Control of the Preferred Orientation of Cu(In,Ga)Se₂Thin Film by the Surface Modification of Mo Film

Orientation control of Cu(In,Ga)Se 2 (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 MoSe 2 layer was formed on the (110)-oriented Mo film and a randomly oriented MoSe 2 layer was formed on the (221)-oriented Mo film. We found that a (112)-oriented CIGS film was grown on the (002)-oriented MoSe 2 surface, while a (220)/(204)-oriented CIGS film was grown on the randomly oriented MoSe 2 surface. The orientation of the MoSe 2 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, MoSe 2 , (In,Ga) 2 Se 3 and Cu(In,Ga)Se 2 films in a three-stage co-evaporation process is examined and discussed.