Possibility of Doping Cu Ga Se 2 n -Type by Hydrogen

Copper-indium-gallium-selenide (CIGS) alloys are successfully applied in thin-film solar cells. For a better use of the solar spectrum, they also offer the possibility of multijunction devices by tuning the composition in the different layers. As-grown CIGS is intrinsically p-type due to copper vacancies (${V}_{\mathrm{Cu}}$), but n-type doping is also useful for applications. While ${\mathrm{Cu}\mathrm{In}\mathrm{Se}}_{2}$ can be easily turned n-type, ${\mathrm{Cu}\mathrm{Ga}\mathrm{Se}}_{2}$ cannot, and this represents a problem, because increasing the band gap of CIGS requires a high $\mathrm{Ga}/\mathrm{In}$ ratio. Investigating the effect of hydrogen on ${\mathrm{Cu}\mathrm{Ga}\mathrm{Se}}_{2}$ by an optimized hybrid functional, we show that hydrogenation from an atomic source, such as, e.g., by a hydrogen plasma treatment, can turn the material n-type due to the formation of shallow donor ${V}_{\mathrm{Cu}}+2\mathrm{H}$ complexes, while ${\mathrm{H}}_{2}$ implantation, producing an internal hydrogen reservoir, can be used to produce semi-insulating material. We also show that under normal process conditions, unintentional hydrogen incorporation does not have a significant effect on ${\mathrm{Cu}\mathrm{Ga}\mathrm{Se}}_{2}$.