization. However, we still have many unclear physical properties of OHP materials such as thermoelectric and THz absorption properties. Studies of these are just beginning and require more experiments and theoretical calculations. In this study, we fabricated formamidinium lead iodide thin films on a flexible substrate using the SVE method and then confirmed its THz-wave absorption property. The formed FAPbI3 using SVE showed the typical ?-phase. After annealing for 10 min, we confirmed a mixed state with ?- and ?-phases and observed THz-wave absorption at 1.62 THz with 40% absorptance. In the C 1s core-level spectra, we found two different chemical states originated from ?- and ?- formamidinium lead iodide. The origin of the THz-wave absorption property is assumed from a significant Pb?I vibration mode from the mixed phases in FAPbI3.

Resume : Triboelectric nanogenerators are those devices that can convert mechanical energy into electrical energy using the triboelectric effect [1?3]. The main structure of the device includes two metal coated polymeric materials. Although solid-solid triboelectric nanogenerators are robust in design, cost effective, and efficient devices to generate electricity, there is a problem of wear and tear after specific cycles of operation [4]. Recently it is discovered that water can replace one of the material and can generate electricity using a single material. As water covers 1/3 of the total area of the earth, it will be an excellent approach to generate electricity from it. In the present work we have fabricated ZnO-PVDF nanocomposite film based liquid-solid interface triboelectric nanogenerator (LSTENG), which can generate electricity from water. The ZnO-PVDF based LSTENG showed much enhanced output voltage and current as compared to pristine PVDF based LSTENG. The main contribution in the enhanced output power comes from the increased in hydrophobicity, polarizability and surface roughness of ZnO-PVDF nanocomposite film. We have also studied the effect of ions present in the water to check the feasibility of these devices to be used in ocean waters. The present work will give a novel strategy to generate electricity from rain water as well as from ocean water. References 1. Wang, Z. L. & Wang, A. C. (2019). On the origin of contact-electrification. Mater. Today, 30, 34?51. 2. H. Guo et al. (2017). Self-Sterilized Flexible Single-Electrode Triboelectric Nanogenerator for Energy Harvesting and Dynamic Force Sensing. ACS Nano, 11, 856?864. 3. Wang, J. et al. (2017). Achieving ultrahigh triboelectric charge density for efficient energy harvesting. Nat. Commun., 8, 88. 4. Singh, H. H. & Khare, N. (2018) Flexible ZnO-PVDF / PTFE based piezo-tribo hybrid nanogenerator. Nano Energy 51, 216?222.

Resume : The piezopotential generated in non-centrosymmetric crystals under external mechanical stimuli can be exploited to modulate the contact characteristics at the metal-semiconductor interface. The extent of electric modulation by the piezopotential was found to be moderate. This is mainly because the piezopotential was designed to alter the band bend of the semiconductor layer, which changed the injection barrier by 0.1 eV. We propose an efficient method to utilize the piezopotential for modulating Schottky barrier, i.e. piezotronic graphene barristor. This was done by capacitively coupling the piezoelectric material with a Schottky barrier (SB)- tunable graphene electrode, using an ion gel electrolyte. Through capacitive coupling, the piezopotential could modulate the work function of a graphene electrode by 0.89 eV. This was visualized directly using Kelvin probe force microscopy experiments for the first time. A large change in the work function of graphene allowed effective tuning of the height of the SB formed at the graphene/semiconductor junction. Consequently, a piezoelectric nanogenerator (PENG) could change the current density of the semiconductor layer by more than three orders of magnitude with strain, and yield a high current density larger than 10.5 A cm-2. Multistage modulation of the height of the SB at the junction was also successfully demonstrated by integrating two PENGs with ion gel. This work presents an efficient method for harnessing the piezopotential generated from PENG to actively control the operation of flexible electronics through external mechanical stimuli.

Resume : Rechargeable lithium-ion batteries (LIBs) are promising power sources that are currently used in many portable electronic devices and electric vehicles due to their high energy density, high operating voltage, low self-discharge, long cycle-life, and low toxicity. One of the interesting and promising polymers for preparation of solid polymer electrolytes (SPEs) is poly(dimethylsiloxane) (PDMS) which has a very low Tg of 125 oC, high flexibility of the polymer chains and large free volume. Here, we prepared series of PDMS based UV-crosslinked flexible polymer films as SPEs. Lithium bis(trifluoromethane)sulfonamide (LiTFSI) was used as Li salt and trimethilolpropane ethoxylate triacrylate (ETPTA) as a crosslinking monomer. Hydroxy terminated PDMS is chosen in order to prepare UV-crosslinked flexible polymer electrolyte with lithium salt. First, PDMS was acrylated with acryloyl chloride. Further crosslinkable polymer blend was prepared with a different ratio of polymer and lithium salt varying mass ratio of EO/Li as 6, 18, 32. Lithium bis(trifluoromethane)sulfonamide (LiTFSI) was used as Li salt. After, polymer blend with photoinitiator casted onto glass plate and exposed to UV-crosslinking for 3 min. Obtained films were dried under vacuum at 60 ? during 18 h, leading to the formation of flexible solid polymer electrolyte. All performed procedure was conducted in the argon-filled glove box. Flexible and transparent SPEs were prepared by UV-curing technique. FTIR spectroscopies were used to confirm the structure of polymer films. The mechanical and thermal properties of obtained SPEs were studied by TGA, DSC and stress-strain analysis. According to TGA results main degradation of polymer electrolytes starts from about 330 oC. Obtained transparent SPEs have excellent mechanical properties and good flexibility. Coin cells were assembled with blocking electrodes using prepared SPEs and exhibited electrochemical stability above 4.8 V (vs. Li/Li ). The ionic conductivities were determined by electrochemical impedance spectroscopy (EIS) analysis. The impedance measurements were carried out with frequency ranges from 10 Hz to 1 MHz from room temperature to 90 oC with a temperature interval of 5 oC. The most suitable percentage of PDMS in the whole polymer was 10%, ETPTTA ? 20% and PEGDA ? 70%. Acknowledgements This research was supported by the targeted state program BR05236524 ?Innovative Materials and Systems for Energy Conversion and Storage? from the Ministry of Education and Science of the Republic of Kazakhstan for 2018-2020.

Resume : With a three-electron redox-mechanism-based high capacity, Al-ion-based electrochemical battery capacitor systems are expected to provide high capacity, low cost and high safety to meet the increasing energy demands. However, the reversible insertion of Al3+ into electrode materials remains a difficult project. Here, we demonstrate a new strategy to achieve reversible Al3+ insertion in a classical conductive polymeric material namely PEDOT:PSS, in aluminum sulfate aqueous electrolyte system. The freestanding composite film with a hierarchical porous structure is prepared through vacuum-assisted curing of a mixed dispersion containing PEDOT:PSS on carbon cloth substrate. The as-prepared PEDOT: PSS composite electrode exhibits extremely high capacitances of 265 F/g at the current density of 0.2 A/g, and enhanced electrochemical stability in the aqueous Al ions electrolyte. The PEDOT:PSS electrode sustains more diffusion of Al ions with more electric quantity in the Al3+ electrolyte, compared to in traditional acid electrolyte. It also exhibits a lower charge transfer resistance in the aluminum ion electrolyte, rather than in other cations electrolyte, which helps reduce the polarization at the electrode/electrolyte interface and improved the aluminum ion migration. Furthermore, the PEDOT: PSS electrode and an activated carbon anode are assembled as aqueous rechargeable Al ion electrochemical supercapacitor. The discharge capacity of this system exhibits to be 51 mAh/g at the current density of 100 mA/g and displays a high energy density of 43.2 Wh/Kg at the power density of 265 W/Kg, demonstrating a promising aqueous energy storage device with high performance and low cost.

Resume : Galvanic replacement (GR) reactions have emerged as a versatile tool in the creation of hybrid materials. Traditionally, a GR reaction involves exchange of metal cations which occur due to the favorable difference in the electrochemical potentials of the two metals involved. Recent works have shown the importance of such processes even in oxide systems where a cation exchange takes place at the organic/aqueous interface. The interface allows stabilization of the oxidation state of the outgoing metal ion as well as the incoming metal during the GR process. However, a GR reaction involving an exchange of two anions has not been achieved. We, for the first time, demonstrate the GR of TCNQ anion in CuTCNQ with TCNQF4 anion in acetonitrile (MeCN). The more positive reversible formal potential of TCNQF4(0/-1) than TCNQ(0/1-) in acetonitrile provides a strong driving force and a thermodynamically favorable condition to achieve anion exchange. Detailed electrochemical studies show that the electron transfer from TCNQ(-) formed as a result of CuTCNQ dissolution in MeCN to TCNQF4(0) occurs even in the absence of the Cu metal thus confirming that the reaction indeed involves the GR of anions. The Cu metal only facilitates the formation of the CuTCNQ/CuTCNQF4 hybrid. The rich optical property of CuTCNQ, which is well-known, is further enhanced due to the formation of a hybrid and results in a significant enhancement of redox catalytic reactions under light illumination.

Resume : Mixed halide perovskites (CH3NH3PbIxBr3-x) are of great interested in optoelectronic devices because they offer many advantages such as tunable bandgap, high electron/hole mobility, high absorption coefficient, and low-cost solution processing. However, solution processed perovskite (PS) film contains many charge traps at the grain boundaries and on the surface, leading to increased non-radiative recombination, and instability of the PS film in air due to humidity. Surface passivation is a common solution for minimizing charge traps and protecting the surface from the moisture in air. Therefore, in this study, CdSe/ZnS core-shell quantum dots (QDs) have been employed to improve the optical properties of PS. We investigated the luminescence properties of surface-passivated mixed halide perovskite (CH3NH3PbI2Br) using photoluminescence (PL) and time-resolved PL spectroscopy. The integrated PL intensity and PL decay time of the QD/PS hybrid structure increased compared to those of the bare PS films, owing to energy transfer (ET) from the CdSe/ZnS QDs to the PS and reduced charge traps. The ET efficiency increased from ~7 to 63% for the QD/PS hybrid structure when the core diameter of the QDs decreased from 6.5 to 2.7 nm, respectively, which can be explained by the enhancement in the charge transfer rate due to the control of energy level alignment of QDs. These results allow us to understand the fundamental mechanisms such as ET process from QDs to PS as a function of core diameter of the QDs.

Resume : Drastic industrialization and increasing use of fossil fuels caused tremendous climate change by increasing atmospheric carbon dioxide concentration. So development of photocatalyst for reducing carbon dioxide to useful fuel with high efficiency and stability is great issue. In natural photosynthesis, leaf shows significant efficiency and stability by combination of three dimensional structure and Z-scheme catalytic system. In this study, we present artificial photosynthesis for carbon dioxide reduction by 3-dimensional bismuth vanadate/carbon coated copper oxide nanowire array. Three dimensional structure of copper oxide nanowire mesh enhanced adsorption, mass transportation. And Z-schematic electron flow between bismuth vanadate and copper oxide enhanced charge separation and transport with high redox potential. And also mediation by ultrathin carbon layer enhances charge transport between two catalysts and enhances stability by protecting copper oxide. The optimized sample achieved ~3micomole/gram/hour CO formation rate in visible light irradiation that is 7times higher than bare copper oxide. And also shows methane production that is higher hydrocarbon. We present characterization with SEM, TEM, XRD, FT-IR, PL intensity and so on. This work provides ideal artificial photosynthesis system for carbon dioxide reduction with high conversion rate and stability that can be developed as practical catalyst for sustainable fuel synthesis and solution of environmental problem.

Resume : Porphyrins as a new class of hole transporter represent a promising alternative for perovskite solar cells since the initial study in 2016. Currently, the best perovskite device using this new paradigm of hole-transporter has approached 20 % power conversion efficiency (PCE). In this poster, we present a series of Prophyrin-based molecules designed and optimized as hole transporting materials (HTMs) for perovskite solar cells.The rational design concepts and structural effect on their photovoltaic performance are investigated. We find that the electronic communication between molecules significantly influences the carrier transporting behavior and their PV characteristics. Structural modification by using dimeric porphyrin core unit yields brand new efficient porphyrin HTM (WT3) which improves device efficiency up to 19.44%. The red-shift and broaden absorption spectra of spin-coated solid film is a highly relevant indicator for the molecule coupling and thus corresponds well to the device performances. Apart from the excellent power conversion efficiency, the porphyrin-based HTMs also demonstrated good stability and moisture resistance with appropriate design. Recently, we have realized a dopant-free porphyrin-based HTMs yielding respectable PCE (~15%).

Resume : Carbon Quantum dots (CQDs) are novel materials, recently appeared in materials science. They are surface-functionalized carbonaceous nanoparticles with very good optical properties, like the intense fluorescence which can be tuned in visible by changing the excitation wavelength. These characteristics along with their non-toxicity and low fabrication costs make CQDs attractive for photocatalysis, optoelectronics, or biological applications. CQDs come into several structural types like graphene quantum dots, graphite quantum dots (several graphene quantum dots in stacked structucture), or amorphous carbon quantum dots. Despite many advances, several important issues still remain open regarding the optical response of CQDs such as their interaction with the environment or the origin of fluorescence tunability. Using the DFTB+ (density functional based tight binding) method and its TD (time dependent) extension we calculated the electronic structure and optical absorption of graphene/graphite quantum dots with diameters up to 2 nm. We present graphene/graphite quantum dots with armchair terminations and saturated with different ligands: H, alipha- and aroma-type molecules as well as NH2 and OH fragments. Our calculations are consistent with the scenario by which the photoluminescence response is a combination of at least two sources: one is the core with subsequent quantization effects and the other resides in functional groups that induce levels in the bandgap.

Resume : Lead halide perovskite compounds have been extensively studied and achieved power conversion efficiencies (PCE) around 25%. However, because these ionic compounds contain carcinogenic Pb2+ ions, replacing lead by less toxic elements has been the prime interest in this technology. The most promising lead-free candidate has been regarded as tin-based halide perovskite materials due to their similar or even better optical properties to lead-based counterparts such as energy bandgap and charge mobility. However, their solar cells suffer from low open-circuit voltages (VOC) arising from mismatched energy levels between tin-based perovskite layer and charge transporting layers (CTLs) in their structure. In this presentation, we report that a new device structure for tin-based perovskite solar cell. We introduce the new CTLs, of which energy levels optimally match with mixed cation formamidinium/phenylammonium tin iodide-based perovskite materials, resulting in a small VOC loss at their interfaces. As a result, the newly designed tin-based perovskite solar cell achieves a power conversion efficiency of 7.05 % with the significantly large VOC of 0.651 V. This work highlights the importance of redesigning device structures for Sn-based perovskite solar cells.

Resume : Layered Mo based semiconductors with mono- or few-layer thickness can potentially advance many applications, ranging from optoelectronics, (photo)catalysis and sensors. By first-principles DFT calculations (at HSE06 level) and Boltzmann transport theory, we explore the electronic, charge transport and optical properties of relevant lamellar materials: alpha-MoO3 with large band gap (2.96 eV) and 2H-MoS2 with small band gap (1.56 eV). To tune their properties, we modify their respective chemical compositions by exchanging O and S inside the two materials at various concentrations. Substituting sulfur atoms by oxygen atoms on 2H-MoS2 does not alter significantly the electronic band gap. By contrast, substituting the Ot sites in MoO3 by sulfur atoms may significantly impact the electronic energy gap which decreases from ~3.0 eV in pristine material to around 1.6 eV in sulfur doped material. Moreover, alpha-MoO3 with high sulfur concentrations (xs = 17%) and 2H-MoS2 with oxygen concentration lower than 50% exhibit dielectric function, optical, charge transport and exciton binding energy which may be interesting for photocatalytic applications. This theoretical work opens new perspectives for the further investigation of lamellar oxy-sulfide materials. In particular, we are currently investigating the corresponding properties of monolayer structure of the corresponding 2D materials.

Resume : Solar water evaporation has been considered as a promising technique to harvest solar energy for the practicable water purification. However, current technology for solar water purification is severely hindering by insufficient solar utilization and complicated operation. Thus, achieving efficient solar absorber that can strengthen the solar energy utilization and improve water purification efficiency remain highly desirable. Herein, we report the development of charge-transfer cocrystals (CTC) that afford absorption-tunable, ultra-stable organic solar absorbers to support efficient water evaporation. By modulating the combination of both donor and acceptor units through charge-transfer effects, full-solar absorbing performance can be realized to achieve good photothermal conversion. This CTC-doped 3D scaffold is designed and fabricated, and our design results in an efficient solar- evaporation rate of 1.67 kg m-2h-1 via 90% solar conversion from 1 sunlight (1.0 kW m?2). Importantly, water purification of seawater, dyestuff pollution, heavy metal, and microorganism pollution are realized and achieve a high purification efficiency of 99.9%. The charge-transfer-mediated approach may offer a major step forward in manufacturing solar absorbers toward practical water purification.

Resume : Co-evaporation can fabricate high quality perovskite absorbers for solar cells, but this fabrication route is still largely underexplored, as most research groups focus on cheap and fast, but industrially unattractive wet-chemical processes. At MLU, we develop dynamic co-evaporation processes for mixed halide perovskites and try to find new material combination with better performance and higher stability. In this contribution, we investigate the film formation during the growth of hybrid lead halide perovskites by co-evaporation with the aid of in situ XRD diagnostics. The detailed analysis of phase evolution, nucleation/reaction/diffusion kinetics and degradation modes allows to pinpoint structure-property relationships between the involved crystalline phases and the device photophysics. We are able to resolve secondary phases already during growth and our time-resolved measurements allows us to report on the kinetics of film formation and thermal degradation. Ultimately, we report on our progress in fabricating efficient devices in a regular n-i-p structure (ITO/SnO2/Perovskite/PTAA/Au).

Resume : Halide perovskites hold exceptional promise as cheap, low temperature solution-processed optoelectronic materials. Yet they are hindered by poor structural and chemical stability, rapidly degrading when exposed to moisture or air. We demonstrate a solution-phase method for infiltrating methylammonium lead bromide perovskite (CH3NH3PbBr3, or MAPbBr3) into nanoporous GaN which preserved the green photoluminescence of the perovskite after up to 1 year of storage under ambient conditions. Besides a protective effect, confinement within the porous GaN matrix also resulted in a blueshift of the perovskite emission with decreasing pore size, suggesting an additional templating effect of the pores on the size of the perovskite crystals within. We investigate the dynamic of the charge recombination process in perovskite, proving the confinement effect of GaN on perovskite. We anticipate that our method may be generalized to related perovskite materials, offering a route to producing composites of interest for use in optoelectronic devices for various applications.

Resume : Perovskite nanomaterials have attracted extensive attention in recent decade owing to their high photoluminescence quantum yield, narrow emission spectrum, high colour purity, and emission wavelength tunable across the entire visible spectrum. Therefore, perovskite nanomaterials are promising candidates for next-generation solid-state lighting sources and display devices. Nevertheless, short working lifetime and non-radiative losses are considered as major problems of these material systems. These problems need to be resolved urgently for practical applications of perovskite light emitters. In my contribution, I will present green perovskite nanocrystals CsPbBr3 and FAPbBr3 synthesized by a new, fast and oleic-acid-free synthetic method at room temperature. I will also share our results on the dynamics of emissive excitons of CsPbBr3 and FAPbBr3 nanocrystals studied by transient absorption spectroscopy and ultrafast fluorescence up-conversion spectroscopy. Such experiments allow observing how the population and energy of the excited states evolve in real time. In addition, I will present the results of optimizations of synthetic processes that are carried out to reduce non-radiative recombination and improve the efficiency of perovskites QDs LED systems.

Resume : Utilizing bulky cation molecules as processing additives in perovskite solar cells (PSC) is a promising approach to improve device performance and stability through defect passivation. However, high levels of additives can result in an undesirable reduction in device power conversion efficiency (PCE) due to the insulating behavior of additive. Here we report our investigations into a new class of bulky cation. The results discuss how the size, concentration, and counterion of the bulky cations affect performance in PSCs.

Resume : Incorporating organic polymers for defects passivation has been used for developing high performance perovskite solar cells (PVSCs). However, the role of polymers on the ion migration and degradation is not yet fully understood. Meanwhile, rare studies investigated the operational stability of devices to electrical stressing. Here, a p-type polymer PCE10 with strong polar group is used as the additive in precursor to study their effects on device performance and operational stability, and a mono-polymer polystyrene (PS) with negligible dipole is chosen as a reference material for comparison. By optimizing the PCE10 concentration, the PVSCs with 0.05 mg/mL PCE10 additive enjoy significantly improved operational stability while maintaining a highest power conversion efficiency (PCE) of 19.64%. From the detailed investigations, we find that no passivation effect from the chosen polymer in perovskite as has been commonly ascribed in the community. The admittance measurement results illustrate that the improved stability is ascribed to the suppression effect of PCE10 on ion dissociation and migration during operation. In addition, both PS and PCE10 incorporation can address the problem of the relatively low operation stability of MAPbI3 solar cells. The electrical stressing tolerance increased dramatically after incorporating additive, which attributed to the obviously reduced mobile ion concentration. This study demonstrates a facile strategy to enhance device stability without sacrificing efficiency and provides insight into the thorough understanding on the suppression effect of polymer on the ion dissociation and degradation in perovskite.

Resume : The trap states in methylammonium lead iodide (MAPbI3) perovskites are the main factor for the loss of the photogenerated charges in the solar cells, i.e., the nonradiative recombination. The deactivation of the trap states can improve the power conversion efficiency. Optical illumination is one of methods to execute the de-activation of trap states. The de-activation kinetics of trap states is investigated by the photoluminescence (PL). The PL intensity increases with time because of the de-activation of trap states. The increase time of PL intensity with illumination power is studied. The saturation time constant of PL intensity is inversely proportional to the illumination power, and the equation for the de-activation is obtained. It is found the de-activation is due to the photoreaction to MAPbI3, but not the filling of the trap states. This results shed light on the properties of the trap states in MAPbI3.

Resume : Thin films of metal chalogenides have been widely used in different applications such as superconducting films, magnetic films, diamond-like films, surface modification, microelectronic devices, hard coatings, photoconductors, IR detectors, solar selective coatings, optical imaging, solar cells, sensors, optical mass memories. The aim of this work is to investigate the conductivity of CdS and CuS films under the light and without it, in order to determine their prospects for organic optoelectronics. The CdS and CuS nanocrystals were synthesized by low-temperature (T = 25 ° C) colloidal synthesis in a semi-periodic full-mixing reactor in the presence of thioglycolic acid as a stabilizer and, in addition, ethylene glycol as a stabilizing promoter. The study found that the conductivity of polymer films is independent of light. The basic mechanisms of conductivity are established, depending on the concentration of nanocrystals in the polymers.The-CdS and CdCu nanocomposites exhibited maximum PL emission around 640 nm. Photoluminescence intensity of the nanocomposite thin ?lms has been signi?cantly increase with the increase of CdCu concentration. PL nanocrystals CdS impurities, both undetected and doped with low concentrations of Cu and Zn caused by radiation recombination of nonequilibrium charge on their surface defects.

Resume : Two-dimensional molecular crystals[1,2] (2DMCs) featuring a monolayer (ML) or few layers of molecules, possess advantages such as long-range molecular ordering, minimized concentration of charge traps, the absence of grain boundaries, providing exciting prospects for (opto)electronic applications. Using n-type doping to enhance the electronic conductivity of organic semiconductors are commonly used in devices and hence of interest to explore for 2DMCs. To date, most theoretical and experimental investigations have focused on doping of amorphous/polycrystalline organic semiconductor films. Here, we study the electronic structure of potassium-doped 2DMCs of C6-DPA as a function of potassium incorporation by ultraviolet photoelectron spectroscopy (UPS) and X-Ray photoelectron spectroscopy (XPS). We compared the 2DMCs films with doping of more disordered spin-coated films, exploring the effect of crystallinity and localization on the doping-induced evolution of the induced polaronic gap states. [1] Yang F. X., Hu W. P., Adv. Mater. 2018, 30, 1702415 [2] Qian J., Li Y., Adv. Mater. Technol. 2019, 4, 1800182 [3] Cheng C. P., Pi T. W., Organic Electronics 2013,14, 942?950 [4] Bussolotti F., Ueno N., Phys. Rev. B 2012, 86, 155120

Resume : Colloidal semiconductor nanoplatelets (NPLs) are regarded as a new, highly promising class of optoelectronic materials thanks to their efficient and narrowband luminescence. NPL-LEDs typically take advantage of the incorporation of organic or inorganic interfacial layers as charge regulators to ensure charge balancing and high performance. Over the years, several engineered cathode interfaces have been successfully proposed to control electron injection, whilst the best efficiencies for hole injection in direct devices are still achieved with the consolidated ITO/PEDOT:PSS interface, eventually combined to a hole transporting polymer layer. However, as recently reported, the operational stability of devices is mostly affected by the intrinsic acidity and high hygroscopic nature of PEDOT:PSS. In this communication, we are proposing a new hybrid ink as interfacial layer, based on a self-doped conductive conjugated polyelectrolyte and exfoliated molybdenum disulfide (MoS2) flakes as an alternative to PEDOT:PSS with the main aim to prolong the lifetime of multilayer solution-processed NPL-LEDs. The ink features a neutral pH and a tunable hydrophobicity driven by the MoS2 content. This design strategy, not yet explored in nanocrystal-LED technology, mainly results in a remarkable stability of LEDs, using CdSe/CdZnS NPLs, with over 50% preservation of the external quantum efficiency of unsealed devices after 100 days storage in air.

Resume : Organic electrochemical transistors (OECTs) based logic circuits have broad applications in flexible sensors, actuators, and artificial synapses. However, most of the reported OECTs circuits are only constructed by p-type transistors, while complementary circuits are less developed. Complementary circuits can simplify circuit design, reduce device power consumption, and improve switching performance. Here, we reported the first example of flexible all-printed complementary OECT logic circuits. Employing surfactant-free p-type and n-type organic semiconductor inks in alcohol, complementary OECT logic circuits are printed by simple screen and inkjet printing. With rational designed hydrogel electrolyte, these solid-state complementary OECT logic circuits presents high electrical performance, with inverter switching gain value of up to 25 at a supply voltage below 0.7 V. We demonstrate these printed complementary OECT logic circuits can be used in signal monitoring and amplification of human electrooculography and plants movement.

Resume : Dispersed ruthenium oxide (RuO2) nanoparticles on W18O49 nanorods with rich oxygen vacancy has been generated by a facile, low-cost two-step solvothermal approach and subsequently characterized for energy storage application. The rational design and controlled synthesis of the hybrid nanostructures are of great importance in enabling the fine-tuning of the properties and functions. The remarkable electrochemical activity of the nanostructure is due to the development of oxygen vacancy, RuO2 active sites, and nanostructure networks which maximize the available sites and surface area for the electrolyte ions. A specific capacitance of 1126 F/g at a scan rate of 1 mV/s and 1050 F/g at a very high current density of 1.25 A/g were calculated in 1M H2SO4 electrolyte. The Galvanostatic charging-discharging (GCD) mechanism of the hybrid nanostructure suggests the transformation from the Pseudocapacitor ? battery mechanism of W18O49 nanorods into the typical supercapacitor mechanism resulting in better stability performance. These experimental results revealed that RuO2 enhances the conductivity, stability and adsorption site for electrolyte ions indicating the good electrochemical activity of the hybrid W18O49/RuO2 electrodes. These findings will have a profound effect on understanding and mechanism of the surface-induced vacancy to the process of electrochemical activity in terms of energy storage.

Resume : Multiple metal selenides (MMSs) have drawn pronounced attraction as promising anodes for sodium ion batteries (SIBs) owing to their greatly enhanced electrochemical performances originating from the superior intrinsic conductivities and richer redox sites, compared to single-metal chalcogenides. Moreover, the use of binder in electrode manufacturing not only causes dead weight inclusion, but also reduces the exposed surface area of active material. Hence, high surface area bearing and hierarchical nanostructures of iron-cobalt selenide (FCSe) and iron-nickel selenide (FNSe) were deposited over carbon fiber cloth (termed as FCSe/CFs and FNSe/CFs, respectively) and employed directly as anodes of SIBs. Carbon fiber cores not only act as intimate current collecting conductive highways for electron transport but also provide strength needed for self-standing electrode of battery. A simple and scalable hydrothermal strategy was employed with to prepare nanowire or nanosphere like morphologies of precursors were prepared under different conditions which were then selenized under optimized conditions to obtain corresponding MMSs. When employed in SIBs, FCSe/CFs and FNSe/CFs exhibited adequately high energy capacities and appreciable rate capabilities. In addition to this, FCSe/CFs and FNSe/CFs electrodes also presented extraordinary stable life of over 200 cycles. Structure robustness of cycled electrodes was also evaluated via ex-situ X-ray diffraction and various microscopic analysis techniques. We are confident that the presented strategy will pave the way for facile synthesis of a large family of MMSs with carbon fiber hybrids which are the potential materials for energy storage and conversion systems.

Resume : Carrier mobility in conjugated polymers continues to increase with recent reports of field-effect mobilities exceeding 10 cm2/V.s. Charge transport is intrinsically dependent on processes occurring across multiple lengthscales. In order to access order parameters at the molecular scale we use charge modulation spectroscopy combined with theory. This technique allows us to further differentiate field-induced and doping-induced charges. Furthermore, we study the mesoscale organization of polymers using new techniques in the transmission electron microscope. These techniques are used on homopolymers and donor-acceptor copolymers and allow to extract information about the microstructure that is typically not visible by inspection. Such multiscale studies of microstructure are instrumental in guiding our understanding of charge transport in conjugated polymers.

Resume : The fundamental structure of all organic electronic devices is a stack of thin layers sandwiched between electrodes with precise intra-layer morphology and inter-layer interactions. The simplest stack includes an active layer composed of the organic semiconductor sandwiched between two charge selective layers. These layers, often termed interlayer, are generally extremely thin and are used to enhance charge injection, blocking or transport. Solution processing the multilayer stack with little to no intermixing is, however, technically challenging and often incompatible with continuous roll-to-roll, high speed manufacturing. Recently, several groups, including ours, reported on self-forming interlayers generated by the spontaneous organization of additive molecules at the top or bottom of the active layer. The additives are initially blended with the organic semiconductor in solution but segregate to an interface either during or after film processing. Here we will show that a tri-layer stack of bottom electron-selective interlayer/active layer/top hole-selective interlayer can spontaneously form in one spin coating process. The application of the multilayer stack is demonstrated in an inverted organic solar cells, but is general and applicable for all organic electronic devices. The one-step three-layer processing is achieved by harnessing two different segregation mechanisms that drive migration of two additives in opposite directions to form interlayers above and below the active layer. Formation of the bottom interlayer, at the organic/substrate interface, is driven by the high surface energy of an amine-based additive; while a thiol-based additive migrates to the upper organic/anode interface due to its chemical affinity to the Ag anode. Generation of the trilayer, confirmed by High Resolution Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy (XPS), leads to improved carrier collection and corroborating the usefulness of this processing methodology for simple and cheap fabrication of organic electronic devices.

Resume : The performance of the organic-based electronic devices critically depends not only to the intrinsic molecular properties of the conjugated backbones but also to the supramolecular arrangement.1 In order to facilitate the design of new materials on a molecular basis and establish clear guidelines to fine tuning electronic and charge-transport parameters, deciphering the mechanisms involved on how sensitive the structural and electronic properties are to specific molecular ordering is essential. In this context, Raman spectroscopy can help to clarify how organic molecular solids respond to external stimuli (i.e., light, pressure, temperature), for instance, by reducing intermolecular interactions and/or changing molecular conformations.2 On the other hand, DFT calculations can help us to rationalize the nature and stability of the formation of aggregates and complexes,3 and also to link the molecular electronic structure and the microscopic factors affecting the charge-transport properties, among other examples.4 In this contribution, we present some of our more recent investigations on this field dealing with the better understanding of the complex structure-properties relationships of organic nanomaterials.2-4 For this purpose, we use a joint experimental and theoretical approach that links Raman spectroscopy and DFT calculations. We hope that this study can not only advance useful structure-property relationships but also guide the design of new pi-conjugated materials.

Resume : In recent years, theoretical description of doping processes in organic materials has evolved from relying on models inherited from doped inorganic materials to using comprehensive models based on ab initio methods. However, existing approaches lack the essential feature to explicitly link the chemical structure along with related properties of the constituting molecules to charge dynamics in doped materials. Here, we present a theoretical approach that consists of three steps: (1) generation of the doped material morphology (DEPOSIT method [J. Comput. Chem. 2013, 34, 2716? 2725]); (2) extraction of quantum mechanical properties of molecules in their unique polarizable environment on the DFT level (Quantum Patch method [J. Chem. Theory Comput. 2014, 10, 9, 3720-3725]) and (3) simulation of charge carrier dynamics using kinetic Monte-Carlo method [Nat. Commun. 2019, 10, 4547]. Using this method, we have analysed charge carrier dynamics in several prototypical amorphous organic materials including TPD, alpha-NPD and SpiroTAD doped with F4TCNQ. We have extracted conductivity, density of states, thermal activation energy and the fraction of mobile charge carriers and assessed good agreement with existing experimental data. Our studies deliver microscopic insight on the doping process in organic semiconductors and we hereby illustrate how the used method can be applied for virtual molecular design of host-dopant combinations to increase performance e.g. in OLED devices.

Resume : Charge transport in organic semiconductors such as conjugated polymers proceeds through a combination of intrachain and interchain charge transfer events. The large conformational phase space of conjugated polymers leads to disorder in the energies of charge sites and results in dispersive and temperature-dependent charge carrier dynamics. The distribution of site energies and resulting charge transport characteristics could, in principle, be inferred from the chemical structure of the material, although this is seldom straightforward. In the limit of very stiff polymers with low conformational freedom, transport will become limited by the nature of the interchain contact points. In this work we focus on two conjugated polymers featuring different degrees of conformational freedom. In the case of poly(9,9-dioctyl fluorene) (PFO) we show that hole transport can be limited by formation of a specific conformational defect, the beta-phase conformer, and that the impact of the defect on the density of states, hole transport dynamics and temperature dependent transport can be explained quantitatively in terms of the impact of the defect on the polymer?s electronic structure [1].To explore the case of intra-chain transfer-limited hole transport we study the stiff indacenodithiophene-co-benzothiadiazole polymer (C16-IDTBT). We observe a weak degree of charge trapping, consistent with the stiff conformation indicated by persistence length measurements and molecular dynamics (MD) simulations and the corresponding electronic structure. In films of this polymer, hole mobility is limited relative to transport in isolated polymer, showing that interchain charge transfer in films is the rate limiting step. This is confirmed by kinetic Monte Carlo modelling of hole transport within chain assemblies modelled using MD simulations. We conclude by reviewing the factors that will ultimately limit charge transport in conjugated polymers. [1] X. Shi et al., Physical Review X (2019) DOI: 10.1103/PhysRevX.9.021038

Resume : Doping of organic semiconductors is typically achieved by adding heterogeneous dopant molecules to the polymer bulk, often resulting in poor stability due to dopant sublimation or aggregation. In small-molecule donor-acceptor systems, charge transfer can yield high and stable electrical conductivities, an approach not yet explored in all-conjugated polymers. We report here on combining low-ionization energy polymers with high-electron affinity counterparts, yielding interfaces with resistivity values 5?6 orders of magnitude lower than the pristine polymers. The increased electrical conductivity originates from two parallel quasi-2D electron and hole distributions confined to nanometer-thin layers, corresponding to a conductivity of ~2 S/cm. The vacuum level shift and spin signals observed in UPS and EPR measurements, respectively, are attributed to the formation of polarons via spontaneous electron transfer at the interfaces. UV-Vis absorption, combined with quantum-chemical calculations, further revealed that both negative and positive polarons are present in the bilayer. We further transferred this concept to 3D all-polymer bulk heterojunctions, obtaining as high conductivity as and superior thermal stability to the equivalent single polymer films doped with molecular dopants. As no mobile dopants are used to dope the system, our findings hold promise for electro-active composites of potential use in, for example, thermoelectrics and wearable electronics.

Resume : The solution derived spin-coated highly transparent tris-(8-hydroxyquinoline)aluminum (Alq3)/ZnO hybrid thin films exhibit the higher transparency of 90.13% at 550 nm. The incorporated Alq3 molecules adsorb onto the grain boundaries of ZnO crystallites and act as scattering centers, thus decreasing the film transparency slightly less than pristine ZnO film (92.37%). The band-edge emission (387 nm) of ZnO upon incorporation of Alq3 in the hybrid films show a four-fold enhancement due to the transfer of excited state energy of Alq3 molecule to ZnO. The SEM images reveal the adsorption of Alq3 molecules on grain boundaries of ZnO creates ZnO particlates in the hybrid film. The XRD studies show the decreased ZnO crystallite size due to capping of Alq3 molecules in the hybrid films. The FTIR studies confirm the presence of luminescent quencher (carbonyly group) created in Alq3 molecule and the XPS studies show the existence of chemical interaction (chemisorption) and/or charge transfer between Alq3 and ZnO in the hybrid films, attributing a fourfold UV PL increase in the films. These studies will be discussed in detail. The electron-only devices were made using the hybrid thin films and the device electrical properties with higher electron current in the device will be discussed and presented in the manuscript.

Resume : Type-II heterostructures are an effective way to separate electron hole pairs, which are desirable for photoelectrochemical and photochemical water splitting. The design of efficient coherent Type-II heterostructure depends on the band gap, band edge positions of exposed facets, translational symmetry at interface, atomic configurations and lattice strain between miller indices of exposed facets. Beyond a critical value, lower band gap is desirable to capture maximum solar radiation, appropriate band edge positions are necessary to perform redox reactions and coherent interface is desirable to avoid defects and trap states. Semiconductor materials can exist in various crystal structurers from bulk to nanoscale level depending upon synthesis methods and can be classified as ?native? and ?non-native structures?. Native structure is thermodynamically stable bulk structure whereas non-native structures have different discrete translation symmetry from their counter native structure. These structures will also have different physical and chemical properties due to their different chemical coordination. We use density functional simulations to calibrate the band gap as well as band edge positions of native and non-native structures of widely used semiconductors such as: TiO2, ZnO, BiVO4, CdSe and ZnS. Band edge calculations show that most of the polymorphs are not only suitable for oxygen evolution reaction but also for hydrogen evolution reaction. On the basis of band edge positions, several isomaterial and heteromaterial type-II combinations of heterostructures have been explored in which 221(out of 297) materials have type-II combinations. However, when of coherency and lattice strain of interface is enforced, screening to account for complement translation symmetry, motif positions and lattice mismatch significantly restricted the combinations to 19. We also discuss qualitatively the decrease in the driving force for electron-hole separation in incoherent interfaces. The study demonstrates importance of coherency at the interface and brings of the ramifications of the lack of coherency in terms of efficiency of electron-hole separation.

Resume : Polymer derived silicon oxycarbide (SiOC) has gained lots of attentions for the past two decades because it has been shown to offer higher capacity than conventional anode materials, graphite (372mA/g). However, due to its unique nanostructure, lithium insertion/extraction mechanism results in large irreversible capacity and poor cycle retention which hinder SiOC from being commercialized. In this work, we picked up two commercialized polymers as the precursor to produce SiOC anode materials: 1. Dow Corning SylgardTM 184 silicone elastomer and 2. Lobster 656® silicone sealant. Both of these polymers undergo same simple pyrolysis process at 1100 in argon atmosphere for three hours. For materials characterization, the chemical bonding in the commercialized polymers precursors were confirmed by Fourier transform infrared spectroscopy, the derived SiOC materials were characterized by both X- ray Diffraction and Scanning Electron Microscope. Raman spectroscopy was used to analyzed the free carbon phase in SiOC, and Magic Angle Spinning Nuclear Magnetic Resonance spectroscopy was used to determine the distribution of Si-O-C phase. Specific surface area was also tested by BET measurement, and the carbon content for both of the derived SiOC materials were obtained from thermogravimetric analyzer. The resulting SiOC anode exhibited the maximum reversible discharge capacity around 1000 mAh/g, and remain 730 mAh/g after 100 cycles at a current density of 100 mA/g. The excellent capacity performance is attributed to the free carbon phase which contains sp3 disordered carbon bonding leading to a great amount of nanovoids where lithium atoms storage can take place; while the Si-O-C glass phase attribute in the structure stability thus enhance the cycle retention. Another advantage of this work is that the commercialized polymer precursor used was relatively cheap (2USD/300mL) comparing to conventional precursor such as polydimethylsiloxane (80USD/25mL) which makes the commercialization of these materials more probable.

Resume : Single Walled Carbon Nanotubes (SWCNTs) are a class of 1D material consisting of very high aspect ratio cylinders of sp2 hybridized carbon and possess exceptional electronic and physical properties.1 In particular, super-growth SWCNTs have greater length and higher purity than their counterparts (e.g. shorter CoMoCAT SWCNTs).2 The improved physical properties of super-growth SWCNTs leads to higher conductivity, which further complements their application in electronics. Since their discovery, SWCNTs have been incorporated into a variety of electrical applications, including photovoltaics.3 The rapid advances in perovskite solar cells (PSC) efficiency has also resulted in a number of exciting avenues for the implementation of SWCNTs in PSCs.4 In particular, the conventional hole transport material in n-i-p PSCs, Spiro-OMeTAD, must be doped with hydroscopic and corrosive materials in order to achieve high efficiency.5 Unfortunately, doping sensitive active layers with such materials results in poor long-term stability and such a critical disadvantage must be overcome in order to develop long term stability in PSCs. Here, we use super-growth SWCNTs to assist Spiro-OMeTAD with hole transport in PSCs without the need for hydroscopic and corrosive dopants. Our PSCs were then compared to devices made with regular CoMoCAT SWCNTs to determine how the use of super-growth SWCNTs impacted both charge transport and degradation processes. 1 Iijima, S. et al. Nature 363, 603?605 (1993) 2 Sekitani, T. et al. Nature Mater 8, 494?499 (2009) 3 Macdonald, T. J. et al. Small Methods 3, 1900164 (2019) 4 Habisreutinger, S. N. et al. ACS Energy Lett. 4, 1872?1879 (2019) 5 Schloemer, T. H. et al. Chem. Sci. 10, 1904?1935 (2019)

Resume : Among the various technologies that convert incident solar radiation into electricity, the Dye-sensitized solar cells (DSSCs) stand out. However, this device has low power-conversion-efficiency, which is a barrier to their use in the photovoltaic market. The metal-organic frameworks (MOFs) have receive considerable attention in photovoltaic applications due to their properties as: tunable porosity and long-distance internal energy migration pathways. MOFs are hybrid materials constructed by the combination of organic binders and inorganic nodes. Currently, ZnO has been used as an alternative material for the manufacture of photoanode, it exhibits electron mobility and electron diffusion coefficient. Considering these facts, the expected advantages of the combination ZnO and Zr-MOF have encouraged us to exploit them in the development of a photoanode for possible application in DSSC devices. ZnO nanoparticles were produced through chemical precipitation method and the ZnO/MOF UiO-66 was synthesized using a conventional hydrothermal method. Photoanodes films were prepared using viscose pastes of ZnO and Zr-MOF (25 and 50% in mass) placed on FTO substrate. The films were characterized by XRD, BET, FEG-SEM, Raman, FTIR, XPS Linear and Sweep Voltammetry (LSV) technics. The characterizations technics confirmed the composite material formation. The BET analysis shows a significant increase in the surface area and of the pore volume in the composite material in comparision of the pure ZnO. The LSV showed a high current density of the FTO/ZnO/Zr-MOF25% (25 mA.cm-2) film being superior to the FTO/ZnO (10 mA.cm-2) film in light condition. The results indicate that the FTO/ZnO/MOF films is promising to be used as photoanode in DSSC.

Resume : Charge transport in inverted polymer solar cell incorporating Ta2O5 cathode buffer layer (CBL) is investigated in this work. Structural, morphological and optical measurements are performed on thin film of Ta2O5 buffer layer deposited on ITO using thermal evaporation technique at 200 °C and 250 °C. Scanning electron microscopy images of the films show small island-like features. X-ray diffraction measurements confirm the films to be polycrystalline with orthorhombic structure. It is observed from optical measurements such as UV-Vis spectroscopy and photoluminescence that the Ta2O5 films show absorbance around 470 nm and the emission to be blue-shifted. Improved device performance and charge transport properties are observed in films deposited at 250 °C compared to films deposited at 200 °C. The inverted polymer solar cell fabricated using the Ta2O5 CBL showed 3.1% efficiency. The results indicating improvement in charge transport behavior in the device due to Ta2O5 deposited at higher substrate temperature will be discussed in detail.

Resume : Manifested by high absorption coefficient, large carrier diffusion length, ambipolar charge transport and moderate mobility of charge carriers, organo-lead halide perovskites recently emerging as a promising candidate for high efficiency and low-cost solution-processed solar cells, needs no introduction. Perovskite Solar Cells (PSCs) have already gathered considerable attention, showing a tremendous hike in efficiency from 3.8%[1] by Kojima et al. (2009) to 22.1%[2] by Yang et al. (2017). A lot of research has been done on the efficiency improvement of PSCs by optimization of the film morphology at the interfaces by various characterization techniques including electrochemical impedance spectroscopy (EIS) in a solid-state active device geometry.[3] Recently, the optimization of the film morphology at the liquid electrolyte interface by EIS is trending as a more simplified approach. Li et. al. have measured the flat band potential, density and type of charge carrier at the perovskite-liquid interface from the Mott-Schottky plot for spin-coated and spray-coated films of methylammonium lead tri-iodide (MAPbI3) perovskite.[4] Srivastava et.al have optimized the morphology of MAPbI3 perovskite thin films at the liquid interface by controlling nucleation and growth during film fabrication by spin coating the films on preheated substrates.[5] However, there is a need for understanding the charge transfer at these interfaces in more detail. Here, we have studied the kinetics of charge transfer and diffusion at the hybrid organic-inorganic perovskite-liquid electrolyte interface under the effect of applied bias. By applying the different dc bias from 0 to 1V and 0 to -1V, it was found that the ion diffusion at the low-frequency regime gets modulated due to charge accumulation. The charge transport resistance is initially increased to a maximum at around 0.4 V applied bias along with the decrease in the space charge capacitance. A transition state is observed at around 0.4 V to 0.6 V due to strong electronic-ion interaction where charge transport resistance decreases and capacitance increases. However, at higher applied bias voltage charge transport resistance increases again and capacitance starts to decrease due to excess ion accumulation. The perovskite films show a similar trend of change in impedance under both positive and negative bias. The Mott-Schottky Plot for forward and reverse voltage scan shows n-type and p-type behavior which indicates the ambipolar nature of perovskite semiconductor. The significant difference in the impedance spectra can be seen in dark and light which is attributed to the high absorption coefficient of the perovskite material. We have proposed a model to explain the charging kinetics across the perovskite-liquid electrolyte interface. References (1) Akihiro Kojima Yasuo Shirai, and Tsutomu Miyasaka, K. T. J. Am. Chem. Soc. 2009, 131, 6050?6051. (2) Yang, W. S.; Park, B. W.; Jung, E. H.; Jeon, N. J.; Kim, Y. C.; Lee, D. U.; Shin, S. S.; Seo, J.; Kim, E. K.; Noh, J. H.; Seok, S.I. Science 2017, 356 (6345), 1376?1379. (3) Bag, M.; Renna, L. A.; Adhikari, R. Y.; Karak, S.; Liu, F.; Lahti, P. M.; Russell, T. P.; Tuominen, M. T.; Venkataraman, D. J. Am. Chem. Soc. 2015, 137 (40), 13130?13137. (4) Li, Z.; Mercado, C. C.; Yang, M.; Palay, E.; Zhu, K. Chem. Commun. 2017, 53 (16), 2467?2470. (5) Srivastava, P.; Parhi, A. P.; Ranjan, R.; Satapathi, S.; Bag, M. ACS Appl. Energy Mater. 2018, 1, 4420?4425.

Resume : In this work, we have explored the possibility to develop inorganic 100 nm thick metal oxide films such as MoOx, TiOx, SnOx, NiOx under three different oxygen partial pressures (2e-4 Torr, 9e-5 Torr, and 2e-5 Torr), where all the films were evaporated reactively under oxygen at room temperature using e-beam evaporator with a gentle deposition rate of 1 A/s. Later, the films were annealed at 200oC and characterized using the ellipsometer, dektak profilometer, XPS, XRD, UV-Vis, and SEM/EDS. The main goal of the work is to study the changes in structural and optical properties to be used for energy conversion devices with annealing temperature of 200oC. XRD results confirm the crystalline phases of treated SnOx and NiOx thin films at 200oC, whereas, TiOx and MoOx layers show amorphous phase and confirm the requirement of high annealing temperature for crystallinity. As expected, metal to oxygen ratios vary significantly as confirmed by EDS and XPS study with a deficiency of oxygen atoms in the films, which confirms the semiconducting behavior of such metal oxide films. The FESEM images illustrate that the surface morphology and the average grain size of the films are strongly dependent on the process parameters of the evaporated films. The transmission and absorbance results prepared under different process parameters confirm the correlation between the optical properties and poor/rich oxygen films. For the studied annealed films, refractive index values vary between 2 and 3. Later, a numerical approach has been considered to investigate the role of optical parameters as experimentally measured by integrating such layers in an optimized energy conversion device structure. The results demonstrate that power conversion efficiencies exceeding 26% can be obtained by optimizing the device design.

Resume : For the high efficient water splitting system, it is necessary to lower the overpotential value in the oxygen evolution reaction (OER) by electrocatalysts. To replace the currently widely used expensive noble metal catalysts (RuO2, Pt), many researchers have reported metal nitrides (NixFeyN, NixN, and CoxN) due to their superior electrocatalytic properties. Furthermore, as stability issues arise in energy fields, encapsulation nitrogen doped carbon shell have been studied by many researchers. Despite the efforts of many researchers, improving electrochemical properties with control of stable morphology and structures is one of the challenging issues. Herein, we report a successful design and synthesis of unique core shell Co3N nanocubes/N doped carbon based on nitridation and dopamine coating technology by Prussian blue analogue (PBA) of Co3[Co(CN)6]2 precursors. The Co3N nanocubes with diameters of 500 nm, which has been reported outstanding electrochemical performance by Dr. Kang, were coated with 200 nm of N-doped carbon shell. This N-doped Carbon shell prevent aggregation of Co3N nanoparticles, which improve the stability of the catalysts during OER process. The morphology of core shell Co3N/N-doped carbon nanocubes was analyzed by SEM and TEM. The composition was confirmed by XRD and XPS. Also, specific surface area is analyzed by BET. Finally, we analyzed electrochemical properties of core shell Co3N/N-doped carbon nanocubes.

Resume : energy conversion materials, Bi-functional electrocatalysts for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) on the air cathodes are the heart of the key in metal-air batteries and reversible fuel cells. Rechargeable metal-air batteries are renewable and eco-friendly sustainable energies that has the potential to replace fossil fuels in the future. However, there still remains the biggest obstacle to the sluggish kinetics of OER and ORR for these devices. Currently, noble metal based cathode electrode, such as Pt/C, IrO2 and RuO2 based electrode, are still the most efficient catalysts for OER, ORR with low overpotentials and fast kinetics. However, the high cost and scarcity of these noble metals seriously hinders the mass process and application. Consequently, Recent research results have focused on the development of catalysts using transition metals and carbon materials based that have abundant reserves rather than noble metals. Herein, we successfully synthesized CoFe@3D N-doped graphene hybrid composite for bi-functional electrocatalyst material through two-step process with hydrothermal method and annealing. The morphology of precursor and CoFe@3D graphene hybrid composite was analyzed by FE-SEM. The crystallinity of sample was confirmed by XRD. 3D N-doped graphene was confirmed by Raman spectroscopy. Furthermore, we analyzed electrochemical properties of synthesized sample.

Resume : An important approach to a sustainable energy future is via the energy conversions based on ?electrochemical water cycle?, that is, conversion of renewable electricity into chemical energy stored by clean H2 fuel, which is subsequently fed to fuel cells for electricity. However, most of the reported electrocatalysts were aiming at only HER or OER half reaction under a particular electrolyte condition (i.e., alkaline or acidic). Whereas in practical applications, it is highly desirable to develop a high-performance catalyst that is universally compatible (pH-universal, and bi-functional for both cathode and anode), so as to enable all kinds of electrolytes to be directly used for hydrogen and oxygen production, and to optimize the reliability during operation. It is a challenging but pressing task to design and synthesize novel, efficient, and robust pH-universal bi-functional (i.e., both OER and HER) electrocatalysts for scalable and sustainable hydrogen and oxygen production through electrochemical water splitting. Here we report a facile method to prepare highly active and durable self-supported Co(OH)xF-CNT nano-arrays electrocatalyst on 3D nickel foam (NF) for overall water splitting over a wide pH range. The optimized Co(OH)xF-CNT/NF nanoarrays achieved not only ultralow overpotentials at 20 mA cm?2 for the OER (243 mV in pH= 13.8, 270 mV in pH= 0.2 and 295 mV in pH= 7) and HER (32 mV in pH= 13.8, 17 mV in pH= 0.2 and 138 mV in pH= 7), but also high-performance overall water electrolysis with a low cell potential of 1.52 V (pH = 13.8) at 10 mAcm?2. The optimized electrolyzer also exhibits superior durability with small potential change over 50 h of operation, showing a class of efficient bifunctional electrocatalysts for overall water splitting.

Resume : The hole transporting material (HTM) is a key component in part ruling both performance and stability of perovskite solar cells (PSCs). The most studied and effective HTM reported so far is the spiro-OMeTAD in combination with Lithium salts. In addition to its tedious and relatively expensive fabrication, this HTM shows some stability issues. In this work, new materials have thus been investigated as substitutes, including carbazole-based polymer materials, ionic liquid molecules along with polymer electrolytes. Our recent work has mainly been focused on the preparation of Hole Transport Materials through the formulation of spiro-OMeTAD with metal-free (e.g. Lithium-free) molecules or macromolecules.1,2 The design of the latter will be presented giving rise to high power conversion efficiencies up to 20% and hysteresis-free Perovskite Solar Cells. References: (1) Geffroy, C. et al. Solar Energy 193, 878-884 (2019). (2) Geffroy, C. et al. ACS Appl. Energy Mater. accepted (2020).

Resume : Recent advances in the use of organic?inorganic hybrid perovskites have been investigated in a variety of applications, such as solar cells, photodetector, light emitting devices (LEDs), and lasers because of their outstanding semiconductor properties. Furthermore, the perovskite structure has the ability to host extrinsic elements, making it a promising candidate for battery field. Previous studies have shown that organic?inorganic hybrid perovskites can be a suitable anode material for both lithium- and sodium-ion batteries. However, the multivalent rechargeable batteries with perovskite material have not yet been realized. Herein, we studied the electrochemical performance of three-dimensional (3D) CH3NH3PbI3 and quasi-two dimensional (C4H9NH3)2(CH3NH3)3Pb4I13 thin films as electrode materials for rechargeable Al-ion batteries. In this work, these electrodes were successfully synthesis on carbon cloth through a feasible solution process. The (C4H9NH3)2(CH3NH3)3Pb4I13 electrode yield a specific capacity of 210 mAh g?1 at the current density of 50mA g?1 . It still delivered 81 mAh g?1 after 250 cycles at the current density of 200mA g?1 with a retention of as high as 95%, indicating a long cycling stability. Compared with the CH3NH3PbI3, the (C4H9NH3)2(CH3NH3)3Pb4I13 presented higher initial capacities, better reversibility, and more excellent high-rate capabilities, all demonstrating the vitally prominent role of isobutyl amine (C4H9NH3). which can be attributed to the unique hydrogen-bonding interaction of isobutyl amine could effectively hinder the shuttle effect of polyiodide. We anticipate that these results open a new direction for the use of organic?inorganic hybrid perovskites for new secondary aluminum ion batteries.

Resume : Perovskite solar cells based on methylammonium lead iodide (CH3NH3PbI3) and related materials have emerged as an exciting development for next generation photovoltaic technologies. Solar cells based on them have achieved impressive energy conversion efficiencies, but their stability is still limited. Understanding degradation mechanisms in such materials is key to developing strategies to increase their lifetime. The present work reports on the nanoscale characterization of perovskite photovoltaic films with respect to their stability and degradation mechanisms. We investigated the local conductance and surface potential variation of perovskite films at the nanoscale using conducting atomic force microscopy (CAFM) and Kelvin probe force microscopy (KPFM). CAFM measurements revealed that the current is larger at grain boundaries. The surface potential at grain boundaries and on top of the grain is almost similar which suggests a negligible energy barrier at grain boundaries. We investigated the effect of sunlight exposure on the nano-scale conductance and surface potential of perovskite thin films towards better understanding of photo-induced degradation mechanisms.

Resume : Chitin nanofiber (ChNF) is one of a promising eco-friendly material because it is non-toxic, biocompatible, robust, and sustainable. It is also the most abundant marine polysaccharide. The ?-ChNF is known to show piezoelectric properties due to its intrinsic molecular polarization arising from the non-centrosymmetric crystal structure. This work, we demonstrate a ?-phase dominant ChNF/poly(vinylidene ?uoride) (PVDF)-based ?exible piezoelectric nanogenerators (PENGs) that exhibit superior electrical output. The PVDF is incorporated with ChNF to significantly enhance its piezoelectric properties. This is primarily because of the electrostatic interaction between the ?-ChNF and the CH2/CF2 dipoles, the crystallinity of the ?-ChNF and ?-PVDF are increased. The ChNF/PVDF film is characterized by scanning electron microscopy (SEM), polarizing optical microscope (POM), and peak force TUNA (PF-TUNA), x-ray di?raction (XRD), Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy to investigate the optical and piezoelectric properties of the ChNF/PVDF film. The ChNF/PVDF film exhibits superior remnant polarization ~10.8 ?C/cm2. Keywords: poly(vinylidene fluoride); chitin; ferroelectric polymer; piezoelectric nanogenerator

Resume : The Li?S based battery is a promising alternative to the present Li-ion battery for energy storage; however, the unwanted long polysulfide species affect the durability and performance of the battery due to dissolution in liquid electrolytes. Rechargeable (Mg-S) batteries have been considered as one of the alternatives to Li-ion/Li-S batteries, due to the high volumetric capacity of the divalent Mg ion which exceeds Li. Organosulfur silanes grafted on Al current collector have been successfully demonstrated to function as a sulfur source as a cathode. In this study, we are investigating the Mg charge carrier interaction with organosilanes like Bis[3-(triethoxysilyl) propyl] disulfide silane (TESPD) and Bis[3-(triethoxysilyl) propyl] tetrasulfide silane (TESPT). The sulfur-containing organosilane compounds (TESPD/TESPT) reacts with Mg from the anode without forming polysulphides. A molecular-level understanding of the chemical processes and properties such as stability of intermediates, the reactivity of intermediates, and reactivity toward the organic electrolytes in the Mg?S batteries is therefore of great interest. In the present study, we exploit quantum chemical methods for in-silico characterization of Mg ?TESPD/TESPT battery discharge products. We computed the energetics of various products from Mg and TESPD/TESPT interaction. The free-energy change for the symmetric and asymmetric break of the central S2/S4 chain of TESTD/TESPT with Mg is elucidated. Also, the computed reduction potentials in these cases are derived and compared with experimentally observed cyclic voltammetry curves. Finally, we investigate the effect of organic electrolyte on the reduction potentials.

Resume : Research in electrochemical energy storage is converging to target systems with battery-level energy density, and capacitor-level cycling stability and power density. One approach is to utilize redox-active electrolytes that add faradaic charge storage to increase energy density of supercapacitors. Aqueous redox-active electrolytes are simple to prepare and to up-scale; and, can be synergistically optimized to fully utilize the dynamic charge/discharge and storage properties of activated-carbon based electrode systems. However, aqueous redox-enhanced electrochemical capacitors (redox ECs) have performed relatively poorly, primarily due to the cross-diffusion of soluble redox couples, reduced cycle life, and low operating voltages. In this presentation, we show that these challenges can be met by the use of liquid-to-solid phase transitions of redox electrolyte molecules, and their reversible confinement in the pores ( > 2 nm) of high-surface-area electrodes. This approach is demonstrated by the use of bromide catholyte and modified hydrophobic cations (e.g., viologens and tetrabutylammonium) that together induce reversible solid-state complexation of Br2/Br3?. This mechanism solves the cross-diffusion issue of redox ECs without using costly ion-selective membranes, and has the added benefit of stabilizing the reactive bromine generated during charging. Furthermore, our device is simple to fabricate and uses large >10 mg carbon electrodes (BET specific surface area of 2470 m2/g, mass loading of 12.7 mg/cm2) to ensure that our performance metrics are practical. Using the concepts learned from this 1st generation configuration, we created a hybrid electrochemical storage system by designing and implementing stackable bipolar pouch cells with corrosion-resistant, non-metallic current collectors. The device using ZnBr2 battery chemistry and tetrabutylammonium cations enables high-power aqueous electrochemical energy storage.

Resume : Growth structure process control for desired properties achievement is possible with the technological parameter correlation- growth conditions / the epitaxial layer property. To obtain a layer with a desired conductivity in structure, it is firstly need to determine a dependence of the measured property (conductivity) versus the technological parameter (precursor flux) at other given parameters (growth conditions) for this layer. For this purpose, 27 samples set was grown by MOCVD (In0.01Ga0.99As epitaxial structure ~ 1.3 ?m thick on Ge substrate (150 ?m thickness) or GaAs (600 ?m) with 100 mm in diameter) with different doping levels (1016, 1017, 1018 cm-3) and conductivity type (n and p). Based on the rocking curves (obtained by X-ray diffractometry), the lattice constant of the investigated epitaxial layers was determined. In the case of Si doping the intensity and the peaks width remain approximately the same. In the case of Zn doping there is a tendency for a intensity reduce and peaks broadening with doping concentration rise. By noncontact conductivity measurement method, the specific resistivity of the investigated layers was determined. The dopant (Si and Zn) concentration profiles were determined based on the distribution profiles in the structure layers. As expected, the conductivity dependence for the samples doped with Si shows a linear increase with increasing the doping component concentration (disilane - Si2H6) in the gas phase.

Resume : The lithium-sulfur batteries are the best candidate for the further improvement among the powering sources due to its high theoretical capacity and affordance in the market. However, the shuttle effect produced during the cycling processes is the limitation of these batteries. As one of the solutions to inhibit shuttle effect, this study developed the ultrathin polyelectrolyte-clay nanocoating on the polypropylene (PP) separator though the layer-by-layer technique. The combination of the weak polyelectrolytes (polyethyleneimine, PEI, and polyacrylic acid, PAA) and montmorillonite (MMT) or halloysite (Hal) clay nanoparticles enabled full control over mass and charge balance of polyelectrolyte/clay film components, which was crucial for achieving superior ion selectivity and reduction of the polysulfide transition. The differences in morphology of MMT and Hal (nanotubes) and the pH-controlled charge density of polyelectrolytes (PEI and PAA) tremendously influenced the thickness and performance of the layer-by-layer assemblies. Especially, The coatings at different pH resulted in the increase in electrolyte uptake, suppressed lithium dendrite growth and e enhanced discharge capacity of the cell. Moreover, the ultrathin polyelectrolyte-clay coatings notably improve thermal and dimensional stability of the PP separator. The results of the experiment validate that ultrathin LbL clay-containing coatings on the PP separator membrane can drastically improve the cyclability of the Li-S cells and suppress the shuttle effect. Acknowledgements This work was supported by the State target program #BR05236524 from the Ministry of Education and Science of the Republic of Kazakhstan and by the Faculty-development competitive research grant #110119DF4514 from Nazarbayev University.

Resume : The sluggish kinetics of the oxygen evolution reaction (OER) is a fundamental impediment to the production of green hydrogen. Molecular catalysts for this reaction show some of the most impressive activity. A computational study of 444 molecular water oxidation catalysts composed of well-known ligands using a set of six metals (Cr, Mn, Fe, Ru, Co & Ni) has been carried out. This leads to the confirmation of a method-independent scaling relationship, a description of routes toward circumventing this relationship and a justification for the ascendency of Ru catalysts in this domain. In previous work, which will be described, we explain why the state-of-the-art catalysts are so active and how molecular catalysts can exhibit near-zero overpotential. With design principles derived from this work, our high-throughput approach identifies novel, earth-abundant molecular Cr, Fe & Mn catalysts as promising leads for experimental realization. The binding energy data of the OH intermediate is used to train a machine learning model, and we describe how this can be applied to advance future catalyst screening studies. The OER could be boosted by immobilizing a molecular catalyst on a support, leading to the realization of a hybrid catalyst. We describe recent research into immobilization strategies which include covalently tethering the catalyst and the direct grafting of molecular complexes onto a solid material. This is expected to advance the state-of-the-art in hybrid OER catalysis.

Resume : For creation of photo- and electroluminescent, charge-transporting and light-absorbing materials, both organic ?-conjugated molecules (OMs) and quantum dots (QDs) of inorganic semiconductors are developed. Forming OM and QDs hybrid composites is of promising trend in the development of materials for optoelectronics and photovoltaic devices. In the report, hybrid composites comprising new organic semiconductors based on ?-conjugated thieno[3,2-b]indoles and conventional QDs (CdSe, PbS) are considered. The work describes the determination of the energy levels of frontier molecular orbitals (CVA, UPS, optical spectroscopy), the degree of crystallinity of thin films (XRD) and charge carrier mobility measurements (CELIV). The correlation between the structure of the materials and optical and electrical properties of the films including the influence of QDs on the charge mobility is discussed. The feasibility of using the OMs and QDs hybrid composites as well as an OM/QDs planar heterojunction in electroluminescent and photovoltaic devices are considered.

Resume : CoFeCu ternary layered hydroxides have been successfully fabricated by facile synthesis method-electrodeposition which is efficient and cost-effective. This ternary layered hydroxide has shown excellent oxygen evolution reaction (OER) as well as hydrogen evolution reaction (HER) performance in 1M KOH solution. For OER, it only required a quite small overpotential of 220 mV to reach the current density of 10 mA.cm-2, which is better than the state-of-art OER electrocatalysts including IrO2 and RuO2. For HER, only 200 mV overpotential is required to reach the target current density of 10 mA.cm-2. Furthermore, it has also demonstrated good durability in alkaline media, indicating its great potential for practical application in industry.

Resume : Doping of organic semiconductors can be considered a key factor for improved device performance of organic electronics. However, doping is difficult to control, in particular in solution processed organic devices. The main challenges are avoiding dissolving previous layers in the device stack when depositing multilayer structures and avoiding diffusion of dopant molecules to adjacent layers. There are several approaches for achieving well-controlled multilayer structures from solution; a common strategy is using orthogonal solvents for the different layers, unfortunately, this approach is restricted to only a few material systems due to limited solubility. In this research work we use a new small molecule additive for azide-based crosslinking of organic semiconductors in order to produce insoluble layers and enable deposition of subsequent layers using the same solvent without intermixing of the layers. The CELIV-method (Charge Extraction by Linearly Increasing Voltage) is used to determine the charge-carrier mobility and doping density in the doped and crosslinked layers. Each layer is measured individually before and after doping and crosslinking in order to clarify the effect of the different additives. Finally, complete multilayer devices are characterized for determining how deposition of subsequent layers affect the doping density and doping profile in the device stack.

Resume : Understanding fundamental processes in organic photovoltaics (OPVs) requires numerical models that reflect the specific features of organic materials, such as hopping transport in a disorder-broadened density of states. One natural approach for this purpose are kinetic Monte Carlo (kMC) simulations. However, using kMC, it has proven to be challenging to simulate the key characteristic of any photovoltaic device, its current-voltage (J-V) curve under illumination. The main challenges arise from the presence of injecting contacts and the importance of charge recombination close to the open-circuit voltage. In this presentation, we demonstrate a kMC model that fully describes the J-V curve of a disordered organic solar cell [1]. We show that it crucial to make realistic assumptions on the injection barriers, the blend morphology, and the kinetics of interfacial charge-transfer states. All these properties were calibrated by independent experimental techniques such as charge extraction, electron microscopy, and transient absorption measurements. Our calibrated model provides clear evidence that the conclusions drawn from microscopic and transient KMC modeling are indeed relevant for real operating OPV devices. [1] arXiv:1912.10110

Resume : The most efficient perovskite solar cells (PSCs) employ an n?i?p device architecture that uses a 2,2?,7,7??tetrakis(N,N?di?p?methoxyphenyl?amine)?9,9??spirobifluorene (Spiro?OMeTAD) for hole transporting material (HTM). However, the Spiro-OMeTAD is susceptible to heat and easily oxidized with atmospheric oxygen. Moreover, Lithium bis(trifluoromethane)sulfonimide (LiTFSI) is hygroscopic and accelerates the rapid deterioration of perovskite structure, leading to the lack of long-term stability of PSCs. In this work, we apply negative dipole self-assembled molecules to modify the zinc oxide nanoparticles (m-ZnO NPs) for replacing the Spiro-OMeTAD HTM. Based on the molecules dipole moment, the m-ZnO NPs energy alignment has been tuning to ohmic contact, which assist charges tunneling to the electrode. The controllable surface dipole can achieve better charges equilibrium further enhance the Fill Factor and Current density. Since m-ZnO NP is a well-protected layer for preventing perovskite from contacting the high-humidity environment, the stability of the devices is greatly improved.

Resume : Hybrid Perovskite Solar Cells (PSC) have recently achieved 25.2 % efficiency [1]. These hybrid materials present outstanding properties such as large light absorption coefficient, high dielectric constant and large mobilities. Besides, the low-cost and easily scalable fabrication technique makes them perfect candidates to substitute or complement silicon solar cells. However, this technology is not in the market yet due to durability and stability issues. Currently, the scientific community is devoted to solve these problems researching on the new materials, combining several cations and halides, as well as new layer structures [2]. In this work, devices based on CsFAPbIBr with different active layer thicknesses (350 nm, 500 nm and 650 nm) have been fabricated and characterized. The temporal evolution of the efficiency under AM1.5 illumination shows that the burn-in process is faster and more pronounced for thicker devices. T80 is 2.9, 3 and 4.9 minutes for 650 nm, 500 nmand 350 nm respectively. The burn-in process has been characterized using impedance spectroscopy. The loop observed at medium frequencies (around 10 Hz) in pristine devices vanishes within the first minutes under illumination, and a new feature appears that might be related to charge recombination at the interlayer/perovskite interface.

Resume : The development of new hole transporting materials (HTM) for perovskite solar cells (PVSK) will help to advance the performance of these devices. New HTMs should surpass spiro-MeOTAD, which is currently the gold standard for PVSK, in terms of charge transport, stability, and ease of preparation. We report new HTMs based on conjugated cyclopentadithiophene core units equipped with triarylamine moieties. The electrochemical properties and high thermal stability make them promising candidates for hole transport layer (HTL) in PVSK devices reaching efficiencies of up to 21%.[1] Owing to its very good film forming properties compared with spiro-MeOTAD, a thin¬ner HTL can be used, maintaining a low defect density (shunts). We have studied hole trans¬port of these new HTMs by time-of-flight (ToF) using a conventional device setup ITO/HTM/ Au. The mobility µ is in the range of 1-2x10^-4 cm^2/Vs at an applied field of 2.5x10^5 V/cm. Analysis of the field dependence exhibits a lower field-dependent mobility of the new HTMs compared with spiro-MeOTAD thus enabling potentially better charge extraction in PVSK solar cells. To obtain transport data comparable to realistic PVSK devices, we investigated in detail the influence of the electrode/HTM interface and film thickness on charge transport. We used thin PVSK on ITO (ITO/PVSK/HTM/metal) as a charge generation layer, enabling HTLs with a thickness comparable to PVSK state-of-the-art solar cells. Due to the rough interface and thin layer the contribution of diffusion to charge transport is increased. This effect leads to more dispersive transport with modified field and temperature dependence. [1] S. Akin, M. Bauer, R. Uchida, N. Arora, G. Jacopin, Y. Liu, D. Hertel, K. Meerholz, P. Baeuerle, S. M. Zakeeruddin, M. I. Dar, M. Graetzel, under revision

Resume : Lithium nickel manganese oxide (LiNi0.5Mn1.5O4) is a promising candidate for next-generation lithium-ion rechargeable batteries due to its high operating voltage of 4.7 V vs. Li/Li+. However, there are lots of drawbacks in using LNMO as a cathode material because of the liquid electrolyte instability. When carbonate-based electrolytes are decomposed at high cut-off voltage, they generate a hydrofluoric acid which attacks the surface of LNMO. This unwanted parasitic reaction at the electrode-electrolyte interface accelerates the decay in cycle life. In this work, Ionic liquid (1M LiFSI in Pyr13FSI) is adopted as an electrolyte for LNMO cathode material. Highly stable ionic liquid mitigates Ni and Mn dissolution even in the high cut-off voltage of 5.1 V vs. Li/Li+. X-ray fluorescence mapping analysis confirmed the mitigation of dissolution by building up a 2D image of the varying composition of a sample.

Resume : In this report quantum dot light emitting diodes (QLEDs) composed of hybrid inorganic/organic hole injection and transport layers (HIL/HTL) and inorganic (Mg)ZnO nanoparticles (NPs) electron injection/transport layer (EIL) with different Mg composition were demonstrated. The maximum luminance could be up to 276,069 cd/m^2 with current efficiency of 10.77 cd/A for the devices with Mg0.15Zn0.85O EIL, corresponded to 18.56 and 6.08 times improvement compared with that of QLEDs comprised of undoped ZnO NPs EIL. Previously most of the QLEDs with superior operation performance were fabricated by utilizing organic HIL/HTL combined with inorganic EIL such as ZnO NPs. The most commonly used HIL and HTL combination in conventional QLEDs is poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) and poly[bis(4-butypheny)-bis(phenyl)benzidine] (Poly-TPD), which provided decent hole transporting capability with the highest occupied molecular orbital (HOMO) level of ?5.2 eV and high-quality film surface morphology [1]. However the use of ZnO EIL could provide much faster electron mobility compared with organic HIL/HTL and led to injection charge imbalance and decreased the radiative recombination efficiency as result. Introducing inorganic metal oxide with higher hole mobility such as NiO as the HIL can help to compensate the charge imbalance issue, but various NiO deposition methods such as sputtering, sol-gel method and synthesis NPs may cause defects and uneven surface and result in exciton quenching at the interface between HIL and QDs emission layer. This is the major obstacle that hindered the performance enhancement of all-inorganic QLEDs. In this research the fabricated QLEDs structure consisted hybrid hole transport materials and inorganic (Mg)ZnO NPs as the EIL, the emission layer was core-shell CdSe/ZnS QDs with photoluminescence peak wavelength of 524mm to 536mm sandwiched between HIL and EIL. The QLEDs were fabricated on ITO glass by spin-costing NiOx NPs as the HIL and Poly-TPD was deposited on NiOx as the HTL, subsequently CdSe/ZnS QDs and (Mg)ZnO NPs were deposited as emission layer and EIL, respectively. Finally the Al cathode was thermally evaporated on top of the (Mg)ZnO EIL and the devices emission pattern were defined by the orthogonally overlapped area of ITO anode and Al cathode which was about 1mm×1mm. For the purpose of obtaining better charge balance and carrier injection efficiency, (Mg)ZnO NPs with different Mg composition were used to tailor the energy band alignment between EIL and QDs emission layer to investigate the influence of operation performance in all solution processed QLEDs. In previous report, Dai et al. demonstrated a high-performance solution processed QLEDs by inserting an insulating layer between the QDs emission layer and ZnO electron transport layer to reduce the excess electron flow and optimize charge balance in the device and preserve the superior emissive properties of the QDs [2]. For the purpose of further suppressing photon (exciton) quenching effect generally arises at the interfaces between metal oxide carrier transport layers and QDs emitting layer, an additional hole transport layer of Poly-TPD was spin-coated between the NiOx HIL and QDs to passivate the residual dangling bonds on the surface of NiOx to prevent exciton quenching and help to modify charge balance. Mg-doped ZnO nanoparticles with different Mg composition ranging from 0, 0.05, 0.10 and 0.15 mole fraction were also used as the EIL for the fabrication of QLED to investigate the performance improvement by tuning the band structure and adjusting carrier injection barriers. The nanoparticle solution been used in this experiment for the preparation of NiOx thin film composed of 0.1846 g nickel formate dehydrate dissolved in the mixture of 10mol/ml Na(OH)(aq) and 100ml DI water. After stirring for 5 minutes, the colloidal precipitation was thoroughly washed with deionized water twice, and dried at 80 °C for 6 hours in thermal oven. The obtained green powder was then calcined at 270 °C for 2 hours to obtain a dark-black powder. Then the synthesized NiOx NPs with diameter of about 4-5nm was dispersed in deionized water to desired concentrations [3]. After cleaning the ITO glass substrate was subjected to UV Ozone treatment for 5 minutes, NiOx nanoparticles with concentration of 30 mg/ml was spin-coated at the speed of 2000 rpm for 30s, and baked at 150°C for 30 minutes. The Poly-TPD solution with concentration of 8 mg/ml was spin-coated at the speed of 4000 rpm for 40s, and baked at 110°C for 30 minutes. The spin speed for QDs and (Mg)ZnO NPs were 2000 rpm and 3000 rpm, respectively, and were both baked at 80? for 30 minutes each. Finally, a thermally evaporated top electrode of 100nm-thick Al served as the cathode. In the beginning the pristine all-inorganic solution processed QLEDs structure comprised of ITO(250nm)/NiOx NPs (25nm)/ CdSe@ZnS QDs (20nm)/ (Mg)ZnO NPs (50nm)/ Al (100nm) were fabricated without inserting organic polymer Poly-TPD as the HTL between NiOx HIL and QDs emission layer, it was found that the maximum luminance of QLEDs with Mg0.10Zn0.90O NPs EIL could be up to 39,483 cd/m^2, which is about twice the value of the QLEDs with undoped ZnO NPs EIL (18,625 cd/m^2). And the maximum current efficiency of QLEDs with Mg0.10Zn0.90O NPs EIL was 4.072 cd/A, corresponded to 147% improvement compared with undoped ZnO devices (2.766 cd/A). This result could be ascribed to the electron mobility and conductivity modification of the MgZnO EIL by adjusting Mg composition, which could help to achieve charge balance and tuning conduction band minimum to improve the electron injection efficiency and suppress excess hole overflow. [4-6] Subsequently an addition Poly-TPD was introduced between NiOx HIL and QDs emission layer served as HTL, and the fabricated devices performance could be significantly improved. Now the QLEDs structure became ITO(250nm)/NiOx NPs (25nm)/ Poly-TPD (20nm)/ CdSe@ZnS QDs (20nm)/ (Mg)ZnO NPs (50nm)/ Al (100nm). The maximum luminance of QLEDs with NiOx/Poly-TPD hybrid HIL/HTL and Mg0.15Zn0.85O NPs EIL could be up to 276,069 cd/m^2, which was 10 times higher than the devices without Poly-TPD (27,890 cd/m^2). Even though the QLEDs with Mg0.10Zn0.90O NPs EIL could acieve maximum luminance of 99,034 cd/m^2. And the maximum current efficiency of QLEDs with NiOx/Poly-TPD hybrid HIL/HTL and Mg0.15Zn0.85O NPs EIL achieved 10.77 cd/A, which was 3 times higher compared with that of Mg0.10Zn0.90O NPs EIL devices (3.58 cd/A). The emission wavelength of QLEDs without Poly-TPD was 536 nm with full-width-at-half-maximum (FWHM) of 22 nm, and the devices with Poly-TPD interlayer emitted at 524nm with FWHM of 23 nm, respectively. Compared with conventional QLED device without Poly-TPD interlayer, the turn-on voltage was decreased from 5.3V to 3.06V which could be ascribed to the stepwise NiOx/Poly-TPD hybrid HIL/HTL structure, this interface gradient help to decrease the hole-injection barrier from anode to QD emitting layer [3] and improve hole injection efficiency and charge balance as a result. Moreover QLEDs with inorganic charge transport layer prone to withstand higher operation current density up to several thousands of mA/cm^2, unlike conventional QLEDs with organic/inorganic hybrid charge transport layer which can only be operated up to couple hundreds of mA/cm^2, the QLEDs in this experiment with NiOx/Poly-TPD hybrid HIL/HTL structure could withstand operation current density up to 2000 mA/cm^2 or even higher but still maintained high current efficiency, and this is the major reason that the devices could reach maximum luminance up to 276,069 cd/m^2 which was higher than most of the previous reported results. In conclusion, the maximum luminance of QLEDs with NiOx/Poly-TPD hybrid HIL/HTL and Mg0.15Zn0.85O NPs EIL could be as high as 276,069 cd/m^2 with maximum current efficiency of 10.77 cd/A. Although introducing Poly-TPD could help to modify NiOx surface morphology and suppress exciton quenching effect, the relatively lower hole mobility and longer hole transportation distance resulted in charge imbalance again, and this is exactly the reason that the optimum Mg mole fraction became 0.15 instead of 0.10 for the QLEDs without Poly-TPD, because the electron mobility should be further reduced to match the retarded hole mobility when introducing an additional Poly-TPD layer. The significant performance improvement could be attributed to the combination of charge balance and suppression of exciton quenching effect. References [1] Q. Huang, et al., Optics Express, 2016, 24 (23), 25955-25963. [2] X. Dai, et al., Nature, 2014, 515(7525), 96-99. [3] F. Jiang, et al., Adv. Mater., 2015, 27, 2930-2937. [4] S. Wang et al., J. Mater. Chem. C, 2017, 5, 4724-4730. [5] J. H. Kim et al., Chem. Mater. 2015, 27, 197-204. [6] H. Zhang and S. Chen, J. Mater. Chem. C, 2019, 7, 2291-2298. [7] Q. Fu, et al., ACS Appl. Mater. Interfaces, 2013, 5, 13, 6024-6029.

Resume : The thermoelectric compound (GeTe)x(AgSbTe2)1-x, in short (TAGS-x), is investigated with the focus on two stoichiometries, i.e. TAGS-50 and TAGS-85. TAGS-85 is currently one of the most studied thermoelectric materials with great potential for thermoelectric applications. Yet, surprisingly, the lowest thermal conductivity is measured for TAGS-50, instead of TAGS-85. To explain this unexpected observation, atom probe tomography measurements are conducted on both samples, revealing clusters of various compositions and sizes. The most important role is attributed to Ag2Te nanoprecipitates found in TAGS-50. In contrast to the Ag2Te nanoprecipitates, the matrix reveals an unconventional bond breaking mechanism. More specifically, a high probability of multiple events (PME) of approximatively 60 % is observed for the matrix by APT. Surprisingly, the PME value decreases abruptly to approximatively 20-30 % for the Ag2Te nanoprecipitates. These differences can be attributed to differences in chemical bonding. The precipitates? PME value is indicative of normal bonding, i.e. covalent bonding with normal optical modes, while materials with this unconventional bond breaking found in the matrix are characterized by metavalent bonding. This implies that the interface between the metavalently bonded matrix and covalently bonded Ag2Te nanoprecipitate is partly responsible for the reduced thermal conductivity in TAGS-50.

Resume : Low dimensional organic nanomaterials have great applications prospects in the field of optoelectronics. In particular, we look for synergies with hybrid lead halide perovskite solar cells (PSCs). We study a novel strategy of doping the active layer with planar triazatuxene core molecules, with either a phenyl group or hexyl group in the nitrogen position of the carbazole side. These molecules have proved its p transport character as hole transport layers in PSCs.[1] Here, we synthetized perovskite CH3NH3PbI3 (MAPbI3) films doped with triphenyl-based triazatruxene (3P-T) and trihexyl-based triazatruxene (3H-T). XRD reveals that the additives do not influence the crystallinity of the doped MAPbI3 thin films, however, we observed an improved morphology with larger grain domains for 3P-T. The typical absorption and steady photoluminescence emission peaking at 1.6 eV are maintained. The electrical conductivity of the layers has been measured at working conditions temperature and it increases for 3P-T based- perovskite film may be due to its facile charge transport between phenyl and triazatruxene groups. On contrary, this parameter was reduced in the 3H-T case of the six-carbon alkyl chain. In this talk, we discuss the effect of these molecules on final cell performance, and further investigate the different electrical mechanims induced by means of impedance spectroscopy (IS) under illumination with AM 1.5 G (100 mW/cm2). [1]Rakstys, Ket al. JACS 2015,137(51),16172-16178.

Resume : Our work has allowed us to clarify the relations structures / properties and the isomerization reactions of icosadeca-ene. As regards the relations structures / properties, our results are: 1- The study of the conduction properties of icosadeca-ene doped with iodine gas at saturation as a function of various parameters regulating morphology and density of the material was optimized. In particular we have shown that the two key parameters governing the electrical conductivity of the polymer are the density and the fibrillar structure of icosadeca-ene. 2- The comparison of samples prepared horizontally and vertically gave a conductivity of greater than ~ 45 % for those deposited vertically, thereby reflecting the difference in morphology of the two types of film.. 3- The study of the ohmic conductivity of undoped and thermally isomerized samples showed a very different behavior depending on whether the icosadeca-ene film is deposited horizontally or vertically, thus confirming the different morphologies of the analyzed films. With regard to isomerization reactions of icosadeca-ene, our results are: i- The study of the thermal isomerization Cis / Trans of undoped icosadeca-ene by differential thermal analysis allowed us to calculate the activation energy of the reaction Ea=30.57 kcal/M, as well as the pre-exponential factor A = 3.7*1014 /s regardless of the type of polymer considered (deposited vertically or horizontally). ii- The kinetic studies by DSC showed that the isomerization reaction was neither of order 1, nor of a simple order. iii- An additional study of the thermal isomerization was carried out by Raman backscattering . This study allowed us in particular to establish a new original method for the determination of the isomeric composition of samples of icosadeca-ene. Also a relation for connecting the laser power to the induced temperature at the impact level was proposed. Finally, the kinetics of isomerization approaches the order 2/3. Note that the activation energy and the pre-exponential factor of the isomerization reaction determined by this method are different from those obtained by DSC.

Resume : In this work, we demonstrate a detailed description of degradation dynamics in mixed halide CsFAMA perovskites at the nanoscale. We identify chemical composition of local defects what may assist in the further improvement of long-term stability of perovskite solar cells. Metal-halide perovskites have been subject of significant research efforts in the second half of the last decade as they are capable of reaching efficiencies close to 25% while enabling room temperature, large area deposition. Their long-term performance was shown to be sensitive to a variety of degrading agents, such as oxygen, water as well as light and temperature. To suppress light and temperature related degradation, a clear understanding of the local and time-dependent formation of degradation products is necessary. We study the effect of continuous illumination of visible light with intensities 100-10000 mWcm-2 and the effect of electrical bias driven degradation on the chemical structure of CsFAMA. Nanocrystal defects are observed to form on the perovskite surface and their growth is monitored under inert atmosphere using advanced modes of scanning probe microscopy combined with confocal photoluminescence spectroscopy. Our results show clear correlation of defect formation with phase segregation by halide migration, and dependence of defect formation with applied voltage polarity.

Resume : Organic photovoltaic solar cells (OPVs) have made remarkable progress. Lightweight and flexible solar modules are commercially available and many large area installations have been demonstrated for outdoor and indoor power generation. The devices fabricated using bulk heterojunctions (BJH) geometry have already demonstrated the power conversion efficiencies of more than 15%.1 Device efficiency depends on exciton harvesting (leading to charge generation) and charge extraction, and both these processes are very sensitive to BHJ morphology. Charge generation occurs at the interface between the electron donor and acceptor, and for efficient exciton harvesting the donor and acceptor domain sizes should be smaller than the exciton diffusion length (LD) which is typically rather short, about 10-20 nm.2 However, small domains have a large donor-acceptor interface area which enhances the encounter probability of non-geminate charge pairs and charge recombination.3 This means that for a given exciton diffusion length, as domain size is varied there is a trade-off between exciton harvesting and charge extraction. Developing a way of increasing exciton diffusion length would overcome this trade-off by enabling efficient light-harvesting from large domains, which would then also give improved charge extraction. We used simple and cost-effective techniques of thermal and solvent vapour annealing to increase both exciton diffusion length and domain size. Our optimised films showed a doubling of exciton diffusion length compared to unannealed films. We fabricated proof of concept bulk heterojunction solar cells using this approach and obtained 20% enhancement in the device efficiency. Our optimized CS2 annealed devices show a charge extraction efficiency above 80% at short circuit conditions which is enabled by a large average domain size of about 30 nm. Large domain size would normally reduce exciton harvesting but in our case higher device efficiency is obtained because of the increase in exciton diffusion length. Our results suggest that larger domains are preferential in photovoltaic blends provided that sufficiently long exciton diffusion is achieved. Hence we show that control of processing conditions can enhance both exciton diffusion length and domain size in organic semiconductors blends. (1) B. T. Luppi, et al., J. Mater. Chem. A, 2019, 7, 2445-2463; Y. Cui et al., Nature Comm. 2019, 10, 2515; Y. Lin, et al; Adv. Mater., 2019, 1902965. (2) O. V. Mikhnenko, P. W. Blom, T.-Q. Nguyen, Energy & Environmental Science 2015, 8, 1867. (3) G. J. Hedley, A. Ruseckas, I. D. W. Samuel, Chem. Rev. 2017, 117, 796.

Resume : Organo-metal halide perovskites are notoriously sensitive to water and this influences device fabrication, performance, and stability. However, questions remain about how water entering the perovskite lattice influences its properties. Ab initio calculations previously suggested that reversible intercalation of water molecules hydrating the perovskite lattice reduces the activation energy for ion migration which could facilitate rearrangement of the lattice and degradation. Experimental work by Garci?a-Fernan?dez et al. on films and pellets suggests that the capacitance and electronic conductivity of films increases in the presence of moisture, however they did not interpret their results in terms of ionic conductivity. To investigate the impact of water on ionic transport we controlled the partial pressure of water in an inert (Argon) atmosphere surrounding perovskite solar cells with three different cation compositions (MAPI, FAMAPI, CsMAPI). In situ temperature dependent impedance spectroscopy measurements of the devices allowed us to determine the influence of water on the conductivity and corresponding activation energy of ionic defects in the device. The impedance data was analysed by fitting the spectra with a circuit model that allows us to assign the ionic and electronic components of the measured impedance. Here, we demonstrate our approach, show the results of these experiments and discuss the fitting of the impedance data. The findings have implications for device performance and stability/degradation of perovskite solar cells and related devices.

Resume : Charge transfer doping of organic semiconductors provides additional avenues for tuning charge transport characteristics in devices. Whether doping in solution or in thin films, structural qualities of polymers play important roles in determining doping efficiencies, including free carrier levels. We examine how polymer conformational and packing order influence interactions with dopants before and after contact. Self-assembled polymer nanostructures are fabricated as platforms for understanding how structure mediate charge transfer doping. This work specifically targets aggregates which have been proposed to facilitate doping. Aggregates of high and low intrachain order are shown to have distinct doping outcomes due to the ability of injected charges to delocalize from the contact site. We also demonstrate the importance of structural displacements accompanying doping which receive far less consideration than electronic factors in selecting suitable polymers and dopants.

Resume : IR and Raman spectra of chemically doped polyconjugated polymers allow investigation of doping and monitoring of its effectiveness. The vibrational modes associated with the doping-induced defects provide information about the polymer structure relaxation associated with the formation of polarons. We present a study on doped the P(NDI2OD-T2) copolymer with differently substituted 1H-benzimidazoles, leading to an increase of conductivity values up to four orders of magnitude. IR and Raman spectra of P(NDI2OD-T2) are analyzed while varying the dopant and its concentration, annealing temperature and time. Marker bands of the polaron, almost independent from the dopant species, are clearly identified and are used to monitor the formation and evolution of charge defects with thermal treatment and sample ageing. Worth noting, n-doped P(NDI2OD-T2) shows IR marker bands with a similar intrinsic intensity as IR bands the pristine species, differently from the anomalously strong IRAV bands of doped polyacetylene, polythiophenes, and related polymers. This experimental observation provides evidence of the confinement of the polaron on the NDI2OD unit, further confirmed by Raman spectra of n-doped P(NDIOD-T2). DFT calculations fully support the diagnosis. Hence, vibrational features indicate that the observed conductivity enhancement is mainly ascribed to interchain hopping involving charged NDI2OD units, whereas polaron diffusion along the chain is unlikely.

Resume : Crystalline naphthalenediimides bearing cyclohexane (NDI-Chex) and n-hexyl (NDI-Hex) demonstrate high electron mobility and are characterized by the specific packing motif with only one molecule per primitive cell (Zred = 1). This makes their studies interesting from both the practical and fundamental viewpoints. In this study, we apply theory and experiment to address the nonlocal electron-phonon coupling ? vibrational modulation of the charge transfer integrals that is now believed to limit the charge transport in efficient organic semiconductors ? in these compounds. We show that low-frequency Raman spectroscopy directly probes the non-local electron-phonon coupling in these organic semiconductors, and that theoretical Raman spectrum reasonably reproduces the experimental frequencies, intensities and anisotropy of Raman in the full frequency range. Finally, we reveal the effect of the non-local electron-phonon coupling on the electron mobility in these crystals. We anticipate that our findings will improve the understanding of the charge transport in high-mobility organic semiconductors and direct the search of efficient materials for organic electronic. Acknowledgements: This work was supported by the Russian Science Foundation, project ? 18-72-10165. Presenting author acknowledge the funding by the President?s PhD Scholarships.

Resume : The spectral line-shape of the mid-IR absorption spectrum provides valuable information about the ?hole? polaron coherence length in doped and undoped conjugated polymer films. Using a theory based on the Holstein Hamiltonian for mobile holes in P3HT, the IR line-shape is successfully reproduced for several recently measured spectra recorded in doped and undoped films, confirming the association of an enhanced peak ratio (A/B) with extended polaron coherence. Emphasis is placed on the origin of components polarized along the intra- and inter-chain directions and their dependence on the spatial distribution of disorder and the position of the dopant relative to the ?-stack. The model has been further adapted to treat donor-acceptor copolymers. References: 1. Raja Ghosh, Christine K Luscombe, Mike Hambsch, Stefan CB Mannsfeld, Alberto Salleo, and Frank C Spano. Anisotropic polaron delocalization in conjugated homopolymers and donor?acceptor copolymers. Chemistry of Materials, 2019 2. Raja Ghosh, Annabel R. Chew, Jonathan Onorato, Viktoria Pakhnyuk, Christine K. Luscombe, Alberto Salleo, and Frank C. Spano. Spectral signatures and spatial coherence of bound and unbound polarons in p3ht films: Theory versus experiment. J. Phys. Chem. C, 122(31):18048? 18060, 2018.

Resume : Organic thermoelectric materials have drawn increasing attention due to their flexibility, lightness, low-cost and environment-friendly fabrication and processing, solution processable and low-temperature workable properties. An organic thermoelectric generator (OTEG) module consists of a p-leg and an n-leg, corresponding to p-doped and n-doped conducting polymers, in analogy with inorganic thermoelectric generators (TEG). Poly{[N,N?-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5?-(2,2?bithiophene)), P(NDIOD-T2), has been selected as a n-type organic material due to its good electron mobility, solubility and air stability; 1H-benzimidazole, 4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl, has been recently proved as a good n-type dopant for P(NDIOD-T2). In order to investigate the doping mechanism and to guide further improvement of the performances, a series of N-substituted benzimidazole derivatives with different alkyl chains (methyl, ethyl, propyl, butyl, iso-propyl and iso-butyl) as n-type dopants were designed and synthesized. The six dopant molecules generate differences in conductivity of doped P(NDIOD-T2). In this study, a combination of Density Functional Theory calculations with several experimental techniques (X-ray Diffraction, Cyclic Voltammetry, Infrared spectroscopy and Differential Scanning Calorimetry) is used to elucidate the working mechanism in1H-benzimidazole/P(NDIOD-T2) systems. The results are consistent with an electron transfer from the HOMO of dopants to the LUMO of the polymer: a simple rationalization is suggested invoking ?-? stacking interactions.

Resume : Molecular p- and n- doping of organic semiconductors has been pivotal for the successful commercialisation of OLEDs and promises to significantly advance the field of organic solar cells and transistors. As recently shown, in-depth comprehension of the doping process is required to guide the design of improved semiconductor materials and molecular dopants. In this context, the electron spin of the species generated in the doping process represents an advantageous probe as it is sensitive to the magnetic interactions acting at a microscopic level which can provide new and complementary insight into the doping physics. In this contribution, we combine electron paramagnetic resonance (EPR) with theoretical calculations and electrical measurements to investigate p-type doping of a layer of ZnPc (host) with the acceptor F6-TCNNQ (dopant). Through EPR spectroscopy, we directly observe the spin-bearing species generated in the doping process, thereby allowing for detailed investigation, at different temperatures (80K ? 280K) and doping concentrations (0 - 5 wt.%), into the integer charge transfer mechanism, which is thought to underpin highly-efficient doping. Through EPR quantitative analysis and theoretical calculations we provide an estimate of the doping efficiency and reveal a new antiferromagnetic coupling mechanism occurring at high doping concentrations. Furthermore, we demonstrate that EPR spectroscopy allows for the determination of the intra-domain activation energy barriers. These microscopic energy barriers cannot be probed using conventional conductivity setups. The comparison of microscopic and macroscopic transport dynamics suggests new guidelines for future organic layer design.

Resume : A charge transport process in polymers can be electronically and geometrically tuned by copolymerization of two different blocks of polymer units. One is an electron donor and the other one is an electron acceptor. With this approach, we synthesized block copolymers which were stable under visible light irradiation and produced high electrochromic contrast. In this work, we present two electrochromic copolymers of a triblock polyaniline-polythiophene-polyaniline [1] and a random diblock polycyclopentadithiophene and diketo-pyrrolo-pyrrole [2]. The electrochromic properties of these two copolymers were investigated via cyclic voltammetry, spectro-electrochemistry, and stability during repeated on-off with an application of external applied voltage. The random block copolymer of polyaniline-polythiophene-polyaniline showed that under ambient and with light irradiation, the polyaniline blocks increased the stability of the copolymer up to 3 times during the application of voltage as comparison to the polymer with the polythiophene block only. The addition of the polyaniline block showed to retard the formation of bipolaron species as a result the stability of the polymer film increased. Another type of copolymer, cyclopentadithiophene-diketo-pyrrolo-pyrrole, was designed by incorporating two fused rigid units of the donor and the acceptor to improve the planarity of the polymer chains shown by the Density Functional Theory (DFT) calculations confirmed the improvement of charge transport and electrochromic properties in films. An optical contrast of the copolymer was increased up to 55%. Therefore, the charge transport process of electrochromic polymers can be tuned both electronically and geometrically. References: 1. Investigation of the electrochromic properties of tri-block polyaniline-polythiophene-polyaniline under visible light. C. Chotsuwan*, U. Asawapirom, Y. Shimoi, H. Akiyama, A. Ngamaroonchote, T. Jiemsakul, K. Jiramitmonkon, Synthetic Metals 2017, 226:80-88. 2. Cyclopentadithiophene and diketo-pyrrolo-pyrrole fused rigid copolymer for high optical contrast electrochromic polymer. K. Jiramitmongkon, C. Chotsuwan* U. Asawapirom, P. Hirunsit, J. of Polymer Research, 2020, 27:17.

Resume : The presence of mobile ionic charge in metal halide perovskite semiconductors requires the introduction of additional charge carrier variables to both time-dependent and steady-state descriptions of their devices. Here we present Driftfusion1: a flexible, open-source, drift-diffusion simulation software capable of describing the evolution of electron, hole and ion concentrations, and electrostatic potential, in one-dimension across any number of different semiconductor layers. The simulations allow the underlying factors controlling the behaviour of optoelectronic devices containing mobile ions such as perovskite solar cells to be understood and predicted2-4. The voltage dropped across space charge formed due to ion accumulation at interface proves to be critical for determining device performance, as well as electronic charge compensation of ion depletion in the bulk of the materials. Based on insights gained from these simulations we have developed an intuitive circuit model of perovskite device behaviour. The circuit model treats interfaces in the device by coupling the electrostatic potential of mobile ionic charge to the rate of charge transfer across interfaces using bipolar transistor elements to describe the process. The model allows impedance spectra of mixed conducting devices to be fit using physically meaningful parameters, and explains the large apparent capacitive and inductive behaviours often observed at low frequencies, as well as giving a more general description of the large perturbation behaviour of the devices.5 1 Calado, P., Gelmetti, I., Azzouzi, M., Hilton, B. & Barnes, P. R. F. (https://github.com/barnesgroupICL/Driftfusion, 2018). 2 Calado, P. et al. Evidence for ion migration in hybrid perovskite solar cells with minimal hysteresis. Nat Commun 7, 13831 (2016). 3 Calado, P. et al. Identifying Dominant Recombination Mechanisms in Perovskite Solar Cells by Measuring the Transient Ideality Factor. Physical Review Applied 11, 044005 (2019). 4 Calado, P. & Barnes, P. R. F. Is it possible for a perovskite p-n homojunction to persist in the presence of mobile ionic charge? arXiv:1905.11892 (2019). 5 Moia, D. et al. Ionic-to-electronic current amplification in hybrid perovskite solar cells: ionically gated transistor-interface circuit model explains hysteresis and impedance of mixed conducting devices. Energy Environ. Sci. 12, 1296-1308 (2019).