Understanding the growth mechanism of BaZrS 3 chalcogenide perovskite thin films from sulfurized oxide precursors

Barium zirconium sulfide (BaZrS 3 ) is an earth-abundant and environmentally friendly chalcogenide perovskite with promising properties for various energy conversion applications. Recently, sulfurization of oxide precursors has been suggested as a viable solution for effective synthesis, especially from the perspective of circumventing the difficulty of handling alkali earth metals. In this work, we explore in detail the synthesis of BaZrS 3 from Ba-Zr-O oxide precursor films sulfurized at temperatures ranging from 700 °C to 1000 °C. We propose a formation mechanism of BaZrS 3 based on a two-step reaction involving an intermediate amorphization step of the BaZrO 3 crystalline phase. We show how the diffusion of sulfur (S) species in the film is the rate-limiting step of this reaction. The processing temperature plays a key role in determining the total fraction of conversion from oxide to sulfide phase at a constant flow rate of the sulfur-containing H 2 S gas used as a reactant. Finally, we observe the formation of stoichiometric BaZrS 3 (1:1:3), even under Zr-rich precursor conditions, with the formation of ZrO 2 as a secondary phase. This marks BaZrS 3 quite unique among the other types of chalcogenides, such as chalcopyrites and kesterites, which can instead accommodate quite a large range of non-stoichiometric compositions. This work opens up a pathway for further optimization of the BaZrS 3 synthesis process, straightening the route towards future applications of this material.