(180c) Barium Polysulfide Breakthrough: The Key to Moderate Temperature Chalcogenide Perovskite Fabrication

Chalcogenide perovskites have garnered the research community's attention as a promising class of semiconductor materials due to their appealing optoelectronic properties. Demonstrated computationally and experimentally, these materials exhibit a high absorption coefficient, tunable bandgap, and dielectric constant. Unlike their lead halide counterparts, they boast stability, earth abundance, and non-toxicity, rendering them viable candidates for diverse electronic applications. However, their growth has been limited by conventional synthesis techniques, typically relying on solid-state and vacuum processes methods, demanding temperatures exceeding 800-1000 °C. This imposes challenges in substrate selection and subsequent device fabrication.

Our research highlights barium polysulfide (BaS_x, x>3) as a potential liquid flux capable of lowering synthesis temperatures to as low as 575°C as well as reaction time to within 5 minutes as opposed to several days previously utilized in the literature. Barium polysulfide, accessible at 525°C in saturated sulfur environments, facilitates using cost-effective substrates such as glass. Upon cooling, it crystallizes into BaS₃ and volatile sulfur, with BaS₃ readily soluble in water, enabling easy removal. In contrast to extrinsic fluxes like I₂, barium polysulfide acts as an intrinsic liquid flux, eliminating unnecessary secondary phases. With these inherent advantages, barium polysulfide emerges as the critical factor towards moderate temperature synthesis of BaMS₃ (M= Ti, Zr, Hf) chalcogenide perovskites.

Implementing this flux has led to the development of various solution processing routes encompassing metal hydrides, metals, metal salts, and organometallic precursors. This study discusses the pivotal role of barium polysulfide in accelerating the formation of BaMS₃ materials and its influence on grain growth.