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Metal halide perovskite single crystals are promising for photovoltaic applications due to their outstanding properties. However, the high surface trap density causes severe nonradiative recombination and ion migration, hindering device performance and stability. Herein, mitigation of the deficient crystal surface is reported by optimized polishing engineering, resulting in stoichiometric lead‐iodine ratio with reduced iodide ion vacancies, increased ion migration activation energy, and suppressed nonradiative recombination. As a result, Cs0.05FA0.95PbI3 (FA = formamidinium) devices exhibit an impressive efficiency of 23.1%, which is one of the highest values for single‐crystal perovskite solar cells (PSCs). Moreover, multiple recycling of the degraded single‐crystal PSCs with higher efficiency and stability is achieved by removing the deteriorated surface, validating crystal surface dominates device degradation while the role of bulk and buried interface is negligible, which is different from polycrystalline devices. The T85 lifetime (remain 85% of initial efficiency) of Cs0.05FA0.95PbI3 devices increases to 1150 h after the recycling process, which is much better than that of previously reported single‐crystal PSCs. Since deficient crystal surface and ion migration are universal issues of perovskite materials, this work will promote the development of stable single‐crystal PSCs and other optoelectronic devices, such as X‐ray detectors, light‐emitting diodes, etc. [ABSTRACT FROM AUTHOR]

Organic-inorganic halide perovskite (OIHP) single crystals are promising for optoelectronic application, but their high surface trap density and associated ion migration hinders device performance and stability. Herein, a one-dimensional (1D) perovskites are designed and proposed as blocking layer at the crystal/electrode interface to mitigate the surface issues. As a model system, the interface ion migration in Cs0.05FA0.95PbI3 (FA=formamidinium) single-crystal perovskite solar cells (PSCs) is obviously suppressed, leading to increase of T90 lifetime from 260 to 1000 hours, five times better than previously reported results. Besides, the reduction of surface iodide ion vacancies inhibits nonradiative recombination, thus increasing the efficiency from 22.1% to 23.8%, which is one of the highest values for single-crystal PSCs. Since the deficient crystal surface is a universal and open issue, our strategy is instructive for optimizing diverse single-crystal perovskite devices., (© 2024 Wiley‐VCH GmbH.)