Effect of cesium for Cu(In,Ga)Se2 and Cu(In,Ga)(S,Se)2 films studied by depth-resolved XAFS

Alkali metal treatment is an indispensable technology for obtaining highly efficient CuInSe2 (CIS) solar cells. This study evaluated the structural change of Cu(In,Ga)Se-2 (CIGSe) and Cu(In,Ga)(S,Se)(2) (CIGSSe) films with and without the CsF post-deposition treatment (CsF-PDT) (for CIGSe) and Cs treatment (for CIGSSe) by the Se K-edge depth-resolved X-ray absorption fine structure. The CIGSe films were deposited by a three-stage process, and the CIGSSe films were deposited by the sulfurization after the selenization method. Although CsF-PDT can re-form the surface of CIGSe film, the Cs treatment cannot modify the surface of the CIGSSe film. Our result suggests that the improvement is due to not only the surface reforming but also an effect on the inside of the CIGSe and CIGSSe films. This study provides useful information for the preparation of highly efficient CIS solar cells.