Phase Stability and Crystal Orientation of Low-Dimensional Hybrid Halide Perovskite Films grown by Chemical Vapor Deposition

Low-pressure chemical vapor deposition offers a scalable and low-cost route for the conformal deposition of perovskite materials. Using a multi-step CVD process, we demonstrate the versatility of the technique in the growth of phase stable 3D and 2D lead-halide perovskite films. An air-processed methylammonium lead iodide (MAPbI₃) planar single-junction solar cell was realized and maintains 85% of its performance up to 2 weeks in the open air. Using large organic cations, such as butylammonium (BA) and phenylethylammonium (PEA), CVD was used to grow BA₂PbI₄ and PEA₂PbI₄ and its mixed halides with chlorine. X-ray diffraction (XRD) and a non-integer dimensionality model of the absorption spectrum provide insights into the orientation of the crystalline planes of PEA₂PbI₄. Furthermore, detailed XRD analysis of the PEA₂PbI₄ film as a function of film thickness show the appearance of 2D powder diffraction spots, highlighting the different orientational properties of the perovskite planes. Contrary to BA₂PbI₄, temperature-dependent photoluminescence of PEA₂PbI₄ show a single excitonic peak throughout the temperature range from 20 – 350 K, highlighting its phase stability and lack of defect states. These results are further corroborated by temperature-dependent XRD analysis.