In this study a co-sensitization strategy is utilized for fabrication of a simple type of quantum dot sensitized solar cells (QDSCs) with high power conversion efficiency. A transparent layer of hydrothermally grown TiO2 nanocrystals (NCs) was sensitized with CdS and CdSe QDs layers and applied as the photoanode of the cells. The CdS layer was deposited through a successive ionic layer adsorption and reaction (SILAR) approach with optimized number of cycles. The CdSe nanocrystalline layer was also formed by a fast and effective chemical bath deposition (CBD) method for co-sensitization. The CBD time was altered in a short range of 6–15 min while the deposition was well-performed and quality of the CdSe layer was quite acceptable. The ZnS passivating layer was finally over-deposited and photoanodes were applied in conventional structure of QDSCs using polysulfide electrolyte and CuS counter electrodes. The CBD time was optimized to find the best bandgap energy/band edge positions and deposition amount of the CdSe layer for higher energy conversion efficiencies. The best photovoltaic performance was achieved for the QDSC with CdSe co-sensitizing layer deposited at 12 min of the CBD process. This optimized cell demonstrated the photovoltaic parameters of Jsc = 22.2 mA/cm2, Voc = 628 mV, and power conversion efficiency of 6.8%. This efficiency was increased about 172% compared to that of reference cell with just CdS QDs as the light sensitizing layer.
