Structural Tolerance Factor Approach to Defect-Resistant I2-II-IV-X4 Semiconductor Design
Copyright © 2020 American Chemical Society. Recent work on quaternary semiconductors Cu2BaSn(S,Se)4 and Ag2BaSnSe4 for photovoltaic and thermoelectric applications, respectively, has shown the promise of exploring the broader family of defect-resistant I2-II-IV-X4 materials (where I, II, and IV refer to the formal oxidation state of the metal cations and X is a chalcogen anion) with tetrahedrally coordinated I/IV cations and larger II cations (i.e., Sr, Ba, Pb, and Eu) for optoelectronic and energy-related applications. Chemical dissimilarity among the II and I/IV atoms represents an important design motivation because it presents a barrier to antisite formation, which otherwise may act as electronically harmful defects. We herein show how all 31 experimentally reported I2-II-IV-X4 examples (with large II cations and tetrahedrally coordinated smaller I/IV cations), which form within five crystal structure types, are structurally linked. Based on these structural similarities, we derive a set of tolerance factors that serve as descriptors for phase stability within this family. Despite common usage in the well-studied perovskite system, Shannon ionic radii are found to be insufficient for predicting metal-chalcogen bond lengths, pointing to the need for experimentally derived correction factors as part of an empirically driven learning approach to structure prediction. We use the tolerance factors as a predictive tool and demonstrate that four new I2-II-IV-X4 compounds, Ag2BaSiS4, Ag2PbSiS4, Cu2PbGeS4, and Cu2SrSiS4, can be synthesized in correctly predicted phases. One of these compounds, Ag2PbSiS4, shows potentially promising optoelectronic properties for photovoltaic applications.
Sun, JP; McKeown Wessler, GC; Wang, T; Zhu, T; Blum, V; Mitzi, DB
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