Improved carrier transport in CIGS solar cells induced by Ag treatment

•Small amounts of Ag were incorporated into three-stage co-evaporated CIGS solar cells.•Ag homogenization occurred and alkali profiles were affected.•Ag-alloyed CIGS solar cells exhibited superior performance relative to that of cells without Ag alloying.•Ag alloying resulted in an increased charge density and a reduced detrimental state density.