Improvement of Electrical Properties of Grätzel Cells by Tuning the Dye Layer with CdS/ZnO Junction

Solar cells based on organic dye have been widely used for the reason of their simplicity of manufacture. A simple structure is composed of a colored layer of TiO2, an electrolyte and a counter electrode. In this study, the layers of TiO2, CdS and ZnO were deposited on conductive glass by different methods to replace organic dye. Metal organic chemical vapor deposition (MOCVD) method was used to prepare the TiO2 layer, chemical bath deposition (CBD) to prepare the CdS layer, and spray pyrolysis (SP) for the preparation of the ZnO layer. Morphological and structural studies have shown a homogeneous morphology of the superposition of TiO2/CdS/ZnO layers. XRD and SEM characterizations have shown that annealing of the CdS layer must be done under a controlled atmosphere in order to avoid the formation of cadmium oxide and to control the particle size. The aim of this work is the substitution of organic dye in the Grätzel cell by CdS(n)/ZnO(n+) junction. Morphological and optical properties of TiO2/CdS/ZnO in addition to photovoltaic performance of this structure junction were investigated with different deposition times of the CdS layer. It is found that the nature of the substrate has no influence on the realization of the junction. It is noticed that each layer added leads to a decrease in the transmittance of the substrate. Characterization of the photovoltaic properties of cells based on the CdS/ZnO junction shows a higher yield compared to conventional cells based on organic dye. It is also recommended to undertake annealing under a controlled atmosphere such as nitrogen in order to eliminate the CdO secondary phase and decrease the size of the grains which may enhance the efficiency of the solar cells.