Synergistic reflective back contact and absorber engineering for high-efficiency ultrathin Cu(In,Ga)Se 2 solar cells

Ultrathin Cu(In,Ga)Se 2 (CIGS) solar cells offer a promising route to reducing material consumption while maintaining the advantages of high-efficiency thin-film photovoltaics.However, reducing the absorber thickness leads to incomplete light absorption and limits device performance. Here, we develop a reflective back contact (RBC) architecture to enhance light trapping in a 600 nm-thick CIGS absorber. Device performance was further improved by tailoring the CIGS deposition process and applying a 15 min RbF post-deposition treatment, leading to enhanced optoelectronic properties. The resulting devices reach a power conversion efficiency of 15.8%, which, to the best of our knowledge, represents the highest reported efficiency for a CIGS solar cell with an absorber thickness of approximately 600 nm. These results demonstrate a pathway to high-efficiency ultrathin CIGS solar cells through the combination of optical engineering, alkali treatment, and absorber growth control.