Optical approaches to improve the photocurrent generation in Cu(In,Ga)Se₂ solar cells with absorber thicknesses down to 0.5 μm

Improving the optical management is a key issue for ultrathin based solar cells performance. It can be accomplished either by trapping the light in the active layer or by decreasing the parasitic absorptions in the cell. We calculate the absorption of the different layers of Cu(In,Ga)Se₂ (CIGSe) based solar cell and propose to increase the absorption in the CIGSe layer by optimizing three parameters. First, by increasing the transmitted light to the cell using a textured surface of ZnO:Al front contact which functions as a broadband antireflection layer. Second, by replacing the CdS/i-ZnO buffer layers with ZnS/ZnMgO buffer layers which have higher energy bandgaps. Third, by replacing the Mo back contact with a higher reflective metal, such as silver or gold. Calculations show that modifying these layers improves the total absorption by 32 in a 0.5 μm thick CIGSe absorber. These predicted improvements of the short circuit current are confirmed experimentally.