Novel Phenanthrocarbazole Based Donor-Acceptor Random and Alternating Copolymers for Photovoltaics

A series of 6H-phenanthro[1,10,9,8-cdefg]carbazole (PC) and benzothiadiazole (BT) based donor-acceptor (D-A) random copolymers PPC-T-BT_3/1, PPC-T-BT_2/1, PPC-T-BT_1/1, PPC-T-BT_1/2, and PPC-T-BT_1/3 were easily prepared by varying the molar ratio of PC to BT from 3:1, 2:1, 1:1, 1:2, to 1:3, respectively. The corresponding alternating D-A copolymer poly{6H-phenanthro[1,10,9,8-cdefg]carbazole-alt-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole} (PPCDTBT) was also synthesized for comparison. Compared with PPCDTBT, PPC-T-BT_1/1, PPC-T-BT_1/2, and PPC-T-BT_1/3 obtained more pronounced intramolecular charge transfer band and extended absorption. Power conversion efficiency of these copolymer-based devices strongly depends on the D/A molar ratio, related to the spectrum absorption and active layer morphology. Among the polymer solar cells based on random copolymers, PPC-T-BT_2/1:PC61BM based device achieved the best efficiency of 1.9%, which is close to the efficiency of PPCDTBT:PC61BM based device (2.3%). Therefore, it is concluded that the random copolymer can achieve the comparable performance to alternating copolymer by precisely adjusting the D/A molar ratio on small scales. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4885-4893