Versatile Holistic Molecular Engineering of Wide‐Bandgap Perovskites for High‐Efficiency Perovskite/Silicon Tandem Solar Cells

ABSTRACT Widebandgap (WBG) perovskites are critical for highefficiency tandem solar cells but suffer from rapid crystallization, photoinduced halide segregation, and interfacial losses. We introduce methyl 2(4,4,5,5tetramethyl1,3,2dioxaborolan2yl)1Hindole7carboxylate (MHIC) as a multifunctional modulator for 1.68 eV WBG perovskites. Its methoxycarbonyl and boronate groups form Lewis acid–base and hydrogenbonding interactions with the perovskite lattice, effectively passivating defects, reinforcing the framework, and suppressing halide segregation via lattice stabilization. Concurrently, MHIC creates a favorable interfacial dipole that lowers the holeextraction barrier, while retarding nucleation and crystal growth to yield largegrained, lowdisorder films. Singlejunction inverted cells achieve a champion efficiency of 23.80% with an outstanding fill factor of 86.27% and negligible hysteresis—among the best reported for this bandgap. The strategy is universally effective across compositions from 1.25 to 1.85 eV, including 1.58 eV without antisolvent. Integrated into monolithic twoterminal tandems with TOPCon silicon bottom cells, devices reach 32.04% (0.9025 cm 2 ). Unencapsulated cells exhibit markedly improved operational stability, retaining 95.26% of initial efficiency after 4500 h storage in nitrogen. This work offers a holistic molecularengineering approach that simultaneously tailors crystallization kinetics, electronic structure, and phase stability, providing a viable route to overcome the persistent efficiency–stability tradeoff in WBG perovskite photovoltaics.