In ternary semiconductors, both stacking disorder and cation disorder can cause the formation of polytypes and extended defects. We perform density functional theory calculations to investigate the stability of polytypes in six ternary sulfides, such as CuInS2, CuGaS2, CuAlS2, AgInS2, AgGaS2, and AgAlS2. The formation energy of polytypes generated by stacking disorders is used to generate the anisotropic next-nearest neighbor Ising models. The estimated stacking fault energy by the model is in good agreement with the calculated stacking fault energy. The incorporation of Ga and Ag tends to suppress and promote the formation of stacking faults, respectively. On the other hand, the electronic bandgap of the polytypes generated by cation disorder is negatively correlated with the formation energy, resulting in the trapping of charge carriers at antisite domain boundaries. The formation of antisite domain boundaries can be suppressed by the incorporation of Ag and Ga.

The relative stability of polymorphs and their electronic structure was investigated for II-IV-V2 materials by using first-principles density functional theory calculations. Our calculation results show that, for Zn-, Cd-, and Be-containing compounds, nitrides favor the 2H polymorph with AB stacking sequence; however, phosphides, arsenides, and antimonides are more stable in the 3C polymorph with the ABC stacking sequence. The electronic band gap of materials was calculated by using hybrid density functional theory methods, and then materials with an ideal band gap for photovoltaic applications were chosen. The experimental synthesis of the screened materials is reported, except for CdSiSb2, which was found to be unstable in our calculation. The absorption coefficient of the screened materials, especially ZnGeAs2, was high enough to make thin-film solar cells. The higher stacking fault energy in ZnGeAs2 than the others is consistent with the larger formation energy difference between the 2H and 3C polymorphs.