Synchronous surface reconstruction and grain boundary healing toward efficient and stable inverted CsPbI3 perovskite solar cells

Cesium lead iodide (CsPbI3) perovskite has gained considerable attentions due to its unique photoelectric properties. However, numerous defects are inevitably existed on the surface and grain boundaries (GBs) of CsPbI3 resulting from the rapid crystallization and growth progress. Herein, different from the traditional ammonium salt treatment mechanism, we propose a facile strategy to synchronously achieve surface reconstruction and grain boundary healing by using 1,3-propylene diamine (PDA) post-treatment on CsPbI3 film. It is discovered that the PDA with suitable concentration can preferentially invade the defect sites of surface and GBs of CsPbI3 film, thereby break the soft perovskite structure in the shallow surface. With further low temperature annealing treatment, the broken CsPbI3 surface would undergo rapid secondary crystal growth to acquire smoother and blurred morphology with reduced GBs and pinholes, primarily derived from the strong interaction between the highly active amino groups of liquid PDA and Pb of perovskite. Meanwhile, the residual PDA molecules mainly anchor at the surface and GBs, and thus connect neighboring perovskite grains, coordinate uncoordinated sites to effectively passivate defects, and also resist the external invasions. Consequently, the inverted PDA-based CsPbI3 device yields a champion PCE of 20.02% with significantly improved long-term storage stability and operational stability.