Synergistic Passivation via Spatial Configuration Engineering of Ammonium Salts for High‐Efficiency Tandem Perovskite Solar Cells

ABSTRACT Defects and non‐ideal energy level alignment at the perovskite/electron transport layer (ETL) interface in inverted perovskite solar cells (PSCs) severely limit open‐circuit voltage (V OC ) and fill factor (FF), thereby restricting further performance improvements in perovskite/silicon tandem solar cells. To address this, we designed and synthesized two ammonium salt‐derived molecules, ZFI‐1 and ZFI‐2, with distinct spatial configurations of functional groups, for synergistic passivation with PEABr at the perovskite interface. By strategically modulating the spatial arrangement of carbonyl, fluorine, and amino groups, these molecules enhance multi‐modal coordination capabilities with defect sites in perovskite. The results demonstrate that ZFI molecules effectively suppress the formation of 2D perovskite phases, improve film crystallinity, modulate the interfacial work function, optimize energy level alignment and electron extraction, and significantly inhibit non‐radiative recombination, thereby reducing V OC and FF losses. The wide‐bandgap perovskite single‐junction device based on ZFI‐2/PEABr synergistic passivation achieved a champion power conversion efficiency (PCE) of 23.45% with a V OC of 1.271 V. Notably, this strategy demonstrated universal applicability in perovskite/silicon tandem cells, attaining a tandem PCE of 31.56%, offering a novel design pathway for interface engineering in high‐performance perovskite photovoltaic devices.