Evaluation of the optical, structural, morphological and electronic properties of Rb₃Bi₂I₉ Perovskites films prepared by Sequential Evaporation

Toxicity and poor stability remain major barriers to large-scale production of hybrid organic-inorganic lead halide perovskite solar cells. Considering the isoelectronic nature of lead (II) and bismuth (III) ions, stable and non-toxic alternatives for developing photovoltaic devices could potentially be found. Rb₃Bi₂I₉ perovskite films inherently suffer from unavoidable pinhole defects and poor surface morphology, which limit device performance. In this work we explored a dual-source thermal sequential evaporation approach to growth uniform and pinhole-free morphology of Rb₃Bi₂I₉ polycrystalline thin films. The influence of post-deposition annealing in a high-pressure N2 atmosphere on the structural, optical, morphological, and electronic properties of the resulting films was studied experimentally using X-ray diffraction (XRD), optical spectrophotometry, scanning electron microscopy (SEM), and computationally via Density Functional Theory (DFT) calculations. The results revealed that post deposition annealing significantly improves both the morphology and degradation processes of Rb₃Bi₂I₉ films, when they are exposed to environmental conditions for long periods of time.