Spectrally Resolved Exciton Polarizability for Understanding Charge Generation in Organic Bulk Hetero-Junction Diodes.

Despite decades of research, the dominant charge generation mechanism in organic bulk heterojunction (BHJ) devices is not completely understood. While the local dielectric environments of the photoexcited molecules are important for exciton dissociation, conventional characterizations cannot separately measure the polarizability of electron-donor and electron-acceptor, respectively, in their blends, making it difficult to decipher the spectrally different charge generation efficiencies in organic BHJ devices. Here, by spectrally resolved electroabsorption spectroscopy, we report extraction of the excited state polarizability for individual donors and acceptors in a series of organic blend films. Regardless of the donor and acceptor, we discovered that larger exciton polarizability is linked to larger π-π coherence length and faster charge transfer across the heterojunction, which fundamentally explains the origin of the higher charge generation efficiency near 100% in the BHJ photodiodes. We also show that the molecular packing of the donor and acceptor influence each other, resulting in a synergetic enhancement in the exciton polarizability.

Phase Stability Improvement of a γ-CsPbI3 Perovskite Solar Cell Utilizing a Barium Bis(trifluoromethanesulfonimide) Solution.

The cesium lead iodide (CsPbI3) perovskite solar cell possesses a wide band gap ranging from 1.65 to 1.75 eV, which is suitable for integration into a tandem structure along with a low-band-gap silicon solar cell. Moreover, CsPbI3 has received considerable attention as a potential solution for the prevalent issues of low thermal stability of organic-inorganic perovskite solar cells and phase segregation encountered in conventional mixed halide wide-band-gap perovskite solar cells. Through the implementation of volatile additives, CsPbI3 has demonstrated substantial advancements in efficiency, process temperature, and stability. This study introduces a novel approach for barium (Ba)-doping by spraying an antisolvent containing barium bis(trifluoromethanesulfonimide) during the spin-coating process. By incorporating Ba2+ through this spraying technique, the formation of the delta phase in CsPbI3 is significantly suppressed; thereby, a power conversion efficiency of 18.56% is achieved, and a remarkable 93% of the initial efficiency is maintained after 600 h.

Exsolution of Ru Nanoparticles on BaCe0.9 Y0.1 O3-δ Modifying Geometry and Electronic Structure of Ru for Ammonia Synthesis Reaction Under Mild Conditions.

Green ammonia is an efficient, carbon-free energy carrier and storage medium. The ammonia synthesis using green hydrogen requires an active catalyst that operates under mild conditions. The catalytic activity can be promoted by controlling the geometry and electronic structure of the active species. An exsolution process is implemented to improve catalytic activity by modulating the geometry and electronic structure of Ru. Ru nanoparticles exsolved on a BaCe0.9 Y0.1 O3-δ support exhibit uniform size distribution, 5.03 ± 0.91 nm, and exhibited one of the highest activities, 387.31 mmolNH3  gRu -1  h-1 (0.1 MPa and 450 °C). The role of the exsolution and BaCe0.9 Y0.1 O3-δ support is studied by comparing the catalyst with control samples and in-depth characterizations. The optimal nanoparticle size is maintained during the reaction, as the Ru nanoparticles prepared by exsolution are well-anchored to the support with in-plane epitaxy. The electronic structure of Ru is modified by unexpected in situ Ba promoter accumulation around the base of the Ru nanoparticles.

Color balanced transparent luminescent solar concentrator based on a polydimethylsiloxane polymer waveguide with coexisting polar and non-polar fluorescent dyes.

Color balance is a critical concept in the application of functional transparent polymers from a customer's standpoint. In this study, multiple polar and non-polar fluorescent dyes are embedded simultaneously for the first time in a polydimethylsiloxane (PDMS) polymer matrix. Five dyes successfully coexist with the optimum blending ratio. Furthermore, simultaneous dispersing of polar and non-polar dyes in the polymer is achieved. Absorption and photoluminescence characteristics of multiple fluorescent dyes in PDMS medium are systemically deconvoluted and discussed. The competitive average visible transmittance and color balance of synthesized multi-fluorescent dye embedded PDMS is demonstrated by high color rendering index and CIE color space coordinates close to the white point. Additionally, the luminescent solar concentrator device demonstrates improved power conversion efficiency and light utilization efficiency than the pure PDMS waveguide-based device. Moreover, the long-term storage stability is demonstrated successfully. The findings, therefore, demonstrate the applicability of multi-fluorescent dye embedded PDMS to advanced transparent devices.

Recent Progress in Interconnection Layer for Hybrid Photovoltaic Tandems.

Hybrid tandem solar cells offer the benefits of low cost and full solar spectrum utilization. Among the hybrid tandem structures explored to date, the most popular ones have four (simple stacking design) or two (terminal/tunneling layer addition design) terminal electrodes. Although the latter design is more cost-effective than the former, its widespread application is hindered by the difficulty of preparing an interface between two solar cell materials. The oldest approach to the in-series bonding of two or more bandgap solar cells relies on the introduction of a tunneling layer in multijunction III-V solar cells, but it has some limitations, e.g., the related materials/technologies are applicable only to III-V and certain other solar cells. Thus, alternative methods of realizing junction contacts based on the use of novel materials are highly sought after. Here, the strategies used to realize high-performance tandem cells are described, focusing on interface control in terms of bonding two or more solar cells for tandem approaches. The presented information is expected to aid the establishment of ideal methods of connecting two or more solar cells to obtain the highest performance for different solar cell choices with minimized energy loss through the interface.

Self-Aggregation-Controlled Rapid Chemical Bath Deposition of SnO2 Layers and Stable Dark Depolarization Process for Highly Efficient Planar Perovskite Solar Cells.

Planar perovskite solar cells (PSCs) incorporating n-type SnO2 have attracted significant interest because of their excellent photovoltaic performance. However, the film fabrication of SnO2 is limited by self-aggregation and inhomogeneous growth of the intermediate phase, which produces poor morphology and properties. In this study, a self-controlled SnO2 layer is fabricated directly on a fluorine-doped tin oxide (FTO) surface through simple and rapid chemical bath deposition. The PSCs based on this hydrolyzed SnO2 layer exhibit an excellent power conversion efficiency of 20.21 % with negligible hysteresis. Analysis of the electrochemical impedance spectroscopy on the charge transport dynamics indicates that the bias voltage influences both interfacial charge transportation and the ionic double layer under illumination. The hydrolyzed SnO2 -based PSCs demonstrate a faster ionic charge response time of 2.5 ms in comparison with 100.5 ms for the hydrolyzed TiO2 -based hysteretic PSCs. The results of quasi-steady-state carrier transportation indicate that a dynamic hysteresis in the J-V curves can be explained by complex ionic-electronic kinetics owing to the slow ionic charge redistribution and hole accumulation caused by electrode polarization, which causes an increase in charge recombination. This study reveals that SnO2 -based PSCs lead to a stabilized dark depolarization process compared with TiO2 -based PSCs, which is relevant to the charge transport dynamics in the high-performing planar SnO2 -based PSCs.

Cellular organization of three germ layer cells on different types of noncovalent functionalized graphene substrates.

Graphene and its derivatives have seen a rapid rise in interest as promising biomaterials especially in the field of tissue engineering, regenerative medicine, and cell biology of late. Despite its proven potential in numerous biological applications, information regarding the relationship between the different forms of graphene and cell lineages is still lacking partly due to its topical emergence in cellular studies. Herein, we explore the biocompatibility of four types of graphene substrates (chemical vapor deposition grown graphene, mechanically exfoliated graphene, chemically exfoliated graphene oxide, and reduced graphene oxide) with three types of somatic cells (keratinocytes, hepatocytes, endothelial cells) derived from the three germ layers in relation to cell adhesion, proliferation, morphology, and gene expression. The results revealed exceptional cell adhesion for all tested groups but enhanced proliferation and cytoskeletal interconnectivity in graphene oxide and reduced graphene oxide substrates. We were unable to detect any adverse effects in gene expression and survivability during a week of culture. We further show topographic changes to graphene substrates under fetal bovine serum adsorption to better illustrate the actual microenvironment of inhabitant cells. This study highlights the extraordinary synergy between graphene and somatic cells, suggesting the discretionary use of extracellular matrix components for in vitro cultivation.

Investigation of Hole-Transporting Poly(triarylamine) on Aggregation and Charge Transport for Hysteresisless Scalable Planar Perovskite Solar Cells.

Organometallic halide perovskite solar cells (PSCs) have unique photovoltaic properties for use in next-generation solar energy harvesting systems. The highest efficiency of PSCs reached 22.1% on a laboratory scale of <0.1 cm2 device area. Thus, scaling up is the next step toward commercialization, but the difficulty in controlling the quality of large-area perovskite thin films remains a fundamental challenge. It has also been frequently reported that the J- V hysteresis is intensified in PSCs with areas larger than 1 cm2. In this study, we have fabricated a large-area perovskite layer using PbICl films, providing an intrinsic porous layer and enhancing the uniformity of the perovskite layer at areas larger than 1 cm2. Furthermore, we have investigated the polymeric properties of the prevalent hole-transporting material poly(triarylamine) (PTAA) with its photovoltaic performance. Two types of PTAAs, poly[bis(4-phenyl)(2,4-dimethylphenyl)amine] and poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine], were compared. A series of PTAAs with different molecular weights ( Mw) and polydispersity indices were studied, as the molecular weight of the PTAA is a key factor in determining the electrical properties and photovoltaic performance of the system. The fabricated PSCs with an aperture area of 1 cm2 based on a high-molecular-weight PTAA achieved a power conversion efficiency of 16.47% with negligible hysteresis and excellent reproducibility.

Highly stretchable, mechanically stable, and weavable reduced graphene oxide yarn with high NO2 sensitivity for wearable gas sensors.

Stretchable gas sensors are important components of wearable electronic devices used for human safety and healthcare applications. However, the current low stretchability and poor stability of the materials limit their use. Here, we report a highly stretchable, stable, and sensitive NO2 gas sensor composed of reduced graphene oxide (RGO) sheets and highly elastic commercial yarns. To achieve high stretchability and good stability, the RGO sensors were fabricated using a pre-strain strategy (strain-release assembly). The fabricated stretchable RGO gas sensors showed high NO2 sensitivity (55% at 5.0 ppm) under 200% strain and outstanding mechanical stability (even up to 5000 cycles at 400% applied strain), making them ideal for wearable electronic applications. In addition, our elastic graphene gas sensors can also be woven into fabrics and clothes for the creation of smart textiles. Finally, we successfully fabricated wearable gas-sensing wrist-bands from superelastic graphene yarns and stretchable knits to demonstrate a wearable electronic device.

Highly conductive and environmentally stable gold/graphene yarns for flexible and wearable electronics.

Here, we fabricated high-performance gold/graphene yarns through a facile method by the electroless deposition of gold nanoparticles onto the surface of graphene yarns. The gold/graphene yarns are fabricated using a completely solution-based process that can be scaled up for practical applications. They possess high electrical conductivity (2.86 × 102 S cm-1) and good gravimetric specific conductivity (6.81 × 102 S cm2 g-1) as well as good reliability under 1000 bending tests with a maximum bending angle of 170° and 10 washing tests with laundry detergents. These stable conducting yarns could also be integrated into textiles and clothes in various forms to create smart fabrics and wearable devices. In addition, this facile approach is easily applicable to various graphene films and devices on soft substrates that are presently used in flexible/wearable electronics.

Electrodeposition of SnO2 on FTO and its Application in Planar Heterojunction Perovskite Solar Cells as an Electron Transport Layer.

We report the performance of perovskite solar cells (PSCs) with an electron transport layer (ETL) consisting of a SnO2 thin film obtained by electrochemical deposition. The surface morphology and thickness of the electrodeposited SnO2 films were closely related to electrochemical process conditions, i.e., the applied voltage, bath temperature, and deposition time. We investigated the performance of PSCs based on the SnO2 films. Remarkably, the experimental factors that are closely associated with the photovoltaic performance were strongly affected by the SnO2 ETLs. Finally, to enhance the photovoltaic performance, the surfaces of the SnO2 films were modified slightly by TiCl4 hydrolysis. This process improves charge extraction and suppresses charge recombination.

A PbI2-xClx seed layer for obtaining efficient planar-heterojunction perovskite solar cells via an interdiffusion process.

Despite the previous reports on the fabrication of CH3NH3PbI3-xClx films via sequential deposition, the positioning and formation of PbI2 in MAPbI3-xClx perovskite films made from the seed layer containing PbI2 and PbCl2 in different ratios have not yet been addressed. In this study, the PbI2 content in a perovskite absorber layer is controlled by changing the PbCl2 ratio in a PbI2-xClx seed layer. The addition of PbCl2 in the seed layer facilitates PbI2 generation and affects the morphology of the perovskite film. By integrating a perovskite absorber via the PbI2-xClx seed-layer into a solar cell, we investigated the effects of the correlation between the chlorine and PbI2 contents on the device performance through intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy. Elemental depth profiling analyses confirm that not only was the formed PbI2 preferentially located near the metal-oxide layer, but residual chlorine was adsorbed at the TiO2 layer. Our findings demonstrate that the geometric features of the formed PbI2 affected the perovskite solar cells according to the chlorine content, likely because of the elemental gradient induced by annealing. The PbI2-xClx-derived planar-heterojunction perovskite solar cells exhibited maximum power-conversion efficiencies of 17.56% at reverse scan and 17.21% at forward scan, suppressed current density-voltage hysteresis, and good performance distributions.

Freeze-dried MoS2 sponge electrodes for enhanced electrochemical energy storage.

In the present study, we have synthesized high surface area MoS2 sponge electrodes via a facile hydrothermal method followed by a freeze drying process. The performance of the MoS2 based symmetric capacitor showed a high specific capacitance value of around 128 F g-1 at a scan rate of 2 mV s-1, and also a single electrode showed a specific capacitance of 510 F g-1, which is a remarkable value to be reported for a MoS2 based material in a symmetric device configuration. Also, a high energy density of around 6.15 Wh kg-1 and a good cyclic stability over 4000 cycles are obtained for the symmetrical cell.

UV Degradation and Recovery of Perovskite Solar Cells.

Although the power conversion efficiency of perovskite solar cells has increased from 3.81% to 22.1% in just 7 years, they still suffer from stability issues, as they degrade upon exposure to moisture, UV light, heat, and bias voltage. We herein examined the degradation of perovskite solar cells in the presence of UV light alone. The cells were exposed to 365 nm UV light for over 1,000 h under inert gas at <0.5 ppm humidity without encapsulation. 1-sun illumination after UV degradation resulted in recovery of the fill factor and power conversion efficiency. Furthermore, during exposure to consecutive UV light, the diminished short circuit current density (Jsc) and EQE continuously restored. 1-sun light soaking induced recovery is considered to be caused by resolving of stacked charges and defect state neutralization. The Jsc and EQE bounce-back phenomenon is attributed to the beneficial effects of PbI2 which is generated by the decomposition of perovskite material.

Highly stable tandem solar cell monolithically integrating dye-sensitized and CIGS solar cells.

UNLABELLED: A highly stable monolithic tandem solar cell was developed by combining the heterogeneous photovoltaic technologies of dye-sensitized solar cell (DSSC) and solution-processed CuInxGa1-xSeyS1-y (CIGS) thin film solar cells. The durability of the tandem cell was dramatically enhanced by replacing the redox couple from to [Co(bpy)3](2+) /[Co(bpy)3](3+)), accompanied by a well-matched counter electrode ( PEDOT: PSS) and sensitizer (Y123). A 1000 h durability test of the DSSC/CIGS tandem solar cell in ambient conditions resulted in only a 5% decrease in solar cell efficiency. Based on electrochemical impedance spectroscopy and photoelectrochemical cell measurement, the enhanced stability of the tandem cell is attributed to minimal corrosion by the cobalt-based polypyridine complex redox couple.

Amorphous MoSx thin-film-coated carbon fiber paper as a 3D electrode for long cycle life symmetric supercapacitors.

Amorphous MoSx thin-film-coated carbon fiber paper as a binder-free 3D electrode was synthesized by a facile hydrothermal method. The maximum specific capacitance of a single electrode was 83.9 mF cm(-2), while it was 41.9 mF cm(-2) for the symmetric device. Up to 600% capacitance retention was observed for 4750 cycles.

Molybdenum diselenide/reduced graphene oxide based hybrid nanosheets for supercapacitor applications.

In the present study, molybdenum diselenide/reduced graphene oxide (MoSe2/rGO) nanosheets were synthesized via a facile hydrothermal process and the electrochemical performance of the nanosheets was evaluated for supercapacitor applications. The MoSe2 nanosheets were uniformly distributed on the surface of the rGO matrix. The MoSe2/rGO nanosheet electrode exhibited an enhanced specific capacitance (211 F g(-1)) with excellent cycling stability, compared with pristine MoSe2. The enhanced electrochemical performance of the MoSe2/rGO nanosheet electrode is mainly attributed to the improved electron and ion transfer mechanism involving the synergistic effects of pseudocapacitance (from the MoSe2 nanosheets) and the electric double layer charge (EDLC, from the rGO nanosheets) storage behavior. These results demonstrate that the enhanced electrochemical performance of MoSe2/rGO nanosheets could be obtained via a facile and scalable approach.

Electrocatalytic activity of NiO on silicon nanowires with a carbon shell and its application in dye-sensitized solar cell counter electrodes.

To improve the catalytic activity of a material, it is critical to maximize the effective surface area by directly contacting the electrolyte. Nanowires are a promising building block for catalysts in electrochemical applications because of their large surface area. Nickel oxide (NiO) decoration was achieved by drop-casting a nickel-dissolved solution onto vertically aligned silicon nanowire arrays with a carbon shell (SiNW/C). Based on the hybridization of the NiO and silicon nanowire arrays with a carbon shell this study aimed to achieve a synergic effect for the catalytic activity performance. This study demonstrated that the resulting nanomaterial exhibits excellent electrocatalytic activity and performs well as a counter electrode for dye-sensitized solar cells (DSSCs). The compositions of the materials were examined using X-ray diffraction, X-ray photoelectron spectroscopy, and energy dispersive spectroscopy. Their micro- and nano-structures were investigated using scanning electron microscopy and transmission electron microscopy. The electrochemical activity toward I(-)/I3(-) was examined using cyclic voltammetry and electrochemical impedance spectroscopy. The obtained peak power conversion efficiency of the DSSC based on the NiO@SiNW/C counter electrode was 9.49%, which was greater than that of the DSSC based on the Pt counter electrode.

Silver Nanowire Top Electrodes in Flexible Perovskite Solar Cells using Titanium Metal as Substrate.

Flexible perovskite solar cells (FPSCs) have various applications such as wearable electronic textiles and portable devices. In this work, we demonstrate FPSCs on a titanium metal substrate employing solution-processed silver nanowires (Ag NWs) as the top electrode. The Ag NW electrodes were deposited on top of the spiro-MeOTAD hole transport layer by a carefully controlled spray-coating method at moderate temperatures. The power conversion efficiency (PCE) reached 7.45 % under AM 1.5 100 mW cm(-2) illumination. Moreover, the efficiency for titanium-based FPSCs decreased only slightly (by 2.6 % of the initial value) after the devices were bent 100 times. With this and other advances, fully solution-based indium-free flexible photovoltaics, advantageous in terms of price and processing, have the potential to be scaled into commercial production.

Wireless Solar Water Splitting Device with Robust Cobalt-Catalyzed, Dual-Doped BiVO4 Photoanode and Perovskite Solar Cell in Tandem: A Dual Absorber Artificial Leaf.

A stand-alone, wireless solar water splitting device without external energy supply has been realized by combining in tandem a CH3NH3PbI3 perovskite single junction solar cell with a cobalt carbonate (Co-Ci)-catalyzed, extrinsic/intrinsic dual-doped BiVO4 (hydrogen-treated and 3 at% Mo-doped). The photoanode recorded one of the highest photoelectrochemical water oxidation activity (4.8 mA/cm(2) at 1.23 VRHE) under simulated 1 sun illumination. The oxygen evolution Co-Ci co-catalyst showed similar performance to best known cobalt phosphate (Co-Pi) (5.0 mA/cm(2) at 1.23 VRHE) on the same dual-doped BiVO4 photoanode, but with significantly better stability. A tandem artificial-leaf-type device produced stoichiometric hydrogen and oxygen with an average solar-to-hydrogen efficiency of 4.3% (wired), 3.0% (wireless) under simulated 1 sun illumination. Hence, our device based on a D4 tandem photoelectrochemical cell represents a meaningful advancement in performance and cost over the device based on a triple-junction solar cell-electrocatalyst combination.