Alkali Metal Pretreatment for Precise Na Doping and Voc Improvement in CIGS Thin-Film Solar Cells.

The pretreatment of the Cu(In,Ga)Se2 (CIGS) absorption layer using an alkali element can effectively improve the photoelectric conversion efficiency (PCE) of CIGS solar cells. Here, we propose using NaF layer pretreatment below the CIGS absorption layer deposited by a three-stage process. Sodium ions in NaF can effectively suppress the diffusion of Ga elements and form a steep gradient backscatter layer on the back of the CIGS absorption layer, thereby passivating solar cell defects, inhibiting carrier recombination, promoting carrier transmission and collection, improving open circuit voltage (VOC), short circuit current (Jsc), and filling factor (FF), and further improving the PCE.