Stopping Phase Separation Enables Durable Wide-Bandgap Photovoltaic Perovskites

Light-induced halide segregation presents a fundamental barrier to the longevity of wide-bandgap (WBG) mixed-halide perovskites. Herein, a multifunctional ionic polymer, polyquaternium-37, is reported as an effective grain boundary passivator to inhibit the degradation pathway. This dual-interaction mechanism concertedly arrests halide migration at grain boundaries, thereby suppressing local electric-field and ultimately curbing light-induced phase separation. Consequently, the modified WBG perovskites demonstrate robust photostability under light stress. The champion inverted perovskite photovoltaic device delivers a power conversion efficiency (PCE) of 22.86% under AM 1.5G illumination and an outstanding indoor PCE of 43.19% under 1000 lux. Remarkably, the modified device exhibits a projected T₉₀ lifetime exceeding 10 000 h under continuous indoor light cycling. This work pioneers a facile solution to halide segregation via grain boundary engineering, paving the way for operationally stable WBG perovskite photovoltaics.