Comprehensive Passivation of Surface and Bulk Defects in Perovskite for High Efficiency Carbon‐Based CsPbI3 Solar Cells

Carbon‐based perovskite solar cells (C‐PSCs) have the advantages of high stability and low cost, but their mean efficiency has become an obstacle to commercialization. Defects, which are widely distributed on the surface and bulk of films, are an important factor in C‐PSCs for low efficiency. The conventional post‐treatment method through forming a low‐dimensional (LD) perovskite layer usually fails in manipulating the bulk defects. Herein, we propose a strategy of combining wet film (uncrystallized) treatment with dry film treatment to in situ form LD perovskite throughout the grain boundaries inside of the film and on the surface of the film, thereby simultaneously passivating the bulk and surface defects in the CsPbI3 film. As a result, the photoluminescence lifetime is significantly improved from 22.5 ns to 92.1 ns. The assembled CsPbI3 C‐PSCs based on the above strategy deliver a champion efficiency of 19.65%, which is a new record efficiency for inorganic C‐PSCs.