First-principles analysis of the intermediate band in CuGa$_{1-x}$Fe$_x$S$_2$

TL;DR

This study uses first-principles calculations to analyze how Fe doping in CuGaS2 creates intermediate bands that enhance solar cell absorption, revealing effects of doping concentration and impurity clustering.

Contribution

It provides detailed insights into the electronic, magnetic, and optical effects of Fe doping in CuGaS2 using hybrid DFT, advancing understanding for IB solar cell development.

Findings

Fe doping creates unoccupied states 1.6-1.9 eV above the valence band.

Intermediate bands enhance optical absorption at lower energies.

Fe impurities tend to cluster and favor antiferromagnetic order.

Abstract

We present a comprehensive study of the electronic, magnetic, and optical properties of CuGa$_{1-x}$Fe$_x$S$_2$, as a promising candidate for intermediate-band (IB) solar cells. We use hybrid exchange-correlation functional within the density functional theory framework, and show that Fe doping induces unoccupied states 1.6-1.9 eV above the valence band. The IBs significantly enhance the optical absorption in lower energy part of the spectrum. We find that at moderate $n$-type co-doping concentration, the added charge occupies part of the IB in the gap, but large concentrations lower the energy of the occupied IB toward the valence band. Moreover, we show that Fe impurities tend to cluster within the compound and they choose antiferromagnetic ordering. The findings can have a significant effect in understanding this material and help to synthesize more efficient IB solar cells.