Over 28% Efficiency Perovskite/Cu(InGa)Se2 Tandem Solar Cells: Highly Efficient Sub-cells and Their Bandgap Matching Xinxing Liu, Junjun Zhang, Liting Tang, Junbo Gong, Wang Li, Zexin Tu, Yanyan Li, Ruiming Li, Xuzhi Hu, Chen Shen, He Wang, Zhiping Wang, Qianqian Lin, Guojia Fang, Sheng Wang, Chang Liu, Zengming Zhang, Jianmin Li and Xudong Xiao Abstract Perovskite/Cu(InGa)Se2 (PSC/CIGS) tandem configuration is an attractive way to achieve an ultra-high efficient and cost-effective...