Competitive Crystallization Modulated Phase‐Homogeneous Wide‐Bandgap Perovskites for Monolithic Perovskite‐Organic Tandem Solar Cells

Abstract Wide‐bandgap (WBG) perovskites with tunable bandgaps can be integrated into organic solar cells to construct tandem solar cells (TSCs), enabling the device to exceed the Shockley‐Queisser efficiency limit. However, ionic mismatches and crystallization kinetics in WBG perovskites trigger inhomogeneous phase distribution and defects. In this work, a triphenyl phosphate (Tri‐PyPA) is utilized to modulate Br/I competitive crystallization and compositional distribution. The preferential coordination of Tri‐PyPA with PbBr 2 reduces the effective charge on Pb 2+ and changes the electrostatic interaction between Pb 2+ and Br − /I − ions. It suppresses the rapid migration of highly diffusive (Br‐rich) components during crystallization. Meanwhile, Tri‐PyPA forms a six‐membered hydrogen‐bonded ring structure with formamidinium cations by H•••O═P interaction to immobilize cations. The π‐π conjugation allows Tri‐PyPA to form a compact molecular coverage on the (100) facet, significantly reducing non‐radiative recombination and elevating the ion migration energy barriers. The homogeneous WBG perovskites boost the efficiency up to record values of 21.39% and 19.64% for 1.72 eV and 1.84 eV devices, respectively. The unencapsulated device can maintain 95% of its initial efficiency after illumination for 1100 h. The champion perovskite‐organic TSC shows an efficiency of 26.11% (certified 25.07%) and retains 80% of its initial efficiency after continuous operation for 1000 h.