Efficient and Stable FA _0.95 Cs _0.05 PbI ₃ Single-Crystal Perovskite Solar Cells via Hierarchical Elimination of Surface Iodide Vacancies

Halide perovskite single crystals hold great promise for photovoltaic applications, yet their iodine-deficient surfaces critically hinder device efficiency and stability. Herein, a hierarchical surface defect management strategy combining growth engineering with postmodification is proposed to eliminate depth-dependent iodide vacancies. Controlled crystal growth in a metastable region via continuous solute replenishment effectively removes iodide vacancies within micrometer depths, while subsequent organic ammonium treatment eliminates residual vacancies at the outermost crystal surface. This synergistic approach significantly optimizes carrier transport and suppresses nonradiative recombination, thereby boosting the efficiency of single-crystal perovskite solar cells (PSCs) from 22.8 to 25.5%. Moreover, suppression of multidirectional iodide migration extends the operational T90 (remaining 90% of initial efficiency) lifetime from 200 to 1000 h. These results highlight the critical role of hierarchical iodide vacancy management in resolving surface issues of perovskite single crystals, which is valuable for developing high-performance, diverse optoelectronic devices, including solar cells, X-ray detectors, light-emitting diodes, and field-effect transistors.