A Novel Planar D-A Alternating Copolymer with D-A Integrated Structures Exhibiting H-Aggregate Behaviors for Polymer Solar Cells

With the D-A integrated structure concept, a new donor-acceptor (D-A) copolymer poly{(N-dodecyl-carbazole[3,4-c: 5,6-c]bis[1,2,5] thiadiazole-alt-4,8-di(2-ethylhexy-loxyl) benzo[1,2-b: 4,5b'] dithiophene)} has been designed and synthesized using a novel architecture N-dodecyl-carbazole[3,4-c: 5,6-c] bis[1,2,5] thiadiazole, and di(2-ethylhexy-loxyl) benzo[1,2-b: 4,5-b'] dithiophene) as the basic building blocks. The copolymer has a low-lying highest occupied molecular orbital energy level of -5.41 eV and a broaden absorption matching well with the main solar photon flux. Note that an H-aggregation beneficial for charge transportation and collection is formed in the macromolecules film, which implies that the planar D-A integrated structure favors the strong intermolecular interaction to render molecules aggregated via face-to-face self-assembly. The aggregation becomes larger scale after thermal annealing. Additionally, obvious intramolecular charge transfer and energy transfer have occurred in created D-A integration. Without any treatment, the resulting polymer achieved a efficiency of 2.0% and relatively high open-circuit voltage (V-oc) value of 0.77 V when blended with [6,6]-phenyl-C61-butyric acid methyl ester in a typical bulk heterojunction. (C) 2012 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 624-634