Adjustable Skeleton of Bilateral Lewis Base Passivator for CsPbI3 Perovskite Solar Cells with PCE over 20% and Superior Stability

•The new additive 4-TBA was introduced to enhance the performance of CsPbI3 PSCs.•Bilateral Lewis base functional groups can effectively reduce film defects and improve film quality.•The PCE of the champion PSC with 4-TBA reaches 20.26%.•Optimized PSC retains 95.6% of the initial PCE after 1000 h of environmental stability test.