Improved fatigue behaviour of perovskite solar cells with an interfacial starch–polyiodide buffer layer

Metal halide perovskite solar cells are expected to lead the revolution in photovoltaics. However, due to their soft and ionic lattice, perovskites are sensitive to external stimuli, and the resulting devices suffer from noticeable fatigue under cyclic stressors in real-world applications. Due to the lack of a fundamental understanding of the metastable dynamics of materials degradation, effective means to alleviate device fatigue under cyclic illumination are lacking. Here we introduce a starch–polyiodide supermolecule as a bifunctional buffer layer at the perovskite interface, which can both suppress ion migration and promote defect self-healing. The modified perovskite solar cells exhibit improved stability by retaining 98% of their original power conversion efficiency after operation for 42 diurnal cycles (12/12 h light/dark cycle). The devices also deliver a power conversion efficiency of 24.3% (certified, 23.9%) and an intense electroluminescence with external quantum efficiencies above 12.0%. Our findings shed light on how supramolecular chemistry modulates the metastable dynamics of degradation in perovskites and other materials with soft lattices. Introduction of a starch-based layer inhibits ion migration and repairs defects generated on light/dark cycles in perovskite solar cells. Cells retain 98.0% of the initial power conversion efficiency after 42 illumination cycles, and achieve a certified power conversion efficiency of 23.9%.