Precursor Reaction Method With High Ga Cu(In,Ga)(S,Se)$_{2}$ to Achieve Increased Open-Circuit Voltage

Abstract

The precursor reaction process for the fabrication of Cu(In,Ga)Se $_{2}$ solar cells potentially allows for low-cost fabrication and scalable processing for manufacturing. Additionally, this process has yielded record efficiencies in lab-scale experiments. Thus far, research on the precursor reaction method has been restricted to relatively low Ga compositions with Ga/(In+Ga) $\approx$ 25%. By increasing the ratio of Ga, it is possible to increase the bandgap, and thus, increase the open-circuit voltage. This work develops and characterizes the precursor reaction process for use with Ga/(In+Ga) $\approx$ 50%, with the goal of improving the open-circuit voltage and efficiency. It is shown that with an increased Ga ratio, increased ${V}_{\rm oc}$ is achieved, but the rate of conversion from the precursor to absorber phases is decreased. Additionally, increased Ga improves the film adhesion at increased selenization temperatures as well as improving the film morphology.