Interface Modification by Ammonium Sulfamate for High‐Efficiency and Stable Perovskite Solar Cells

Abstract Defects in perovskite films are still the dominant destroyer of both power conversion efficiency (PCE) and long‐term stability in perovskite solar cells (PSCs). As the most popular electron transport layer (ETL), TiO 2 film is used in many PSCs to achieve high PCE. However, pristine TiO 2 by itself is not sufficient as an ETL due to lattice mismatch, poor alignment of the energy level gap, and hysteresis of the PSC. Herein, ammonium sulfamate (AS), with desired NH 4 + and S═O functional groups, is designed to modify the TiO 2 surface and interface to improve the PCE of PSCs. It is found that the AS works like a seed layer for the perovskite deposition, and, in addition, it effectively forms a bridge between the TiO 2 surface and the perovskite. As a result, PSCs are successfully fabricated with a champion power conversion efficiency of 24.78% with smaller hysteresis. The PSCs prepared using the AS‐modified TiO 2 also show excellent stability, and the bare device without any encapsulation retains 96% of its initial PCE after 1056 h of ambient exposure at 25 °C and 25% relative humidity.