Composition and Dimension Dependent Static and Dynamic Stabilities of Inorganic Mixed Halide Antimony Perovskites

Halide intermixing is an important approach to stabilise halide perovskite in the phase that gives the best optoelectronic properties, whereas replacing Pb is critical for eliminating the material toxicity to meet the requirements for domestic applications. Recently, all-inorganic lead-free Cs3Sb2I9 emerges as a promising lead-free absorber, with its optoelectronic properties being further controllable by manipulating its structural dimensionality (0D or 2D) via composition engineering. In particular, superior photoconversion efficiency (up to 5 %) under indoor illumination with high photostabilities have been demonstrated experimentally in 2D Cs3Sb2ClyI9-y}. To gain a more thorough understanding on how the properties of this family of materials are controlled by their chemistry and dimensionality, here, we employ density functional theory calculations to explore the phase stability, structural and electronic dynamics of Cs3Sb2X9 (X=Br and Cl) across 74 different combinations of composition/dimensionality. The results show that Cs3Sb2X9 solid solutions are predominantly stabilised by configurational entropy rather than enthalpy. In stark contrast to cubic inorganic lead/tin halides perovskites, Cs3Sb2X9 are dynamically more stable at 300 K, as reflected by their low vibrational anharmonicities, the values of which also exhibit weak compositional dependency. This consequentially reduces the strength of electron-phonon couplings, thus enhancing the photoexcited carrier lifetime in these materials, which further demonstrates their promising potential to be integrated into indoor photovoltaic devices.