Control of the Preferred Orientation of Cu(In,Ga)Se2 Thin Film by the Surface Modification of Mo Film

Abstract

Orientation control of Cu(In,Ga)Se2 (CIGS) thin film could be critical to achieve conversion efficiency of CIGS solar cells that exceeds 20%. The preferred orientation of CIGS thin film is investigated here by modifying the surface of an underlying Mo film. The orientation and surface morphology of the Mo film were modified by varying the deposition pressure during the sputtering process. The Mo surface showed a (110)-preferred orientation at low deposition pressures and a (221)-preferred orientation at high deposition pressures. With a Se pretreatment at 400°C, a strong (002)-oriented MoSe2 layer was formed on the (110)-oriented Mo film and a randomly oriented MoSe2 layer was formed on the (221)-oriented Mo film. We found that a (112)-oriented CIGS film was grown on the (002)-oriented MoSe2 surface, while a (220)/(204)-oriented CIGS film was grown on the randomly oriented MoSe2 surface. The orientation of the MoSe2 layer that was dependent on the surface morphology of the Mo film played a role in determining the preferred orientation of the CIGS thin film. The sequential progress of the orientation development of Mo, MoSe2, (In,Ga)2Se3 and Cu(In,Ga)Se2 films in a three-stage co-evaporation process is examined and discussed.