Understanding the Role of the Electron-Transport Layer in Highly Efficient Planar Perovskite Solar Cells.

Solar cells based on perovskite absorbers are rapidly emerging as attractive candidates for photovoltaics development. Understanding the role of the electron-transport layer (ETL) is very important to obtain highly efficient perovskite solar cells. Herein, the effect of the ETL on device performance in planar perovskite solar cells is investigated in detail, and the band bending in different situations is discussed. The ET barrier is shown to be responsible for the poor fill factor (FF) of J-V curves. Introduction of a thin bathocuproine interlayer increases the interface inversion and results in an increase of FF from 56 to 76 %. Some experimental and theoretical results verify these conclusions. Furthermore, this study can provide an interface-engineering strategy to improve device performance.