Accurate band gaps for earth-abundant photovoltaic absorber from density functional theory

First-principles calculations of the electronic and optical properties of Cu₂ZnSnSe₄ (CZTSe) and Cu₂ZnSnS₄ (CZTS) are simulated within the framework of the Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) a sufficiently adequate approach, namely self-interaction-corrected local-density-approximation (SIC-LDA) exchange correlation potential is employed for calculating the energy band gap and electronic structure of Cu₂ZnSnSe₄ and Cu₂ZnSnS₄ based solar cells systems. This work presents detailed information about total and atom projected density of states functions, for different atoms in Cu₂ZnSnSe₄ and Cu₂ZnSnS₄. We show that density functional theory is a very powerful tool for: studying the local doping effects, defects effect, size and disorder effect on optical and electronic properties of these materials, and predicting properties of new materials.