Materials, components and characterization of energy harvesters for self-powered electronics

Resume : High-performance piezoelectric materials are used for kinetic energy harvesting and piezoelectric energy harvesters made from these materials are considered the most efficient among counterparts. High-performance piezoelectrics are usually oxide perovskite ferroelectrics which also exhibit photovoltaic effect. This fact offers a unique opportunity to integrate light harvesters with the piezoelectric ones in a single material to achieve multi-source energy harvesting. Coupling multiple energy in one material promotes self-sufficiency and sustainability of energy harvesters and associated electronic systems. Strong piezoelectricity has been thought to inevitably lead to wide photonic band gaps, and vice versa, narrow band gaps eliminate piezoelectricity. This view, however, is being changed. In order to efficiently absorb visible lights, e.g., solar and indoor lights, the band gap needs to be reduced whilst retaining the piezoelectricity. This talk will walk through the achievements in recent years in terms of band gap engineering of piezoelectric materials with an emphasis on works carried out by the speaker’s research group. It has not been an easy task so this talk will highlight lessons learnt through recent experimental studies. It will also tell the tricks of obtaining truly reduced band gaps instead of misleading observations or unfavoured in-gap states. The speaker aims to motivate peer researchers working in similar fields to explore this emerging research topic by giving insights of future opportunities for both fundamental investigations and applications.

Resume : The current digital transformation creates a huge demand on smart, interconnected objects. To monitor the object’s inner state or environment, smart sensor systems are required that can form an integral part of the object while being energy self-sustained. A strong focus is hereby on enabling technology that relies on non-toxic, recyclable materials and low-cost, sustainable fabrication methods. Within the H2020 EU-project SYMPHONY [1] we aim at developing an innovative energy autonomous sensor system. The energy harvesting is completely realized by printed, recyclable and non-toxic materials including the ferroelectric polymer P(VDF-TrFE), printable silicon-based rectifiers, redox polymer batteries and cellulose based supercaps. Multiple energy sources such as mechanical deformation, vibration and magnetic stray fields are harvested with piezoelectric, triboelectric and magnetoelectric transducers. Main application fields are condition monitoring of renewable energy infrastructure, urban mobility and smart living. We will present novel material developments as well as innovative integration concepts. These include stretchable piezoelectric materials and conductors, printed magnetic nanocomposites as well as power management and rectifier materials. Cost effective and scalable methods to print these materials on flexible films and to combine them with energy efficient electronics and sensor technologies are introduced. [1] https://www.symphony-energy.eu

Resume : With the consumption of fossil fuels and the increasing awareness of environmental protection, more and more efforts are being put into the development of renewable and clean energy. Mechanical energy is the one of the most abundant and accessible energy sources, and has been widely harvested by large-scale technologies such as wind power or tidal stream generators. Piezoelectric nanogenerators (PENGs) provide a potential way to convert small mechanical energy such as body motion or vibration into electricity, which can be used to power small portable electronics, medical bio implants, remote wireless sensors etc. Also, solar energy offers the potential to provide much higher power levels than motion since the sun delivers more energy to the earth in 1 h than the entire planet consumes in one year. However, light is not always available, nor is movement, therefore a hybrid energy harvester that can make use of both sources provide a more reliable and high-level of power for small, portable or self-powered devices. Here, a simple solar and piezoelectric hybrid energy harvester (HEH) combining PENGs and perovskite solar cell with the structure of PET/ITO/ZnO seed layer/ZnO nanorods/perovskite/hole transport layer/Au was designed, fabricated and tested. Oscillation (NG) and illumination (PV effect) testing indicated that HEHs operated as kinetic and solar energy harvesters both separately and simultaneously. The length and diameter of ZnO nanorods were optimised to achieve the enhancement of both PV and NG output performance. The coupling effect between perovskite and piezoelectric ZnO nanorods, as known as the piezo-phototronic effect, was also found and investigated.

Resume : Microelectronics and wireless technologies have spread all over the globe in recent decades. The new paradigm of smart cities and wireless sensor networks is becoming a reality, but the unstoppable demand for wearables, smart electronics, and tiny connected sensors bring us some issues on how to deal with the energy management of billions of wireless and portable devices. Providing a little battery to every single portable piece of electronics and charging it once and again from the electricity produced hundreds of kilometers far away is completely unsustainable in terms of maintenance, energy losses, waste or pollution, and due to the lack of resources. Energy harvesters and nanogenerators propose a solution by generating the necessary electric power from the local environment and the residual distributed energies. The eventual realization of self-powered microsystems and on-site energy harvesting yet requires the development of multisource and multifunctional energy scavengers and scalable, high yield, and low costs fabrication processes. Physical vapor deposition, plasma enhanced chemical vapor deposition, and plasma polymer functionalization have been already scaled and optimized in areas such as microelectronics, optics, and solar cells where they are present at several levels of the fabrication and materials and device processing. Herein we share a multi-step process combining these techniques for the fabrication of 1D core@shell functional nanostructured surfaces for its application on hybrid piezo and triboelectric nanogenerators [1]. The methodology is based on the application of small-molecule organic nanowires as supported 1D scaffolds [2]. These ONWs serve as well as flexible support for the deposition of a core@multishell system including a thin metallic shell working as an inner electrical contact and a highly texturized ZnO piezoelectric shell. The fabrication method is compatible with the use of polymeric supports as PET and the growth in high density of the core@multishell nanowires with under design length and thickness[3]. Finally, the NWs are embedded in PDMS to build a top-bottom triboelectric architecture. Factors like crystalline texture, ZnO thickness, nanowires aspect ratio, and surface chemical modification of the PDMS are explored to optimize the power output of the nanogenerators aimed for harvesting from low-frequency vibrations. Just by manual triggering, the hybrid device can charge a capacitor to switch on an array of color LEDs. Outstandingly, this simple three-layer architecture allows for harvesting vibration energy in a wide bandwidth, thus, we show the performance characteristics for frequencies between 1 Hz and 50 Hz and demonstrate the successful activation of the system up to ca. 800 Hz. 1. Garcia-Casas, X., Borras, A. et al. (2022) Nano Energy 91: 106673 2. Macias-Montero, M., Borras, A. et al. (2013) Adv. Func. Mater. 23:5981-5989. 3. Filippin, A. N., Borras, A. et al. (2019) Nano Energy 58:476-483.

Resume : With rising population of the world, demand of energy and portable electronics is on its full swing. Self-powered devices and sensors are like the panacea to full fill this gap. Triboelectric nanogenerator (TENG) is a promisingly desired technology to fabricate a self-powered devices and sensors, due to its low cost, wide choice of materials and easy fabrication techniques.1-3 The working principle of the TENG is primarily based on the coupled effect of contact electrification and electrostatic induction. Surface area, roughness and charge density of the contacting surfaces plays a key role to determine the overall performance of TENG. Conventionally, to fabricate a TENG, two materials with two different triboelectric nature is preferred. However, choice of a combination of different materials based on their charge density is one of the prime challenging tasks. Here, we have proposed, an effective way to fabricate a TENG with a single active material only (abbreviated as S-TENG). For instances, S-TENG comprises of electrospun nylon nanofibers, surface potential of the nanofibers are tuned by changing the voltage polarity in the electrospinning setup. The difference in surface potential leads to generate different charge density, gives rise to change in work function, a key factor to design S-TENG. Further, S-TENG is demonstrated as an ultrahigh sensitive wearable acoustic sensor with mechanoacoustic sensitivity of ≈27 500 mV Pa–1. Owing to its high sensitivity in the low-to-middle decibel (60–70 dB) sounds, S-TENG is plausibly capable in recognizing different voice signals depending on the condition of the vocal cord. Effective voice recognition ability of S-TENG indicates that it has high potential to open an alternative pathway for medical professionals to detect several diseases such as neurological voice disorder, muscle tension dysphonia, vocal cord paralysis, and speech delay/disorder related to laryngeal complications. References: 1. Babu, A; Malik, P; Das, N; Mandal, D. Surface Potential Tuned Single Active Material Comprised Triboelectric Nanogenerator for High Performance Voice Recognition Sensor. Small. 2022, 2201331. 2. Wu, C.; Wang, A. C.; Ding, W.; Guo, H.; Wang, Z. L. Triboelectric Nanogenerator: A Foundation of the Energy for the New Era. Adv. Energy Mater. 2019, 9, 1–25. 3. Guo, H.; Pu, X.; Chen, J.; Meng, Y.; Yeh, M. H.; Liu, G.; Tang, Q.; Chen, B.; Liu, D.; Qi, S.; Wu, C.; Hu, C.; Wang, J.; Wang, Z. L. A Highly Sensitive, Self-Powered Triboelectric Auditory Sensor for Social Robotics and Hearing AIDS. Sci. Robot. 2018, 3, 1–10.

Resume : In this digital era, from lifestyle to sports and health to security, wearable technology is an inevitable trend, which has the capability of transforming businesses into smarter, informative, and more communicative through an impact on human-machine interaction. For an example, a simple heating cloth of 10W power requires 1 Kg of Li-ion battery to run 10h. Powered prostheses for walking consume up to 20 W with a 0.49 kg-battery, that needs charging every 3 h. Such high demand of power may not be fulfilled by batteries alone which has a limitation of flexibility, recharging or replacement. Therefore, the biggest challenge in the smart technology is sustainable power source, that can back up the electronics unconditionally. This situation considers a new platform of self-powered technology, operating without any external power sources! In this context, the principal vision of us is to speed up the concept of self-powered technology based on different wearable and low-cost platform, by constructing in such a way, that will buckle paper/textiles and electronic platform to bring a new smart technology which will have inbuilt self-powered system. The core idea is mechano-stimuli power harvesting mechanism, when two different layers comes together and make a contact with stress (either rubbed/sliding or pressing), resulting a current generation due to charge transfer mechanism. Given that, conjugated polymer (CP) is a new low-cost option. Energy harvesting abilities of CPs are based on the energy-transfer process through the π─π* interaction in its backbone, that can easily be modulated through a simple doping-dedoping process. Proof of concept of our manufactured devices based on paper and textile platforms has been used for security system and gesture monitoring applications. References: 1. Nandy, S.; Goswami, S.; Marques, A.; Gaspar, D.; Grey, P.; Cunha, I.; Nunes, D.; Pimentel, A.; Igreja, R.; Barquinha, P.; et al. Cellulose: A Contribution for the Zero e‐Waste Challenge. Adv. Mater. Technol. 2021, 6, 2000994. 2. Nandy, S; Fortunato, E; Martins, R., Green economy and waste management: An inevitable plan for materials science. Prog. Nat. Sci. 2022. 3. Ferreira, G.; Opiniao, A.; Das, S.; Goswami, S.; Pereira, L.; Nandy, S.; Martins, R.; Fortunato, E. Smart IoT Enabled Interactive Self-Powered Security Tag Designed with Functionalized Paper. Nano Energy 2022. 4. Ferreira, Guilherme; Goswami, Sumita; Nandy, Suman; Pereira, Luis; Martins, Rodrigo; Fortunato, Elvira. "Touch-Interactive Flexible Sustainable Energy Harvester and Self-Powered Smart Card". Advanced Functional Materials 30 5 (2019): 1908994. 5. Goswami, Sumita; Santos, Andreia dos; Nandy, Suman; Igreja, Rui; Barquinha, Pedro; Martins, Rodrigo; Fortunato, Elvira. "Human-motion interactive energy harvester based on polyaniline functionalized textile fibers following metal/polymer mechano-responsive charge transfer mechanism". Nano Energy 60 (2019): 794-801. 6.Goswami, Sumita; Nandy, Suman; Banerjee, Arghya Narayan; Kiazadeh, Asal; Dillip, Gowra Raghupathy; Pinto, Joana V.; Joo, Sang Woo; Martins, Rodrigo; Fortunato, Elvira. "“Electro-Typing” on a Carbon-Nanoparticles-Filled Polymeric Film using Conducting Atomic Force Microscopy". Advanced Materials 29 47 (2017): 1703079.

Resume : The unexpected discovery of ferroelectricity and in turn pyroelectricity in hafnium oxide (HfO2), lead to a plethora of new applications in the field of sensors, energy harvesters, thermal imaging and so on. In comparison to the commonly used pyroelectric materials like lithium tantalite (LiTaO3) and lead zirconate titanate (PZT), doped HfO2 is CMOS compatible with a pyroelectric coefficient that can be enhanced through 3D structures. Recent studies show that Al doped HfO2 (HAO) with 1.0 to 1.4 % aluminum can achieve a pyroelectric coefficient of up to 71 µCm-2K-1 [2]. An even higher pyro-coefficient of 79 µCm-2K-1 was reported for hafnium zirconium oxide (HZO) with 75 % Zr [1]. In this study, 10 nm HfO2 thin films were deposited through atomic layer deposition (ALD) using Hafnium(IV)-chloride and water. These films were doped by adding ALD cycles of ZrO2 and Al2O3 to HfO2 in a controlled manner to generate our novel co-doped films (HZAO). Zirconium doped hafnium oxide (HZO) with a ratio of 1:1 was used as the base material and zirconium was gradually replaced by aluminum in small increments. The resulting thin films were measured with spectral ellipsometry (SE) and x-ray photoelectron spectroscopy (XPS) before being treated with rapid thermal annealing at 400, 650, 800, 1050 °C. The XRD revealed that the HZAO films mainly consist of orthorhombic/ tetragonal orientated crystals, which are the crystalline phases showing ferroelectricity. HZAO films with higher Al dopant concentration have to be annealed at higher temperatures (> 800°C) to show these crystal phases. For the electrical characterization, the pyroelectric films were implemented into an MIM stack with Ti/Pt as top electrode. The pyroelectric coefficient is measured using the Sharp-Garn method [2]. Prior to the pyroelectric measurement, the films were polarized using an electrical field of 3 MV/cm for 10000 cycles. The influence of doping concentration and thermal treatment of HZAO thin films on the pyroelectric coefficient is discussed in this work. [1] C. Mart, 2021; Pyroelectric and electrocaloric effects in hafnium oxide thin films, doctoral dissertation, https://nbn-resolving.org/urn:nbn:de:bsz:14-qucosa2-748605 [2] L.E. Garn, E.J. Sharp; Use of low‐frequency sinusoidal temperature waves to separate pyroelectric currents from nonpyroelectric currents. Part I. Theory; Journal of Applied Physics 53, 8974 (1982)

Resume : Energy harvesting technologies are currently being advanced in order to realize and build self-powered battery-free devices. Renewable energy harvesting technologies such as tribo-, piezo-, and pyroelectricity are drawing substantial interest owing to their unique advantages of simple design, readily available materials, low cost, biocompatibility, eco-friendly feature, importantly, high conversion efficiency, and high-power density. As compared to the traditional materials used in energy harvesting, composite semiconductor materials have a great potential application in ferroelectric photovoltaic devices along with pyroelectric and piezoelectric generators. Among various ferroelectric materials, bismuth-based composites have gained more interest due to their tunable properties. For example, bismuth ferrite has a bandgap of 2.2-2.7 eV and large remnant polarization, which is highly advantageous in photovoltaic technologies. Furthermore, owing to its ferroelectric property, it can also be used in piezoelectric energy harvesting. In this presentation, we reported the synthesis of various bismuth composite materials and its material and electrical properties were investigated. Especially, enhancing the efficiency of energy harvesting was systematically studied by optimizing the dopant material in the bismuth ferrite crystal structure. The optimized composite material was further loaded in the ferroelectric polymer to produce a flexible and durable film. Due to the fabrication of a hybrid metamaterial flexible film, it was further used in the fabrication of pyro-, piezo-, and triboelectric nanogenerators for energy harvesting. The fabricated device produces high electrical output and also has a high ability to harvest various energies. The harvested energy was finally used in self-powered electronic gadgets.

Resume : Triboelectric nanogenerator is an emerging technology which can be employed to harvest kinetic energy generated from various mechanical motions into electricity. The energy generated while human walking is one of the most commonly available non-utilized mechanical energy around us. In this presentation, we proposed a multistage consecutively-connected hybrid nanogenerator (MCHCF) and it was employed for floor mechanical energy harvesting system. Initially, Sr doped BaTiO3 microparticles were prepared and then, loaded into a PDMS polymer to form a hybrid film with piezo- and triboelectric properties. Furthermore, the Sr-BaTiO3/PDMS film was operated against the aluminum to fabricate a top-contact mode hybrid nanogenerator (HNG) device. The Sr was doped in BaTiO3 to enhance its ferroelectric and dielectric properties to result in producing high electrical output. The Ba0.8Sr0.2TiO3 loading concentration in PDMS was further optimized to get constant and stable electrical output. Eight similar HNG devices were fabricated and assembled within the 3D printed MCHCF system along with a simple electronic circuit. The force applied to a single HNG device within the MCHCF system could produce a highly stable direct-current voltage of 15.5 V. The harvested electricity was further stored and used to power small electronics. This prototype MCHCF system can be implemented in real-time flooring systems with an enlarged surface area to harvest mechanical energy from human walking.

Resume : Triboelectric energy harvesting technologies have received a substantial amount of attention as they constitute one of the most efficient ways of transforming vibrational and frictional energy into electrical energy, regardless of location and environmental conditions. One of the most significant advantages of this technology is in the suitability of a very wide range of materials that can be readily incorporated into devices. In order to achieve efficient energy harvesting performance, advances in materials science and nanotechnology have been applied to develop high-performance triboelectric nanogenerators. In this talk, I will discuss materials-driven progress related to triboelectric energy harvesting, with emphasis on the study of materials-related operating mechanisms and emergent materials design strategies for highly efficient triboelectric devices. In particular, I will focus on the role of polymer crystallinity and surface polarization in determining the triboelectric energy harvesting properties of polymeric nanowires. As an example, the strong hydrogen bonding in α-phase nylon-11 serves to enhance the molecular ordering, resulting in exceptional intensity and thermal stability of surface potential, and consequently enhanced triboelectric performance compared to other polymorphs of nylon-11. In this context, I will also discuss how we developed smart triboelectric yarns comprising a conducting carbon nanotube yarn electrode coated with polymer fibers with optimised triboelectric properties, deposited by a customized electrospinning process for textile-based applications. [1] Y Choi, S-W Kim, S Kar-Narayan, Advanced Energy Materials DOI: 10.1002/aenm.202003802 (2021) [2] T Busolo, PK Szewczyk, M Nair, U Stachewicz, S Kar-Narayan, ACS Applied Materials & Interfaces 13, 16876-16886 (2021) https://www.kar-narayan.msm.cam.ac.uk/

Resume : There is an increasingly need to monitor crucial safety and environmental parameters in extraction wells in order to prevent disasters. However, present solutions to feed sensors are inefficient, costly and risky. Furthermore, present energy harvesting technologies do not cope well with the extreme conditions encountered in oil and gas wells that operate at high temperatures, high pressures and involve a highly corrosive environment. The demonstration of new energy harvesting technologies able to operate in these extreme conditions would make a leap forward in their applicability. Triboelectric nanogenerators (TENGs) appearing just in 2012 are the most promising energy harvesting technology able to convert ambient mechanical energy into usefull electrical power [1-3]. Here, we demonstrated a TENG able to generate electrical energy in harsh conditions similar to those found in extraction wells (pressures up to 830 bar and temperatures up to 120 ºC) in direct contact with methane and crude oil [4]. The electrical performance of the assembled device shows a slight increase with increasing pressure from 28 to 119 bar, in methane. However, the electrical outputs decreased strongly with increasing temperature from 25 up to 80 ºC. This clearly demonstrates that temperature is the most critical parameter for TENGs operating in harsh environments. Furthermore, energy harvesting experiments performed in crude oil reveal a decrease of the electric outputs with increasing crude temperature and pressure, but the assembled device continued to generate electrical energy up to pressures of 830 bar and temperatures of 120 ºC. This study clearly demonstrates the suitability of triboelectric devices to harvest energy in harsh environments opening a wide new range of possible applications. References: 1. F-R. Fan et al, Nano Letters,12 (2012). 2. C. Rodrigues et al., Energy and Environmental Science,13 (2020). 3. T. Cheng et al, Advanced Materials Technologies, 4 (2019). 4. C. Rodrigues et al., Nano Energy, 72 (2020)

Resume : harvesting the energy of rainfall drops as a clean and renewable source of energy is being investigated by researchers where it is a young concept compared to solar and wind powers. triboelectric nanogenerators have been revealed among the most promising technology for this process. However, despite widespread attempts by researchers, the drop energy harvesters' output power is still low, mainly due to the limitations in triboelectric and wetting properties and also the non-optimal and centimeter-scale device architecture that prevents the conversion of the complete kinetic energy of falling drops. In this report, a microscale triboelectric nanogenerator is introduced that can harvest a high density of electrical power from drops through a single, micro-second long-lasting step. The mechanism relays on instantaneous capacitance variation due to the high-speed contact of the drops with the electrodes' active area. The capacitive and micro-scale structure of the device resembles the pixels in a charge-coupled device (CCD), allowing for the production of densely packed arrays. The proposed architecture can be adjusted to different liquids, and scales and is compatible with a variety of triboelectric surfaces, including thin-film approaches

Resume : Energy demand has increased a lot in the recent era due to modernization and the industrial revolution. Smart wearable devices and low-power electronics depend on battery units that own less lifetime and less accessibility. Hence, a sustainable power source is necessary to develop which can act as an alternative to batteries. Nanogenerators having piezoelectric, triboelectric and pyroelectric effects have become popular. Triboelectric nanogenerators (TENG offers many advantages like wide material choice, high power density, simple fabrication process, and several working modes. In this present work, the zeolite imidazole framework (ZIF-8) is synthesized by two approaches: solvent-assisted (SA) and solvent-free (HG), and used for the fabrication of TENG. The structural and morphological analysis elucidates a highly crystalline ZIF-8 is formed. The surface roughness and surface potential were investigated to explore their possibility in addition to conventional triboelectric series. A cost-effective 3D printing of waste printed models was reused to design the TENG. ZIF-8 (HG)/Kapton-based dual-mode TENG device to deliver higher electrical output. The triple-unit TENG was designed and fabricated using an additive manufacturing route which delivered a voltage of 150 V and a current of 4.95 µA. Further, TENG devices were utilized to explore self-powered applications by integration with robotics tilt table as well as biomechanical energy harvesting.

Resume : Introduction Triboelectric Nanogenerators (TENGs), that can convert ambient movements into electricity, are a major candidates in powering next generation portable electronics [1]. TENGs can work as energy harvesters and self-powered sensors, which will massively benefit future internet of things, 5G and advanced wearable developments. Despite reaching high instantaneous power densities (>100W/m2) and efficiencies (>50%), the main drawback of TENGs is their discontinuous and irregular electrical outputs [1]. Typically, a TENG would have a current crest factor of ~7, being 500% higher than a sinusoidal signal. This severely disrupts their ability to continuously power electronic devices [2]. Various power management circuits were developed to counter this, however, such circuits consume significant amounts out of scavenged energy of the TENG, while being unable to eliminate the discontinuity issues [3]. As a solution, several direct current TENGs (DC-TENGs) were reported to generate near-DC output signals, however, these were restricted to sliding mode operation [3]. Therefore, developing DC TENG technologies which can operate on contact-separation mode excitations is a critical need as it would encompass the majority of all TENG types [3]. Methods We introduce a novel contact-separation mode DC-TENG with built-in phase shifting of multiple poles. Multiple TENG units are used which act as different poles of the device, whose spatial position is engineered to systematically control their excitation. When the DC-TENG is subjected to movements (linear or rotary), the poles are excited with engineered time-intervals, creating a phase shift between their output signals. These outputs are rectified and superimposed to develop the sustainable DC-TENG. Results and Discussion The design of this technology was based on the distance-dependent electric field (DDEF) theory [4], which was used to simulate and optimise the structure of the poles and their spatial arrangement. The simulations predicted a current crest factor of ~1.08. A demonstrator DC-TENG device was constructed with 6 poles, each consisting of polyethylene terephthalate and polyethylene triboelectric surfaces, and operating in contact-mode free-standing TENG architectures. The device provided excellent electrical outputs with a current crest factor of 1.1 (~80% reduction in output variations) at relatively low operating frequencies (<8 Hz), one of the best current crest factors reported for TENGs. The applicability of the technology was demonstrated by continuously lighting LEDs and a photodetector. Therefore, this technology addresses one of the key drawbacks of TENGs, accelerating the path towards their commercialisation. References [1] Wu et al., Adv. Energy Mater. 2018, 1802906 [2] Ryu et al., Energy Environ. Sci. 2018, 11(8), 2057-2063 [3] Dharmasena et al., Nano Energy, 2020, 75, 104887 [4] Dharmasena et al., Energy Environ. Sci. 2017, 10(8), 1801-1811

Resume : Hybrid molecular crystals have gained attention due to their promising piezoelectric properties. The piezoelectric coefficients of these materials are reported as large as 100 pC/N [1, 2]. In this work, we compute dielectric, piezoelectric and ferroelectric properties of 11 materials using van der Waals density functional theory. These materials are built up of small organic molecular cations and inorganic anions. The best performing materials have organic cations with a cage-like globular geometry. We find the piezoelectric coefficients dij of the hybrid molecular crystals to be comparable to phase-pure inorganic piezoelectrics, such as AlN and LiNbO3. Particularly, the shear piezoelectric responses are large, with a d24 of −94 pC/N calculated for HQReO4*. The same material also shows a large piezoelectric anisotropy with a d16/d33 of 119. Phase pure inorganic perovskites have far smaller anisotropies, such as BaTiO3 with d15/d33 = 6 [1]. The large piezoelectric anisotropy of the molecular piezoelectrics can in part be understood from rotations of the constituent molecules. This effect is similar to the rotation of the polarization vector observed in inorganic perovskites with compositions near a morphotropic phase boundary [1]. The computed electromechanical coupling coefficients vary for the hybrid molecular crystals. However, HdabcoReO4 ** has a coupling coefficient of 0.8, making the material competitive with PZT-5H which has a coupling coefficient of 0.76 [2]. Coupling coefficients this large make hybrid molecular crystals promising for piezoelectric energy harvesting devices. * Quinuclidinium perrhenate ** 1,4–diaz-abicyclo[2.2.2] octane perrhenate [1] J. Harada, Y. Kawamura, Y. Takahashi, Y. Uemura,T. Hasegawa, H. Taniguchi, and K. Maruyama, Plastic/Ferroelectric Crystals with Easily Switchable Polarization: Low-Voltage Operation, Unprecedentedly High Pyroelectric Performance, and Large Piezoelectric Effect in Polycrystalline Forms, J. Am. Chem. Soc. 141, 9349 (2019). [2] J. Harada, N. Yoneyama, S. Yokokura, Y. Takahashi, A. Miura, N. Kitamura, and T. Inabe, Ferroelectricity and Piezoelectricity in Free-Standing Polycrystalline Films of Plastic Crystals, J. Am. Chem. Soc. 140, 346 (2018). [3] M. Davis, M. Budimir, D. Damjanovic, and N. Setter, Rotator and extender ferroelectrics: Importance of the shear coefficient to the piezoelectric properties of domain-engineered crystals and ceramics, Journal of Applied Physics 101, 054112 (2007). [4] B. Chen, H. Li, W. Tian, and C. Zhou, PZT Based Piezoelectric Sensor for Structural Monitoring, Journal of Electronic Materials 48, 2916 (2019)

Resume : With the growing demand for portable electronics, self-powered devices and sensors are promising, it need not give any external source or energy storage device to operate, rather can employ our daily activities such as walking, jogging, and even talking as input for functioning. To make the devices self-powered, piezoelectric polymer shows superiority as these are stretchable, flexible, and mostly biocompatible in nature and not required any external bias like piezoresistive and piezo capacitive to operate. Dipole alignment and crystallinity are the key parameters to determine the piezoelectricity in a material, researchers used numerous complex methods such as stretching, bending, and quenching to enhance piezo response. Here, we have proposed an effective way to enhance the degree of dipole alignment and crystallinity, leads to increase the piezo response in the material. This phenomenon is observed in the nanofibers, producing from the electrospinning by applying negative polarity voltage. Conventionally, nanofibers are produced by applying the positive voltage (positive electric field) between the tip of the syringe and the collector in an electrospinning setup. Here, we have reversed the electric field direction by applying the negative voltage polarity, which results in a high degree of dipole alignment and subsequently elevates the crystallinity, achieving a piezoelectric charge coefficient d33 of 27 pm/V; this was three times higher than their positive voltage counterpart. Piezoelectric nanogenerators (PNGs) are fabricated to assess the piezoelectric performance of nanofibers manufactured by applying positive and negative polarity voltage. It is further noticed that the PNG based on negatively biased nanofibers exhibited mechanosensitivity 11 times higher than the PNG based on positively biased nanofibers. As a result, excellent bio-sensing capabilities of negative bias generated nylon-11 nanofibers enable tracking of physiological events such as arterial pulse, carotid pulse, and various facial expressions for a next-generation health care system.

Resume : “Internet of Things” (IoT) has attracted intensive interest for the field of wireless, portable and monitoring fields. In the regard, wearable nanogenerators hold great potential because they can harvest the energy from body movement and surrounding environment to provide sustainable power supply for these electronic devices. Zinc oxide (ZnO) nanostructures have been extensively investigated for harvesting mechanical power owing to its low cost, non-toxicity and easy synthesis. [1-3] Flexible substrates, such as textile and carbon fibre, have attract lots of attention due to its unique properties of lightweight, comfort and mechanical durability. Herein, PEDOT:PSS/CuSCN/ZnO based devices are successfully fabricated on conductive Cu/Ni coated textile and carbon fibres, respectively. PEDOT:PSS/CuSCN structure was fabricated on ZnO nanorods to reduce the rate of screening to achieve higher performance output. The textile-based device generated increasing output voltage from 0.2 V to 1.81 V as the shaking frequency increases from 19 Hz to 26 Hz. The output voltage from the device can activate an LCD screen display by shaking at its resonant frequency. Carbon fibre-based devices were also fabricated, which generated increasing output voltage from 1.4 V to 7.6 V as the acceleration from an impacting force increased from at 0.1 m/s2 to 0.4 m/s2. Both of the above flexible devices exhibited high stability and durability under 26000 cycles test, which were also able to harvest energy from biomechanical forces such as impacting, flicking and gentle finger tapping and bending. In addition, based on carbon fibre its composite, carbon fibre-reinforced plastic (CFRP), CFRP-based self-power sensor was also fabricated, which exhibited output voltage from 0.27 V to 3.53 V under different impacting acceleration from 0.1 to 0.4 m/s2 with good stability during the 26000 cycles test. The results provides an efficient method to develop energy harvester on carbon fibres, which hold great potential for the future designing of flexible self-powered devices and wearable electronics.

Resume : Polymer contact electrification (CE) has taken an important role for harvesting wasted mechanical energy from ambient noise, biomechanical movements, or mechanical vibrations. Devices which exploit polymer CE are called triboelectric nanogenerators (TENG). These devices can be integrated in various systems to harvest energy from different sources. Harvested energy can be used for powering microdevices, thus replacing batteries, or excluding the necessity for wiring to supply power. This is especially important for Internet of Things (IoT). IoT describes the network of physical objects, that are embedded with sensors, software, and other technologies for the purpose of connecting and exchanging data with other devices and systems over the internet. It is estimated that the IoT will host at least 40 billion connected devices by 2025. The successful integration of TENG devices highlight the pathway to reduce the environmental burden. Different approaches exist to magnify the surface charge on polymer from CE, including surface functionalization, adjustment of the physicochemical properties between contacting materials, or by increasing the specific contact area via nanostructuring. In addition, strategy inspired from natural spider silk can be applied. It has been shown that the irregularities in surface hardness end up with the stress accumulation, which reduce the energy for covalent bond break. Covalent bond break and material transfer is well proven mechanism for polymer contact electrification. The output of the TENG device can be enhanced also by applying ferroelectric polymers in contacting layers where piezoelectric charges contribute to surface charge for electrostatic induction, thus increasing the output. The combination of different approaches allows to develop high performance TENG devices.

Resume : A number of studies have reported the use of vibration coupled with ferroelectric materials for water splitting. However, improving the efficiency and stability of these systems continues to remain a challenge, including long-term stable produce of products and the formation of a stable suspension. Here we report the production of a nanofluid based on BaTiO3 containing a mixture of cubic and tetragonal phases that splits water under ultrasound. X-ray analysis shows that the BaTiO3 is a mixture of cubic and tetragonal phases. The particle size reduces from an initial distribution of approximately 400 nm as delivered to a distribution of approximately 150nm after the application of ultrasound. This fine scale nature of the particulates leads to the formation of a stable nanofluid of suspended BaTiO3 particles. We demonstrate stable H2 and O2 evolution at the predicted 2:1 ratio. In further lifetime tests we show repeatable H2 evolution over a period of 4 days with a continuous 24-hour period of stable catalysis. The maximum rate of H2 evolution found was 270 mmol/h/g for a loading of 5mg/L of BaTiO3 in 10% MeOH/H2O leading to the highest efficiency of piezoelectrically driven water splitting that has been reported thus far. This work indicates that the potential of harnessing vibration for water splitting in functional materials systems.

Resume : Introduction Triboelectric Nanogenerators (TENGs) are a leading candidate to power the future portable and wearable electronics [1]. TENGs operate through triboelectric charging and electrostatic induction to convert ambient movements into electricity [2]. Studies on triboelectric charging have been limited to symmetric charging, where dissimilar TENG contact surfaces obtain equal amounts of static charges with opposite polarities [3]. This leaves a gap on the understanding of TENG outputs during asymmetric charging situations. Moreover, reports on how identical TENG surfaces can be used successfully for TENG output generation are scarce. Such drawbacks limit the versatility of TENGs in terms of optimising materials, device designs and output generation [4]. Methods This work studies triboelectric charging of dielectric TENG surfaces by analysing the material transfer between their contact surfaces. The nanoscale materials transfer during the operation of a contact-mode TENG is studied using X-ray photoelectron spectroscopy and electron microscopy for different material types, contact pressures and motion profiles. Based on these outcomes, a charge density engineering technique is introduced where selected TENG surfaces are contact charged at nanoscale against an external material surface. This creates an asymmetrically charged TENG with significantly improved outputs. Consequently, the distance-dependent electric field platform is used to develop the first theoretical model which can simulate the outputs of asymmetrically charged TENGs. This platform is used to design and fabricate asymmetrically charged TENGs consisting of dissimilar contact surfaces [TENG surfaces - polydimethylsiloxane (PDMS) and polyethylene terephthalate (PET), external surface - nitrile] as well as identical TENG contact surfaces [contact surfaces - PET and PET, external surface - nitrile]. Results and Discussion The TENG with dissimilar contact surfaces provided 469% power output increase (avg. power under 1m, 1Hz sine motion) through asymmetric charging (24.4 mW/m2) compared to the conventional TENG design (5.2 mW/m2), whereas the TENG with identical contact surfaces provided 6076% power output increase (9.48 mW/m2) via asymmetric charging compared to conventional TENG (0.156 mW/m2), showing remarkable improvements. This method enables the identical contact surfaces to be used to generate significant TENG outputs. The stability of the asymmetrically charged TENGs were examined, showing only 2.5% output reduction within 24 hours. Moreover, this study revealed several new factors affecting triboelectric charging, and significantly improved the outputs and design versatility of TENGs, paving the way towards practical TENG applications. References [1] Wu et al., Adv. Energy Mater. 2018, 1802906 [2] Dharmasena et al., Energy Environ. Sci. 2017, 10(8), 1801-1811 [3] Dharmasena et al., Adv. Energy Mater. 2018, 8, 1802190 [4] Dharmasena et al., Nano Energy 2021, 90, 106511

Resume : There is an increasing demand in smart sensor nodes for condition monitoring and predictive maintenance of industrial engines and critical energy infrastructure. These sensor nodes collect data of a target object (e.g. an electric engine or generator) and/or its environment in order to detect any malfunction or failure and instantly trigger necessary maintenance actions. This way, further damage and extended downtimes can be prevented and consequently enable an extended lifetime, reduced material waste and CO2 emission. To power such deployed sensor nodes, energy harvesting of environmental energy is most suitable and preferred over environmentally problematic batteries. One energy source readily available especially in industrial environments or power plants is vibration energy from machines driven by electric engines or electric generators. Since this vibration has usually a fixed fundamental frequency of 50 Hz or 25 Hz, resonating structures like cantilevers with piezoelectric transducers are promising harvesters. While piezoelectric ceramics offer higher piezoelectric parameters, piezoelectric polymers are less brittle, more flexible and easier to process in large scale, reducing costs per unit. Usually, these transducers consist of the piezoelectric layer sandwiched between two electrodes on a flexible substrate. To push their output power level, stacking of multiple transducers or processing multilayers of the piezoelectric material is required. In this work, we compare such approaches for P(VDF-TrFE)-based transducers under realistic conditions. These conditions imply the aforementioned fixed low vibration frequency and rather low vibration acceleration, around 1-2 m/s² (RMS value). Furthermore, a higher output voltage level improves the conversion efficiency during rectification and storage, but should be adjusted to the operation voltage of the sensor node. For a given active volume, multistacking increases the current output due to higher electrode area, but a single, thick layer increases the voltage output of the transducer. Thus, output voltage/current optimization is necessary. For doing so, P(VDF-TrFE) transducers were fully screen-printed on PET substrates both in single and multiple stack configuration. The resonance frequency was kept constant by controlling the length of the cantilever as well as by adding a tip mass. A normalized average output power of 42 µW/ms-2 was achieved at 25 Hz (24.6 cm² transducer area). The performance of the transducers in combination with a full wave rectifier and a charging capacitor is demonstrated both in lab as well as in industrial environments.

Resume : Flow-electrode Capacitive Mixing(F-CapMix) system is a new renewable energy technology that generates electricity using the ion adsorption/desorption system made of porous carbon material in flow electrode and the difference in concentration between flow electrode and feed water. However, activated carbon (AC) with relatively low electrical conductivity compared to other carbon materials(graphene, CNT) causes low electron percolation and power generation. In this study, to improve power generation performance of the F-CapMix, Nitrogen-rich precursor Melamine was heat-treated to dope the AC surface with nitrogen, and then surface analysis, powder resistance and change in F-CapMix power generation performance were measured. C-N, C=N binding to activated carbon surfaces was confirmed through XPS and Raman, FT-IR, and the power generation of N-doped AC (6 wt%) was 41.38% higher than that of conventional AC. Through these results, it is believed that the limitation of F-CapMix power generation, which still has a lower power generation amount than other Salinity Gradient Power(RED, PRO), can be improved.

Resume : 2D transition metal dichalcogenides (2D TMDs) have attracted considerable attention recently owing to their superior physical and chemical properties. These 2D materials have shown great potential for thermoelectric (TE) energy generation due to their unique electrical and thermal transport properties originated from their unique atomic structures. The calculated and predicted thermoelectric performance should exhibit outstanding TE performance, however, it still lacks of experimental confirmation. Furthermore, a reliable and a robust preparation and characterization methodologies for proving the 2D TMDs-based TE materials are underdeveloped. The measured and reported TE performance of 2D TMDs is still much lower than that of conventional bulk TE materials such as BST, because of higher thermal conductivity and lower seebeck coefficient. Here, we demonstrate that the enhanced TE performance of 2D TMDs by a facile anion-engineering. Phosphorus doped 2D TMDs show the highly enhanced seebeck coefficient and electrical conductivity, which can lead high power factor. Furthermore, the low thermal conductivity can be achieved by defects and doped phosphorous atoms in 2D TMDs atomic structure. This work can pave a way to achieve high TE performance of 2D TMDs-based TE materials.

Resume : The fabrication of SnOx in thin film form via chemical solution deposition (CSD) processes is favored over vacuum-based techniques as it is cost effective and simpler. The precursor employed plays a central role in defining the process conditions for CSD. Particularly for fabricating SnO2 layers that are appealing for sensor or electronic applications, there are limited precursors available for CSD. Thus, the focus of this work was to develop metalorganic precursors for tin, based on the ketoiminate ligand class. By systematic molecular engineering of the ligand periphery, a series of new homoleptic Sn(II) β-ketoiminate complexes was synthesized and thoroughly analyzed by spectroscopy and thermogravimetry methods. The solid state molecular structure of [Sn(MPKI)2] was analyzed by means of single crystal X-ray diffraction (SCXRD). Interestingly, this class of compounds features excellent solubility and stability in common organic solvents alongside good reactivity towards H2O and low decomposition temperatures, thus fulfilling the desired requirements for CSD of tin oxides. In this study, we have demonstrated the possibility to directly deposit SnOx layers via hydrolysis upon exposure to air followed by heat treatment under oxygen at moderate temperatures. Most importantly, the precursor solution is readily prepared without need for additives or long stirring times which are often required in the preparation of CSD precursor solutions. A range of complementary analytical methods were employed, namely X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis (NRA), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) to analyze the structure, morphology, and composition of the deposited SnOx layers. The deposited nanocrystalline, oxygen rich SnO2 thin films feature a high surface area and oxygen vacancies based on film composition analysis, thus bear promising properties for application as sensor material.

Resume : Nowadays, the copper nitride (Cu3N) is of great interest as a new solar absorber material, flexible and lightweight thin film solar cells. This material is a metastable semiconductor, non-toxic, composed of earth-abundant elements, and its band gap energy can be easily tunable in the range 1.4 to 1.8 eV. Cu3N shows different properties depending on the structure of the material: Cu-N bonds can offer metallic electrical properties (Cu4N) or a semiconductive behavior (Cu3N). For this reason, it has been proposed for many applications in the solar energy conversion fields. For the deposition of Cu3N films, reactive magnetron sputtering is one of the most used because the film properties can be easily modified by changing the sputtering parameters. The main aim of this work is to evaluate the properties of the Cu3N thin films fabricated by reactive radio-frequency (RF) magnetron sputtering at different RF power values to determine its potential as light absorber. The Cu3N films were fabricated at room temperature (RT) from a commercial 3-inch diameter Cu metallic target (purity: 99,99%) on different substrates (silicon and glass). The layers were deposited at the RF power values ranged from 25 to 200 W. The pure nitrogen flux was set to 20 sccm, and the working pressures were 3,5 Pa and 5 Pa. The morphology and microstructure of the Cu3N thin films were characterized by Atomic Force Microscopy (AFM), Fourier Transform Infrared Spectroscopy (FTIR), RAMAN spectroscopy and X-ray Diffraction (XRD), respectively. AFM images revealed a granular morphology, while FTIR and RAMAN spectra exhibited the characteristics peaks related to Cu-N bonds of Cu3N, that became narrower when the RF power increased. Finally, to stablish the suitability of these films to be used as absorber, the optical properties were obtained from transmission spectra carried out with a Perkin Elmer 1050 spectrophotometer.

Resume : One of the most important problems facing humanity nowadays is the production and storage of clean, renewable and low-cost energy. Solar photoelectrochemical (PEC) hydrogen production could potentially meet the above criteria, through the direct conversion of solar energy into hydrogen, one of the most eagerly awaited solar fuels. Developing stable, low cost and efficient photoelectrodes for PEC cells is thus an essential step of this research field. Among the forecast materials for photoelectrodes, group III-V semiconductors have exhibited remarkable performance thanks to their appropriate and tunable band gap [1], transport properties and high quantum yield [2], making them good candidates for unassisted PEC water splitting. In particular, GaAs was shown to have a high theoretical solar energy conversion efficiency of 33% [3]. However, the most significant drawbacks of III-Vs are the overall instability of the semiconductor/liquid interfaces, their high substrate cost and their composition, based on critical resources. To address these issues, in this work, we report on the photoelectrochemical behavior of a 1 µm-thick GaAs film grown on a low-cost p-type Si substrate by Molecular Beam Epitaxy. GaAs/Si photoelectrodes exhibited both cathodic and anodic photocurrents in 0.2 M H2SO4 (aq), indicating that our electrodes could be used to trigger both hydrogen and oxygen evolution reactions. A photocurrent density of 7 mA/cm2 at -1 V vs Reversible Hydrogen Electrode (RHE) was measured in the photocathode regime and 17 mA/cm2 at 1.5 V vs RHE in the photoanode regime. These values are competitive compared to the performances of electrodes based on GaAs commercial wafers. More than this, the GaAs/Si photoelectrode showed a good lifetime of more than 15 hours in cathodic regime. Electrochemical impedance spectroscopy and Mott-Schottky measurements were also performed, revealing additional surface or interface states in GaAs/Si photoelectrodes compared to GaAs-wafer based electrodes. These findings reveal interesting optimization paths for our photoelectrodes based on III-V thin films on silicon and towards the fabrication of unassisted PEC cells for green hydrogen production. References [1] S. Tiwari et D. J. Frank, «Empirical fit to band discontinuities and barrier heights in III–V alloy systems,» Applied physics letters, vol. 60(5), pp. 630-632, 1992. [2] G. Siddiqi, Z. Pan et S. Hu, «III–V semiconductor photoelectrodes.,» Semiconductors and Semimetals , vol. 97, pp. 81-138, 2017. [3] J. R. Bolton, S. J. Strickler et J. S. Connolly, «Limiting and realizable efficiencies of solar photolysis of water.,» Nature, vol. 316(6028), pp. 495-500, 1985.

Resume : Copper(I) thiocyanate (CuSCN) is known as a wide bandgap p-type semiconductor and recently demonstrated its high ability as a hole-transporting material in perovskite solar cells and light emitting diodes fabricated by simple solution coating and drying [1]. In fact, little is known for physical properties of CuSCN, such as bandgap, band positions, optical transparency and mobility. We have established methods to electrodeposit well-crystallized CuSCN thin films in various forms. Although the electrochemistry is fairly simple as limited by diffusion of 1 : 1 complex ([Cu(SCN)]+), the [Cu2+] : [SCN-] ratio, its absolute concentration and solvent can alter the morphology and crystal orientation of resulting CuSCN [2]. These unique features of the electrodeposition technique let us anticipate possibilities to tailor-tune physical properties of CuSCN to match the demands for flexible device applications. In this study, we have carried out electrodeposition of CuSCN to vary its morphology and crystal orientation by tuning the bath composition and studied their band structure to explore the room for tuning its physical properties for thin film diodes and hybrid electroluminescence devices. Morphologies of CuSCN thin films electrodeposited from stoichiometric (REF), Cu-rich and SCN-rich baths are changed. While the REF sample has an open structure made of relatively large bulky particles, the Cu-rich sample is dense, made of tiny grains to expose their hexagonally shaped top. XRD patterns have found almost parallel orientation for the SCN-rich and a high degree of preference of the Cu rich to orient the c-axis of β-CuSCN perpendicular to the substrate. Although all these films indicate nearly the same energy gap of about 3.6 eV estimated by Tauc plot, significant difference was found for their work function (WF) measured by photoelectron yield spectroscopy (PYS). The threshold energy moved downwards from 5.23 to 5.66 eV vs. VAC from Cu-rich to SCN-rich film. The result indicates a high level of p-type doping in the presence of excess SCN-, probably due to increased concentration of Cu2+ as stabilized by SCN- bound to it. Simple devices as ITO / electrodeposited CuSCN / Aluminium were fabricated to examine their diode behaviour. While all of the devices employing the electrodeposited CuSCN thin films showed good rectifications in the J-V curves, the change in onset voltage from Cu-rich to SCN-rich samples confirm tunability of the device property by conditions of the electrodeposition. Successful operation of organic light emitting diode was also achieved by employing the electrodeposited CuSCN as a hole-injection layer. The device employing the electrodeposited CuSCN achieved a smaller turn-on voltage than that with spin-coated CuSCN in the I-V-L measurements. Furthermore, the electrodeposited CuSCN also functioned as perovskite solar cells. ［1］ Vinod E. Madhavan et al., ACS Energy Lett., 1, 1112, 2016 ［2］ Lina Sun et al., Physics Procedia, 14,12, 2011

Resume : Complex oxides are of great interest for their rich variety of chemical and physical properties including magnetism, ferroelectricity, multiferroicity, catalytic behavior, and superconductivity. Up to date, the preparation of crystalline complex oxide thin films has been mainly limited on substrates that can stand high temperature thermal treatments and on single crystal substrates when epitaxial growth is pursued. These requirements dramatically limit their applicability excluding the possibility to prepare many artificial multilayered architectures to investigate emergent phenomena that arise in thin films and at their interfaces. To tackle this bottleneck, herein, we will present a facile and sustainable chemical route to prepare water-soluble epitaxial Sr3Al2O6 thin films to be used as sacrificial layer for future free-standing epitaxial complex oxide manipulation. Two solution processes are put forward based on metal nitrate and metalorganic precursors to prepare dense, homogeneous and epitaxial Sr3Al2O6 thin films that can be easily etched by milli-Q water. [1] Thorough investigation of the precursor-solvent compatibility, thermogravimetric analysis and film crystallization is performed. Additionally, we demonstrate the viability of Sr3Al2O6 to subsequently prepare and transfer a wide variety of atomic layer deposited functional oxides (Al2O3, Co3O4, Fe2O3, CoFe2O4, BiFeO3) on arbitrary substrates ranging from flexible polymers to silicon substrate. [2] This robust and low-cost procedure could be adopted to prepare a wider family of thin film compositions to fabricate artificial heterostructures and 2D materials with monolayer by monolayer control to go beyond the traditional electronic, spintronic, and energy storage and conversion devices. [1] P. Salles, M.Coll et al. Adv. Mater. Interf, (2021), 8, 2001643 [2] P. Salles, M. Coll ACS Applied Materials Interfaces (2022) doi.org/10.1021/acsami.1c24450

Resume : Production of a transparent and conductor silver nanowire (AgNW) network involves a trade-off between the two main variables that are optical transmittance and sheet resistance. Even though AgNWs themselves have a defect free structure, the surrounding polyvinyl pyrrolidone (PVP) layer hinders the wire-to-wire electron transfer and creates junction resistance in the order of M? levels. This incomplete metal-metal contact of AgNWs create a challenge in the production of high-performance transparent conductors. Great efforts have been made to solve this problem. However, the literature still is incomplete as in all of the works, the used AgNWs have different lengths, diameters, PVP thicknesses and purities. As a result, the effectiveness of a particular post treatment on AgNWs with different properties is still unknown. There is no consensus on what a good and facile combination of methods is. In this study, various post treatment methods available in the literature are examined and the most successful post treatment method was developed. The combination of the optimal post treatments on the AgNW networks resulted in the reduction of the sheet resistance from 5000 ?/sq to 24 ?/sq with an optical transmittance of 92%. Furthermore, the use of optimized AgNW networks in a liquid-solid interface triboelectric nanogenerator system as the current collector layer is explored. A thin PDMS layer is spin coated onto the AgNW network to fabricate transparent TENG electrodes. The triboelectric response between water droplets and the PDMS layer is investigated. The TENG device is found to produce up to 1.8 V and 40 nA per water droplet. The resulting transparent self-powered sensor with optimized AgNW network is suitable for many sensing applications such as chemical concentration measurement and heater activation. This work was supported by The Scientific and Technological Research Council of Turkey (TUBITAK) under Grant No: 121N708 and No: 119N413.

Resume : Triboelectric nanogenerators (TENGs) have been of great interest since they were proposed. Power is generated by static electricity caused by the contact of two separate surfaces. Therefore, any place where there is motion can be an effective workplace for TENGs to be used as both self-powered sensors and energy harvesting units. Given situations like these, water waves are one of the best places to get most out of TENGs to harness waste energy. In this study, a low-cost adaptation of a TENG is made by modifying a commercial buoy used by sailors and marine workers for an alarm or guidance system. TENG is prepared by coating inside of a buoy with polyurethane (PU) foam and hiring a pendulum mechanism as a counter triboelectric layer by coating an aluminum ball with poly (dimethyl siloxane) attached to a spring in the buoy. As a result, triboelectrification is provided in a frequency independent regime by contact-separation. From the measurements taken in a coastal port laboratory to simulate a real case of sea waves an open circuit voltage (Voc) of 141 V and short circuit current (Isc) of 8.89 µA is obtained. In addition, a power of 1.07 W/m2 is obtained under a wave frequency of 1 Hz and a wave height 11.8 cm, which is characteristic of Turkey’s typical coastal waves, at an impedance match of 300 MΩ.

Resume : The present study demonstrates a significant enhancement in the Seebeck coefficient and thermoelectric (TE) power factor in Sb2Te3- AgSbTe2 nanocomposite thin film. The addition of Ag leads to the in-situ formation of AgSbTe2 secondary phase in the Sb2Te3 matrix during the growth resulting in a large Seebeck coefficient. X-ray photoelectron spectroscopy (XPS) valance band spectra in conjunction with first-principal density functional theory-based electronic structure calculation provide conclusive evidence of the formation of Ag induced deep resonant-like states in the valance band, which modifies the density of states (DOS) and results in a two-fold increase in DOS effective mass in the composite samples. In addition, the formation of hetero interface is responsible for carrier filtering in Sb2Te3, which also contributed to the enhanced TE properties. The results highlight the importance of a combined effect of band structure modification and energy-dependent charge carrier scattering for enhancing thermoelectric properties.

Resume : The development of low-cost solar cells based on technology that uses only earth-abundant and non-toxic elements is always in demand and of great interest. Antimony sulphide (Sb2S3) is one such material that is suitable for semi-transparent solar cell applications. The low cost, earth abundance, the suitable direct band gap of around 1.7 eV and the single stable phase1 make Sb2S3 a promising material for use as the absorber in thin-film solar cells. It has been shown2, that ultrasonic spray pyrolysis (USP), which is a low-cost, simple and scalable thin film deposition method, is a suitable technique for depositing Sb2S3 solar cells. The following study aims to investigate the means of controlling the Sb2S3 absorber layer growth and properties, by varying the Sb to S precursor ratios and the deposition temperatures. The Sb2S3 absorber was deposited from a precursor solution of SbCl3/SC(NH2)2 = 1:3 and 1:6 (60mM SbCl3) at 3 different temperatures ? 195°C, 220°C, and 245°C using Glass/FTO/TiO2 as a substrate. Afterwards, the absorber was annealed in a flowing Nitrogen atmosphere at 250°C for 5 minutes. Films were characterized by SEM, XRD, Raman and UV-Vis spectroscopies. The films grown at 195°C were amorphous, whereas when grown at 220°C or 245°C, crystalline stibnite films were obtained, as was confirmed by XRD and Raman spectroscopy measurements. Annealing of amorphous films in a nitrogen atmosphere resulted in crystalline Sb2S3 films, no other phases were detected. The optical bandgap value of crystalline films depended on the film deposition temperature and decreased from 1.78 to 1.66 eV when increasing the deposition temperature from 195°C to 245°C. The crystalline films grown under different conditions were used as an absorber in solar cell devices. Solar cells were built in superstrate configuration Glass/FTO/TiO2/ Sb2S3/P3HT/Au where TiO2 as electron transport layer was grown by USP technique and P3HT as hole transport material was applied by spin coating, followed by annealing in a flowing Nitrogen atmosphere at 175 °C for 5 minutes before the Au back contacts were thermally evaporated. Current-voltage (I-V) measurements were used to evaluate the photovoltaic performance of the fabricated solar cell devices. The results have shown, that there is a drop in open-circuit voltage and power conversion efficiency (PCE) values when increasing the Sb2S3 deposition temperature from 195°C to 245°C. The highest PCEs of ca 5.2 % were achieved using a two-step procedure for the absorber preparation ? first depositing amorphous Sb2S3 and then crystallizing afterwards. Differences in growth mechanisms and properties of crystalline Sb2S3 films deposited at different temperatures will be discussed. 1. Yang Yang, et al. Solar Energy, 2021, 217, 25-28 2. Jako S. Eensalu, et al. Beilstein J Nanotechnol. 2019; 10: 2396?2409. 3. Xin Jin, et al. Adv. Funct. Mater, 2020, 30: 2002887

Resume : Perovskite solar cells (PSC’s) have revealed remarkable development in recent years with rapid increases in efficiency, from about 3% in 2009 to over 25% today. While perovskite solar cells have emerged to be highly efficient in a very short time, still various challenges remain before they can become a competitive commercial technology. Hence it is a dire need to improve the PSC’s stability, degradation and efficiency by enhancement of thin film homogeneity, grain size (eliminating grain boundaries) and by morphological and compositional modification. However, solvent processing and thermal annealing generates relatively small grains during rapid perovskite crystallization. The presence of small grains is an indication of the existence of local inhomogeneity in these films in terms of lattice strains and material composition with the local inhomogeneity being observed not only intergrain but also intragrain. In addition, the grain boundaries can host defects an increase recombination rates, as well as degradation. Therefore, eliminating the local inhomogeneities, particularly at the grain boundaries, is a crucial path to enhance performance of perovskite optoelectronic devices[1]. Formamidinium lead iodide (FAPbI3)-based perovskites have emerged as one of the most promising candidate materials for high efficiency and stable perovskite solar cells due to their high thermal sta-bility, excellent optoelectrical properties and ideal bandgap energy. However, the phase degradation of black FAPbI3 perovskite phase to yellow non perovskite phase at ambient conditions restricts the long-term stability of FAPbI3 perovskite solar cells. We have previously demonstrated a method for performance and stability improvements in formamidinium lead iodide (FAPbI3)-based perovskites by crystallisation in the presence of a solvent aerosol[2]. Here, we develop this method further by adding methylammonium thiocyanate (MASCN) to the solvent aerosol for crystallisation of FAPbI3 perovskite films, following our previous work demonstrating additive-enhanced post-treatment of perovskite films[3]. Adding MASCN to the aerosol leads to further improvements in crystallinity and grain size compared to solvent-only treated films. These changes lead to prolonged charge-carrier lifetimes and ultimately improved device efficiencies. By demonstrating the benefit of additives in this aerosol-assisted crystallisation process, this work opens up wider processing options to enhance the crystallinity, grain size, film homogeneity and efficiency of perovskites. References [1] T. Du, S.R. Ratnasingham, F.U. Kosasih, T.J. Macdonald, L. Mohan, A. Augurio, H. Ahli, C.‐T. Lin, S. Xu, W. Xu, R. Binions, C. Ducati, J.R. Durrant, J. Briscoe,* M.A. McLachlan,*Adv. Energy Mater. 2101420 (2021). [2] Du, T., Macdonald, T. J., Yang, R. X., Li, M., Jiang, Z., Mohan, L.,& Briscoe, J. (2022),Advanced Materials, 34(9), 2107850. [3] T. Du,F. Richheimer,K. Frohna, N. Gasparini, L. Mohan, G. Min, W. Xu, T.J. Macdonald, H. Yuan, S.R. Ratnasingham, S. Haque, F.A. Castro, J.R. Durrant, S.D. Stranks, S. Wood, M.A. McLachlan, J. Briscoe,Nano letters.(2022).

Resume : With an increasing demand for powering various electronics, energy-harvesting devices have attracted considerable attraction in the fields of self-powered systems [1]. In this regard, researchers have demonstrated various types of nanogenerators such as triboelectric, piezoelectric, and pyroelectric nanogenerators [2]. However, these nanogenerators produce instantaneous alternating output current and exhibit low energy conversion efficiency, which is not suitable for self-powered electronics requiring sustainable direct current (DC) power [3]. In this presentation, we will demonstrate solution-processed nanocomposites for high-performance hygroelectric generators, which enable to produce continuous and stable electricity for self-powered systems. Effective collecting charges directly generated from atmospheric humidity are investigated to investigate the effect of nanocomposition on the device performance of hygroelectric generators. We will also discuss the characteristics of open-circuit voltage and short-circuit current in nanocomposite-based hygroelectric generators under different relative humidity conditions. Long-term sustainability and reliability of the electrical output performance are demonstrated in the developed hygroelectric generators. We believe that this work can open-up a new route for emerging nanocomposite materials for self-powered electronics. [1] M. Ha, J. Park, Y. Lee, H. Ko, ACS Nano 9, 3421-3427 (2015). [2] S. Korkmaz, İ. A. Kariperbc, Nano Energy 84, 105888 (2021). [3] D. Liu, X. Yin, H. Guo, L. Zhou, X. Li, C. Zhang, J. Wang, Z. L. Wang, Sci. Adv. 5, eaav6437 (2019). Acknowledgments This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (NRF-2021R1A2C2012855)

Resume : It is not hidden to any of us the impact that the different environmental issues have on the health of living organisms in general, and on humans in particular. Polluted water and climate change can be considered as the most challenging problems threatening the global health. CO2 capture, storage, and conversion (Leung, Caramanna, and Maroto-Valer 2014) are now being researched in a variety of research fields and technologies. In addition to that, a great attention was given to the studies focusing in the possible techniques that can be applied in the purification of water through heavy metals removal (Senguttuvan et al. 2021). In the recent decades, the porous polymers showed a significant role in many applications that enhance the environmental health aspects. One category of these polymers is the conjugated microporous polymers (CMPs)(Cooper, 2009): the materials that known to combine many favourable properties like; π-conjugated networks with permanent porosity and high chemical and thermal stabilities. Therefore, polyaniline-based conjugated microporous polymers have attractive capabilities due to the inherent redox states of polyaniline and the ability to fine-tune their pore size distribution and surface area (Liao, Weber, and Faul 2014) & (Chen et al. 2019). In this approach, we synthesized different forms of aniline-based redox-active polymers based on Tris(4-bromophenyl)amine as a core with different linkers through Buchwald-Hartwig cross coupling reaction. Different characterizations were done to understand the properties of the polymers including determination of porosity parameters like, surface area and pore size distribution (PSD). The synthesized polymers showed moderate surface area (468 m2/g and good CO2 uptake (9.3 wt %).

Resume : Co-production of carbon nanotube composites (CNCs) and hydrogen (H2) via the pyrolysis-catalysis method provides a promising way for the sustainable upcycling of waste plastics. However, the state-of-the-art catalysts used for the pyrolysis-catalysis of waste plastics suffer from poor conversion efficiency in terms of specific carbon and H2 yields mainly manipulated by the (micro)structure and materials types of the catalysts, thus seriously limiting their industrial applications. In this work, multiscale designed 3 dimension (3D) rose-like CoxMn3–xO4 spinels providing an active site rich structure were developed as smart pre-catalysts for the high-efficiency upcycling of waste plastics. The targeted Co catalysts were formed in situ on a smart support material (here: MnO from reduced CoxMn3–xO4), combining supporting and promoting functionality and hence enabling superior carbon and H2 yields and unprecedented high specific carbon and H2 yield. At a pre-catalyst to plastic weight ratio of 1:14, the carbon and H2 yields can reach 41 wt.% and 36 mmol·g˗1pla., respectively, while the specific carbon and H2 yield can reach as high as 7.48 g˗1cat. and 634 mmol·g˗1pla·g˗1cat., which is more than one order of magnitude higher than that reported in the literature. Density functional theory calculations indicate that the in situ Co based catalyst exhibits an excellent activity in the dissociation of alkanes (e.g., CH4 and C2H6). The resulting carbon demonstrated an excellent discharge capability and extended cycling performance when they were used as a lithium-ion battery anode. This work finds an innovative idea and novel insight for developing advanced catalyst materials as the next generation catalysts for the upcycling of waste plastics.

Resume : Cupric oxide (CuO) is considered a sustainable semiconductor for large scale photovoltaic (PV) applications. This is because it is a p-type material with a direct band gap of 1.3-2.1 eV, and high absorption coefficient. In this work, CuO films were deposited on non-heated substrates by RF magnetron sputtering to determine its suitability as light absorber material for solar cells applications. A pure 99.99% CuO target of 3-inch diameter was used to deposit the thin films on Corning glass and silicon substrates. The effect on the film properties of argon and hydrogen + argon atmospheres under chamber pressures of 5, 15, 25, 35 and 45 mTorr at 200 W were studied. Structural, optical and electrical properties of the films were obtained through electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV-visible-NIR optical transmittance, FTIR spectroscopy, and four-point probe analysis. X-ray diffraction patterns present a crystalline CuO layer for the samples deposited in argon atmosphere. However, it is observed a mixture of CuO and Cu2O phases in the samples deposited in hydrogen+argon atmosphere. The latter agrees with the observed FTIR spectra of these samples under these conditions since a little Cu2O shoulder appears in addition to the dominant CuO peak, decreasing when increasing deposition pressure. These peaks could be related to the electrical resistivity observed in the samples. The effect of annealing on the samples at 300°C in forming gas and air, revealed an effect on their electrical and optical properties. Increased resistivity after annealing is found in samples deposited with argon, meanwhile decreased resistivity was observed in samples deposited under hydrogen + argon atmosphere.

Resume : With ~60% of all generated energy wasted as heat[1], energy harvesting is an important avenue of study to help provide for our worlds increased power demand in a sustainable way. Thermoelectrics (TEs) offer the unique opportunity to recover this previously wasted energy, and improve performance, via a direct conversion of heat to electricity in a solid state device. The key limitation of TEs is their poor power conversion efficiency, characterised by the dimensionless figure of merit, ZT. This value depends on both the electron and phonon transport characteristics, which themselves are heavily interdependent. For optimal TE behavior the electronic conductivity should be high whilst the thermal conductivity is kept to a minimum. However, in the majority of cases an increase in electrical conductivity is accompanied by an increase in thermal conductivity due to the Wiedemann-Franz Law[2], which links the thermal conductivity of electrons to the charge carrier density. It is this interdependence which has effectively limited the maximum ZT achievable to its current value of ~3[3]. Therefore, the ideal technique for raising ZT further would break this interdependence and optimise these characteristics independently. With this in mind, we investigate interfacial patterning as a method for controlling the transport properties of phonons. This method utilises the fundamental difference in electron and phonon wavelengths to selectively scatter phonons and hence reduce thermal conductivity, whilst having a minimal effect on electronic transport. Using density functional theory, we demonstrate the effectiveness of interfacial patterning on Si/Ge structures. We investigate three differently patterned interfaces, noting how subtle changes in the patterning can have dramatic effects on properties such as the effective mass and the lattice thermal conductivity. This patterning provides a technique to enhance ZT and a framework for producing more viable devices from any heterostructure-based TE materials, including materials not traditionally considered for the application. 1. Perspectives on thermoelectrics: from fundamentals to device applications, Energy & Environmental Science, 2012, 5, 5147 2. Ueber die Wärme-Leitungsfähigkeit der Metalle, Annalen der Physik, 1853, 165, 8, 497 3. Advances in thermoelectric materials research: Looking back and moving forward, Science, 2017, 357, 6358, 9997

Resume : Temperature-dependent photo-Seebeck effect is reported in a bulk single crystalline Bi2Te3 topological insulator. On light illumination, inhomogeneous laser heating of the thermoelectric material Bi2Te3 leads to the development of a thermoelectric potential across its two ends. The sample shows distinguishable contributions in the measured current due to both the Seebeck effect and the normal photo-generated carriers within a narrow layer of the sample. Experiments are performed to distinctly separate the Seebeck contribution from the photogenerated current. The temperature-dependence of the photocurrent without Seebeck contribution shows a sign reversal from negative to positive at ~220 K with the increasing sample temperature. Moreover, the temperature corresponding to the sign reversal of the photocurrent is not unique and depends on the wavelength of the excitation light. These results are significant for the understanding of Seebeck effect and the photocarrier generation in bismuth telluride for its potential use in thermoelectric and photodetector applications.

Resume : The losses in the solar cells are due to a large amount of solar radiation is dissipated by heat. A significant part of the photons has an energy greater than that required for photogeneration of charge carriers and the residual energy is converted into kinetic energy, that is, into heat. Therefore, an important task is to use the dissipated energy. Our main idea is in the combination of photo- and thermo-electrical properties in a single hybrid system to the most efficient conversion of solar energy as well as using the supercapacitor function to increase the energy density of the system and energy storage. We propose the photo-thermoelectric cell based on transitional metal oxide (Fe2O3 and Cr2O3) combined into a hybrid material with organic photo- and thermal- active conjugated polymers (poly-3-hexylthiophene (P3HT), poly (3,4) -ethylene dioxythiophene, polystyrene sulfonate (PEDOT: PSS) on Si substrate. Transitional metal oxide component will be created in the form of nanoscale amorphous films and/or nanoparticles by laser deposition and chemical synthesis respectively. The combination of silicon with a layered system of organometallic compounds will make it possible to obtain a new multifunctional structure for solar energy converters. Additional function of the proposed converter is collecting and storing energy by supercapacitors. The concept of energy storage is based on the combination of iron oxide with carbon nanomaterials.

Resume : A blue light-emitting conjugated polymer, namely aryl-polyfluorene (aryl-F8), having a high neat-film photoluminescence quantum yield (73%) and radiative decay rate (2 × 109 s-1) is reported. Excimer emission from the polymer is significantly reduced in its neat film unlike many other wide band-gap blue-emitters achieved as a result of the bulky aryl groups attached in the polymer chain. Amplified spontaneous emission (ASE) under optical excitation is observed in pristine film at an excitation fluence, Eth ~ 3 μJ cm-2, which is one of the lowest among polymer-based optical gain media in this spectral range, reported so far. The well-separated spectra of stimulated emission and long-lived triplet absorption and very low triplet yields explain the achievement of a low ASE threshold. Under electrical excitation, no singlet-triplet annihilation (STA) is detected in the light-emitting diode (LED) fabricated with this polymer in a hybrid structure. Thus, aryl-F8 emerges as an attractive optical gain medium for lasing application.

Resume : Perovskite solar cells (PSCs) are the fastest growing photovoltaic devices in the solar cells community and offer a bright future for cheap solar electricity. In the last few years, it has been observed that the efficiency and stability of the PSCs can be enhanced by introducing multi cations into the perovskite crystal structure. Herein, we have examined the triple monovalent cation-based PSC (FA0.83MA0.17)0.95 Cs0.05Pb(I0.90Br0.10)3 (CsFAMA) over single monovalent cation based PSC MAPbI3 (MAPI) through frequency-dependent photo-current and dielectric measurements in terms of the dielectric relaxation process. The dielectric relaxation time constant (τd) is lower for the CsFAMA based PSC as compared to the MAPI based PSC. The lower τd is attributed to lower defect density in the CsFAMA based PSCs. Unprecedentedly, the relaxation process is correlated with the presence of monovalent cation of CsFAMA vs MAPI as an absorber in PSCs, which is well correlated with the presence of relative defect density. Our study suggests that τd is higher for higher defect density semiconductors in PSCs. Further, defects formation under illumination conditions reduces JSC as major in the case of MAPI, however, it is relatively insignificant in CsFAMA based PSCs and can be hypothesized based on relative ion density accumulation at the interface of charge extracting contact. This study provides a unique in-depth knowledge towards the role of monovalent cation in the dielectric relaxation process and their connection with the defects and thermal stability of halide perovskite semiconductors-based solar cells.

Resume : Organic materials gained a lot of attention as promising materials for solar cells, field-effect transistors and detectors, due to their solution processability and tunable optoelectronic properties by chemical structure modification. Although organic materials suffer from instability under ambient conditions, various techniques are used to improve chemical stability and mechanical strength. One of the promising methods is cross-linking. Cross-linkable materials possess solvent/heat/ resistance, high hydrophobicity, mechanical durability and excellent film-processing ability [1, 2, 3]. At the same time cross-linking can affect material properties such as charge transfer, charge mobility, energetic and spatial disorders. In this work novel cross-linkable hole transporting materials containing vinyl groups were investigated. Temperature-dependent measurements of mobility were made in room and below ambient temperatures using the time-of-flight (TOF) technique. Herein we present, how cross-linking affects charge carrier mobilities, spatial and energetic disorder in crosslinked and non-crosslinked thin films made from investigated compounds. References 1. X. Sun, X. Deng, Z. Li, B. Xiong, C. Zhong, Z. Zhu, Z. Li, A. K.-Y. Jen, Advanced Science 2020, 7, 13 1903331. 2. Z. Li, Z. Zhu, C.-C. Chueh, J. Luo, A. K.-Y. Jen, Advanced Energy Materials 2016, 6, 21 1601165. 3. J. Wu, M. Hu, L. zhang, G. Song, Y. Li, W. Tan, Y. Tian, B. Xu, Chemical Engineering Journal 2021, 422 130124.