Complementary Dual‐Stage Modulation via Ionic‐Electrostatic Interactions for Highest Efficiency 2.03 eV Perovskite Device and Triple‐Junction Tandems

Ultra‐wide bandgap (UBG >2 eV) perovskites are notoriously plagued by rapid crystallization for high defect densities produced that have so far precluded their use as the top cell in triple‐junction tandem solar cells (TSCs). Herein, we introduce ammonium benzenesulfonate (ABS) as a molecular electrostatic “handle” that is active in two complementary stages of film formation. During crystallization, ABS slows nucleation rate and suppresses bulk defect generation; during post‐treatment it drives surface‐ion rearrangement that simultaneously passivates cation vacancies and eliminates interstitial halide defects. Collectively, this complementary dual‐stage modulation (CDM) yields strain‐relaxed films with reduced non‐radiative recombination, prolonged carrier lifetimes, and efficient charge extraction. Consequently, single‐junction 2.03 eV devices deliver 15% power conversion efficiency ranking among the highest reported for >2.0 eV perovskites, while monolithic perovskite/perovskite/silicon triple‐junction TSCs reach 24.4%, both with substantially improved operational and thermal stability. This work establishes electrostatically mediated, multi‐stage processing as a general route to ultra‐wide‐bandgap absorbers for next‐generation photovoltaics.