Band structures of Cu2nSnS4 and Cu2nSnSe4 from many-body methods

TL;DR

This study employs advanced many-body GW methods to accurately compute the band structures of Cu2ZnSnS4 and Cu2ZnSnSe4, highlighting the importance of non-local exchange-correlation effects and assessing the reliability of approximate methods.

Contribution

It provides a detailed comparison of self-consistent GW results with hybrid functionals and GGA+U, revealing discrepancies in band-edge corrections affecting defect level predictions.

Findings

Self-consistent GW yields more accurate quasiparticle states.

Hybrid functionals can reproduce band gaps but misestimate band-edge positions.

Non-local exchange-correlation effects are crucial for structural and electronic accuracy.

Abstract

We calculate the band structures of kesterite and stannite Cu2ZnSnS4 and Cu2ZnSnSe4, using a state-of-the-art self-consistent GW approach. Our accurate quasiparticle states allow to discuss: the dependence of the gap on the anion displacement; the key-role of the non-locality of the exchange-correlation potential to obtain good structural parameters; the reliability of less expensive hybrid functional and GGA+U approaches. In particular, we show that even if the band gap is correctly reproduced by hybrid functionals, the band-edge corrections are in disagreement with self-consistent GW results, which has decisive implications for the positioning of the defect levels in the band gap.