New compounds Mg3IV6V8 (IV=Si, Ge, Sn; V=P, As, Sb) and their potential application to photovoltaic materials

A new non-centrosymmetric Mg-based ternary compounds Mg3Si6As8 with bandgap of about 2.0 eV has been recently synthesized [Woo et al., Advanced Functional Materials, 2018, 28, 1801589], which indicates there exists a new class of Mg-based spinel crystals denoted as Mg3IV6V8 in the II-IV-V family. In this work, through substituting the IV and the V elements in Mg3IV6V8, more stable crystals in this new class are theoretically predicted. It is found that the bandgaps of these Mg3IV6V8 (IV=Si, Ge, Sn; V=P, As, Sb) compounds range from 2.5 eV to 0.88 eV, and each of these compounds shows good performance in photovoltaic (PV) efficiencies. Furthermore, multilayer tandem solar cells consisting of these compounds are proposed, and the PV efficiencies of these solar cells are predicted to reach 30%, exceeding that of silicon and Cu(In,Ge)Se2 (CIGS).