Polishing the Lead-Poor Surface for Efficient Inverted CsPbI Perovskite Solar Cells.

Triiodide cesium lead perovskite (CsPbI ) 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 CsPbI 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 CsPbI /PCBM interface, leading to the considerable open-circuit voltage (V ) 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 V of the inverted CsPbI 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.