(284a) Misconceptions Around Tolerance Factor Analysis and Implications for the Search to Find New Chalcogenide Perovskites

Chalcogenide perovskites have recently emerged as an interesting class of semiconductors with earth-abundant, non-toxic compositions and bandgaps in the visible to near-IR range.¹ Additionally, they have markedly enhanced stability compared to the related organic-inorganic halide perovskites.² Yet, in contrast to the halide perovskites and their highly tunable compositions, the vast majority of chalcogenide perovskite research has focused on a single compound, BaZrS₃. This material has a bandgap of around 1.8 eV, making it a target for the top absorber layer in tandem photovoltaics. But, it has yet to experimentally achieve the optoelectronic quality necessary to realize high-performance semiconductor devices.³ While there is still much to learn about the defect chemistry of BaZrS₃, resting all the hopes for chalcogenide perovskites on a single candidate material reduces optimism on the long-term outlook for this class of semiconductors. Ideally, a broader range of chalcogenide perovskites would be investigated.⁴ However, common screening methods, such as the tolerance factor, have often been cited to conclude that few combinations of cations will form a perovskite crystal structure with chalcogenide anions.^3,5

In this work, we show that tolerance factor analysis has frequently been misapplied to chalcogenide perovskites by not accounting for the more covalent nature of chalcogenide materials that leads to changes in the effective ionic radii.⁶ By adjusting these radii, the predictions from the octahedral factor and tolerance factor better match with the real-world observations of chalcogenide perovskites. This analysis also points to additional factors which need to be satisfied in order to form a chalcogenide perovskite, especially related to the total electronegativity differences between the anions and cations in these materials. When considering these factors together, a more hopeful picture emerges that a wider breadth of chalcogenide perovskites can be studied, including the prediction of several so-far undiscovered perovskites. Additionally, a better understanding of the geometric and chemical factors governing the formation of chalcogenide perovskites can point to ways in which new perovskite-inspired materials can be synthesized, further broadening this class of semiconductors.

(1) Sun, Y.-Y.; Agiorgousis, M. L.; Zhang, P.; Zhang, S. Chalcogenide Perovskites for Photovoltaics. Nano Lett. 2015, 15, 581–585. https://doi.org/10.1021/nl504046x.

(2) 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, 33 (24), 4135–4143. https://doi.org/10.1557/JMR.2018.419.

(3) Sopiha, K. V.; Comparotto, C.; Márquez, J. A.; Scragg, J. J. S. Chalcogenide Perovskites: Tantalizing Prospects, Challenging Materials. Adv. Opt. Mater. 2022, 10 (3), 2101704. https://doi.org/10.1002/adom.202101704.

(4) Turnley, J. W.; Agrawal, R. Solution Processed Metal Chalcogenide Semiconductors for Inorganic Thin Film Photovoltaics. Chem. Commun. 2024, 60, 5245. https://doi.org/10.1039/d4cc01057d.

(5) Tiwari, D.; Hutter, O. S.; Longo, G. Chalcogenide Perovskites for Photovoltaics: Current Status and Prospects. J. Phys. Energy 2021, 3, 034010. https://doi.org/10.1088/2515-7655/abf41c.

(6) Turnley, J. W.; Agarwal, S.; Agrawal, R. Rethinking Tolerance Factor Analysis for Chalcogenide Perovskites. Mater. Horizons 2024. https://doi.org/10.1039/d4mh00689e.