Successive Reactions of Trimethylgermanium Chloride to Achieve > 26% Efficiency MA‐Free Perovskite Solar Cell With 3000‐Hour Unattenuated Operation

Abstract The rapidly increased efficiency of perovskite solar cells (PSCs) indicates their broad commercial prospects, but the commercialization of perovskite faces complex optimization processes and stability issues. In this work, a simple optimized strategy is developed by the addition of trimethylgermanium chloride (TGC) into FACsPbI 3 precursor solution. TGC triggers the successive interactions in perovskite solution and film, involving the hydrolysis of vulnerable Ge─Cl bond forming Ge─OH group, then forming the hydrogen bonds (O─H···N and O─H···I) with FAI. These successive interactions effectively safeguard FA + from decomposition, accelerate crystallization, restrict ion migration, and passivate film defects. Thus, a high‐quality perovskite is obtained with the super‐hydrophobic surface, maintaining the light‐active phase ( α ‐phase) even after exposure to high‐humidity air (RH: 85%) for 10 days. Consequently, the TGC‐treated conventional (n‐i‐p) and inverted (p‐i‐n) FACsPbI 3 PSCs achieve 26.03%‐ and 26.38%‐ efficiencies, respectively, retaining unattenuated operation initial efficiency after tracking at the maximum power point (MPP) under illumination for 3000 h.