(358f) A Low-Temperature Growth Mechanism for Chalcogenide Perovskites

Chalcogenide perovskites have attracted increasing research attention in recent years due to their promise of unique optoelectronic properties combined with stability. However, the synthesis and processing of these materials has been constrained by the need for high temperatures and/or long reaction times. As a representative of chalcogenide perovskites, BaZrS₃ has been mainly synthesized by (1) heating BaS and ZrS₂; (2) sulfurizing BaZrO₃ and elemental powders; (3) post sulfurization of co-sputtered Ba-Zr-O/S film, all of which require high temperatures and/or long reaction times. Recently, BaS₃ has been hypothesized to be a liquid flux that has potential to reduce the reaction temperature and shorten the reaction time for BaZrS₃ formation considerably.

In this work, we address the open question of a low-temperature growth mechanism for BaZrS_3. Ultimately, a liquid-assisted growth mechanism for BaZrS₃ using molten BaS₃ as a flux is demonstrated at temperatures ≥ 540 ^oC in as little as 5 minutes. The role of Zr-precursor reactivity and 𝑆_{(𝑔.)} on the growth mechanism and formation of Ba₃Zr₂S₇ is discussed, in addition to the purification of resulting products using a straightforward H₂O wash. The extension of this growth mechanism is shown for other Ba-based chalcogenides, including BaHfS₃, BaNbS₃, and BaTiS₃. In addition, an alternative vapor-transport growth mechanism is presented using S₂Cl₂ for the growth of BaZrS₃ at temperatures as low as 500 ^oC in at least 3 h. These results demonstrate the feasibility of scalable processing for the formation of chalcogenide perovskite thin films.