Indium-Gallium Segregation in CuIn$_{x}$Ga$_{1-x}$Se$_2$: An ab initio based Monte Carlo Study

TL;DR

This study uses ab initio Monte Carlo simulations to investigate indium-gallium segregation in CuIn$_x$Ga$_{1-x}$Se$_2$, revealing phase coexistence at low temperatures and persistent inhomogeneity in Ga-rich compositions, impacting solar cell efficiency.

Contribution

It provides the first detailed atomistic insight into temperature-dependent phase behavior and segregation in CIGS alloys using combined ab initio and Monte Carlo methods.

Findings

Phase coexistence occurs below room temperature.

Higher temperatures lead to more homogeneous alloys.

Ga-rich CIGS remains inhomogeneous over a wide temperature range.

Abstract

Thin-film solar cells with CuIn$_x$Ga$_{1-x}$Se$_2$ (CIGS) absorber are still far below their efficiency limit, although lab cells reach already 19.9%. One important aspect is the homogeneity of the alloy. Large-scale simulations combining Monte Carlo and density functional calculations show that two phases coexist in thermal equilibrium below room temperature. Only at higher temperatures, CIGS becomes more and more a homogeneous alloy. A larger degree of inhomogeneity for Ga-rich CIGS persists over a wide temperature range, which may contribute to the low observed efficiency of Ga-rich CIGS solar cells.