Analysis of Atomic and Electronic Structures of Cu₂ZnSnS₄ Based on First-Principle Calculation

Atomic and electronic structures of Cu₂ZnSnS₄ (CZTS) are discussed on the basis of the first-principle pseudopotential method. CZTS is usually assumed to have the stannite or kesterite structure, but one can consider three other structures under the condition that a S atom is bonded to two Cu, one Zn, and one Sn atom. For each of the five structures, the lattice constants and atom positions are optimized, and the total energy and density of states are calculated. The energy difference per atom between the structures is smaller than the thermal energy at room temperature, and therefore, CZTS is expected to be composed of five phases with different crystal structures. X-ray diffraction patterns simulated on the basis of the calculation results are consistent with the experimental results.