Cesium Acetate-Induced Interfacial Compositional Change and Graded Band Level in MAPbI Perovskite Solar Cells.

Compositional engineering and interfacial modifications have played pivotal roles in the accomplishment of high-efficiency perovskite solar cells (PSCs). Different interfaces in the PSCs influence the performance remarkably either by altering the crystallization of the active material or shifting the energy levels or improving the electrical contact. This work reports how a thin layer of cesium acetate on the TiO electron transport layer (ETL) induces generation of a PbI-rich methylammonium lead iodide (MAPbI) composition at the ETL/MAPbI interface, which downshifts the conduction band level of MAPbI to create an energy level gradient favorable for carrier collection, resulting in higher photocurrent, fill factor, and overall power conversion efficiency.