Ion-Exchange-Induced 2D-3D Conversion of HMA1−x FAx PbI3 Cl Perovskite into a High-Quality MA1−x FAx PbI3 Perovskite

High-quality phase-pure MA1−xFAxPbI3 planar films (MA=methylammonium, FA=formamidinium) with extended absorption and enhanced thermal stability are difficult to deposit by regular simple solution chemistry approaches owing to crystallization competition between the easy-to-crystallize but unwanted δ-FAPbI3/MAPbI3 and FAxMA1−xPbI3 requiring rigid crystallization conditions. Here A 2D–3D conversion to transform compact 2D mixed composition HMA1−xFAxPbI3Cl perovskite precursor films into 3D MA1−xFAxPbI3 (x=0.1–0.9) perovskites is presented. The designed Cl/I and H/FA(MA) ion exchange reaction induced fast transformation of compact 2D perovskite film, helping to form the phase-pure and high quality MA1−xFAxPbI3 without δ-FAPbI3 and MAPbI3 impurity. In all, we successfully developed a facile one-step method to fabricate high quality phase-pure MA1−xFAxPbI3 (x=0.1–0.9) perovskite films by 2D–3D conversion of HMA1−xFAxPbI3Cl perovskite. This 2D–3D conversion is a promising strategy for lead halide perovskite fabrication.