First-principles Study of Cu2ZnSnS4 Photovoltaic Absorber

The quaternary semiconductor Cu2ZnSnS4 (CZTS) is a relatively new photovoltaic material whose constituents are non-toxic and abundant in the earth's crust. The highest conversion efficiency reported so far is 6.7{\%}, demanding further improvement. The key computational issue is to predict optical properties as accurate as possible, which is not possible using conventional semi-local density functionals. To this end, we have employed the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional as implemented in the Vienna Ab-initio Simulation Packages (VASP) code, which allows us to obtain results in good agreement with the experimental data for the lattice constants and the band gap of CZTS [1]. We then predicted optical properties and determined the dominant optical transitions for solar-light absorption. The defect formation energies of CZTS were also calculated in the allowed range of the chemical potentials bound by the precipitation conditions of the metal-sulfides. \\[4pt] [1] J. Paier et al., Phys. Rev. B 79 115126 (2009).