(91)A Benzo[1,2-b:4,5-b′]Benzo[1,2-b:4,5-b′]dithiophene-Based copolymer with deep HOMO level for Efficient solar cells, Pengfei Li, Shanpeng Wen , Weidong Cheng, Jibo Zhang, Shiyu Yao, Bin Xu, Wenjing Tian*, Sol. Energy Mater. Sol. Cells., 2012, 100, 239-245