Dual-source vacuum deposition of pure and mixed halide 2D perovskites: Thin film characterization and processing guidelines

The dual-source vacuum deposition of 2D perovskite films of the type PEA₂PbX₄, (PEA = phenethylammonium and X = I^-, Br^-, or a combination of both) is presented. Low-temperature deposited 2D perovskite films showed high crystallinity with the expected trend of bandgap as a function of halide type and concentration. Importantly, we observed an unavoidable halide cross-contamination among different deposition runs, as well as a strong dependence of the material quality on the type of halide precursors used. These findings should be taken into account in the development of vacuum processing for low-dimensional mixed halide perovskites.