In this study, an Na source was integrated into the back contact stack, which is a MoNa layer. MoNa layers with varying thicknesses were deposited on Al2O3 substrate as intermediate layers of an Mo back contact by DC magnetron sputtering of a Mo-10 at% Na target. We examined the effect of MoNa thickness on the standard production of Cu(In, Ga)Se2 (CIGS) solar cell fabricated using three-stage evaporation. The structure of the MoNa layer was composed of fibers with considerably small grain size (~5 nm). By contrast, the Mo layer presented a columnar structure with relatively large grain size. The Na concentration in the CIGS absorber can be adjusted by varying the thickness of the MoNa layer. Cell efficiency was heavily raised from 2.08% to 11.7% using MoNa layer as Na source. However, the enhanced deliquescence property with MoNa thickness limited further improvement in cell efficiency.
