LAUSR

Triiodide cesium lead perovskite (CsPbI3) has promising prospects in the development of efficient and stable photovoltaics in both single‐junction and tandem structures. However, achieving inverted devices that provide good stability and are compatible to tandem devices remains a challenge, and the deep insights are still not understood. This study finds that the surface components of CsPbI3 are intrinsically lead‐poor and the relevant traps are of p‐type with localized states. These deep‐energy‐level p traps induce inferior transfer or electrons and serious nonradiative recombination at the CsPbI3/PCBM interface, leading to the considerable open‐circuit voltage (Voc) loss and reduction of fill factor (FF). Compared to molecular passivation, polishing treatment with 1,4‐butanediamine can eliminate the nonstoichiometric components and root these intrinsically lead‐poor traps for superior electron transfer. The polishing treatment significantly improves the FF and Voc of the inverted CsPbI3 photovoltaics, creating an efficiency promotion from 12.64% to 19.84%. Moreover, 95% of the initial efficiency of the optimized devices is maintained after the output operation for 1000 h.