IntrinsicDXCenters in Ternary Chalcopyrite Semiconductors

In III-V and II-VI semiconductors, certain nominally electron-donating impurities do not release electrons but instead form deep electron-traps known as “$DX$ centers.” While in these compounds, such traps occur only after the introduction of foreign impurity atoms, we find from first-principles calculations that in ternary $\mathrm{I}\mathrm{\text{−}}\mathrm{III}\mathrm{\text{−}}{\mathrm{VI}}_2$ chalcopyrites like ${\mathrm{CuInSe}}_2$ and ${\mathrm{CuGaSe}}_2$, $DX$-like centers can develop without the presence of any extrinsic impurities. These intrinsic $DX$ centers are suggested as a cause of the difficulties to maintain high efficiencies in ${\mathrm{CuInSe}}_2$-based thin-film solar-cells when the band gap is increased by addition of Ga.