Growth of Cu(In,Ga)Se 2 thin films by coevaporation using alkaline precursors

Abstract CIGS layers were grown using NaF and LiF precursor layers with different thicknesses deposited on top of the Mo back contact layer prior to the CIGS deposition. The substrates were soda lime glass with and without Na diffusion barriers. Two types of barriers were used, silica and alumina. The CIGS layers were analysed structurally with SEM, TEM and XRD, and solar cell devices were prepared. We found improvements in grain structure, film texture and surface flatness when NaF precursor layers were used as compared to Na-free and Na-poor samples. Also electrically we found that the solar cell efficiency increased with modest additions of Na. Changes in film morphology saturated at an NaF thickness of 30 A and the solar cell efficiency saturated with an NaF precursor thickness of about 100 A. NaF precursor layers were also used at lower deposition temperatures and we observed improved solar cell efficiencies using the NaF precursor layer, even at substrate temperatures as low as 310°C.