CdSe-CdS quantum dots co-sensitized ZnO hierarchical hybrids for solar cells with enhanced photo-electrical conversion efficiency.

We have developed a facile method to fabricate CdSe-CdS quantum dot sensitized hierarchical ZnO nanostructures for quantum dot sensitized solar cells (QDSCs) by combining a hydrothermal method, successive ionic layer adsorption and chemical reaction (SILAR) techniques. The method consists of the growth of the ZnO hierarchical structure on ITO substrates via a hydrothermal method and the layer deposition of double quantum dots CdSe and CdS by SILAR. The CdSe-CdS QDs co-sensitized ZnO hierarchical structures show enhanced light absorption in the entire visible light range. The photovoltaic performance of QDCSs based on CdSe-CdS QDs co-sensitized ZnO hierarchical structures was evaluated. As photoanodes for QDSCs, the CdSe-CdS QDs double-sensitized ZnO hierarchical structures demonstrate an increased Jsc and improved power conversion efficiency of up to 1.39%. Under light illumination, photons are captured by QDs, yielding electron-hole pairs that are rapidly separated into electrons and holes at the interface between the ZnO and the QDs. The electrons are transferred to the conduction band of ZnO and the holes are released by redox couples in the liquid polysulfide (S(2-)/Sx(2-)) electrolyte, resulting in greatly improved photo-electrical conversion efficiency of QDSCs. The results suggest that it is very promising and feasible to enhance light absorption, carrier generation, and effective carrier separation via band engineering by CdSe-CdS QDs co-sensitization, and the method reported here displays a great potential for applications to be scaled up.