Suppressing Light-Induced Phase Segregation via Dual Interface Modification for High-Performance and Stable Inverted CsPbIBr₂ Perovskite Solar Cells

Wide-bandgap perovskite materials are gaining enormous attention recently, particularly in multijunction photovoltaics. Despite the encouraging development, light-induced phase segregation still impedes their operational stability, primarily due to the high content of bromide constituents. Here, we report a bilateral interface design to mitigate the phase instability of 2.1 eV bandgap all-inorganic CsPbIBr₂ perovskite solar cells (PSCs)─(1) buried interface: strong chemical interactions occur between nickel oxide (NiO_<i>x</i>) and self-assembled monolayer (SAM) via phosphonic acid anchoring groups, establishing an interfacial bridge that promotes efficient hole extraction. (2) Top surface: a solution-processed BCP (s-BCP) layer is introduced to passivate the perovskite film and suppress trap-assisted recombination, resulting in reduced phase segregation. The synergistic effect of dual interfaces reduces defect formation, moisture penetration, and phase transition, contributing to enhanced phase stability. Optimal energetic alignment and defect passivation lead to improved photovoltaic (PV) performance. As a result, the dual interface modification delivers a power conversion efficiency (PCE) of 10.2% with a fill factor of 82.3%. Additionally, the modified device retains >87% of its initial efficiency after 110 h of continuous operation and exhibits merely 5% degradation after 300 days of storage, which is one of the most stable performances reported for all-inorganic CsPbIBr₂ PSCs. This work reveals a key strategy to address inherent phase instability in wide-bandgap perovskites through interface engineering.