Cascade structure of TiO2/ZnO/CdS film for quantum dot sensitized solar cells

Highlights: → Solar cells based on a cascade structure of TiO2/ZnO/CdS photoanode are fabricated. → ZnO is one-step deposited on TiO2 layer by ultrasonic spray pyrolysis technique. → As-prepared cell achieves a power conversion efficiency of 1.56%. - Abstract: Quantum dot sensitized solar cells based on cascade structure of TiO2/ZnO/CdS electrode and polysulfide electrolyte were fabricated. The ZnO layer was deposited on screen-printed TiO2 layer by ultrasonic spray pyrolysis method. The structure, morphology and impedance of TiO2/ZnO film photoanode and the photovoltaic performance of TiO2/ZnO/CdS cell were investigated. It is found that the short circuit current density and conversion efficiency are significantly improved by the introduction of ZnO layer into TiO2/CdS film. A power conversion efficiency of about 1.56% has been obtained for TiO2/ZnO/CdS cell, which is about 57% higher than that for TiO2/CdS cell (0.99%). The formation of an inherent energy barrier between TiO2 and CdS films and the passivation of surface traps on the TiO2 film caused by the introduction of ZnO layer, which reduces the charge recombination and favors the electron transport, should be mainly responsible for the performance enhancement of TiO2/ZnO/CdS cell.