High Efficiency CdS/CdSe Quantum Dot Sensitized Solar Cells with Two ZnSe Layers.

CdS/CdSe quantum dot sensitized solar cells (QDSCs) have been intensively investigated; however, most of the reported power conversion efficiency (PCE) is still lower than 7% due to serious charge recombination and a low loading amount of QDs. Therefore, suppressing charge recombination and enhancing light absorption are required to improve the performance of QDSCs. The present study demonstrated successful design and fabrication of QDSCs with a high efficiency of 7.24% based on CdS/CdSe QDs with two ZnSe layers inserted at the interfaces between QDs and TiO2 and electrolyte. The effects of two ZnSe layers on the performance of the QDSCs were systematically investigated. The results indicated that the inner ZnSe buffer layer located between QDs and TiO2 serves as a seed layer to enhance the subsequent deposition of CdS/CdSe QDs, which leads to higher loading amount and covering ratio of QDs on the TiO2 photoanode. The outer ZnSe layer located between QDs and electrolyte behaves as an effective passivation layer, which not only reduces the surface charge recombination, but also enhances the light harvesting.