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

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 reduces the effective charge on Pb and changes the electrostatic interaction between Pb 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.