Effects of Mo surface oxidation on Cu(In,Ga)Se₂ solar cells fabricated by three-stage process with KF postdeposition treatment

The surface oxidation condition of the Mo back contact on a soda lime glass (SLG) substrate was varied by air annealing and chemical etching. Then, the evolution of a photovoltaic property was studied for Cu(In,Ga)Se 2 (CIGS) solar cells grown by a three stage process with KF postdeposition treatment. Upon the removal of the oxidized layer from the Mo surface by chemical etching, the c -axis orientation of MoSe 2 tended to be random, whereas the c -axis was perpendicular when the Mo surface was oxidized. An enhancement of the diffusion of Na and K from SLG to CIGS was observed upon removing the molybdenum oxide, which functions as a barrier to alkali-metal diffusion. The varied orientation of MoSe 2 can also affect the alkali-metal diffusion kinetics. The open-circuit voltage ( V OC ) markedly increased after removing the oxidized layer from the Mo surface, mainly as a result of an increase in carrier density in CIGS.