Band gap control via tuning of inversion degree in CdIn$_2$S$_4$ spinel

TL;DR

This study proposes a method to control the band gap in CdIn₂S₄ spinel by tuning the inversion degree through synthesis conditions, supported by ab initio calculations showing the impact on electronic properties.

Contribution

It introduces a theoretical approach linking synthesis parameters to inversion degree and band gap tuning in CdIn₂S₄, a promising photovoltaic material.

Findings

Inversion degree correlates with synthesis temperature and cooling rate.

Adjusting synthesis conditions can tune the material's band gap.

Theoretical calculations confirm the sensitivity of band gap to inversion degree.

Abstract

Based on theoretical arguments we propose a possible route for controlling the band-gap in the promising photovoltaic material CdIn$_2$S$_4$. Our \textit{ab initio} calculations show that the experimental degree of inversion in this spinel (fraction of tetrahedral sites occupied by In) corresponds approximately to the equilibrium value given by the minimum of the theoretical inversion free energy at a typical synthesis temperature. Modification of this temperature, or of the cooling rate after synthesis, is then expected to change the inversion degree, which in turn sensitively tunes the electronic band-gap of the solid, as shown here by accurate screened hybrid functional calculations.