Air-Processed Perovskite Films with Inner-to-Outside Passivation for High-Efficiency Solar Cells

Metallic halide perovskite films are usually fabricated in inert environment due to their high sensitivity to moisture and oxygen. However, the fabrication process in the strictly controlled environment is not economical for mass production. Therefore, the fabrication of high-quality perovskite films in ambient air is more practical for optoelectronic devices. Herein, a spinning-bathing-spinning (SBS) method is demonstrated to deposit pinhole-free perovskite films with large grains in ambient air for solar cells. The effect of moisture on the rapid crystallization and grain coarsening can be suppressed using this SBS method. Furthermore, the moisture is found to encourage the halogen separation in the perovskite films when using PbI2-PbCl(2)as the lead halide precursor, resulting in the formation of I-dominant perovskite grains and Cl-enriched boundaries and surface in the films. The Cl-enriched grain boundaries and film surface, which mainly originate from the confined methylammonium chloride (MACl), can passivate defects and prevent further damage from moisture and oxygen. This spontaneous inner-to-outside passivation enables the air-processed perovskite solar cells with the high power conversion efficiencies of more than 20% and improved stability.