Crystal structure and electronic structure of quaternary semiconductors Cu$_2$ZnTiSe$_4$ and Cu$_2$ZnTiS$_4$ for solar cell absorber

TL;DR

This study introduces two new quaternary semiconductors, Cu$_2$ZnTiSe$_4$ and Cu$_2$ZnTiS$_4$, analyzing their crystal and electronic structures to evaluate their potential as solar cell absorbers.

Contribution

It provides a systematic first-principles analysis of the crystal and electronic structures of these new materials, identifying their suitable band gaps and high absorption coefficients for solar applications.

Findings

Band gaps originate from Cu 3d and Ti 3d orbitals.

Kesterite structure confirmed as ground state.

Materials exhibit high absorption coefficients.

Abstract

We design two new I2-II-IV-VI4 quaternary semiconductors Cu$_2$ZnTiSe$_4$ and Cu$_2$ZnTiS$_4$, and systematically 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$_2$ZnTiSe$_4$ and Cu$_2$ZnTiS$_4$ originate from the full occupied Cu 3$d$ valence band and unoccupied Ti 3$d$ conducting band, and kesterite structure should be the ground state. Furthermore, our calculations indicate that Cu$_2$ZnTiSe$_4$ and Cu$_2$ZnTiS$_4$ have comparable band gaps with Cu$_2$ZnTSe$_4$ and Cu$_2$ZnTS$_4$, but almost twice larger absorption coefficient $\alpha(\omega)$. Thus, the materials are expected to be candidate materials for solar cell absorber.