Spray-Pyrolyzed ZnO as Electron Selective Contact for Long-Term Stable Planar CH3NH3PbI3 Perovskite Solar Cells

Electron selective contacts (ESCs) play an important role in the performance of perovskite solar cells (PSCs). ZnO has attracted important attention as a good material for ESCs because of its matched energy levels with those of perovskite, its high transmittance in the visible region, and its high electron mobility. Here we reported the use of ZnO thin layers prepared by spray pyrolysis as ESC for PSCs. Our ZnO based planar CH3NH3PbI3 (MAPbI3) devices not only were stable in a humidity of 35% but also improved the performance even after more than 1 month of preparation, due to an increase of charge transfer at the ZnO interface as it has been characterized by impedance spectroscopy. The formation of ZnO depends on preparation conditions such as gas flow, zinc acetate solution concentrations, and substrate temperatures, all of which have an effect on the performance of stability of MAPbI3 solar cells. Also, the low hysteresis reported for these samples was discussed in this study. We have also observed that long-term structural evolution of perovskite film also depends on the ZnO substrate and its deposition method.