Understanding the growth mechanism of BaZrS₃ chalcogenide perovskite thin films from sulfurized oxide precursors

Abstract

Barium zirconium sulfide (BaZrS3) 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 BaZrS3 from Ba-Zr-O oxide precursor films sulfurized at temperatures ranging from 700 °C to 1000 °C. We propose a formation mechanism of BaZrS3 based on a two-step reaction involving an intermediate amorphization step of the BaZrO3 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 H2S gas used as a reactant. Finally, we observe the formation of stoichiometric BaZrS3 (1:1:3), even under Zr-rich precursor conditions, with the formation of ZrO2 as a secondary phase. This marks BaZrS3 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 BaZrS3 synthesis process, straightening the route towards future applications of this material.

Moderate temperature sulfurization and selenization of highly stable metal oxides: an opportunity for chalcogenide perovskites

“…The observation of clear BaZrO 3 and BaZrS 3 peaks in XRD is evidence that there is no crystalline BaZr(O,S) 3 , though there could be amorphous Ba–Zr–O–S phases. This observation is in line with the recent findings of Márquez et al and Ramanandan et al 18,19 To further investigate how BaZrO 3 is converted to BaZrS 3 a 1 h sample was studied, leading to the observation of binary BaS 4 ·H 2 O as an intermediate (Fig. S13–S15, ESI†).…”

Interplay between Growth Mechanism, Materials Chemistry, and Band Gap Characteristics in Sputtered Thin Films of Chalcogenide Perovskite BaZrS3

“…Both observations imply that the observed small crystallites are not of BaZrS 3 −BaZrO 3 solid solutions. 50 Rather, these are pure BaZrS 3 crystallites that grow from the amorphous phase by expelling O from the perovskite lattice. During the thermal process, O also crystallizes predominantly as ZrO 2 , as identified in XRD and STEM-EDS.…”

Chalcogenide Perovskite, An Emerging Photovoltaic Material: Current Status and Future Perspectives

“…Processing of thin film devices is not compatible at high temperature. So far only BaZrS 3 , [24,93,[108][109] LaYS 3 , [12,96] BaHfS 3 [110] and CaSnS 3 [111] have been realized in thin film form. New techniques such as solution processed moderate temperature synthesis using a single phase molecular precursor, [110,112] liquid flux assisted mechanism, [113] colloidal nanoscale synthesis, [114][115][116] molecular beam epitaxy [117] and post processing techniques need to be explored more for synthesis of chalcogenide perovskite.…”