High-Pressure Behavior and Disorder for Ag₂ZnSnS₄ and Ag₂CdSnS₄

Abstract

We carried out first-principles\ncalculations to simulate Ag₂ZnSnS₄ and Ag₂CdSnS₄ and\ncalculated enthalpies of different plausible structural models (kesterite-type,\nstannite-type, wurtzkesterite-type, wurtzstannite-type, and GeSb-type)\nto identify low- and high-pressure phases. For Ag₂ZnSnS₄, we predict the following transition: kesterite-type→[8.2GPa]→\nGeSb-type. At the transition pressure, the electronic structure changes\nfrom semiconducting to metallic. For Ag₂CdSnS₄, we cannot decide which of the experimentally observed structures\n(kesterite-type or wurtzkesterite-type) is the ground-state structure\nbecause their energy difference is too small. At 4.7 GPa, however,\nwe predict a transition to the GeSb-type structure with metallic character\nfor both structures. Regarding the sensitivity of the material to\ndisorder, a major drawback for solar cell applications, Ag₂CdSnS₄ behaves similar to Cu₂ZnSnS₄, both showing a high tendency to cationic disorder. In contrast,\nthe disordered structures in Ag₂ZnSnS₄ are much\nhigher in energy, and therefore, the material is less affected by\ndisorder.