Structure-Property Engineering in Multinary Chalcogenide Semiconductors

Multinary chalcogenides play a vital role in commercial and emerging photovoltaic (PV) and related photoelectrochemical (PEC) devices. I₂-II-IV-X₄ semiconductors, wherein “I” is Ag or Cu, “II” is a divalent metal or alkaline earth, “IV” is a tetravalent metal and “X” is a chalcogen (generally S or Se) form a particularly interesting branch of emerging solar absorbers, with a target of replacing more traditional systems such as CdTe or Cu(In,Ga)(S,Se)₂ that suffer from toxicity or elemental abundance issues. Large efforts have been focused on Cu₂ZnSn(S,Se)₄ as an earth-abundant and reduced-toxicity absorber, leading to significant performance improvement. However, similarity of component atom size and preferred coordination gives rise to facile anti-site defect formation, which has limited performance improvement. In this talk we will explore a broader class of I₂-II-IV-X₄ (I = Ag, Cu; II = Ba, Sr, Eu, Pb; IV = Si, Ge, Sn; VI = S, Se) multinary semiconductors, which involve a II atom with significantly larger disparity in atomic radius and preferred coordination. Beyond the more thoroughly studied Cu₂BaSn(S,Se)₄, II = Eu systems have been recently identified as providing potentially suitable crystal and band structures for PV/PEC.¹ We have also been extending the II²⁺-IV⁴⁺ component of these systems to I⁺-V⁵⁺ analogs, to provide opportunity to explore whether a structural tolerance factor approach derived for the II²⁺-IV⁴⁺ systems² still proves useful for structure prediction, as well as to broaden the prospects for property tunability (e.g., bandgap and defect tolerance). As many of these structures crystallize in non-centrosymmetric space groups and contain heavy atoms (with significant spin-orbit coupling), we also explore the implications for engineering systems with a large degree of spin splitting,³ of prospective interest for spintronics and as has also been pursued in 2D halide perovskites.⁴ If desirable electronic structure tunability associated with a multi-element stoichiometry can coincide with earth-abundant components and control over defect formation, such multinary chalcogenides will provide an interesting path forward in the quest for high-performance, low cost and scalable PVs and other optoelectronic devices. <br/> <br/><b>References:</b><br/>[1] T. Wang, T. M. McWhorter, G. C. McKeown-Wessler, Y. Yao, R. Song, D. B. Mitzi, V. Blum, <i>Chem. Mater.</i> 36, 340 (2024).<br/>[2] J.-P. Sun, G. C. McKeown Wessler, T. Wang, T. Zhu, V. Blum, D. B. Mitzi, <i>Chem. Mater.</i> 32, 1636 (2020).<br/>[3] E. T. Chang, G. Koknat, G. C. McKeown Wessler, Y. Yao, V. Blum, D. B. Mitzi, <i>Chem. Mater.</i> 35, 595 (2023).<br/>[4] M. K. Jana, R. Song, H. Liu, D. R. Khanal, S. M. Janke, R. Zhao, C. Liu, Z. V. Vardeny, V. Blum, D. B. Mitzi, <i>Nature Comm.</i> 11, 4699 (2020).