Core-shell structure of ZnO@TiO2 nanorod arrays as electron transport layer for perovskite solar cell with enhanced efficiency and stability

Abstract

The serious charge recombination originates from the thermal instability of perovskite/ZnO and the low electron injection efficiency of ZnO. It is the important issue to be improved in ZnO-based perovskite solar cell (PSC). In this paper, the core-shell structure of ZnO@TiO2 nanorod arrays (NRs) is designed as electron transport layer (ETL) for PSC. A novel synthesis of PSC based on ZnO@TiO2 NRs in ambient atmosphere was proposed. The photoelectric conversion efficiency (PCE) of the core-shell device is 50.46% higher than that of common ZnO nanorod device. This is due to the improved interface contact between nanorods and perovskite layer, and the suppression of charge recombination. The PCE of the TiO2 modified device shows still more than 83% after 168 h, compared to that of the pristine one which decreased to less than 50%. This is due to TiO2 modification which can serve as a buffer layer to avoid direct contact between perovskite films and ZnO NRs, and inhibits the decomposition of perovskite film on ZnO NRs. Both theoretical calculation and Raman test result show that the interaction between CH3NH3PbI3 and TiO2 is mainly the bonding between I atoms of PbI2 slabs and Ti atoms of the TiO2 surface at PbI2/TiO2 interface. The mechanism of carrier transport and recombination in the PSC based on ZnO and ZnO@TiO2 NRs was also discussed. These results highlight the potential of ZnO@TiO2 NRs as ETL for all-solid-state PSC with high efficiency and good stability.