Novel Donor–Acceptor Random Copolymers Containing Phenanthrocarbazole and Diketopyrrolopyrrole for Organic Photovoltaics and the Significant Molecular Geometry Effect on Their Performance

A series of donor–acceptor (D–A) random copolymers PPC-T-DPP and PPC-TT-DPP based on electron-rich 6H-phenanthro[1;10,9,8-cdefg]carbazole (PC) and electron-deficient 3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (DPP) building blocks with two different linking units, thiophene (T) and thieno[3,2-b]thiophene (TT), were successfully synthesized. All of the copolymers show excellent light absorption, and their photoelectric properties can be easily adjusted by tailoring the molar ratio of PC to DPP. Among the polymer solar cells (PSCs) based on the copolymers with T linking unit, the PPC-T-DPP_1/2 (the molar ratio of PC:DPP = 1:2):PC61BM ([6,6]-phenyl-C61-butyric acid methyl ester) based device achieves the best efficiency of 2.0%. After replacing T with TT, a slightly enhanced power conversion efficiency (PCE) of 2.2% is obtained from the PPC-TT-DPP_1/2:PC61BM-based device due to the better charge mobility of TT. However, with the addition of 1-chloronaphthalene (CN) to a volume ratio of 10%, ...