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.

Low-dimensional (quasi-) 2D perovskites are being extensively studied in order to enhance the stability and the open-circuit voltage of perovskite solar cells. Up to now, thin 2D perovskite layers on the surface and/or at the grain boundaries of 3D perovskites have been deposited solely by solution processing, leading to unavoidable intermixing between the two phases. In this work, we report the fabrication of 2D/3D/2D perovskite heterostructures by dual-source vacuum deposition, with the aim of studying the interaction between the 3D and 2D phases as well as the charge transport properties of 2D perovskites in neat 2D/3D interfaces. Unlike what is normally observed in solution-processed 3D/2D systems, we found a reduced charge transport with no direct evidence of surface passivation, in spite of larger open-circuit voltage. This is likely due to a nonfavorable orientation of the 2D perovskite with respect to methylammonium lead iodide and to the formation of 2D phases with very low dimensionality (pure 2D).

Methylammonium lead halide perovskites have emerged as high performance photovoltaic materials. Most of these solar cells are prepared via solution-processing and record efficiencies (>20%) have been obtained employing perovskites with mixed halides and organic cations on (mesoscopic) metal oxides. Here, we demonstrate fully vacuum deposited planar perovskite solar cells by depositing methylammonium lead iodide in between intrinsic and doped organic charge transport molecules. Two configurations, one inverted with respect to the other, p-i-n and n-i-p, are prepared and optimized leading to planar solar cells without hysteresis and very high efficiencies, 16.5% and 20%, respectively. It is the first time that a direct comparison between these two opposite device configurations has been reported. These fully vacuum deposited solar cells, employing doped organic charge transport layers, validate for the first time vacuum based processing as a real alternative for perovskite solar cell preparation.