Reconstructing subsurface lattice for stable perovskite photovoltaics

Formamidinium (FA)-based perovskites with an ideal tolerance factor still face structure stability challenges because of corner-sharing and face-sharing octahedra competition. This seriously limits the long-term operational stability of FA-based perovskite solar cells (PSCs). Here, we demonstrate a subsurface lattice reconstruction strategy by simultaneously tuning the position of Pb2+ and I- planes. The reconstructed lattice configuration favors corner-sharing octahedra and makes the crystal lattice more stable, ultimately stabilizing FA-based perovskites. Additionally, the subsurface modification reduces defects and simultaneously tunes the valence band alignment, thereby increasing the charge carrier lifetime and improving carrier-selective transfer. Consequently, the resultant PSCs achieve a stabilized power conversion efficiency of similar to 25%. Moreover, these PSCs exhibit excellent stability, retaining 96% initial efficiency after 6,000 h of storage in a dry box with similar to 20% relative humidity at 25 degrees C and 95% of their initial efficiency after over 3,000 hmaximum power point test under simulated AM1.5 illumination.