Halogen-halogen bonds enable improved long-term operational stability of mixed-halide perovskite photovoltaics

Mixed-halide perovskite provides band-gap tunability, which is essential for tandem solar cell application. However, ion migration inducing phase segregation seriously affects the device's long-term operational stability. The issue thus represents an important challenge for the whole perovskite community and urgently needs effective solutions. We showcase here for the first time that a strong chemical interaction, a halogen-halogen bond, is introduced at the phase interface to suppress the ion migration by increasing the corresponding activation energy. Various characterizations have proved that halogen-halogen bonds form between 2D and 3D phases, which do suppress the halide segregation. As expected, the encapsulated device retains 90% of initial power conversion efficiency (PCE) after maximum power point (MPP) tracking for ∼500 h under continuous simulated 1-sun illumination (AM 1.5) in ambient conditions, representing one of the most stable, wide-band-gap, mixed-halide perovskite photovoltaics reported so far.