Chlorine incorporation engineering has been widely used in optoelectronic devices based on methylammonium lead iodide (MAPbI₃) perovskites. However, the characteristics of I/Cl alloying structures in MAPbI_3−xCl_x mixed-halide perovskites and their influences on the optoelectronic properties have been issues of a long-standing controversy. Here, we present a detailed study of the I/Cl alloying structures in MAPbI_3−xCl_x (x = 0.0 to 0.3) single crystals. We found that a small amount of Cl can substitute for the iodide of the PbI₃ inorganic lattice, leading to a phase transition from the tetragonal to cubic phase and anomalous cation dynamics evolution. Analyses based on time-dependent X-ray diffraction, ²⁰⁷Pb NMR, and ²H NMR indicate that the alloying structures of the MAPbI_3−xCl_x crystals are metastable and decompose over time. In addition, the photocurrent response measurement of MAPbI_3−xCl_x proved a close correlation between the alloying structures and photoelectric properties of the material. This work sheds light on the essential understanding of the I/Cl alloying structure and provides a plausible explanation for the controversy regarding the role of chloride ions in optoelectronic devices.

氯结合工程已广泛用于基于甲基铵碘化铅（MAPbI ₃）钙钛矿的光电器件中。然而，MAPbI _{3− x} Cl _x混合卤化物钙钛矿中I / Cl合金结构的特性及其对光电性能的影响一直是一个长期存在的问题。在这里，我们对MAPbI _{3- x} Cl _x（x  = 0.0至0.3）单晶中的I / Cl合金结构进行了详细研究。我们发现少量的Cl可以代替PbI ₃的碘化物无机晶格，导致从四方相到立方相的相变以及异常的阳离子动力学演化。基于时间相关的X射线衍射，²⁰⁷ Pb NMR和² H NMR的分析表明，MAPbI _{3 - x} Cl _x晶体的合金结构是亚稳态的，并随时间分解。另外，MAPbI _{3 − x} Cl _x的光电流响应测量证明合金的合金结构与光电性能之间密切相关。这项工作阐明了对I / Cl合金结构的基本理解，并为有关氯离子在光电器件中作用的争论提供了合理的解释。