Stopping Phase Separation Enables Durable Wide‐Bandgap Photovoltaic Perovskites

Abstract 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 T 90 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.