Improved performance and stability of perovskite solar cells with bilayer electron-transporting layers.

Zinc oxide nanoparticles (NPs) are very promising in replacing the phenyl-C-butyric acid methyl ester (PCBM) as electron-transporting materials due to the high carrier mobilities, superior stability, low cost and solution processability at low temperatures. The perovskite/ZnO NPs heterojunction has also demonstrated much better stability than perovskite/PCBM, however it shows lower power conversion efficiency (PCE) compared to the state-of-art devices based on perovskite/PCBM heterojunction. Here, we demonstrated that the insufficient charge transfer from methylammonium lead iodide (MAPbI) to ZnO NPs and significant interface trap-states lead to the poor performance and severe hysteresis of PSC with MAPbI/ZnO NPs heterojunction.