Fabrication and characterization of emerging transparent conductive materials

Resume : Poly (3,4-ethylenedioxythiophene) (PEDOT) is probably the most used conductive polymer because of its commercial availability, and because of its high performance for various applications such as organic electronics, photovoltaics or thermoelectricity. Modifications of PEDOT thin films have led to high conductivity enhancements, unfortunately not always clearly understood. In this communication, we report the development of highly conductive PEDOT films by controlling the crystallization of the PEDOT chains and by a subsequent dopant engineering approach. XRD, HRTEM, Synchrotron GIWAXS analyses and conductivity measurements down to 3 K allowed us to unravel the organization, doping, and transport mechanism of these materials. We propose a charge transport model that corroborates our experimental observations. The best thin films exhibit conductivities up to 5400 S cm−1, combined with a high transparency (> 85% in the visible spectrum and with a very low haze value). Thanks to these remarkable properties, we were able to fabricate the first all-polymeric transparent heaters. Excellent performances were achieved in terms of heating rate at low applied bias, cyclability and stability.

Resume : Electrochromism is the phenomenon where the color of a material changes by applying a voltage. Electrochromic devices (ECDs) made of such electrochromic materials have been studied extensively and applied to wearable displays, smart windows, and electronic papers. As for electrochromic material, conducting conjugated polymer, in particular, poly(3,4-ethylenedioxythiopene) (PEDOT), has been used due to fast response time by its small electronic bandgap(~1.6eV) and low redox potential. However, since PEDOT exhibits very low solubility in most solvents, the processing of PEDOT into nanofibers for flexible electrode is still challenging. In this study, a new manufacturing route for PEDOT nanofibers is developed using in-situ polymerization of EDOT after electrospinning. For this, first EDOT (monomer of PEDOT) is mixed with polyvinylpyrrolidone (PVP) and silver nitrate (AgNO3). PVP is selected as the skeleton material of nanofibers. AgNO3 is chosen as a precursor of silver nanoparticles (AgNPs). Here, AgNPs are aimed for both a catalyst for oxidative polymerization of EDOT on their surface and enhanced conductivity of nanofibers. Through electrospinning and a series of post-treatments, sophisticatedly-structured nanofibers are manufactured; PVP constitutes the skeleton of the nanofiber, whose surface AgNPs and PEDOT are uniformly coated on. AgNPs and PEDOT are expected to function excellent electrical conductivity and the electrochromic properties, resulting in flexible electrochromic nanofiber electrode. Detailed processing conditions and material characterizations will be presented at the conference.

Resume : Transparent conductive materials (TCM) are commonly used in numerous optoelectronic devices such as photovoltaics, light emitting diodes, smart windows, transparent heaters (TH) and more. Among TCMs, Indium Tin Oxide (ITO) is the most widely used. However, owing to its intrinsic brittleness and indium scarcity, alternative materials have to be developed to cope with the increasing demand for flexible devices. Carbon nanotubes, graphene, and metallic nanowires have been considered in the last decade, but conductive polymers reveal promising features for such applications. Recently, we developed highly conductive poly(3,4-ethylenedioxythiophene) (PEDOT) based materials with very high electrical conductivity, up to 5400 S.cm-1, through structure and dopant engineering [1]. These thin films exhibit low sheet resistance (<60 Ω.sq-1) associated with good transparencies (>87%) and a very low haze factor (<1%). We demonstrated for the first time the efficient use of thin films of PEDOT for transparent heater applications [2]. It is known that PEDOT materials might lack chemical stability overtime or under harsh conditions, making device integration tricky. In order to overcome this drawback, we extensively studied ageing mechanisms and efficient encapsulations. Ageing mechanisms under high humidity (90 % RH, 38°C) and sun illumination (1000 W/m², 35°C, 20% RH) were analyzed through UV-vis-NIR, Raman spectroscopy, XPS and GIWAXS measurements. After identifying main damaging factors, we studied different encapsulation systems which allowed us to significantly lower the degradation rate. [1] M. Gueye et Al, Chem. Mater., 28, 3462-3568 (2016) [2] M. Gueye et Al, ACS Appl. Mater. Interfaces, 9, 27250-27256 (2017)

Resume : Silver nanowire (AgNW) networks offer excellent electrical and optical properties and have emerged as one of the most attractive alternatives to transparent conductive oxides to be used in flexible optoelectronic applications. However, AgNW networks still suffer from chemical, thermal, and electrical instabilities, which in some cases can hinder their efficient integration as transparent electrodes in devices such as solar cells, transparent heaters, touch screens, and organic light-emitting diodes. We have used atmospheric pressure spatial atomic layer deposition (AP-SALD) [1] to fabricate hybrid transparent electrode materials in which the AgNW network is protected by a conformal thin oxide layer, typically ZnO. The choice of AP-SALD allows us to preserve the low-cost and scalable processing of AgNW-based transparent electrodes, and to maintain the possibility to obtain flexible transparent electrodes. The effects of the coating thickness on the physical properties of AgNW networks are presented. A simple physical model shows that the origin of the stability improvement conferred by the oxide layer is the result of hindered silver atomic diffusion thanks to the presence of the thin oxide layer and the quality of the interfaces of hybrid electrodes. The effects of the oxide coating on both the network adhesion and optical transparency are also discussed, and a simple strategy to improve the latter is proposed. We also present a simple model to account for the enhanced conductivity of oxide-AgNWs composite electrodes for AgNW networks areal mass density below the percolation threshold. Finally, we show that the AP-SALD-coated AgNW networks can be effectively used as very stable transparent heaters [2,3]. [1] Muñoz-Rojas, D., Viet Huong Nguyen, Masse de la Huerta, C., Jiménez, C. & Bellet, D. Spatial Atomic Layer Deposition. in Intech open 1 (2019). doi:10.5772/32009 [2] Khan, A., Nguyen, V. H., Muñoz-Rojas, D., Aghazadehchors, S., Jiménez, C., Nguyen, N. D. & Bellet, D. Stability Enhancement of Silver Nanowire Networks with Conformal ZnO Coatings Deposited by Atmospheric Pressure Spatial Atomic Layer Deposition. ACS Appl. Mater. Interfaces 10, 19208?19217 (2018). [3] Viet Huong Nguyen, Joao Resende, Dorina T. Papanastasiou, Nil Fontanals, Carmen Jiménez, David Muñoz-Rojas, Daniel Bellet, Nanoscale, accepted 2019

Resume : Transparent conductive electrode (TCE) with high optoelectronic performance (i.e. high transparency and low sheet resistance) is of great interest due to the significant demand of the electronic field to replace conventional indium tin oxide (ITO). Even though ITO exhibit high optoelectronic performance (sheet resistance lower than 10 Ω.□-1 and a transmittance higher than 90%), the price is tremendously increasing due to the scarcity of indium. In this context, new technologies have been established to avoid the use of ITO while keeping high optoelectronic performance such as electrode made of silver nanowires, nanocarbons, conductive polymers, and metal nanomeshes. Among all, the nanomesh technology show good optoelectronic performance but also a high stability under severe mechanic deformation. Indeed, the high bendability of the TCE become an important asset for the electronic market due to the huge progress of flexible electronic. In this contribution, an innovative way of synthesis of nanomesh will be presented including the use of the dealloying process. The hint to overcome the drawback link to the use of this unusual process will be presented. The resulting nanomesh show high optoelectronic properties (sheet resistance of 44 Ω.□-1 and 79% of transmittance) with the ability to stay conductive after severe mechanic deformation. Moreover, a successful process to transfer these nanomeshes on various material or over substrate with complex shape while remaining conductive will be exhibited.

Resume : Ultra-thin conducting fibres possess unique mechanical, optical and electrical properties due to the high aspect-ratio, low bending stiffness and transparency. Those fibre arrays made with different conducting materials could enable a variety of novel applications, ranging from transparent textile-based circuits to cell electrophysiology sensors. Current fibre fabrication techniques usually deposit fibres onto substrates, and the optomechanical properties of substrates largely compromise the advantages of ultra-thin fibres. Herein, we present an efficient fibre printing method to produce conducting and substrate-free sub-micron fibres arrays. The fibre printing and fibre to circuit connection are completed in one step under a sub-100°C mild temperature, without needing post processing steps such as annealing. With this printing method, we demonstrate the capability to print metallic based (silver) fibres for transparent electronic applications, and conducting polymer based (PEDOT:PSS (poly(3,4-ethylenedioxythiophene) polystyrenesulfonate)) fibres for tissue engineering applications. The fibres produced have an average diameter of ~2μm, and can span across a freestanding distance up to 10mm, having both ends attached to outer circuit with negligible contact resistance. Floating electronics are demonstrated with silver based fibre, small electronics such as LEDs and photodiodes are mechanically supported and electrically connected by suspended fibre arrays. Cell attachment and viability results with suspended PEDOT:PSS based fibre arrays lay potentials for future work on biosensors.

Resume : Single-walled carbon nanotubes (SWCNTs) are among the strongest candidates for the replacement of commonly used transparent and conductive films (TCFs) based on doped metal oxides, such as indium tin oxide. SWCNTs possess unique multifunctional nature, which is based on their outstanding combination of mechanical strength and flexibility, chemical stability, exceptional electrical conductivity and optical properties. However, to fully utilize these properties in modern transparent electrode applications, SWCNT-based TCFs have to demonstrate the optoelectronic performance at the level of high-end ITO-based TCFs. This has not been achieved for SWCNT films yet and as a result limit their practical usage. Using gold chloride as the most effective dopant for the SWCNTs, we improve their optoelectrical characteristics by optimizing the doping solvent and conditions. We examined various solvents to push the optoelectrical performance of the TFCs based on SWCNTs. As a result, we obtained the sheet resistance below 40 ?/? at the transmittance of 90% (at 550 nm). This optoelectrical performance is better than that of ITO on PET substrates and satisfy most of the requirements for modern applications and relatively stable without additional protection over two years storing under ambient conditions. Also, we examine the effect of ionic liquid gating on the electronic structure of the SWCNTs and their optical and electrical properties. This work was supported by the Russian Science Foundation (Project identifier: 17-19-01787).

Resume : Transparent conductive oxides are essential for applications such as solar cells where they can filter the carriers and play the role of the front contact. Most commonly these electrodes are constituted of transition metal oxides such as ZnO or TiO2 doped with Al, Ga, N… These materials present advantages such as a chemical stability, antireflective properties, and large bandgap insuring a good transparency in the visible range. In most cases such materials are deposited in thin film form using PVD techniques. This work focuses on SnOx sputtered TCO layers that are used as front electrode in CIGS based solar cells. Although these layers present a good conduction and transparency, they can be also doped with rare earths (RE) ions. Such doping allows SnOx to serve also as photon down-shifting converter. The direct excitation of the SnOx host matrix with UV photons leads to a strong emission of near infrared photons from the RE3+ ions suggesting an efficient energy transfer from SnOx to the RE. Doping SnOx with Yb leads to an enhancement of the photoluminescence emission and to the improvement of the transport properties. The optimized Yb:SnOx films exhibit a transmittance around 80 % in the visible region, a resistivity of 6×10−3 Ω.cm, and a mobility as high as 50.1 cm2/(V.s). When replacing the i-ZnO layer by Yb:SnOx in CIGS based solar cells, an efficiency increase of 0.6 % is observed. This result can be attributed to both the electrical properties of the Yb:SnOx layer that show an improved charge collection and to the down shifting properties which reduce the thermal losses in the cell.

Resume : Nowadays, more and more building surface areas are covered by windows to maximise the utilisation of sun light to brighten and warm up the building. Integrating bifacial and semi-transparent high efficiency perovskite solar cells (PSC) into power generating windows as part of building integrated photovoltaics (BIPV) application offer great potential to deliver energy-positive and zero-emission buildings. In this work, we fabricate PSC using transparent conductive oxides (TCO) as both top and back electrode on window glass to enable perovskite to absorb light from both outdoor sunlight and indoor light sources to generate electric power for consumer electronic devices and low-power Internet-of-Things (IoT) throughout the day. The device structure used in this work is Glass/FTO/SnO2/Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3/Spiro/IZO. Furthermore, the fabricated semi-transparent solar cells showed a high transmission in the near-infrared region of the spectrum which is desirable to transmit the thermal energy into indoor spaces. For simulated one sun light source, the resulting semi-transparent solar cells showed power conversion efficiency of 15% illuminated from fluorine doped tin oxide (FTO) side and 12.3% illuminated from indium zinc oxide (IZO) side. Under 1000 lux and 200 lux fluorescent tube light, those PSC devices showed highest maximum power density of 85.11 µWcm-2 and 17.67 µWcm-2 (illuminated from the IZO side), respectively. The low-light performance of these semi-transparent PSCs is among the best for indoor-use PSCs. We demonstrate that an unencapsulated semi-transparent perovskite solar cell showed excellent device stability under continuous one-sun equivalent visible illumination for over 500 hours in a N2 environment.

Resume : In the fourth Industrial Revolution, which is now the hottest, the display is one of the core technologies, along with the ability to communicate and share information with 5G network system. These displays can be divided into LCDs that rely on Backlight and OLEDs with self-luminance. OLED displays show almost true deep black and fast responsive, more than 1,000,000:1 contrast ratio. Therefore, these OLEDs can be the ultimate form factor free's display implementation, such as foldable, rollable, wearable, and stretchable. Because it is a multi-layer film which is composed of organic materials, it is most important to improve storage reliability and life time. In this paper, we review the recent progress of research on improving the characteristics, storage reliability and life time by replacing organic multilayer film with water-and oxygen-resistant transparent conducting inorganic layer in OLEDs.

Resume : There are many oxide semiconductors used as photocatalysts such as TiO2. ZnO is one of them, and it is an advantage that ZnO thin films and nanostructures can be formed at relatively low temperatures using a simple non-vacuum process. In this study, we investigate photocatalytic activity of ZnO thin films with defects formed by annealing and electrochemical treatment. ZnO thin films were deposited on glass substrates by using a spin coating method. Zinc acetate dissolved in ethanol was used as a precursor solution. Spin coating and drying were repeated and then the samples were annealed at 500°C for 1 hour in air. Defects were formed in the ZnO thin films by annealing in H2 and electrochemical treatment. The electrochemical treatment is a process of applying a current between the H2-annealed ZnO thin film and the platinum electrode in an electrolyte. Sheet resistance of the ZnO thin films was decreased by the H2-annealing and further decreased by the electrochemical treatment. To evaluate photocatalytic activity, the ZnO thin films dipped in a methylene blue solution were irradiated with a high-pressure mercury lamp. The ZnO thin films after the H2-annealing and electrochemical treatment showed better photocatalytic activity. The H2-annealing and electrochemical treatment are effective methods to improve photocatalytic activity of ZnO films.

Resume : With the rapid development of flexible electronics, transparent conducting oxides (TCO) alternative to ITO (indium tin oxide) have attracted increasing attention because their constituent raw materials are nontoxic, abundant and low cost. TCO materials [1] are utilized as electrode materials in a wide variety of optoelectronic devices. Atomic layer deposition (ALD) has been the thin-film deposition method of choice for a number of challenging applications in microelectronics, and it would be highly relevant technology for the transparent flexible electronics as well [2]. High-performance conducting Al-doped ZnO (AZO) thin film electrodes are deposited on flexible substrates by alternating diethylzinc Zn(CH2CH3)2, DEZ; Al(CH3)3, TMA and deionized water (H2O) in an ALD reactor (Beneq TFS-200) at 100-200 °C using both thermal and plasma-enhanced modes . Structural, electrical, and optical properties of deposited AZO films are measured towards the TCO application. It is found that AZO/flexible substrates retains its low electric resistivity, even after continuous bending of up to 1000 times due to the unique layered structure of mica and the low thermal budget plasma-enhanced process. Flexible liquid crystal devices with AZO electrodes are developed and their performance assessed. Acknowledgment: the financial support through TOCHA project funded by the European Commission through H2020-FETPROACT-01-2018 under Grant Agreement 824140 is greatly appreciated. REFERENCES [1] M. Morales-Masis, S. De Wolf, R. Woods-Robinson, J. W. Ager, and C. Ballif, Adv. Electron. Mater. 3 (5)1600529 (2017) [2] R. W. Johnson, A. Hultqvist, S. F. Bent, Materials Today, 17 (5) 236 (2014)

Resume : The properties of a photodetector device with a balanced photodetector, which includes an avalanche silicon photodiode with a Schottky barrier, have been analyzed. Advantages of the analyzed semiconductor photodetectors as compared with other detectors of the optical signal, in particular, their ability to register long-wave radiation, since the formation of mobile carriers in them is not related with overcoming a significant surface potential barrier are noted. To realising a high multiplication factor of an avalanche silicon photodiode with a Schottky barrier, an approach consisted of using the latter together with a receiving optical module for fiber-optic telecommunications systems has been proposed. A spectral characteristic for the Si-Au system has been obtained, it is not inferior to a germanium photodiode with the possibility of further optimization. The frequency and noise characteristics of the device are presented. The dynamic range and the threshold of its sensitivity have been determined. The physical equivalent circuit of the photodiode of the specified type is obtained. The frequency characteristics of the output power and the noise characteristics of the receiving optical module have been presented. It was determined that the sensitivity threshold is -36 dB at an information transfer rate of 5 Gbit/s. Reduction of intersymbol interference has been experimentally detected, which will be especially effective in the case of propagation of a signal of the corresponding form. The obtained characteristics totally satisfy the requirements imposed on photodetectors of this type

Resume : Transparent conducting oxide (TCO) thin films have received increasing attention in the last decade due to their use in solar cells as electrodes. As one of the deposition methods, spray pyrolysis is well suited for the preparation of doped tin oxide thin films because of its simple, low cost experimental arrangement, ease of doping with various elements, reproducibility, high growth rate and ability for uniform and large area coatings. Fluorine-doped tin oxide (FTO) exhibits highly chemical stability, high resistance to physical abrasion, especially when compared with indium tin oxide (ITO) and it is also an abundant material in nature. As an n-type semiconductor material, SnO2 with a wide band gap (3.5 ~4.0 eV at 300 K) and a high excitation binding energy (~130 meV) has excellent electrical/optical properties and high chemical stability. It is expected to have higher reliability than ITO because it has less oxygen vacancies. FTO films which was deposited on a glass layer by spray pyrolysis method at 450℃ shows preferred orientation along (200) plane with very high intensity corresponding to the SnO2 polycrystalline structure. We did the reliability test and compared the measurement results before and after (duration time is 48hr) the resistance humidity (85℃, 85%), thermal shock test (450℃, 30min↔ room temperature, 30min), high- temperature test (450℃, 48hr). Unlike expectation, Resistance and mobility showed rapidly changes in the humidity environment. In this study, the deterioration mechanism of FTO was analyzed by observing deterioration tendency at high temperature, high humidity condition, and thermal shock condition.

Resume : Compared to sputtered zinc oxide (ZnO) films, ZnO films prepared by low-pressure chemical vapor deposition (LPCVD) method have some advantages in CIGS solar cell applications such as low defects in CIGS absorber layers due to the absence of ion bombardment damage and high light absorption in CIGS solar cells due to low light absorption and rough surface structures. In this study, boron-doped zinc oxide (ZnO:B) films were grown by LPCVD technique using diborane (B2H6) gas for boron doping and diethylzinc (DEZ) and water (H2O) as precursors. Also, the argon (Ar) gas used as the carrier gas for bubbling was injected along with liquid DEZ and liquid H2O into CVD reactor. 2 micrometer-thick ZnO:B thin films was deposited at various substrate temperatures (Tsub) by LPCVD system for application as TCO layers in copper indium gallium di-selenide (CuIn1-xGaxSe2, CIGS) thin film solar cells. The DEZ, H2O vapor and B2H6 flux were kept constant at 350 sccm, 250 sccm and 0.7 sccm, respectively. The Tsub at the front surface of substrate was varied from 140 to 210℃. In the experimental results, surface roughness and electrical resistivity of ZnO:B films were about 72 nm and 2.1×10-3 ohm·cm, respectively. As a result of processing conditions on LPCVD ZnO:B films for application in CIGS solar cell, the best cell was fabricated with Al/ZnO:B/CdS/CIGS/Mo/SLG structure and yielded a conversion efficiency of 17.6% with Voc = 0.667 V, Jsc = 35.9 mA/cm2 and FF = 0.732.

Resume : Multilayer films with Mn (2.59 wt.%)-doped tin oxide (MTO)/Ag/Mn-SnO2 (MTO) hybrid structure were prepared on a flexible polyethylene terephthalate (PET) substrate using a DC/RF sputtering system at room temperature. The dependence of the optical and electrical properties of MTO multi layer films on the O2/(Ar+O2) ratio was systematically investigated. The transmittance of the MTO single layer (24 nm) at 550 nm gradually increased from 85.9 % to 88.2 % with an increase of the O2/(Ar+O2) ratio from 0 % to 7.9 %. The optical band gap was also affected by the O2/(Ar+O2) ratio, varying from 3.30 to 3.64 eV. The MTO film deposited at an O2/(Ar+O2) ratio of 2.7 % showed the minimum resistivity (0.03 Ω·cm) while the sheet resistance (RS) of the multilayer films increased from 6.3 to 9.8 Ω/sq upon increasing the O2/(Ar+O2) flow rate. The highest figure of merit (φTC) of MTO/Ag/MTO multilayer film was 45.7 × 10-3Ω-1 at an O2/(Ar+O2) flow rate of 2.7%. XPS spectra with different oxygen concentration indicate that a multiphase with SnO and SnO2 coexisted in the sputtered MTO thin films. Thus, this sputtering process can be used to prepare flexible MTO films with a wider optical band gap, improved transmittance, and decreased resistivity.

Resume : Metal fluorides are important material for optical coatings applications due to their good transparent from infrared (IR) to ultraviolet (UV) range. Physical vapor depositions like sputtering and evaporation are the most popular deposition techniques for metal fluorides. Atomic layer deposition (ALD) is a chemical gas phase thin film deposition method based on sequential, self-saturating surface reactions. Because of the separation of two precursors, ALD has excellent conformality and accurate thickness control. In the study, magnesium fluoride (MgF2) and lanthanum fluoride (LaF3) were deposited by ALD using Mg(thd)2, La(thd)3 and TiF4 as precursor. The saturation curves and growth rates of MgF2 and LaF3 were obtain from thickness measurement using spectroscopic ellipsometer. The growth rates of MgF2 and LaF3 at 400oC were 0.72 Å and 3.16 Å per cycle respectively. The composition analysis of metal fluoride films that fabricated at different substrate temperature were carried out by X-ray photoelectron spectroscopy. From the XPS spectrum, the films were with high impurity levels when the substrate temperature was lower than 400oC. The Impurity of carbon was not detected in the films at a substrate temperature of 450oC. However there is still a small amount of oxygen in the film even at 450oC. The residual oxygen may be from the metal organic precursor. The post annealing processes were also carried out to reduce the impurity of fluoride films.

Resume : Thin films of copper (I) bromide were grown by direct thermal vacuum evaporation of the related compound on mono silicon or soda lime glass substrates. X-ray diffraction of as deposited layers indicates randomly oriented well crystallized cubic, face centered Cu(I)Br with grain sizes about 100 nm. Scanning Electron Microscopy revealed a dense, compact morphology of the deposits with characteristic pillar structure. FTIR spectra presented the specific vibrations of the compound Cu(I)Br. The X-ray photoelectron spectroscopy was applied for characterization of the thin film samples and confirm the stoichiometry CuBr. Optical spectrometry present more than 80 % transparency in visible region and zone of strong absorption near 2.98 eV with a split off band at near 0.5 eV above the valence band edge. Spectral elipsometry measurements show extinction coefficient about 10 -5 after 480 nm and refractive index near 2.10 at 600 nm. Electrical measurements of the films indicated definitely p-type of conductivity with resistivity near 400 Ohm/□. Solid state thin films structures in configuration of Cu / CuBr / Cu have presented straight line I-V dependence indicating formation of ohmic contact in the structure

Resume : Printed electronics easily manufactures electronic circuits and devices on highly flexible substrates made of plastics and rubber composites, and it has recently attracted attention of many researchers. Characteristically, devices exhibiting high flexibility and elasticity are durable with a high degree of shape freedom. Flexible solar cells, displays, and sensors have therefore been studied actively. Developing a high-performance and flexible transparent conductive film has been anticipated to practically use these devices. Widely used indium tin oxide (ITO) is not suitable for flexible devices, as ITO is susceptible to bending stress and prepared by high-temperature vacuum treatment. We focused on conductive polymer poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) as a substitute for ITO to solve these problems. We prepared a film on polyethylene naphthalate substrate using an inkjet printer. Our previous studies reported that characteristics of a thin film could be improved by annealing after printing operations, the application of a polar solvent between printing operations and the use of low-viscosity and high-boiling point dimethyl sulfoxide as a solvent for ink. Applying polar solvent using a printer, however, increased thin film surface roughness. This greater surface roughness affected thin film electrical and optical characteristics. This study aimed to further improve the thin film characteristics by adding to a polar solvent a surface-active agent that decreases surface tension. When an ionic surface-active agent (Surflon S-231) was added to a polar solvent, transmittance of the obtained thin film was not less than 90 %. Thin film surface homogeneity also improved. This revealed that transmittance of obtained thin film was improved by adding an ionic surface-active agent to a polar solvent. However, thin film resistivity increased. In addition, when a non-ionic surface-active agent (Surflon S-243) was added to a polar solvent, transmittance of obtained thin film was not less than 90 % and its homogeneity also improved. Although thin film resistivity increased, resistivity was lower than when ionic surface-active agent was added. Transparent conductive film having applicable transmittance could be prepared, therefore, by adding a surface-active agent to a polar solvent. These results will be useful for the practical application of flexible devices manufactured using only inkjet printing.

Resume : CVD graphene has been attracted as flexible transparent electrode due to its high electrical conductivity, mechanical deformability and mass-processability. However, defects in CVD graphene such as grain boundaries, wrinkles and microscale defects from its growth and transfer process critically disturb large-area uniformity. In this work, graphene/In2O3 bilayer-structure composite (GI) was systematically investigated as a transparent conducting electrode (TCE) to overcome reliability issue of graphene electrode. Firstly, electrical and optical properties of GI were evaluated by varying a thickness of In2O3 from 10 to 50 nm. The percolation model on Hall measurement makes it possible to extract the electrical properties of graphene sublayer in GI from that of composite. Sheet resistance of graphene in GI reduced from 863 to 510 Ω/sq, which is interpreted as a result of doping on graphene in GI. Hall effects measurement, Raman spectroscopy analysis, and ultraviolet photoelectron spectroscopy (UPS) were performed to elucidate p-type doping of graphene in GI. Most importantly we noted that extreme sheet resistance uniformity of GI is achieved compared to typical monolayer graphene electrodes. A standard deviation of sheet resistance of GI shows only 12 Ω/sq within 7 x 7 cm2 scale, which decreased by almost an order of magnitude than that of bare graphene. Homogeneously deposited conducting In2O3 film could act as current bypath below the microscale defects on graphene, compensating a conductance of defective region on graphene. Our method suggests a new way to fabricate a transparent conducting electrode with extreme large-area uniformity for mass production of future electronics.

Resume : We report the deposition of minute amount (less than a monolayer) of transition metals (TM = Fe, Co, Ni) on ta-C films prepared by pulsed laser ablation (PLD) on transparent quartz (TM/ta-C/quartz sample). Apart from the nature and dose of metal evaporated, the thickness and the sp3/sp2 ratio controlled by the PLD parameters (time and fluence) are key parameters investigated in order to grow by thermocatalytic treatments a thin graphitic layer from ta-C ((1). The location of the metallic nanoparticles was investigated by XPS while the formation of graphitic domains was investigated by Raman spectroscopy. The choice of the transition metals has been operated as a function of their high reactivity to carbon-carbon bond reactivity but also to their ability to absorb carbon. The formation of the graphitic layers is depending both on temperature and time (2). The system TM/thin graphitic layer/DLC/quartz exhibits under optimized conditions, high transmission and high surface conductance, with figures of merit for transparent conductivity equal or even higher than ITO. We observed an optimum in the fluence as well as the thickness of the DLC layer. (1) “Kinetics of graphitization of thin diamond-like carbon (DLC) films catalyzed by transition metal”, N. Boubiche, J. El Hamouchi, J. Hulik, M. Abdesslam, C. Speisser, F. Djeffal and F. Le Normand, Diamond and Related Materials, 91 (2019) 190-198 (2) “High performance diamond-like carbon layers obtained by pulsed laser deposition for conductive electrode applications, F. Stock, F. Antoni, F. Le Normand, D. Muller, A. Abdesselam, N. Boubiche and I. Komissarov, Applied Physics A: Materials Science & Processing - 'New Frontiers in Laser Interaction', 123 (2017) 590-595

Resume : Development of high-performance p-type transparent conductive materials (TCMs) remains a grand challenge in materials science. Existing p-type TCMs, such as LaSrCrO3 or SnO, still fall short of the required transparency and hole transport properties necessary for successful application in optoelectronic devices. One major challenge lies in the curvature of the valence band: in typical p-type TCMs, valence bands are flat and states are localized due to the oxide chemistry of these materials. A new class of materials has recently been predicted to overcome this challenge by utilizing mixed-anion chemistry (e.g. oxy-chalcogenides or oxy-pnictides) to enhance valence band dispersion.1 Zirconium oxy-sulfide (ZrOS) is one such material with a light hole effective mass of 0.37m0 and a bandgap of 4.2 eV in the cubic phase.2 Although this material has been prepared via bulk synthesis routes and is a known secondary phase in the sulfurization of Zr metal, no examples of thin film synthesis have yet been reported. In this work, we present the results of post-sulfurization treatment on Zr-based thin films with the aim of obtaining ZrOS. Treatment time, pressure, temperature, and partial pressure of oxygen were varied over a wide range and structural changes were tracked with X-ray diffraction. UV-Vis-NIR transmission spectroscopy was used to observe the effects of each sulfurization treatment on film transparency. Finally, X-ray photoemission spectroscopy was used to assess film composition, with a particular focus on the bonding environment of sulfur under different sulfurization conditions.

Resume : The work is devoted to ascertainment of the regularities for thermostimu-lated formation of the phase composition and structure of CoSb3-scutterudite-based films deposited by the vacuum condensation method, as well as the effect of the nanoscale factor on their thermoelectric properties. It was determined that the presence of the nanoscale factor (the single-phase crystalline structure of CoSb3 scutterudite with an extended area of existence in the film with increased structural defect due to the sublimation of antimony and reduction in the grain size) causes an increase in the thermoelectric efficiency coefficient of Co-Sb films in 8 times as compared to the bulk material. In studies, to increase the ZT, we plan to dope of nanosize Co–Sb films with different chemical elements Fe, Yb, Li, Eu, La, Се, Ba to form a structure that can better conduct electric current (as a crystalline conductor) and poorly conduct a heat (like a glass). This will make possible to reduce a phonon component of the heat conductivity and much more increase thermoelectric efficiency coefficient ZT. Doping elements occupy voids in the crystal lattice – atomic polyhedrons of large sizes. This provides an effective phonon scattering, which in turn results to decreasing of the heat conductivity without a substantial impact on electrical conductivity due to mainly ionic character of interaction between phonons and atoms of scutterudite carcass and covalently bonded carcass with a small probability of chemical bonds. This has a practical importance when these materials are used for providing the autonomous power supply for low-power electronic devices and creating film coolers in the elemental base of the nanoscale range for computer equipment and infrared sensors.

Resume : The understanding of the dynamics of photogenerated charge carriers is of real interest for the development of devices such as photodetectors, photovoltaic cells and optoelectronics in general. The photocarriers dynamics can be measured by different techniques such as time-resolved photoluminescence spectroscopy, Electron-Beam-Induced Current (EBIC) [1]. Nevertheless, it is still difficult to obtain nanometric resolution and to separate the surface recombination from bulk recombination. Kelvin Force Probe Microscopy (KPFM), which is an electric mode of Atomic Force Microscopy (AFM), is one of the most sensitive method to detect change in surface potential induced by the injection of photocarriers (Vph≈5mV). As a consequence, KPFM is well suited to probe the photocarrier dynamic through Vph measurement at a nanometric scale. To the notion of recombination dynamics we can derive two quantities, the carrier diffusion length (L) and the carrier lifetime (τ). Carrier diffusion length can be estimated from Vph measured in the function of illumination wavelength [2]. Lifetime can be obtained from averaged Vph measured under frequency modulated illumination at a given sample illumination wavelength [3]. In this poster, we will present the principle of these optical methods to measure nanometrically resolved lifetime and carrier diffusion length from KPFM Vph measure. We will show as well the result on p-type silicon sample passivated by aluminum oxide where measured quantity are dependent on passivation. Finally, we will demonstrate the possibility to separate the surface recombination from the bulk recombination by tuning the sample illumination wavelength. [1] L. Kronik, Y. Shapira/Surface Science Reports 37 (1999) 1-206 [2] Dieter K Schroder Meas. Sci. Technol. 12(2001) R16-R31 [3] Borowik Ł. et al Nanotechnology 2014, 25, 265703.

Resume : Strain sensor has been spotlighted for its versatility on healthcare, soft robot, and human-robot interface. Despite of large potential demands, traditional metal-based strain gauges have limitations of stretchability (ε ≤ 2 %) and flexibility. Extensive studies have been presented for stretchable sensors using various nanomaterials and metal films. However, it is still hard to satisfy parameters such as sensitivity, stretchability, linearity, hysteresis, applicability to mass production. Herein, we propose a highly sensitive strain sensor with solution-processed metal grid structures. We investigated the effects of width and width/spacing ratio of the metal grid on piezoresistivity of the strain sensors. Our strain sensors exhibit high sensitivity (GF = 4685.9) and superior strain range (ε ≤ 5%) compared to other metal-based sensors. In addition, our metal grid strain sensors can be produced with eco-friendly and low-cost procedure, due to all water-based solution process.

Resume : We report the web-like network of silver nanowires (AgNW) bundles using the dewetting phenomenon of liquid thin films to produce highly transparent electrodes. These web structures can be formed by dewetting of the liquid thin film on hydrophobized coating substrates. We deposited AgNW suspension mixed with isopropyl alcohol (IPA) and ethylene glycol (EG) on the substrates by using meniscus-dragging deposition (MDD) technique. Length and diameter of the AgNW bundles and the open space area of the AgNW-web structure can be easily controlled by varying the contact angle of substrate, the EG concentration of suspension, and coating parameters of the MDD process. We analyzed the principle of such phenomenon by calculating dewetting and drying times of the liquid thin films. The AgNW-web structured transparent thin films is superior in optical and electrical properties to the electrodes that have random network of AgNW, which is described well by the high ratio of DC to optical conductivity and percolation theory in a two-dimensional matrix model. Our simple coating technique enables the AgNW bundles to be deposited on the substrates forming the web-like structure which show high optical transparency directly on the rigid substrates and flexibility, and stretchability on the plastic substrates.

Resume : Research on conductivity mechanism in ZnO deposited by ALD is particularly important due to its decisive role in practical applications of the material. Based on previous research it can be concluded that this mechanism is strongly dependent on native defects and non-intentional dopants introduced during the deposition process. In this work we investigated structural, electrical and optical properties of epitaxial ZnO layers deposited by ALD on GaN/Sapphire substrates by XRD, RBS, LT-PL and temperature dependent Hall measurements. Following an established routine to achieve epitaxial samples deposition process was carried out at high temperature (300°C). RBS measurements confirmed a value for the crystalline quality indicator χmin. equal to ~2.8% which is comparable with commercial single crystal ZnO (Mateck). Grown layers are anticipated to be conductive (ρ~0.02 Ωcm) with carrier concentration ~1E19 cm^(-3). To lower the conductivity for performing further detailed electrical characterization portion of the samples from the same batch were annealed at 400°C and 600°C for 30 min. in N2 flow. This allowed to distinguish presence of at least 3 donors with activation energies around ~40, ~45 and ~50meV. By comparison with temperature dependent Hall measurements their contribution to the electrical properties of the layers is discussed. Acknowledgments. This work was supported by the Polish National Science Center (NCN) through the project UMO-2016/22/E/ST3/00553.

Resume : Gallium oxide, a transparent semiconducting oxide, is promising for a wide range of applications in the fields of electronics, optoelectronics, and sensors [1]. In this work thin gallium oxide layers were prepared by plasma-enhanced atomic layer deposition (PEALD) on silicon four inch wafers in the SENTECH SI PEALD system [2] at substrate temperatures ranging from 80 °C to 200 °C. The films were characterized by ellipsometry, X-ray photoelectron spectroscopy (XPS), and electrical measurements. The growth rate per cycle was almost constant in the investigated substrate temperature range and reached values of about 0.67 Å/cycle. The thickness distribution of the layers across the four inch wafers was very uniform, with low inhomogeneity values of 2.0% and below. The refractive index and the permittivity were determined to 1.86±0.01 (at 632.8 nm) and 9.9±0.4 (at 10 kHz), respectively. Fixed and mobile oxide charges in the order of 1E12 cm-2 were observed in the capacitance-voltage characteristics. For the gallium oxide films, the gallium to oxygen ratio is very close to the ideal stoichiometric ratio (2:3) in the full investigated substrate temperature range as evaluated by XPS analysis of the Ga3d and O1s core levels. Results from depth profiling analysis of the layer composition based on cyclic Ar ion sputtering combined with XPS will also be reported. [1] Z. Galazka, Semicond. Sci. Technol. 33, 113001 (2018). [2] K. Henkel et al., J. Vac. Sci. Technol. A 32, 01A107 (2014).

Resume : The photovoltaic devices like CIGS & CZTSSe solar cells have been using CdS as a buffer layer. Because of its’ toxic nature, an eco-friendly buffer layer should be replaced. In this study, Zn-based materials such as ZnO, ZnS & Zn (O,S) were studied as an alternative buffer layer to CdS. Atomic Layer Deposition (ALD) method has been adapted to deposit the above-mentioned materials because of its coating conformality and precise thickness control. 0.2 s of Diethylzinc (DEZ), 0.1 s of H2O separated by 10 s of N2 purge is the ALD cycle sequence for the deposition of ZnO film. While the ZnS film was deposited by using 0.2 s of Diethyl zinc (DEZ) and 0.1 s of H2S. On the other hand, Zn(O,S) films were fabricated by alternating the m number of ZnO cycle and n number of ZnS cycle with the ratio m:n. Here, we deposited Zn(O,S) films with a ratio of 3:1 and 5:1. All of the above materials were deposited at 200°C with the growth rate of 1.6 Å/cyc for ZnO and 1 Å/cyc for ZnS. The elemental composition of the Zn, O & S in these materials, was measured by X-ray electron spectroscopy (XPS). Surface morphology of the Zn(O,S) film with a ratio of 5:1 was analyzed by SEM. Changes in the electrical properties of the Zn(O,S) films with the changes in the oxygen to sulfur ratio will be studied by Hall measurement.

Resume : The optical transmittance and sheet resistance of oxide/metal(Ag)/oxide transparent electrodes are easily degraded at over 300°C because of the aggregation of the Ag layer. In order to improve the thermal stability of the oxide/Ag/oxide transparent electrodes, we inserted the 3nm-thick Al layer as a thermal protection barrier. At the 3nm-thick Al barrier, the oxide/Ag/Al/oxide transparent electrode could sustain the high optical transmittance of 86.4% (at 550nm wavelength) and low sheet resistance of 3.5Ω/sq after annealing at 550°C for one hour, and show the good environmental stability after moisture test (relative humidity 85%, 85°C, 120hr).

Resume : Indium free abundant amorphous transparent conducting oxide (a-TCO) materials have high chances to take a prominent place in the field of optoelectronic devices due to their high conductivities along with innate resistance to degradation upon bending and relatively low deposition temperatures. Currently, InGaZnO4 (a-IGZO)[1] is the most widely used amorphous TCO, that has an In content that raises concerns about scarcity, supply and rising costs. The development of low cost electronics industry requires an In-free alternative made of cheap and abundant elements. a-ZnSnO (a-ZTO)[2] is fulfilling aforementioned parameters. This work illustrates an extensive Zn/Sn composition maps of co-sputtering grown ZnSnO. The combination of Hall measurements, X-Ray Diffraction/Reflection (XRD/XRR), X-ray Photoelectron Spectroscopy (XPS) and post deposition heat treatment with in-situ monitoring of the electrical properties allowed us to link the mobility, conductivity and carrier concentration of a-ZTO to its composition. As a result, an optimised electrical properties were established with conductivities of up to 225 S/cm2 and motilities of 16 cm2/Vs that are achievable via both reactive and non-reactive magnetron deposition. This analysis brings to light a fact that the relationship between the Zn/Sn ratio and the electrical properties of the material can vary depending on the deposition technique utilised. 1. Kamiya, T., K. et al., Science and Technology of Advanced Materials, 2010. 11(4). 2. Fernandes C., et al, Advanced Electronic Materials, 2018, 4, 1800032

Resume : In this work the results of air wetting of tin dioxide films by metal melts of Ag-Cu system were obtained. The films of tin dioxide (300 nm thickness) were deposited onto sapphire surface and were annealed in air at 1073 K during 10 min. Concentration, temporal and temperature dependences of contact angles for a number of metallic melts on SnO2 films were obtained. The microstructure of the contact zone was investigated.

Resume : ZnS, a II-VI semiconductor, is deemed to be one of the most promising II-VI semiconductors due to high direct bandgap (~3.6 eV), low electrical resistivity, high transparency and and nontoxicity. Traditionally ZnS thin films have been deposited using a wide range of vacuum-based and potentially expensive deposition methods. To address the manufacturing cost issues, we report on the deposition and characterisation of ZnS films deposited by spray coating at substrates temperatures in the range between 300 oC and 500 oC from single precursor solutions of zinc diethyldithiocarbamate. The films were investigated by means of UV–Vis spectroscopy, FTIR, x-ray diffraction, AFM, and field-effect measurements. Analyses of ZnS reveal ZnS films of wide band gaps on the order of 3.5 eV, cubic structure and preferential growth along the (111) orientation. TFTs employing solution processed ZnS semiconducting channels deposited at optimal conditions on Y2O3 and SiO2 dielectrics, show excellent carrier transport characteristics such as low off currents, electron mobility between 1 and 12 cm2 /Vs and on/off current modulation ratio in the range between 10^4 and 10^7.

Resume : In thin film transistors (TFTs) a wide range of binary metal oxides, such as Al2O3, Y2O3, ZrO2, HfO2, TiO2, Nb2O5 and Ta2O5 have already been demonstrated as promising gate dielectrics with superior properties compared with SiO2. Gate dielectric materials with high dielectric constants are desirable, but the band offset condition that requires a reasonably large band gap should also be satisfied. The latter point constitutes a significant drawback when wide band gap semiconducting channels need to be employed as such dielectrics cannot possess at the same time wide band gaps and high permittivity. The obvious solution to both the low dielectric constant and narrow band gap issues could be the use of a composite dielectric material, i.e. a ternary oxide that combines wide band gap, high permittivity and low leakage current. To that end, the use of ternary oxides, such as La2O3.Al2O3[1] and Al2O3.TiO2[2]has already been reported. Here we report on the deposition and characterisation of Ta2O5 . Al2O3 gate dielectrics as a function of the Ta to Al atomic ratio and their implementation in TFTs employing ZnO semiconducting channels. The films were deposited by spray coating at moderate substrate temperatures (about 400 oC) in air and characterised by UV-Vis, FT-IR, impedance spectroscopy, AFM, XRD and field-effect measurements. Analyses showed Ta2O5 . Al2O3 smooth films with dielectric constant in the range between 9 and 25 and optical band gap between 4.9 eV and 5.8 eV. TFTs employing Ta2O5 . Al2O3 dielectrics and In2O3 semiconducting channels show low leakage currents (<1 nA/cm2), high on/off current modulation ratio (>10^6) and electron mobilities in excess of 25 cm2 V−1 s−1. [1] D. Afouxenidis, R. Mazzocco, G. Vourlias, A. Krier, W. I. Milne, O. Kolosov and G. Adamopoulos, ACS Applied Materials and Interfaces, 7, 7334, 2015. [2] M. Esro, R. Mazzocco, G. Vourlias, O. Kolosov, A. Krier, W. I. Milne and G. Adamopoulos, Appl. Phys. Lett. 106, 203507, 2015.

Resume : This study reports the influence of the deposition conditions of SiO2 and ZnO oxide thin films on their structural characteristics. These films were deposited by radio frequency magnetron sputtering technique on quartz substrates. The film thickness values of 0.100-0.250 μm were measured using an interferometric method. The orientation of crystallites, surface morphology, mass density, structure and composition were investigated by X-ray diffraction (XRD), X-ray photon spectroscopy (XPS) and atomic force microscopy (AFM). AFM analyses showed that all the films had a granular-like and pinhole-free microstructure. The surface topography of samples was analyzed using scanning electron microscopy (SEM). Optical constants (refractive index n, extinction coefficient k, and absorption coefficient α) of the ZnO and SiO2 oxide films deposited by radio frequency magnetron sputtering on quartz substrates were determined using Swanepoel’s method. These values vary depending on the the deposition conditions and the thickness of the analyzed sample. The values of the energy band gap were calculated from the absorption spectra, for ZnO and SiO2 samples, deposited onto quartz substrates. By calculating the average value of the refractive index in the investigated wavelength range it was found that, in general, the refractive index of the layer increased with its thickness. As a result, depending on the deposition conditions, the ZnO and SiO2 oxide films showed a good optical quality and adhesion to the substrate. This research was supported by ELI [contract number 17/2017].

Resume : A mechanically robust, transparent, and healable strain sensor was successfully developed by embedding Ag nanowires (AgNWs) on the surface of healable-polydimethylsiloxane (H-PDMS) cross-linked by Diels–Alder (DA) adducts. When commercial polydimethylsiloxane (PDMS) was used, there was a problem that no binding chains remained on the surface of the polymer after it cured, making it poor adhesion with hydrophilic materials. To solve this, we designed H-PDMS with DA adducts which is characterized by thermally reversible intermolecular bonding reaction. The reversibility of the DA reaction enabled the heated methyl ethyl ketone (MEK) vapor to induce multiple cross-linking of the H-PDMS. A combination of the retro-DA reaction and the vaporized solvent effect softened the polymer surface and embedded the transferred AgNWs beneath the surface of the H-PDMS. With this simple process, the surface roughness and mechanical stability of the electrode could be largely enhanced. Further, swelling of the H-PDMS film owing to the MEK vapor facilitated the healing properties of the cracked electrodes. Subsequently, we fabricated two kinds of strain sensor using H-PDMS and the embedded AgNWs. First, AgNWs were placed on a neutral plane to create bending-insensitive strain sensor. Sensitivity of the fabricated sensor could be confirmed by measuring change in resistance sensitively depending on the strain applied to the sensor during repeated stretch-and-release test. Furthermore, the fabricated strain sensor has shown a resistance variation of 0.02% upon bending in the curvature radius of 3mm, revealing that it is bending-insensitive. The second form of the sensor is a capacitive sandwich-structured strain sensor fabricated by face-to-face lamination of the identical H-PDMS sheets with fully embedded AgNWs underneath their surface. In this case, since the AgNWs were located well underneath the surface of the polymer, a thin dielectric layer was formed between the facing AgNWs layers. The thickness of the dielectric layer sensitively varied with various mechanical deformation of the sensor, implying that it could be used as a highly efficient deformation sensor.

Resume : Nanostructured SnO(x) films were obtained by molecular beam epitaxy (MBE) by depositing Sn in an oxygen flux on the SiO2/Si substrate. The morphology, structure, and optical properties of obtained films annealed in the temperature range of 200 – 1000 ˚C were studied. The reflection high-energy electron diffraction during the film deposition by the molecular beam epitaxy method and the X-ray phase analysis showed that the initial films are in the polycrystalline phase. A single orthorhombic SnO2 phase was obtained for the first time after annealing the SnO(x) film in the air at a temperature of about 500 ˚C. The sharp change in the optical constants near the temperature of 500 ˚C was established using ellipsometry. The pronounced absorption edge appears in the short-wave region at temperatures above 500 ˚C and it disappears at lower temperatures. Thus, the temperature, at which the SnO2 phase is formed with the absorption edge in the energy range from 3.7 to 3.9 eV, was determined. The broad absorption band in the range 1.9 – 3.4 eV is apparently associated with an insignificant (approximately 1 % of the total) number of unoxidized metallic Sn clusters. The film thickness changed non-monotonically during the annealing in the air. At first, it grows from 45 nm to 65 nm (active oxidation to 500 ˚C), and then (above 600 ˚C) it begins to decrease. The annealing at temperatures of 500 – 1000 ˚C leads to the film compaction, since the film thickness decreases to 50 nm, but the refractive index increases by 10 – 15 %. Optical constants track the progress of film phase and morphological changes.

Resume : Transparent film heaters are widely used in diverse applications, such as window defrosters, outdoor panel displays, wearable electronics and the temperature-triggered release of antibiotics. They are predominantly prepared by using indium tin oxide (ITO) due to its high electrical conductivity and optical transmittance in the visible wavelength region. Nevertheless, ITO shows several disadvantages with respect to insufficient thermal response, mechanical bending, stability in acid or base and fabrication costs. Recently, silver nanowire (AgNw) based layers attracted significant attention as a replacement for the brittle and expensive ITO in the development of transparent thin film heaters. These reported film heaters are prepared by a multilayer approach of AgNw on the top or bottom surface of transparent polymer materials. However, this does not provide sufficient mechanical and chemical protection due to weak bonding interactions. Therefore, a one-step coating technique of a highly conductive, heat resistant and multifunctional AgNw-hybrid-composite is in great demand. Thin film conductors fabricated with this process can reach a sheet resistance of 8 Ohm*sq-1 with a transmittance of 80 % at 550 nm. At low operation voltage, the composite film acts as an efficient film heater generating temperatures up to 250 °C. This composite film heater demonstrates higher saturation temperatures at constant voltage, fast heating response and mechanical resistance to stress.

Resume : Thin film electronics has been developing rapidly in the last years, to a large extent through the advent of amorphous oxide semiconductors such as GIZO (In-Ga-Zn-O) [1], currently in use for display backplanes. Its brother from abundant, low toxicity materials is ZTO (Zn-Sn-O); we will present some recent results on ZTO devices including world-record inverters and ring oscillators [2, 3]. What is seriously lacking are matching p-type amorphous semiconductors with higher hole mobility than in amorphous p-type Si (about 0.1 cm2/Vs). Nanocrystalline CuCrO2:Mg was reported with hole mobility of 0.2 cm2/Vs, all other reported amorphous p-type materials, including a-ZnRh2O4, a-CuAlO2, a-SnO, a-Bi-Ru-O or a-NiO, exhibit signifi¬cantly smaller mobilities. Thus, a complementary, energy-saving technology following the CMOS principle, could not yet be developed yet for thin film electronics. For the last five years we have worked on crystalline copper iodide (CuI) [4] thin film deposition and epitaxy; we have reported record performance of CuI as p-type electro¬de, transparent conduc¬tor and thermoelectric material [5]. Our recent efforts into sputter deposition of CuI thin films have yielded nanocrystalline and fully amorphous thin films with Hall mobilities in the range of 3-4 cm2/Vs [6], i.e. ten times higher hole mobility than a-p-Si. Thus, amorphous CuI-based semiconductors open the path to high-performance complementary thin film electronics in conjunction with n-type amorphous semiconductors. Different parts of this work are funded by Deutsche Forschungsgemeinschaft within SPP 1796 FFlexCom (GR 1011/31-1 and GR 1011/31-2) and GR 1011/36-1 and by Sächsische Aufbaubank (COSIMA, SAB 100282338). [1] K. Nomura, H. Hosono et al., Nature 432, 488-492 (2004). [2] O. Lahr, H. von Wenckstern, A. Thiede, MG et al., Full-swing, High-gain Inverters Based on ZnSnO JFETs and MESFETs, IEEE Transact. Electr. Dev., accepted (2019). [3] O. Lahr, S. Vogt, H. von Wenckstern, MG, Low-voltage operation of ring oscillators based on room-temperature-deposited amorphous zinc-tin-oxide channel MESFETs, submitted (2019). [4] M. Grundmann et al., Phys. Status Solidi A 210, 1671-1703 (2013). [5] Ch. Yang, MG et al., Sci. Rep. 6, 21937 (2016), PNAS 113, 12929 (2016), Nat. Comm. 8, 16076 (2017). [6] Ch. Yang, E. Rose, MG et al., unpublished (2019).

Resume : SrVO3 is a newly discovered transparent conductor, belonging to the group of perovskite oxides with strong electronic correlations [1]. This group of oxides offers also an important interplay between the structure of the material and the transport properties, having its impact on the optical properties through the modification of the charge carrier effective mass. We will show results on the possible tuning of the optical properties of SrVO3 when the material is grown on different monocrystalline substrates, where the observed modifications are rather a result of the oxygen stoichiometry in the samples than related directly to strain [2]. Apart the tuning of the optical properties in original ways, the technological potential of this new transparent conductor is largely related to the possibility of integrating SrVO3 on low cost substrates and especially on glass. In its amorphous form, SrVO3 is not conducting [3], imposing a growth approach keeping the crystalline character of the material. We will show that by the use of Ca2Nb3O10- nanosheets as a growth template, it is possible to integrate crystalline SrVO3 thin films on glass at intermediate temperatures around 500°C with functional properties competing with the best transparent conducting oxides known so far. [1] L. Zhang, Y. Zhou, L. Guo, W. Zhao, A. Barnes, H.-T. Zhang, C. Eaton, Y. Zheng, M. Brahlek, H. F. Haneef, N. J. Podraza, M. H. W. Chan, V. Gopalan, K. M. Rabe, R. Engel-Herbert, Nature Materials 2015, 15, 204. [2] A. Boileau, A. Cheikh, A. Fouchet, A. David, C. Labbé, P. Marie, F. Gourbilleau, U. Lüders, Advanced Optical Materials 2019, 7, 1801516. [3] A. Boileau, A. Cheikh, A. Fouchet, A. David, R. Escobar-Galindo, C. Labbé, P. Marie, F. Gourbilleau, U. Lüders, Appl. Phys. Lett. 2018, 112, 021905.

Resume : Off-stoichiometry copper chromium oxide delafossite has received lately a great deal of attention, due to its high p-type conductivity and adequate transparency in the optical range. As-deposited films show a carrier concentration beyond 1021 cm -3, which is not suitable for their direct integration into active devices, such as a p-n junctions or transistors, which require an accurate control of the holes concentration. Here we show that thermal treatment is an efficient approach to tailor the optoelectronic properties of this material. Carrier concentration (1021 cm -3 - 1017 cm -3), Fermi level and visible transparency can be engineered. Finite chains of copper vacancies randomly distributed within the crystalline grains were observed in Transmission Electron Microscopy and were suggested as the source of high p-type conductivity presented in these films [1]. The annealing process triggers Oswald ripening mechanisms, leading to a shrinkage of the less stable copper chained vacancies and consequently impacts the doping of these peculiar thin-films. The activation energy of the defects, Ea = 1.35 eV, is consistent with migration energies of vacancies in similar oxide semiconductors. To demonstrate the suitability of this process, transparent p-n heterojunction based on engineered copper chromium oxide and ZnO was fabricated in a novel and simple five-step-process compatible with common industrial processes (easily scalable, large area deposition, low temperature) [2]. The annealing of the junction is proved to be key to tune the electrical responses of the almost transparent p-n junction, resulting in an increase in the rectifying behavior featured by ideality factor, η = 6.3, being a value commonly reported for large band-gap heterojunctions. The annealing process also increased the averaged optical transparency of the stack (sapphire substrate – delafossite (250 nm) – ZnO (70 nm)), in the visible range, from 38 to 50%. Actual studies are concentrated on inducing local heating in order tailor electronic properties on confined areas. 1. P. Lunca-Popa, J. Afonso, P. Grysan, J. Crêpellière, R. Leturcq, and D. Lenoble, Sci. Rep. 8, 7216 (2018). 2. J. Afonso, R. Leturcq, P. Lunca, and P. Damien, J. Mater. Sci. Mater. Electron. 30, 1760 (2019).

Resume : For applications to polycrystalline thin-film tandem-type solar cells, p-type conductive BaCuSeF and the related compound films were studied. We prepared polycrystalline BaCuSeF films by pulsed laser deposition (PLD) and obtained 9.9% efficiency CdS/CdTe solar cell with the back contact of BaCuSeF film [1]. The conductivities of BaCuSeF were much lower than those of n-type TCOs such as In2O3:Sn (ITO). Therefore, a bilayer film of p-type BaCuSeF and n-type ITO was studied. We achieved a higher efficiency of 14.3% for the CdTe solar cell with a back contact of SrCuSeF and ITO bilayer [2]. In this study, in order to increase the conductivity of BaCuSeF film, we investigated BaCu(Se0.5Te0.5)F films. BaCu(Se0.5Te0.5)F was prepared from BaF2, BaSe, and CuTe by solid-state reaction method. The synthesized BaCu(Se0.5Te0.5)F powder was pressed in a disk and heated in N2 gas at 800 °C for 3 h. The obtained ceramic target had a relative density of 86%. BaCu(Se,Te)F films were deposited by PLD. The BaCu(Se,Te)F films showed high transmittance of about 40 % in the visible region (400 < λ < 800 nm). All the BaCu(Se,Te)F films showed p-type conductivity of about 1 S/cm. Then, we fabricated BaCu(Se,Te)F/ITO bilayer film and applied it to the back contact of CdS/CdTe solar cell. The BaCu(Se,Te)F/ITO bilayer film showed an ohmic I–V characteristic, which indicated the formation of a tunnel junction between the p-type BaCuSF and n-type ITO layers. The. preliminary CdTe solar cell with BaCu(Se,Te)F/ITO bilayer back contact showed a high efficiency of 12%. [1] K. Yamamoto et al., Jpn. J. Appl. Phys. 54, 08KC01 (2015). [2] S. Kitabayashi et al., Jpn. J. Appl. Phys. 56, 08MC18 (2017).

Resume : Transparent electrodes (TE) are essential components in a huge variety of optoelectronic and heating devices. Indium tin oxide (ITO) has been the most efficient and widely used TE but suffers from brittleness and scarcity of indium. Among emerging transparent conductive materials, metallic nanowire networks and especially silver nanowire (AgNW) networks appear to be one of the most promising candidates to replace ITO. Their highly promising optical and electrical properties combined with their superior mechanical properties and low cost fabrication, have attracted a huge interest the last years. Their optimization has led to figure of merit values similar or even higher than traditional transparent conductive oxides (TCOs). However, in order to build a robust and mature technology, there are still challenges to be tackled. The challenges concern for instance instability which is a crucial issue since it involves electrical, thermal and mechanical aspects, ageing and chemical degradation. We will discuss the origin of failure in AgNW networks and ways to enhance their stability. The integration of AgNW based TE into several industrial devices has been thoroughly investigated. This brief overview aims at presenting the main features related to stability and integration, as well as the fundamental understanding of the physical phenomena that take place at both nanoscale and macroscale thanks to both experimental and modelling approaches.

Resume : Bio-inspired conductive binary-network of vein-silver nanowires (AgNWs) was embedded in poly (dimethysiloxane) (PDMS) to prepare semi-transparent stretchable conductor (vein-AgNWs-PDMS) by a simple dipping process (see Figure). The special conductive structure was constructed by using vein with porous structure as an ideal skeleton to load AgNWs networks, which allowed vein-AgNWs-PDMS composite to show a low sheet resistance of 1 Ω sq-1 with 74% transmittance. The figure of merit of vein-AgNWs-PDMS is as high as 2502 and can be adjusted easily by controlling the times of dipping cycle. Furthermore, the vein-AgNWs-PDMS conductor can retain high conductivity after 150% mechanical elongation and exhibit excellent electromechanical stability in repeated stretch/release tests with 60% strain (500 cycles). As an example of applications, vein-AgNWs-PDMS conductors with patterned light-emitting diode (LED) arrays have been fabricated, which worked well under deformation. Moreover, the photo-thermal properties of vein-AgNWs-PDMS composite have been demonstrated by a position heating experiment induced by near-infrared (NIR) laser irradiation, and the generated heat can be effectively dissipated through vein network to avoid local overheating. Due to the high-performance and facile fabrication process, vein-AgNWs-PDMS conductors will have multifunctional applications in the stretchable electronic devices.

Resume : Transparent conducting electrodes (TCEs) is a necessary component in various optoelectronic devices and indium tin oxide (ITO) is the most commonly used TCE owing to its low sheet resistance (< 20 Ω/sq) and its visible transmittance (> 90%). However, ITO has several drawback such as its brittleness (prone to cracking), high deposition temperature, very low indium abundance in the earth and the high synthesis cost. Several alternatives have been introduced to replace ITO and silver nanowires (Ag NWs) is one of the most promising materials because of their sheet resistance and visible transmittance comparable to ITO. This presentation aims to demonstrate the facile route, fast and low cost synthesis of TCEs based on AgNWs network and their competitive electrical and optical properties. The Ag NWs were deposited on glass substrate by a large-scale spray deposition system specifically developed. Several experimental parameters such as deposition time, spray distance and droplet size were investigated in order to optimize the performances and uniformity of the resulting films. The best figure-of-merit in this work was obtained with a sheet resistance of 10Ω/sq and a visible transmittance of 93% where the ITO performance was reached, with good. Moreover, we show that light scattering can be controlled when Ag NWs are embedded in metal oxide coatings, which is an opportunity for solar cells efficiency improvement compared to ITO-based solar cells.

Resume : Flexible transparent conductive films (TCFs) fabricated using indium tin oxide (ITO)-alternative materials are essential for a variety of present and future optoelectronic devices such as touch panels, flexible solar cells and wearable electronics. The advanced devices require lower resistivity, higher transmittance than before and flexibility. The oxide-metal-oxide(OMO) multilayer structure has been researched because it can be obtained lower resistivity and higher transmittance than single oxide layer. Also, it has flexibility due to metal layer with ductility. As a metal layer in OMO multilayer, Ag is widely used due to lowest electrical resistivity and optical loss in the visible spectral range among known metal. However, for metal thin film(Ag), the transmittance and resistivity change rapidly with thickness because silver(Ag) has grown as distinct island below a critical film thickness according to Volmer-Weber growth mode. In addition, Ag thin film is aggregated at high temperature and oxidized in humid atmosphere. These causes a degeneration of OMO multilayer electrode. In order to solve these problem, Ag based alloys such as Ag-Pd-Cu, Ag-Au instead of Ag have been researching as metal layer. In this work, we explored new Ag based alloy composition as metal layer using continuous composition spread(CCS) method. Also we fabricated OMO multilayer using optimized Ag based alloy composition. Then the electrical and optical properties of M-doped SnO2/Ag-based alloy/M-doped SnO2 deposited on PET were measured by 4-point-probe and UV-Visible-spectrometer, respectively.