Enhancing the Humidity Resistance of Perovskite Photovoltaics: Comprehensive Pbi2 Management Utilizing Long-Chain Ionic Liquid

Effectively managing residual PbI2 in two-step perovskite fabrication, while simultaneously enhancing the device performance, especially its humidity stability, poses a significant challenge. Herein, we introduced a novel ionic liquid (IL) molecule, long-chain alkane-based 1-octyl-3-methylimidazolium chloride (OMIMCl), with excellent hydrophobicity to regulate the perovskite conversion process, aiming to enhance the performance of resulting perovskite solar cells. The introduction of OMIMCl contributes to the formation of a uniform porous PbI2 film, facilitating comprehensive penetration of the second-step organic salt to fully convert PbI2 into perovskite material. Interestingly, nearly no residual PbI2 clusters are observed at both the top and bottom surfaces of OMIMCl-modified perovskite films. Meanwhile, depth-resolved grazing incidence wide-angle x-ray scattering (GIWAXS) measurements have quantitatively demonstrated the reduction of PbI2 in OMIMCl-modified perovskite thin films. Notably, the incorporation of OMIMCl retards the growth rate of perovskite crystals efficiently, thereby assisting in generating high-quality of perovskite films with larger grain size. Moreover, density functional theory (DFT) calculations of binding energy numerically demonstrate the hydrophobic property of IL OMIMCl, which plays a crucial role in improving the humidity stability of PSCs, as evidenced by direct water-dipping test. Consequently, we achieved a champion power conversion efficiency (PCE) of 24.72% and significantly improved long-term stability.