Low-Temperature, Solution-Based Synthesis of Luminescent Chalcogenide Perovskite BaZrS₃ Nanoparticles and Their Phase Stability

Chalcogenide perovskites are an emerging earth-abundant, non-toxic, and robust semiconductor family with the potential to compete with hybrid perovskites as a high-quality photovoltaic absorber. Promising optoelectronic properties have been identified from theory for a number of chalcogenide perovskite compounds. Additinally, increased covalent bonding in the lattice relative to halide perovskites results in enhanced structural stability. However, the cost of structural stability for chalcogenide perovskites can be associated with a high crystallization energy barrier for these materials. As a result, a low-temperature, solution-based synthesis route ideal for realistic semiconductor fabrication has eluded researchers in this area for c. 60 years. In this work, we present the first bottom-up colloidal synthesis of chalcogenide perovskite nanoparticles, demonstrated here for BaZrS₃ which is known to crystallize in the desired distorted perovskite crystal structure. The nanoparticles were synthesized in organic solvent at 330 °C using single-source, reactive metal-dithiocarbamate precursors with a low thermal decomposition temperature, confirmed with XRD, Raman spectroscopy, and HRTEM. The nanoparticles (10-20 nm) are found to be comprised of smaller (3-5 nm) crystalline domains. Promising optoelectronic properties for the nanoparticles are measured, with photoluminescence decay times as high as 4.7 ns.<br/><br/>In addition to the described synthesis, we present a compelling phase stability analysis of sulfide-, selenide-, and telluride-based chalcogenide perovskites based on ionic radii and electronegativity arguments -- related to their increased covalent bonding. A modified tolerance factor for chalcogenide perovskites is proposed, accounting for the expected variations in the bond lengths of constituent atoms in the ABX₃ (X = S, Se, Te) structure. Resulting structural predictions are in good agreement with experimentally reported ABS₃ and ABSe₃ phases. This analysis is a useful tool to identify undesirable phases as well as motivate further experimental research into several unrealized perovskite materials.