Su-Huai Wei 1*

 1Beijing Computational Science Research Center, Beijing, 100193, China

EXTENDED ABSTRACT: Conventional semiconductors, e.g., Si and GaAs with tetrahedral coordination (four-fold) structures, possess good stability but relatively low optical absorption compared with halide perovskites with octahedral coordination (six-fold) structures, which exhibit superior optical absorption but relatively poor stability. It is thus desirable to combine the complementary properties of four-fold and six-fold semiconductors to have a system with both good stability and optical absorption. To achieve such a goal, we investigate the spinel compounds A2B4(X = 0, S and Se) as potential candidates because they possess both four-fold and six-fold coordination in one structure. Here, we built four basic structure units as material genes to design various types of spinel compounds with optimal optical absorption. The optical absorption of a semiconductor is fundamentally determined by the dipole transition matrix element (IMl2) and joint density of states (Jcv). Our first-principles calculations show that in AB2X4 systems the type of cation at the B site determines the optical absorption. Two rules are identified through our study: (i) the sv cations with the valence s orbital at the valence band maximum at the B site (type-I, type-II) will lead to allowed transitions, Figure 1. The crystal structures of four types of whereas the sc cations with the valence s orbital at the conduction band minimum at the B site (type-III, type-IV) will lead to partially forbidden or fully forbidden transitions; (ii) when the sv cation is located at the B site, the A site with the sc cations (type-I) has higher IMl2, while the A site with the sv cations (type-II) has higher Jcv. Our study, therefore, provides guidelines to optimize the Jcv and IMl2, and thus absorption, through cation engineering in AB2X4compounds.

Keywords: inverse design; optical absorption; materials genome
REFERENCES：
[l] Q. Sun and S.-H. Wei, J. Mater. Chem. A, 10, 12503 (2022).