B‑Site Metal Cation Exchange in Halide Perovskites

Abstract

We demonstrate exchange\nof the B-site metal cation in hybrid organic–inorganic\nhalide perovskite thin films. We exchange tin in formamidinium tin\ntriiodide (CH­(NH₂)₂SnI₃, or FASnI₃) with lead at controllable levels, forming CH­(NH₂)₂Sn_<i>x</i>Pb_1–<i>x</i>I₃ alloys with partial substitution and\nfully converting the film to CH­(NH₂)₂PbI₃ with a large excess of Pb²⁺. We observe no evidence\nfor phase segregation or bilayered films, indicating that conversion\nis uniform throughout the film. This facile technique provides a new\nway to control composition independently from the crystallization\nprocesses, allowing formation of the black phase of CH­(NH₂)₂PbI₃ at much lower temperatures than those\npreviously reported while also opening the door to new morphology–composition\ncombinations. The surprising observation that the B-site metal cations\nare mobile may also provide insight into the nature of transient processes\nin these materials, suggesting that they may be involved in ionic\nconduction, and will be a critical consideration for long-term stability.