SiOxNy back-contact barriers for CZTSe thin-film solar cells

The formation of molybdenum diselenide (MoSe 2 ) is widely observed at the back-contact interface for copper zinc tin selenide (CZTSe) thin-film solar cells. Depending on individual selenium (Se) supply and thermal conditions for forming CZTSe absorbers on molybdenum (Mo) substrates, the thickness of MoSe 2 can vary from a few hundreds of nanometers up to ≈ 1 μm, which is comparable to the commonly adopted thickness of 1 ~ 1.5 μm for CZTSe absorbers. In this study, for controlling the thickness of interfacial MoSe 2 , thin diffusion barrier layers of silicon oxynitride (SiO x N y ) are deposited onto Mo layers prior to the growth of CZTSe absorbers in the fabrication process. As a result, a reduction in the thicknesses of MoSe 2 layers is achieved. In terms of energy conversion efficiency ( η ), CZTSe solar cells grown on Mo/SiO x N y back contacts suffer a deterioration as the SiO x N y layers get thicker. CZTSe solar cells grown on Mo/SiO x N y /Mo back contacts preserve their efficiencies at ≈ 11% with thin 10 nm SiO x N y layers.