Crystal structure and electronic structure of quaternary semiconductors Cu ₂ZnTiSe ₄ and Cu ₂ZnTiS ₄ for solar cell absorber

We design two new I2-II-IV-VI4 quaternary semiconductors Cu ₂ZnTiSe ₄ and Cu ₂ZnTiS ₄, and study the crystal and electronic structure by employing first-principles electronic structure calculations. Among the considered crystal structures, it is confirmed that the band gaps of Cu ₂ZnTiSe ₄ and Cu ₂ZnTiS ₄ originate from the full occupied Cu 3d valence band and unoccupied Ti 3d conducting band, and kesterite structure should be the ground state. Furthermore, our calculations indicate that Cu ₂ZnTiSe ₄ and Cu ₂ZnTiS ₄ have comparable band gaps with Cu ₂ZnTSe ₄ and Cu ₂ZnTS ₄, but almost twice larger absorption coefficient α(ω). Thus, the materials are expected to be candidate materials for solar cell absorber.