Current Photovoltaic Research ISSN:2288-3274(Print) 2508-125X(Online)

High-efficiency in Cu(In,Ga)Se₂ (CIGS) solar cells were usually achieved on soda-lime glass substrates due to Na incorporation that reduces deep-level defects. However, this supply of sodium from sodalime glass to CIGS through Mo back electrode could be limited at low deposition temperature. Na content could be more precisely controlled by supplying Na from known amount of an outside source. For the purpose, an Na₂S layer was deposited on Mo electrode prior to CIGS film deposition and supplied to CIGS during CIGS film. With the Na₂S underlayer a more uniform component distribution was possible at 350°C and efficiency was improved compared to the cell without Na₂S layer. With more precise control of bulk and surface component profile, CIGS film can be deposited at low temperature and could be useful for flexible CIGS solar cells.