ZnS/CdSe0.2S0.8/ZnSSe heterostructure as a novel and efficient photosensitizer for highly efficient quantum dot sensitized solar cells

Abstract

Herein, we systematically studied the influence of ZnS, ZnSe and ZnSxSe1-x, with S:Se molar ratio of 1:4, layers as both inner and outer layers on photovoltaic properties of QDSSCs based on CdSexS1-x QDs when the molar ratio of S:Se is 4:1. The results show that ZnS and ZnS0.2Se0.8 layers are the best choice for the CdSe0.2S0.8-based QDSSCs as an inner and outer layer, respectively. Hence, we successfully designed and fabrication of QDSSCs based on ZnS/CdSe0.2S0.8/ZnS0.2Se0.8 photosensitizer with a high efficiency of 6.31%, which is almost more than double the efficiency of 3% for bare CdSe0.2S0.8-based QDSSCs. Our results indicated that in this heterostructure structure the ZnS layer acts as both a seed layer and a blocking layer, which leads to an increase in the light harvesting efficiency and a decrease in the interfacial charge recombination. On the other hand, the ZnS0.2Se0.8 layer acts as an effective passivation layer which not only reduces the charge recombination process, but also improves the light absorption range. Therefore, when both of these layers were employed in the CdSe0.2S0.8 QDSSCs, the electron lifetime and thereby the accumulation of photo-injected electrons in the TiO2 film greatly improved and reached to 104 ms and 1.21E + 18 cm3, respectively.