Moisture‐Induced High‐Quality Perovskite Film in Air for Efficient Solar Cells

The quality of perovskite light‐harvesting layer is known to be the most critical factor for the performance of perovskite solar cells (PSCs). Herein, a facile ambient air‐aging process (AAP, 20%–30% RH) is adopted to realize the fabrication of high‐quality Cs 0.15 FA 0.75 MA 0.1 PbI 3 perovskite films, thereby upgrading device performance. We find that the perovskite crystallinity after AAP for 10 d is greatly intensified, with large grain size and preferred crystal orientation along (110) and (220) planes. Comparative studies on the Ag‐based devices employing the perovskite films upon exposing to different atmospheres, i.e., dry N 2 , dry O 2 , N 2 , and H 2 O (20%–30% RH) and ambient air (20%–30% RH), demonstrate that H 2 O molecules in air rather than O 2 molecules induce an effective defect passivation that holds the multiple functions in enhancing the quality of perovskite film, inhibiting the nonradiative recombination, prolonging the carrier lifetime, and improving the energy level matching, etc. Moreover, the positive effect of H 2 O in ambient atmosphere on cell performance is irreversible and remains even if moisture escapes. Finally, the average power conversion efficiency (PCE) of device based on the AAP‐induced film is increased from 18.24 ± 1.49 to 21.34 ± 0.76, with the champion PCE up to 22.60%. Also, the device with AAP exhibits better moisture resistance capability. Herein, it offers a viable AAP‐induced route for the perovskite films with superb optoelectronic properties that can be subsequently extended to the design and construction of other photovoltaic devices for practical application.