AbstractThe electron‐transport layer (ETL) plays an important role in improving the performance of flexible perovskite solar cells (F‐PSCs). Herein, a room‐temperature‐processed SnO₂:OH ETL is demonstrated, that exhibits reduced defect density, in particular lower oxygen vacancy concentration, with better energy band alignment and more wettable surface for quality perovskite deposition. More importantly, an efficient electron‐transfer channel is produced between the ETL and the perovskite layer due to the formation of hydrogen bonds at the interface, resulting in enhanced electron extraction from the perovskite. As a result, the efficiency of a large‐area (36.50 cm²) flexible perovskite solar module based on MAPbI₃ is increased to as high as 18.71%; this is thought to be the highest reported PCE value for flexible perovskite solar modules to date. In addition, it exhibits high durability while maintaining over 83% of its initial PCE after flexing test cycles. Further, F‐PSCs with SnO₂:OH show remarkably long‐term stability, owing to a high quality of the perovskite film and a strong coupling between the SnO₂:OH and perovskite layer caused by hydrogen bonds, which successfully inhibits moisture permeation.