(328e) Low-Temperature Synthesis Approaches for BaZrS3

Chalcogenide perovskites have been proposed as a class of semiconducting materials which could exhibit the high stability found in oxide perovskites while retaining the narrow bandgap and high light absorption seen in halide perovskites.¹ Of the chalcogenide perovskites, BaZrS₃ has emerged as a promising semiconductor for photovoltaic applications. Computationally, this material is predicted to be defect tolerant.² Experimentally, it has been shown to have a bandgap around 1.75 eV and is stable when heated in air.³

Device compatible synthesis, however, remains one of the major challenges for BaZrS₃ and the other chalcogenide perovskites. Generally, these materials have been synthesized via solid state reactions or through the sulfurization of an oxide film. However, both methods are often done between 800°C and 1000°C, temperatures that are generally incompatible with device manufacturing.^4,5 To create devices with these chalcogenide perovskites, a lower-temperature method for synthesis and thin film fabrication is needed.

One potential reason that synthesis of chalcogenide perovskites has been difficult is that the constituent metals (primarily a combination of calcium, strontium, or barium with zirconium or hafnium) are generally considered to be highly oxyphilic.⁶ Once a metal-oxygen bond is formed for these metals, it is very difficult to convert to the desired metal-sulfide bond. This means that both the precursors and delivery method need to be carefully controlled to eliminate the potential for metal oxide formation.

In this work we demonstrate that BaZrS₃ can be synthesized at the low temperatures needed for device manufacturing. To bypass the limitation of traditional synthetic approaches we have investigated several methods to deliver the barium and zirconium precursors while preventing the formation of oxide secondary phases. These methods include both solution-based approaches using soluble molecular precursor and nanoparticle slurries, as well as vacuum-based methods. For cases where oxygen impurities can be avoided, subsequent sulfurization at temperatures below 600°C is able to produce the BaZrS₃ distorted perovskite material, as confirmed by X-ray diffraction and Raman spectroscopy.

In summary, this work seeks to develop synthesis methods for BaZrS₃ that are compatible with device fabrication, laying the groundwork for chalcogenide perovskite use in solar cells and other semiconductor devices.

(1) Sun, Y.-Y.; Agiorgousis, M. L.; Zhang, P.; Zhang, S. Chalcogenide Perovskites for Photovoltaics. Nano Lett. 2014, 15. https://doi.org/10.1021/nl504046x.

(2) Wu, X.; Gao, W.; Chai, J.; Ming, C.; Chen, M.; Zeng, H.; Zhang, P.; Zhang, S.; Sun, Y.-Y. Defect Tolerance in Chalcogenide Perovskite Photovoltaic Material BaZrS3. Sci. China Mater. 2021 2021, 1–11. https://doi.org/10.1007/S40843-021-1683-0.

(3) Niu, S.; Milam-Guerrero, J.; Zhou, Y.; Ye, K.; Zhao, B.; Melot, B. C.; Ravichandran, J. Thermal Stability Study of Transition Metal Perovskite Sulfides. J. Mater. Res. 2018 3324 2018, 33 (24), 4135–4143. https://doi.org/10.1557/JMR.2018.419.

(4) Meng, W.; Saparov, B.; Hong, F.; Wang, J.; Mitzi, D. B.; Yan, Y. Alloying and Defect Control within Chalcogenide Perovskites for Optimized Photovoltaic Application. Chem. Mater 2016, 28, 10. https://doi.org/10.1021/acs.chemmater.5b04213.

(5) Márquez, J. A.; Rusu, M.; Hempel, H.; Ahmet, I. Y.; Kölbach, M.; Simsek, I.; Choubrac, L.; Gurieva, G.; Gunder, R.; Schorr, S.; et al. BaZrS3 Chalcogenide Perovskite Thin Films by H2S Sulfurization of Oxide Precursors. J. Phys. Chem. Lett. 2021, 12. https://doi.org/10.1021/acs.jpclett.1c00177.

(6) Kepp, K. P. A Quantitative Scale of Oxophilicity and Thiophilicity. Inorg. Chem 2016, 55, 9461–9470. https://doi.org/10.1021/acs.inorgchem.6b01702.