Bandgap optimization of submicron-thick Cu(In,Ga)Se2 solar cells

Reducing Cu(In,Ga)Se-2 (CIGS) absorber thickness into submicron regime provides an opportunity for reducing CIGS solar cell manufacturing time and cost. However, CIGS with submicron-thick absorber would suffer strong absorption loss in the long-wavelength region. In this paper, we report a new fabrication route for CIGS solar cells on soda-lime glass substrates with different Ga content (0.3<[Ga]/([Ga]+[In])<0.6), all with absorber thicknesses around 0.9 mu m. Efficiency of 17.52% has been achieved for cells with high Ga content of [Ga]/([Ga]+[In])=41%, which is currently the best reported efficiency for submicron-thick CIGS solar cells. Unlike the normal-thickness absorber (2-3 mu m) that has an optimal [Ga]/([Ga]+[In]) of similar to 32%, the increased value of optimal [Ga]/([Ga]+[In]) in submicron-thick absorber greatly enhances the open-circuit voltage, by nearly 15% compared with that of samples with Ga content optimized at normal absorber thickness. This large gain in V-OC well compensates the absorption loss in the long-wavelength region and contributes to the enhancement of final solar cell efficiency. Copyright (c) 2014 John Wiley & Sons, Ltd.