A facile preparation of phase-stable cesium lead triiodide perovskite for high-performance solar cells.

The mixed cation lead halide perovskite solar cells exhibited improved performance and enhanced stabilities.

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With HCl addition, both the one step and sequential deposition methods can be used to fabricate high quality planar perovskite films.

High-quality phase-pure MA FA PbI 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-FAPbI /MAPbI and FA MA PbI requiring rigid crystallization conditions. Here A 2D-3D conversion to transform compact 2D mixed composition HMA FA PbI Cl perovskite precursor films into 3D MA FA PbI (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 MA FA PbI without δ-FAPbI and MAPbI impurity. In all, we successfully developed a facile one-step method to fabricate high quality phase-pure MA FA PbI (x=0.1-0.9) perovskite films by 2D-3D conversion of HMA FA PbI Cl perovskite. This 2D-3D conversion is a promising strategy for lead halide perovskite fabrication.