Organic Crosslinked Tin Oxide Mitigating Buried Interface Defects for Efficient and Stable Perovskite Solar Cells

Tin dioxide (SnO2) stands as a promising material for the electron transport layer (ETL) in perovskite solar cells (PSCs) attributed to its superlative optoelectronic properties. The attainment of superior power conversion efficiency hinges critically on the preparation of high‐quality SnO2 thin films. However, conventional nanoparticle SnO2 colloids often suffer from inherent issues such as numerous oxygen vacancy defects and film non‐uniformity. In this study, we report a strategy to homogenize SnO2 with reduced defects for high‐performance PSCs. The commercial SnO2 colloid is modulated with bisphenol S (BPS) crosslinking to achieve a better annealing intermediate state. The phenolic hydroxyl groups on BPS bond with the hydroxyl groups on the SnO2 surface, passivating defects as well as promoting superb regularity of the films by forming a network of the SnO2 nanoparticles. Additionally, the sulfone groups on BPS coordinate with Pb2+, regulating the crystallization of PbI2 and FAPbI3, which leads to better interface contact at the buried interface. The FAPbI3 perovskite solar cells based on BPS‐crosslinked SnO2 layers achieved a champion efficiency of 24.87 % and retained 95 % of their initial PCE after 1000 hours of continuous light soaking under N2 atmosphere. The gelation‐promoting effect of BPS causes SnO2 to gel faster, resulting in a better intermediate state during the gelation and annealing crystallization processes, achieving a slightly larger and more uniform electron transport layer and an orderly perovskite layer.