Xiong Yin

Hybrid of MoS2 and Reduced Graphene Oxide: A Lightweight and Broadband Electromagnetic Wave Absorber

Electromagnetic wave absorbing materials that can exhibit effective absorption in a broad bandwidth at a thin thickness are strongly desired due to their widespread applications in electronic devices. In this study, hybrids of MoS2 and reduced graphene oxide (RGO) were prepared and their microwave absorption performance was investigated for the first time. It was found that a thin sample consisting of 10 wt % MoS2/RGO hybrid in the wax matrix exhibited an effective microwave absorption bandwidth of 5.72 GHz at the thickness less than 2.0 mm. The highest reflection loss of -50.9 dB was observed at 11.68 GHz for a sample with a thickness of 2.3 mm. Results obtained in this study indicate that hybrids of MoS2 and RGO are promising microwave absorbing materials, which can exhibit broad effective absorption bandwidth at low filler loading and thin thickness.

Performance enhancement of perovskite-sensitized mesoscopic solar cells using Nb-doped TiO2 compact layer

Perovskite solar cells are one of the most promising alternatives to conventional photovoltaic devices, and extensive studies are focused on device optimization to further improve their performance. A compact layer of TiO2 is generally used in perovskite solar cells to block holes from reaching the fluorine-doped tin oxide electrode. In this contribution, we engineered a TiO2 compact layer using Nb doping, which resulted in solar cells with a power conversion efficiency (PCE) of 10.26%, which was higher than that of devices with the same configuration but containing a pristine TiO2 compact layer (PCE = 9.22%). The device performance enhancement was attributed to the decreased selective contact resistance and increased charge recombination resistance resulting from Nb doping, which was revealed by the impedance spectroscopy measurements. The developed strategy highlights the importance of interface optimization for perovskite solar cells.

Facile Synthesis of Poly(3,4-ethylenedioxythiophene) Film via Solid- State Polymerization as High-Performance Pt-Free Counter Electrodes for Plastic Dye-Sensitized Solar Cells

A high-performance Pt-free counter electrode (CE) based on poly(3,4-ethylenedioxythiophene) (PEDOT) film for plastic dye-sensitized solar cells (DSCs) has been developed via a facile solid-state polymerization (SSP) approach. The polymerization was simply initiated by sintering the monomer, 2,5-dibromo-3,4-ethylenedioxythiophene (DBEDOT), at the temperature of 80 °C, which can be applied on the plastic substrate. The cyclic voltammetry measurements revealed that the catalytic activity of the SSP-PEDOT CE for triiodide reduction is comparable with that of the Pt CE. Under optimized conditions, the power conversion efficiency of a DSC with a N719-sensitized TiO2 photoanode and the SSP-PEDOT CE is 7.04% measured under standard 1 sun illumination (100 mW cm(-2), AM 1.5), which is very close to that of the device fabricated under the same conditions with a conventional thermally deposited Pt CE (7.35%). Furthermore, taking advantage of the compatibility of the SSP-PEDOT with the plastic substrates, a full plastic N719-sensitized TiO2 solar cell was demonstrated, and an efficiency of 4.65% was achieved, which is comparable with the performance of a plastic DSC with a sputter-deposited Pt CE (5.38%). These results demonstrated that solid-state polymerization initiated at low temperature is a facile and low-cost method of fabricating the high-performance Pt-free CEs for plastic DSCs.

Two-Step Electrochemical Synthesis of Polypyrrole/Reduced Graphene Oxide Composites as Efficient Pt-Free Counter Electrode for Plastic Dye-Sensitized Solar Cells

Polypyrrole/reduced graphene oxide (PPy/RGO) composites on the rigid and plastic conducting substrates were fabricated via a facile two-step electrochemical process at low temperature. The polypyrrole/graphene oxide (PPy/GO) composites were first prepared on the substrate with electrochemical polymerization method, and the PPy/RGO composites were subsequently obtained by electrochemically reducing the PPy/GO. The resultant PPy/GO and PPy/RGO composites were porous, in contrast to the dense and flat pristine PPy films. The cyclic voltammetry measurement revealed that resultant composites exhibited a superior catalytic performance for triiodide reduction in the order of PPy/RGO > PPy/GO > PPy. The catalytic activity of PPy/RGO was comparable to that of Pt counter electrode (CE). Under the optimal conditions, an energy conversion efficiency of 6.45% was obtained for a rigid PPy/RGO-based dye-sensitized solar cell, which is 90% of that for a thermally deposited Pt-based device (7.14%). A plastic counter electrode was fabricated by depositing PPy/RGO composites on the plastic ITO/PEN substrate, and then an all-plastic device was assembled and exhibited an energy conversion efficiency of 4.25%, comparable to that of the counterpart using a sputtered-Pt CE (4.83%) on a plastic substrate. These results demonstrated that electrochemical synthesis is a facile low-temperature method to fabricate high-performance RGO/polymer composite-based CEs for plastic DSCs.

High-Performance Plastic Dye-sensitized Solar Cells Based on Low-Cost Commercial P25 TiO2 and Organic Dye

High-performance plastic dye-sensitized solar cells (DSCs) based on low-cost commercial Degussa P25 TiO(2) and organic indoline dye D149 have been fabricated using electrophoretic deposition (EPD) with compression post-treatment at room temperature. The pressed EPD electrode outperformed the sintered EPD electrode and as-prepared EPD electrode in short-circuit current density and power conversion efficiency. About 150% and 180% enhancement in power conversion efficiency have been achieved in DSC devices with sintering and compression post-treatment as compared to the as-prepared electrode, respectively. Several characterizations including intensity modulated photocurrent spectroscopy, incident photon-to-electron conversion efficiency and electrochemical impedance spectra have been employed to reveal the nature of improvement with post-treatment. Experimental results indicate that the sintering and compression post-treatment are beneficial to improve the electron transport and thus lead to the enhancement of photocurrent and power conversion efficiency. In addition, the compression post-treatment is more efficient than sintering post-treatment in improving interparticle connection in the as-prepared EPD electrode. Under optimized conditions, the conversion efficiency of plastic devices with D149-sensitized P25 TiO(2) photoanode has reached 5.76% under illumination of AM 1.5G (100 mW cm(-2)). This study demonstrates that the EPD combined with compression post-treatment provides a way to fabricate highly efficient plastic photovoltaic devices.

Facile Synthesis of ZnO Nanocrystals via a Solid State Reaction for High Performance Plastic Dye-Sensitized Solar Cells

AbstractWe report the facile synthesis of ZnO nanocrystals via a one-step solid state reaction at room temperature and their application as the photoanode in plastic dye-sensitized solar cells (DSCs). ZnO nanoparticles were prepared utilizing zinc acetate dihydrate and sodium hydroxide with a short grinding time and without a sintering process. The as-prepared samples with the polycrystalline hexagonal wurtzite structure were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The obtained ZnO nanoparticles exhibited high crystallinity even without a high temperature sintering treatment during the preparation process. The effects of compression post-treatment on the photovoltaic performance of DSCs were also investigated using intensity modulated photocurrent spectroscopy (IMPS), incident photo-to-current conversion efficiency (IPCE), and electrochemical impedance spectroscopy (EIS). The results indicate that the improvement of power conversion efficiency after compression post-treatment of ZnO photoelectrode can be attributed to its high photoelectron collection efficiency and effective electron transport. Under the optimized conditions, a full plastic D149-sensitized ZnO solar cell measured under illumination of 100 mW·cm−2 (AM 1.5G) presents an energy conversion efficiency of 3.76% with open-circuit voltage of 0.688 V, short-circuit current density of 8.55 mA·cm−2, and fill factor of 0.64. These results demonstrate that the one-step solid state reaction is a convenient and effective method for the synthesis of ZnO nanocrystals for use in plastic DSCs.

Enhanced conversion efficiency of flexible dye-sensitized solar cells by optimization of the nanoparticle size with an electrophoretic deposition technique

To optimize the conversion efficiency of plastic dye-sensitized solar cells fabricated by the electrophoretic deposition technique, anatase TiO2 nanoparticles of various sizes from 10 nm to 27 nm have been synthesized via a simple hydrothermal process. The obtained TiO2 nanoparticles have been characterized by X-ray diffraction and high resolution transmission electron microscopy, which confirmed that the synthesized nanoparticles are in the pure anatase phase. Rigid devices based on D149-sensitized TiO2 particles with a size of 19 nm showed the highest conversion efficiency of 7.0% among the four different devices, which was measured under illumination of AM 1.5G, 100 mWcm−2. The effect of the particle size on the photovoltaic performance of DSSCs has been systemically studied using photoelectrochemical characterizations, including intensity modulated photocurrent spectroscopy and intensity modulated photovoltage spectroscopy. The good photovoltaic performance for 19 nm TiO2 is ascribed to the good dye loading, an efficient electron transport and the high charge collection efficiency in the photoanode. Moreover, plastic DSSCs based on 19 nm TiO2 presented a conversion efficiency of 6.0% (AM 1.5G, 100 mWcm−2) under optimized conditions, showing about a 20% enhancement in the conversion efficiency as compared to that based on commercial Degussa P25 TiO2 (5.2%). These results demonstrate that optimization of the TiO2 nanoparticle size for devices fabricated using the EPD technique is an alternative method to achieve highly efficient plastic dye-sensitized solar cells.

Simultaneous N-doping of reduced graphene oxide and TiO2 in the composite for visible light photodegradation of methylene blue with enhanced performance

The nitrogen-doped P90 TiO2 (N-P90), nitrogen-doped reduced graphene oxide (N-RGO) and their composite were synthesized via a one-step annealing treatment process under NH3 atmosphere using commercial P90 TiO2 and GO as starting materials. The as-prepared N-P90, N-RGO and N-P90/N-RGO composite were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and ultraviolet–visible diffuse reflectance spectroscopy (DRS). The results indicated that both the reduction of graphene oxide and the incorporation of nitrogen into both RGO and TiO2 matrices were accomplished simultaneously in the facile process. The photocatalytic activity of the as-prepared samples was evaluated using the degradation of methylene blue (MB) under visible light irradiation. N-P90/N-RGO composites showed a significantly enhanced photocatalytic performance compared with P90 TiO2, N-P90 and N-P90/RGO composites. The higher photocatalytic activity of N-P90/N-RGO composites can be ascribed to the more efficient separation of the photogenerated charges resulting from the improved electrical conductivity of the N-RGO sheets, as well as the enhanced absorption in the visible light region. Overall, this work demonstrated a facile approach of incorporating nitrogen into commercial TiO2 and RGO simultaneously and a novel strategy of fabricating a visible light-active photocatalyst with improved efficiency for mass application.

Hydrothermal growth of MoS 2 /Co 3 S 4 composites as efficient Pt-free counter electrodes for dye-sensitized solar cells

MoS2/Co3S4 composite films were prepared via a facile one-step hydrothermal method, and used as efficient and low-cost Pt-free counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). Characterizations revealed that Co3S4 and MoS2 were obtained simultaneously during the facile hydrothermal process. The composites afforded a promising synergistic effect on the catalyzing of triiodide reduction. Enhanced electrocatalytic performance of the resultant composite films was confirmed through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analyses. DSSCs using MoS2/Co3S4 composite CEs outperform the devices with pristine MoS2 or Co3S4 CEs in power conversion efficiency (PCE). Furthermore, a PCE of 6.77% is obtained for the optimized devices using MoS2/Co3S4 composite CEs measured under standard 1 sun illumination (100 mW cm−2, AM 1.5G), which is comparable to that of the devices fabricated under the same conditions with conventional thermally deposited Pt CEs (7.14%). The results demonstrate that MoS2/Co3S4 composites are promising alternatives to Pt to be applied as CEs for DSSCs.摘要染料敏化太阳电池因其成本低、稳定性好、工艺简便而备受关注. 发展高性能、廉价的材料代替传统的贵金属铂对电极是当前染 料敏化太阳电池领域的研究热点之一. 二硫化钼纳米材料具有高比表面积和大量的催化位点, 是较为理想的铂对电极替代材料之一, 但较 低的电导率限制了二硫化钼对电极性能的进一步提高. 本文首次报道了由二硫化钼纳米材料与金属性的四硫化三钴复合制备染料敏化 太阳电池对电极, 该复合对电极可以利用水热方法一步合成. 研究结果表明, 使用该复合对电极的染料敏化太阳电池光电转换效率可达 6.77%, 接近于使用铂对电极的器件(7.14%), 优于使用单一二硫化钼(4.64%)或四硫化三钴(5.11%)作为对电极的器件.

In Situ Growth of Highly Adhesive Surface Layer on Titanium Foil as Durable Counter Electrodes for Efficient Dye-sensitized Solar Cells.

Counter electrodes (CEs) of dye-sensitized solar cells (DSCs) are usually fabricated by depositing catalytic materials on substrates. The poor adhesion of the catalytic material to the substrate often results in the exfoliation of catalytic materials, and then the deterioration of cell performance or even the failure of DSCs. In this study, a highly adhesive surface layer is in situ grown on the titanium foil via a facile process and applied as CEs for DSCs. The DSCs applying such CEs demonstrate decent power conversion efficiencies, 6.26% and 4.37% for rigid and flexible devices, respectively. The adhesion of the surface layer to the metal substrate is so strong that the photovoltaic performance of the devices is well retained even after the CEs are bended for 20 cycles and torn twice with adhesive tape. The results reported here indicate that the in situ growth of highly adhesive surface layers on metal substrate is a promising way to prepare durable CEs for efficient DSCs.