Controlling Nucleation and Growth of Metal Halide Perovskite Thin Films for High-Efficiency Perovskite Solar Cells

Metal halide perovskite thin films can be crystallized via a broad range of solution-based routes. However, the quality of the final films is strongly dependent upon small changes in solution composition and processing parameters. Here, this study demonstrates that a fractional substitution of PbCl₂ with PbI₂ in the 3CH₃ NH₃ I:PbCl₂ mixed-halide starting solution has a profound influence upon the ensuing thin-film crystallization. The presence of PbI₂ in the precursor induces a uniform distribution of regular quadrilateral-shaped CH₃ NH₃ PbI₃ perovskite crystals in as-cast films, which subsequently grow to form pinhole-free perovskite films with highly crystalline domains. With this new formulation of 3CH₃ NH₃ I:0.98PbCl₂ :0.02PbI₂ , this study achieves a 19.1% current-voltage measured power conversion efficiency and a 17.2% stabilized power output in regular planar heterojunction solar cells.