First principles calculation of the electronic properties and lattice dynamics of Cu 2ZnSn(S 1-xSe x) 4

Using density functional theory, we calculated the electronic structure, the lattice dynamics, and the Raman spectra of Cu2ZnSn(S1-xSex)(4), (CZTSSe) an emerging photovoltaic material for thinfilm solar cells. In particular, we investigated the effects of the local arrangement of S and Se within the unit cell on the electronic properties of these materials. We find that the S-to-Se ratio (e. g., x) and the spatial distribution of the anions in the unit cell can significantly alter the band structure. In particular, the S-to-Se ratio and anion distribution determine the energy splitting between the electronic states at the top of the valence band and the hole mobility in CZTSSe alloys and solar cells. Moreover, we find that x-ray diffraction patterns and phonon dispersion curves are sensitive to the local anion ordering. The predicted Raman scattering frequencies and their variation with x agree with experimentally determined values and trends.