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Cu2ZnSnSxO4-x and Cu2ZnSnSxSe4-x: First principles simulations of optimal alloy configurations and their energies

Chaochao Dun, N. A. W. Holzwarth, Yuan Li, Wenxiao Huang, and David L. Carroll, Journal of Applied Physics 115, 193513 (2014) Local copy

With the aim of exploring oxidation and selenization of the photovoltaic material Cu2ZnSnS4,we used first principles methods to study the structure and stability of Cu2ZnSnSxO4-x and Cu2ZnSnSxSe4-x alloys for 0 ≤ x ≤ 4. Pure Cu2ZnSnO4 was found to have the lowest heat of formation, followed by Cu2ZnSnS4, and finally Cu2ZnSnSe4. This suggests that oxidization is very likely to occur, whereas selenization can only be accomplished under high temperature. For the alloys, the energetically favorable chalcogen configurations are very different for oxygen and selenium. While the energies of the selenium alloys are insensitive to the distribution of S and Se configurations, the lowest energy oxygen alloys have alternating S and O sites in the a-b planes. In considering the heats of formation of the Cu2ZnSnSxO4-x alloys, we find that they are unstable with respect to decomposition into binary oxides and sulfdes except for small concentrations of O. Our results also show that it is energetically more favorable to sulfurize Cu2ZnSnSe4 than to selenize Cu2ZnSnS4.