Fabrication of CIGS solar cells with a Na-doped Molayer on a Na-free substrate

The photovoltaic properties of CIGS cells on an alumina substrate were improved through the use of Na-doped Mo as the bottom layer of a Mo back contact. Na was supplied to the CIGS bulk region from an alumina/Na-doped Mo/Mo structure, similar to the Na diffusion from soda-lime glass. The diffusion of Na from the Na-doped Mo was controlled effectively compared to that from Soda-lime glass (SLG). The present results indicate that Na-doped Mo acts as a Na source material and that the Na amount can be controlled by adjustment of thickness of Na-doped Mo layer, without the use of an alkali barrier layer. The highest conversion efficiency of 13.34% (Jsc = 34.62 mA/cm2, Voc = 0.58 V and FF = 66%) for an active area of 0.45 cm2 on an alumina substrate was obtained for 100 nm Na-doped Mo/1000 nm Mo.