Spatially selective defect management of CsPbI₃ films for high-performance carbon-based inorganic perovskite solar cells

Defects formed at the surface, buried interface and grain boundaries (GB) of CsPbI₃ perovskite films considerably limit photovoltaic performance. Such defects could be passivated effectively by the most prevalent post modification strategy without compromising the photoelectric properties of perovskite films, but it is still a great challenge to make this strategy comprehensive to different defects spatially distributed throughout the films. Herein, a spatially selective defect management (SSDM) strategy is developed to roundly passivate various defects at different locations within the perovskite film by a facile one-step treatment procedure using a piperazine-1,4-diium tetrafluoroborate (PZD(BF₄)₂) solution. The small-size PZD²⁺ cations could penetrate into the film interior and even make it all the way to the buried interface of CsPbI₃ perovskite films, while the BF₄⁻ anions, with largely different properties from I⁻ anions, mainly anchor on the film surface. Consequently, virtually all the defects at the surface, buried interface and grain boundaries of CsPbI₃ perovskite films are effectively healed, leading to significantly improved film quality, enhanced phase stability, optimized energy level alignment and promoted carrier transport. With these films, the fabricated CsPbI₃ PSCs based on carbon electrode (C-PSCs) achieve an efficiency of 18.27%, which is among the highest-reported values for inorganic C-PSCs, and stability of 500 h at 85 °C with 65% efficiency maintenance.