Influence of the selenium flux on the growth of Cu(In,Ga)Se2 thin films

Abstract In order to control the selenium to metal flux ratio (SMR) during the co-evaporation process for the fabrication of Cu(In,Ga)Se 2 (CIGS) thin films, we establish a new method for the determination of the fluxes. CIGS absorber layers prepared at varying SMRs exhibit either metal rich (at SMR⩽1.5) or Na-rich (SMR=4.5) segregations, which limit the performance of the cells, and thereby define a minimum SMR needed to obtain good quality material. This minimum SMR and, therefore, the overall selenium consumption are lower when using fast processes. A systematic study on the texture of absorber layers prepared by three stage processes shows that increasing the selenium flux leads towards a (2 2 0/2 0 4) orientation, while either a high Na supply (NaF precursor) or a lack of Na (Na-barrier layer) promotes the (1 1 2) orientation.