Interfacial engineering of CuO nanorod/ZnO nanowire hybrid nanostructure photoanode in dye-sensitized solar cell

Developing efficient and cost-effective photoanode plays a vital role determining the photocurrent and photovoltage in dye-sensitized solar cells (DSSCs). Here, we demonstrate DSSCs that achieve relatively high power conversion efficiencies (PCEs) by using one-dimensional (1D) zinc oxide (ZnO) nanowires and copper (II) oxide (CuO) nanorods hybrid nanostructures. CuO nanorod-based thin films were prepared by hydrothermal method and used as a blocking layer on top of the ZnO nanowires’ layer. The use of 1D ZnO nanowire/CuO nanorod hybrid nanostructures led to an exceptionally high photovoltaic performance of DSSCs with a remarkably high open-circuit voltage (0.764 V), short current density (14.76 mA/cm² under AM1.5G conditions), and relatively high solar to power conversion efficiency (6.18%) . The enhancement of the solar to power conversion efficiency can be explained in terms of the lag effect of the interfacial recombination dynamics of CuO nanorod-blocking layer on ZnO nanowires. This work shows more economically feasible method to bring down the cost of the nano-hybrid cells and promises for the growth of other important materials to further enhance the solar to power conversion efficiency.     

Photo‐enhanced catalytic activity of spray‐coated Cu2SnSe3 nanoparticle counter electrode for dye‐sensitised solar cells

Cu₂SnSe₃ nanoparticles are synthesised using oleylamine as both a solvent and capping agent and spray coated to form dye‐sensitised solar cell (DSSC) counter electrodes (CEs) using earth‐abundant elements. The film requires annealing at only 400 °C in nitrogen, which is a lower temperature than previous reports of both Cu₂SnSe₃and Cu₂ZnSnSe₄ films, also avoiding the use of Se gas. The composition and phase of the material is confirmed to be kesterite Cu₂SnSe₃. DSSCs using Cu₂SnSe₃ CEs give a power conversion efficiency of 4.87%, compared to 5.35% when using Pt. Electrochemical impedance spectroscopy indicates that the performance of the Cu₂SnSe₃ CE is enhanced under illumination, leading to a drop in the charge transfer resistance. This illumination‐induced enhancement of the catalytic activity provides a novel mechanism for the enhancement of CE performance in DSSCs.

     

Performance characteristics of dye-sensitized solar cells with counter electrode based on NiP-plated glass and titanium plate

The counter electrodes based on NiP-plated glass and titanium plate were prepared. The performance characteristics of the dye-sensitized solar cells with platinized NiP-plated glass electrode (Pt/NiP electrode) and platinized titanium plate electrode (Pt/TP electrode) were discussed. Pt/NiP electrode and Pt/TP electrode showed the same catalytic activity for triiodide reduction compared with platinized fluorine-doped tin oxide conducting glass electrode (Pt/FTO electrode). However, Pt/NiP electrode and Pt/TP electrode have the advantage over Pt/FTO electrode in reducing the sheet resistance and increasing light reflectivity, which resulted in improving the photovoltaic performance of dye-sensitized solar cells effectively. Compared with the cell using Pt/FTO electrode, the incident photon conversion efficiency of dye-sensitized solar cells with Pt/NiP electrode and Pt/TP electrode was increased by 20% and 5%, respectively, the overall energy efficiency of dye-sensitized solar cells with Pt/NiP electrode and Pt/TP electrode was increased by 32% and 27%, respectively.     

Graphene/carbon nanotubes composites as a counter electrode for dye-sensitized solar cells

As an alternative platinum counter electrode in dye-sensitized solar cells (DSSCs), carbon materials based counter electrode were prepared using multi-walled carbon nanotubes (MWNTs)/graphene nano-sheets (GNS) composite by simple doctor blade method. We found that the photovoltaic performance was strongly influenced by the concentration of GNS in composite electrode. The composite electrode with 60% MWNTs and 40% GNS based DSSCs showed the maximum power conversion efficiency of 4.0% while sputter deposited platinum counter electrode based DSSCs showed a power conversion efficiency of 5.0%.     

Graphene-CdS composite, synthesis and enhanced photocatalytic activity

Graphene-CdS (G-CdS) composites were synthesized through a simple solvothermal method. The formed CdS nanospheres were homogeneously scattered on the surface of graphene sheets. Fluorescence quenching effect of the G-CdS composites indicated effective transfer of photo-excited electrons from CdS to graphene, suppressed the recombination of photo-generated electron-hole pairs, so that the enhanced visible light induced photodegradation activity for Rhodamine B (RhB) was achieved. Based on the high photocatalytic activity and well stability, the G-CdS composite containing 70% CdS can be expected to be a practical visible light photocatalyst.     

Prickly polyaniline nano/microstructures as the efficient counter electrode materials for dye-sensitized solar cells

Two kinds of prickly polyaniline samples, prickly polyaniline nanorods and microgranules, are prepared through the chemically oxidative polymerization method by regulating the concentration of aniline. Scanning electron microscopy images indicate that the diameter of prickly polyaniline nanorods (PPNRs) is about 80 nm and the size of prickly polyaniline microgranules (PPMGs) is about 400 nm. The as-prepared prickly polyaniline samples are subsequently explored as the Pt-free counter electrode materials for dye-sensitized solar cells (DSCs). Electrochemical impedance spectroscopy and cyclic voltammetry measurements demonstrate that PPNR electrode displays superior electrocatalytic activity for the I₃ ^? reduction reaction to PPMG electrode, which can be attributed to the unique prickly nanorod structure that provides abundant electrocatalytic active sites and the fast charge transport pathway simultaneously. As a consequence, the DSC fabricated with PPNR counter electrode achieves a high conversion efficiency of 6.86% under illumination of 100 mW cm^?2, which is close to the efficiency of a Pt electrode-based device. This work presents a promising way to develop Pt-free and high-efficiency counter electrode in DSCs.     

Sol-gel preparation and enhanced photocatalytic performance of Cu-doped ZnO nanoparticles

Cu-doped ZnO nanoparticles were prepared by a sol-gel method for the first time. XRD, XPS, UV-vis and FS techniques were used to characterize the Cu-doped ZnO samples. The photocatalytic activity was tested for methyl orange degradation under UV irradiation. The results show that the crystal sizes of ZnO and 0.5% Cu/ZnO nanoparticles with wurtzite phase are 32.0 and 28.5 nm, indicating that Cu-doping hinder the growth of crystal grains. The doped Cu element existed as Cu²⁺. The optimal Cu doping concentration in ZnO is 0.5%. The optimal calcination condition is at 350 °C for 3 h. The MO degradation rate of 0.5% Cu/ZnO reaches 88.0% when initial concentration of MO is 20 mg/L, exceeding that of undoped ZnO. The enhanced charge carrier separation and increased surface hydroxyl groups due to Cu-doping contributed to the enhanced photocatalytic activity of 0.5% Cu/ZnO.     

Efficient one-pot synthesis of Ag nanoparticles loaded on N-doped multiphase TiO2 hollow nanorod arrays with enhanced photocatalytic activity

The simultaneous Ag loaded and N-doped TiO₂ hollow nanorod arrays with various contents of silver (Ag/N-THNAs) were successfully synthesized on glass substrates by one-pot liquid phase deposition (LPD) method using ZnO nanorod arrays as template. The catalysts were characterized by Raman spectrum, field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscope (HRTEM), ultraviolet-vis (UV-vis) absorption spectrum and X-ray photoelectron spectroscopy (XPS). The results suggest that AgNO₃ additive in the precursor solutions not only can promote the anatase-to-rutile phase transition, but also influence the amount of N doping in the samples. The photocatalytic activity of all the samples was evaluated by photodegradation of methylene blue (MB) in aqueous solution. The sample exhibited the highest photocatalytic activity under UV light illumination when the AgNO₃ concentration in the precursor solution was 0.03 M, due to Ag nanoparticles acting as electron sinks; When the AgNO₃ concentration was 0.07 M, the sample performed best under visible light illumination, attributed to the synergetic effects of Ag loading, N doping, and the multiphase structure (anatase/rutile).     

Facile synthesis of nitrogen-doped reduced graphene oxide as an efficient counter electrode for dye-sensitized solar cells

A nitrogen-doped reduced graphene oxide (N-RGO) nanosheet was synthesized by a simple hydrothermal method and characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and scanning electrode microscopy. After being deposited as counter electrode film for dye-sensitized solar cells (DSSCs), it is found that the synthesized N-RGO nanosheet has smaller charge-transfer resistance and better electrocatalytic activity towards reduction of triiodide than the reduced graphene oxide (RGO) nanosheet. Consequently, the DSSCs based on the N-RGO counter electrode achieve an energy conversion efficiency of 4.26%, which is higher than that of the RGO counter electrode (2.85%) prepared under the same conditions, and comparable to the value (5.21%) obtained with the Pt counter electrode as a reference. This N-RGO counter electrode offers the advantages of not only saving the cost of Pt itself but also simplifying the process of counter electrode preparation. Therefore, an inexpensive N-RGO nanosheet is a promising counter electrode material to replace noble metal Pt.

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Graphical abstract A nitrogen-doped reduced graphene oxide nanosheet was synthesized by a simple hydrothermal method, which is a promising counter electrode material to replace noble metal Pt.

     

Facile synthesis of porous CuS film as a high efficient counter electrode for quantum-dot-sensitized solar cells

In this paper, porous CuS film has been successfully prepared by a facile method and employed as a counter electrode (CE) in quantum-dot-sensitized solar cells (QDSSCs) for its highest catalytic activity. This CuS thin film was deposited on FTO substrate via spin coating process which is simple to operate, and its electrochemical properties were further studied by EIS and Tafel measurement. With the cycling time of depositing CuS up to 8, it displays high electrocatalytic activity toward polysulfide reduction, rationalizing the improved QDSSCs performance. Using the CdS/CdSe-sensitized QDSSCs, the cells exhibit improved short-circuit photocurrent density (J _sc) and fill factor (FF), achieving solar cell conversion efficiency (η) as high as 5.60 % under AM 1.5 illumination of 100 mW cm^?2. This work provides a novel and simple method for the preparation of CEs, which could be utilized in other metal sulfides CEs for QDSSCs.     

Nanostructured solar cell based on solution processed Cu2ZnSnS4 nanoparticles and vertically aligned ZnO nanorod array

Cu₂ZnSnS₄ (CZTS) has attracted intensive interest for application in photovoltaic technology due to its excellent semiconductor properties. We report a nanostructured CZTS solar cell which was fabricated by infiltrating of CZTS nanoparticles into CdS coated ZnO nanorod arrays. The well aligned ZnO nanorods facilitate the efficient infiltration of CZTS nanoparticles. A hole transport layer was deposited to facilitate the transport of holes. The nanostructured CZTS solar cell demonstrated a remarkably high short‐circuit current density (11.0 mA/cm²). As a result, a power conversion efficiency of 2.8% was obtained. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

基于薄膜电极溶胶修饰的染料敏化太阳电池光电特性研究

染料敏化太阳电池(DSC)中的纳米薄膜电极 是决定太阳电池光电转换性能的重要组成部分. 为改善薄膜电极特性, 采用了不同浓度的TiO₂溶胶对DSC光阳极导电玻 璃和纳米TiO₂多孔薄膜进行不同方式的界面处理. 利用X射线衍射方法对制备得到的多孔薄膜以及溶胶经高温处理 后致密层中纳米TiO₂颗粒的尺寸及晶型进行了测试. 采用高分辨透射电子显微镜和场发射扫描电子 显微镜观察了纳米颗粒及薄膜微结构形貌. 采用强度调制光电流谱/光电压谱分析了TiO₂溶 胶的不同处理方式对电子传输和复合的影响. 在100 mW· cm^-2光强以及暗环境下分别测试了DSC的伏安输出性能以及暗电流. 结果表明, 不同浓度和处理方式均能较好地抑制暗电流. 溶胶处理后光生电子寿命τ_n延长, 电子传输平均时间τ_d相应缩短. 采用浓度为0.10 mol·L^-1的 溶胶对导电玻璃和多孔膜同时处理, DSC的宏观输出特性最佳, 短路电流密度J_sc提高了10.9%, 光电转换效率η提高了11.9%.     

Boron and nitrogen co-doped titania with enhanced visible-light photocatalytic activity for hydrogen evolution

A visible-light boron and nitrogen co-doped titania (B-N-TiO₂) photocatalyst was prepared by sol-gel method with titanium tetra-n-butyl oxide, urea and boric acid as precursors. The photocatalyst was characterized by Fourier Transform Infrared (FT-IR), UV-vis diffusive reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), BET and electrochemistry method. Photocatalytic activity for hydrogen production over platinized B-N-TiO₂ under visible-light (λ ≥ 420 nm) irradiation was investigated. In nitrogen doped titania (N-TiO₂) NTiO bond is formed, which extends the absorption edge to the visible-light region. A part of doping boron enters into titania lattice and most of the boron exists at the surface of the catalyst. The crystallite size of B-N-TiO₂ decreases compared to N-TiO₂, while its photocurrent and the surface hydroxyl group increase. Furthermore, doping boron could act as shallow traps for photoinduced electrons to prolong the life of the electrons and holes. Therefore, the visible-light activity of B-N-iO₂ increases greatly compared with that of N-TiO₂.     

三维多孔复合碳层对电极的制备及其光伏性能研究

基于TiO_2光阳极、Pt对电极的染料敏化太阳能电池(DSSC)因其优异的光电转换特性受到了广泛的关注,然而Pt昂贵的价格制约了其发展与应用.针对这一问题,本文设计、制备了一种由相对致密且高导电的石墨膜(PC层,底层)及多孔碳纳米颗粒膜(CC层,顶层)构成的低成本、高性能三维多孔复合碳层对电极.基于该CC/PC对电极的DSSC具有优异的光伏性能:在1.5标准太阳光照射下,其填充因子高达65.28%(较Pt对电极高4.1%)、光电转换效率高达5.9%(为Pt对电极的94.2%). CC/PC对电极的优异光伏性能主要归因于其独特的三维多孔导电结构,该结构有极高的比表面积和丰富的催化反应活性位,有利于电子的快速传输及离子的快速转移,在这些因素的协同作用下,其光电转换性能大大改善.     

Improved performance of solar cell based on porous silicon surfaces

Porous silicon (PS) surfaces were fabricated by electrochemical etching for both sides of the Si wafer. The objective of the present study is to investigate the PS effect on performance of silicon solar cells. Moreover, enhancement of solar cell efficiency can be obtained by manipulating of the reflected mirrors, and the process is very promising for solar cells manufacturing due to its simplicity, lower cost and suitability for mass production. The surface of PS is observed to have been discrete pores with smooth walls, and with short branches pores for the polished wafer side. In contrast, the etched backside of the wafer was observed to have bigger pore size than the etched polished side, and pores on the surface are in random location. PS formed on the both sides has lower reflectivity value in comparison to the other researcher group. The increase in efficiency of solar cell fabricated with PS formed on both sides of the wafer were extremely observed in comparison to one side PS and bulk silicon solar cells respectively. Solar cell fabricated shows that the conversion efficiency increased to 14.5% in comparison to unetched sample. The porous surface texturing properties could enhance and increased the conversion efficiency of silicon solar cells, these results also showed that the efficiency with this procedure is more promising in comparison to other solar cells, which are fabricated under similar conditions.     

Improvement of ZnO nanorod based quantum Dot (cadmium sulfide) sensitized solar cell efficiency by aluminum doping

This study investigates the performance of quantum dot sensitized solar cells (QDSSCs) based on aluminum (Al)-doped and undoped ZnO nanorods. Current density–voltage (J–V) characterization shows that Al doping into ZnO nanorods (AZO NRs) can improve short circuit current density (J_sc) and the energy conversion efficiency (η) of QDSSCs. The maximum η=1.15% is achieved in QDSSCs when Al concentration is 0.5 wt%, as compared to undoped state where η=0.57%. These current densities and the energy conversion efficiency improvement are studied using the electrochemical impedance spectroscopy (EIS). EIS results indicate that the electron transport resistance in the photoanode of QDSCs is reduced with introduction of Al into ZnO structure, which leads to increasing J_sc. It is also found that recombination resistance reduces with introduction of Al into ZnO because of the upward displacement of Fermi level with respect to AZO conduction band (CB) and increasing electron density in the ZnO CB. This reduction of recombination resistance causes higher recombination rate in QDSCs based AZO NRs.     

Graphene-based hollow TiO2 composites with enhanced photocatalytic activity for removal of pollutants

Catalytically active graphene-based hollow TiO₂ composites(TiO₂/RGO) were successfully synthesized via the solvothermal method. Hollow TiO₂ microspheres are uniformly dispersed on RGO. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) were used for the characterization of prepared photocatalysts. The mass of GO was optimized in the photocatalytic removal of rhodamine B (RhB) as a model dye pollutants. The results showed that graphene-based hollow TiO₂ composites exhibit a significantly enhanced photocatalytic activity in degradation of RhB under either UV or visible light irradiation. The formation of the graphene-based hollow TiO₂ composites and the photocatalytic mechanisms under UV and visible light were also discussed.