Ion Migration and Accumulation in Halide Perovskite Solar Cells†

Comprehensive SummaryThe halide perovskite semiconductors-based solar cells (PVSCs) show great promise as next-generation renewable energy sources, with the merits of low cost, high performance, good flexibility, etc. A major difference distinguishing the perovskite semiconductors from others lies in their ionic feature. This intrinsic property induces "freely-moving" ions to migrate and accumulate in the perovskite films and devices under different external stresses. As a charge carrier, these processes will strongly couple with the electronic process, and dramatically affect the performance and stability of PVSCs. This review summarizes and discusses the recent progresses and fundamental understandings of ion migration and accumulation behaviors in PVSCs. First, the basic principles of the general ion migration are reviewed. Second, following the fundamental understandings, the critical factors, e.g., ion migration activation energy, ion density, ion diffusion coefficient, etc., are extracted to understand the ion migration and accumulation in perovskite film. Third, the principles governing ion accumulation behaviors under different external stresses are discussed. Finally, the effect of ion migration and accumulation on band bending, and device performance is presented. Therefore, we hope this review provides a tutorial and insightful perspective regarding the most prominent ionic feature of perovskite semiconductors and their application for photovoltaics.