Xingtian Yin,Wenxiu Que,Duan Fei,Haixia Xie,Zuoli He,Gangfeng Wang
Strategies employed to fabricate an efficient photoanode with ZnO nanowires (NWs) arrays and CdS–CdSe co-sensitizers were investigated. A detailed procedure for growing long ZnO NWs which are suitable for the application in quantum dot sensitized solar cells was discussed, and several optimized parameters were obtained for fabrication of the ZnO NWs with large aspect ratio. CdS and CdSe layers were deposited on the surface of the ZnO NWs by a successive ionic-layer adsorption and reaction method and the deposition process was optimized according to the performance of the solar cells fabricated with the ZnO/CdS NWs and the ZnO/CdS/CdSe NWs arrays, respectively. The relationship between the thickness of the sensitizer layer and the performance of the devices was also discussed in detail. Transmission electron microscopy observation shows that ∼7 nm thick CdS layer and ∼5 nm thick CdSe layer can be easily achieved on the ZnO NWs at an optimal deposition condition. UV–vis absorption spectra demonstrate that the light absorption range of the ZnO/CdS/CdSe NWs can be almost extended to the whole visible range. Through an optimization of the photoanode fabrication, which mainly includes the synthesis of the ZnO NWs arrays and the deposition of the CdS and CdSe layers, a short circuit current density as high as 18.63 mA/cm 2 with an overall efficiency of 3.06% can be obtained for the resulting device.
SnO 2 nanoparticles were synthesized by hydrothermal method and applied to photo-electrodes of quantum dots-sensitized solar cells (QDSSCs). After sensitizing SnO 2 films via CdS quantum dots , CdSe quantum dots was decorated on the surface of CdS/SnO 2 photo-electrodes to further improve the power conversion efficiency. CdS and CdSe quantum dots were deposited by successive ionic layer absorption and reaction method (SILAR) and chemical bath deposition method (CBD) respectively. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to identify the surface profile and crystal structure of SnO 2 photo-electrodes before and after deposited quantum dots. After CdSe co-sensitized process, an overall power conversion efficiency of 1.78% was obtained in CdSe/CdS/SnO 2 QDSSC, which showed 66.4% improvement than that of CdS/SnO 2 QDSSC.
SnO 2 nanosheet-structured films were prepared on a fluorine-doped tin oxide (FTO) substrate using ZnO nanosheet as template. The as-prepared SnO 2 nanosheets contained plenty of nano-voids and were generally vertical to the substrate. TiO 2 nanoparticles were homogeneously deposited into the intervals between the SnO 2 nanosheets to prepare a hierarchically structured SnO 2 /TiO 2 hybrid film. The hybrid films were co-sensitized with CdS and CdSe quantum dots. The sensitized solar cells assembled with the SnO 2 /TiO 2 hybrid film showed much higher photoelectricity conversion efficiency than the cells assembled with pure TiO 2 films. The lifetime of photoinduced electron was also investigated through electrochemical impedance spectroscopy, which showed that the SnO 2 /TiO 2 hybrid film electrode is as long as the TiO 2 film electrode.
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