Impact of roll-over-shaped current-voltage characteristics and device properties of Ag(In,Ga)Se2 solar cells

The roll-over shape often observed in the current-voltage curve of Ag(In,Ga)Se-2 (AIGS) solar cells degrades the open circuit voltage (V-OC) and particularly the fill factor (FF). The origin of the roll-over shape was investigated by experimental measurements and device simulation. By combining AC Hall measurement and the peel-off process, we estimated the AIGS hole concentration to be 2.2 x 10(12) cm(-3). Theoretical simulation revealed that the roll-over shape is attributed to this low hole concentration. Under an applied forward bias, the band bending near the back contact of the AIGS layer forms an intrinsic semiconductor owing to the injected electrons, leading to the formation of an inverted diode. To solve this issue, the addition of NaF by the postdeposition treatment of the AIGS layer was performed. As a result, the hole concentration of the AIGS layer increased, significantly improving its VOC, FF, and conversion efficiency. (C) 2017 The Japan Society of Applied Physics