Strategies to prepare an efficient photoanode for ZnO nanowires-based CdS-CdSe co-sensitized solar cells

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/cm² with an overall efficiency of 3.06% can be obtained for the resulting device.