Characterization of an In2Se3 Passivation Layer for CIGS Solar Cells with Cd-free Zn-containing Atomic-layer-deposited Buffers

Abstract

Even though above 22% efficiencies have been reported in Cd-free Cu(In,Ga)Se2 (CIGS) solar cell with Zn-containing buffers, the efficiencies with Zn-containing buffers, in general, are well below 20%. One of the reasons is Zn diffusion from the Zn-containing buffer layer to CIGS film during buffer growth. To avoid the degradation, it is necessary to prevent the diffusion of Zn atoms from Zn-containing buffer to CIGS film. For the purpose, we characterized an In2Se3 film as a possible diffusion barrier layer because In2Se3 has no Zn component. It was found that an In2Se3 layer grown at 300°C was very effective in preventing Zn diffusion from a Zn-containing buffer. Also, the In2Se3 had a large potential barrier in the valence band at the In2Se3/CIGS interface. Therefore, In2Se3 passivation has the potential to achieve a super-high efficiency in CIGS solar cells that employ Cd-free ALD processed buffers containing Zn.