Boosting Open‐Circuit Voltage to a Record 0.692 V in Solution‐Processed CIGSSe Solar Cells Through Surface Ga‐Rich Engineering
Shuxia Wei, Xuejun Xu, Zongjie Su, Hongyi Lu, Yue Liu, Han Xu, Qianqian Gao, Yunfeng Wang, Ming Li, Tianyu Xing, Siyu Wang, Haoran Li, Li Wu, Yi ZhangABSTRACT
The open‐circuit voltage ( V OC ) deficit remains a primary bottleneck hindering the efficiency of solution‐processed Cu(In,Ga)(S,Se) 2 (CIGSSe) solar cells, largely due to the uncontrolled elemental diffusion during high‐temperature selenization that prevents the formation of a beneficial bandgap gradient. Here, we propose a novel and highly effective low‐temperature surface treatment strategy to overcome this long‐standing challenge. By spin‐coating a gallium‐thiourea complex solution onto the pre‐fabricated CIGSSe absorber, we construct a strategic Cu‐poor, Ga‐rich surface layer. Such design widens the surface bandgap, leading to an optimized band alignment at the CIGSSe/CdS heterojunction with a reduced conduction band offset (0.15 eV) and an enlarged valence band offset (1.13 eV). This synergistic effect drastically suppresses interface recombination. As a consequence, we achieve a champion device with a V OC of 0.692 V—the highest value reported to date for solution‐processed CIGSSe—and a power conversion efficiency of 16.65% (17.93% with an MgF 2 anti‐reflection layer). This work presents a simple yet powerful pathway for targeted front interface engineering, paving the way for high‐efficiency, low‐cost chalcopyrite photovoltaics.