Control of conduction band offset in wide-gap Cu(In,Ga)Se2 solar cells

The effects of conduction band offset of window/Cu(In,Ga)Se2 (CIGS) layers in wide-gap CIGS based solar cells are investigated. In order to control the conduction band offset, a Zn1−xMgxO film was utilized as the window layer. We fabricated CIGS solar cells consisting of an ITO/Zn1−xMgxO/CdS/CIGS/Mo/glass structure with various CIGS band gaps (Eg≈0.97–1.43 eV). The solar cells with CIGS band gaps wider than 1.15 eV showed higher open circuit voltages and fill factors than those of conventional ZnO/CdS/CIGS solar cells. The improvement is attributed to the reduction of the CdS/CIGS interface recombination, and it is also supported by the theoretical analysis using device simulation.