Ammonium Fluoride Interface Modification for High‐Performance and Long‐Term Stable Perovskite Solar Cells

As a new generation of promising photovoltaic devices, perovskite solar cells (PSCs) have rapidly evolved in efficiency from 3.8% in 2009 to 23.5% recently. Numerous studies indicate that interface defects and the recombination of charge carrier at the interface, which hinders the improvement of photovoltaic performance and stability of PSCs, remains an important research area. Herein, a novel method for modifying the interface between the electron transport layer and the perovskite layer with ammonium fluoride (NH 4 F) is presented. After the TiO 2 film is modified with NH 4 F, the TiO 2 /perovskite interface defects are mitigated and passivated, the carrier recombination decreases, and the electron extraction and injection capacity increase. Consequently, the planar PSC interface modified with an optimal NH 4 F concentration maintains over 95% initial efficiency for 32 days at 20% relative humidity, and achieves a champion power conversion efficiency of 20.47%, whereas the pristine device achieves an efficiency of 18.59% under the same conditions. This work demonstrates a low‐cost and efficient strategy to obtain high‐performance and stable PSCs.