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). We herein adopt a facile ambient air‐aging process (AAP, 20‐30% RH) to realize the fabrication of high‐quality Cs_0.15FA_0.75MA_0.1PbI₃ 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 N₂, dry O₂, N₂ & H₂O (20‐30% RH), and ambient air (20‐30% RH) demonstrate that H₂O molecules in air rather than O₂ 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 H₂O in ambient atmosphere on cell performance is irreversible and remains even if moisture escapes. Finally, the average 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. This work offers a viable AAP‐induced route for the perovskite films with superb optoelectronic properties that can be subsequently extend to the design and construction of other photovoltaic devices for practical application.