Buried Interface Engineering via an Ultrathin MACl Interlayer for Enhanced Crystallization and Performance of Wide‐Bandgap Perovskite Solar Cells

Wide‐bandgap perovskites (WBGPVSK), as key top‐cell materials for tandem solar cells, are often limited by poor film crystallinity and interfacial defects. Herein, an ultrathin MACl interfacial layer is introduced between the hole transport layer and the perovskite in an inverted architecture to regulate the buried interface. The MACl interlayer effectively improves substrate wettability, facilitating uniform precursor spreading and enabling controlled nucleation, which promotes ordered crystal growth. As a result, the perovskite films exhibit enlarged grain size, reduced surface roughness, and suppressed void formation, along with enhanced optical absorption and improved crystallinity. Photoluminescence results reveal reduced carrier recombination and enhanced charge extraction. Consequently, the optimized device with 0.5 mg mL −1 MACl achieves a power conversion efficiency (PCE) of 22.79%, with the fill factor (FF) increased from 79.14% to 81.38%. This work demonstrates that buried interface engineering is an effective strategy to simultaneously regulate perovskite crystallization and interfacial charge transport for high‐performance WBGPVSK solar cells.