B-Site Metal Cation Exchange in Halide Perovskites

We demonstrate exchange of the B-site metal cation in hybrid organic inorganic halide perovskite thin films. We exchange tin in formamidinium tin triiodide (CH(NH2)(2)SnI3, or FASnI(3)) with lead at controllable levels, forming CH (NH2)(2)SnxPb1-xI3 alloys with partial substitution and fully converting the film to CH(NH2)(2)PbI3 with a large excess of Pb2+. We observe no evidence for phase segregation or bilayered films, indicating that conversion is uniform throughout the film. This facile technique provides a new way to control composition independently from the crystallization processes, allowing formation of the black phase of CH(NH2)(2)PbI3 at much lower temperatures than those previously reported while also opening the door to new morphology composition combinations. The surprising observation that the B-site metal cations are mobile may also provide insight into the nature of transient processes in these materials, suggesting that they may be involved in ionic conduction, and will be a critical consideration for long-term stability.