All-Inorganic Metal-Halide Perovskite Epitaxy: CsSnI3/Ag(100) at the Atomic Scale

Abstract

An all-inorganic perovskite, CsSnI3 constitutes one of the most promising candidates for next-generation photovoltaic devices in light of its stability, power conversion efficiency, and low toxicity, compared to other perovskite compositions. In this work, we report the structural evolution of CsSnI3 upon epitaxial growth on the Ag(100) surface in ultra-high vacuum. By means of multiple techniques, namely, low-energy electron diffraction (LEED), (temperature-programmed) X-ray photoelectron spectroscopy (XPS, TP-XPS), low-temperature scanning tunnelling microscopy and spectroscopy (LT-STM, STS), temperature-programmed desorption (TPD), and density functional theory (DFT), we describe the formation of an interfacial SnIx layer, on top of which the perovskite islands nucleate and merge to form extended terraces. Due to an imbalance in the stoichiometry of SnI2 during molecular-beam epitaxy, we identify separate Sn addition and subsequent CsI + SnI2 codeposition at 375 K as the most effective method for the growth of high-quality CsSnI3 surfaces. Finally, we provide evidence of the presence of both CsI and SnI2 surface terminations in the grown CsSnI3, paving the way for atomic-scale insights into the electronic and chemical properties of this highly promising class of materials.