Rationalizing Patterns in the Cation Ordering, Geometric Distortion, and Electronic Properties of a Class of I-V-VI2 Chalcogenide Semiconductors.

Chalcogenide semiconductors are of interest as light absorbers for solar energy conversion applications. To fully realize their potential, it is crucial to understand how to tune the optoelectronic properties of these compounds through changes in their composition and atomic structure. In this paper, we use density functional theory calculations as a guide to understanding and tuning a class of ABX2 (I-V-VI2) compounds (A = Li, Na, K, Rb; B = As, Sb, Bi; X = S, Se). While these compounds can all be viewed as superstructures of NaCl, they have remarkable variety in their patterns of cation ordering and geometric distortion. By exploring a novel model that connects the sequences of atoms along B-X bond axes to local bonding motifs (2-center 2-electron and 3-center 4-electron), we rationalize the structural variety in this class of compounds and suggest how it can be leveraged to tune their properties such as band gap.