Improved carrier transport in CIGS solar cells induced by Ag treatment

Abstract In this work, to improve the performance of three-stage co-evaporated Cu(In,Ga)Se2 (CIGS) solar cells, a small amount of Ag was incorporated during the third stage, and the materials/device characteristics were investigated. Although the amount of added Ag was limited to less than 1 at%, both the film microstructure and the resulting device performance were affected. The Ag-alloyed CIGS thin films exhibited enhanced recrystallization and homogenous Ag distribution throughout the CIGS film bulk, even though the Ag incorporation was performed near the end of the three-stage co-evaporation process. Well-controlled Ag alloying into CIGS solar cells (approximately 0.6 at%) led to increased fill factors, accompanied by increased charge carrier densities as well as reduced detrimental state densities. The approach performed in the present work suggests that the device quality of CIGS solar cells can be tuned by small Ag additions in a similar manner to extrinsic alkali incorporation.