Critical issues for Cu(InAl)Se/sub 2/ thin film solar cells

Cu(InAl)Se/sub 2/ thin film solar cells have been demonstrated with 16.9% efficiency using an absorber layer with Al/(In+Al)=0.13 giving a bandgap of 1.16 eV. However, the cell efficiency decreased as the Cu(InAl)Se/sub 2/ bandgap increased up to 1.7 eV. A critical development for these cells was the inclusion of a 5 nm thick Ga seed layer to improve the adhesion between the Cu(InAl)Se/sub 2/ and the Mo back contact. In this paper, critical issues for Cu(InAl)Se/sub 2/ thin film solar cells will be discussed, focusing on the film adhesion, and solar cell behavior with increasing bandgap. The effects of different flux-temperature-time profiles used for the elemental evaporation of Cu(InAl)Se/sub 2/ films, and different back contact structures will be characterized with respect to film morphology, structure, and adhesion, and to device behavior for Cu(InAl)Se/sub 2/ films with bandgaps from 1.1 to 1.5 eV. Finally, the prospects for Cu(InAl)Se/sub 2/ as the absorber layer in wide bandgap solar cells will be reviewed.