Behavior of $\mathbf{\Sigma 3}$ grain boundaries in \CISe\ and \CGSe\ photovoltaic absorbers as revealed by first-principles hybrid functional calculations

TL;DR

This study uses hybrid functional calculations to analyze extless 112 extgreater and extless 114 extgreater extless 3 extgreater grain boundaries in extless 1 extgreater CIGSe and CGSe, revealing their different impacts on electronic properties relevant for solar cells.

Contribution

It provides a detailed first-principles analysis of extless 3 extgreater grain boundaries in CIGSe and CGSe using hybrid functionals, clarifying their effects on electronic structure and device performance.

Findings

extless 3 extgreater GBs create gap states, but their impact varies between CIGSe and CGSe.

Band alignment and gap size changes mitigate defect effects in CIGSe.

extless 3 extgreater GBs are non-detrimental in CIGSe but harmful in CGSe.

Abstract

The inconclusive results of the previous first-principles studies on the \S3 \ grain boundaries (GBs) in \CISe\ reveal the importance of employing a method that can correctly describe the electronic structure of this solar-cell material. We have employed hybrid functional calculations to study the \S3 (112) and \S3 (114) GBs in \CISe\ and \CGSe. The electronic structure changes introduced by the formation of GBs are threefold: creation of gap states, shift in band edges, and alteration of bandgap sizes. Gap states commonly behave as recombination centers, but the band alignment and the change in the bandgap size induced by GBs mitigate the destructive effect of these states in \CISe. That means, \S3 \ GBs are not detrimental for the carrier transport in devices based on \CISe. Conversely, these GBs are destructive for the carrier transport in \CGSe. The different behaviors of the \S3 \ GBs in CISe and CGSe might be considered by experimentalists to optimize the device fabrication to achieve high-performance solar cells.