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New alternating copolymers based on benzo[1,2-b:4,5-b′]dithiophene and thieno[3,4-d]thiazole derivatives have been synthesized by using different combinations of side chains and spacers in order to study their effect on the optical, electrochemical and photovoltaic properties. Optical and electrochemical characterization were performed and the resulting copolymers exhibit optical bandgaps ranging from 1.66 to 1.80 eV, HOMO energy levels between −5.19 and −5.30 eV and LUMO energy levels between −3.60 and −3.72 eV. Photovoltaic devices were fabricated and characterized after a careful optimization of the active layer fabrication by using different solvents, additives and acceptors. Following this process, PCEs up to 4.4% were obtained.

We report the synthesis of new push-pull conjugated polymers for bulk heterojunction solar cells based on benzo[1,2-b:4,5-b′]dithiophene (push) and thieno[3,4-d]thiazole (TTz) (pull) derivatives. Stille polycondensation between distannyl-BDT derivatives with 4,6-dibromo-2-octylthieno[3,4-d]thiazole led to two alternating copolymers, namely PBDTTTz-1 and PBDTTTz-2, which have a bandgap of 1.8 and 1.7 eV, respectively. Both copolymers are stable in air with HOMO energy level of -5.3 eV for PBDTTTz-1 and -5.4 eV for PBDTTTz-2. Both copolymers have been tested in bulk heterojunction solar cells, and preliminary results (without any optimization process) show promising power conversion efficiency of 1.4% for PBDTTTz-1 and 1.7% for PBDTTTz-2. © 2011 American Chemical Society.

New alternating copolymers based on thieno[3,4-d]thiazole (TTz) derivatives were synthesized by Stille, Suzuki or direct (hetero)arylation polycondensation (DHAP) reactions using either benzodithiophene (BDT), dithienosilole (DTS), thieno[3,4-c]pyrrole-4,6-dione (TPD), diketopyrrolopyrrole-1,4-dione (DPP) or isoindigo units as comonomers. In particular, the direct hetero(arylation) polycondensation reaction has been shown to be a very interesting tool for a more efficient and economical access to new conjugated polymers. Modifications of the TTz moiety and of the polymer backbone show that it is possible to efficiently modulate the HOMO and LUMO energy levels of TTz-based copolymers. These conjugated polymers exhibit bandgaps between 1.07 and 1.82 eV with HOMO energy levels ranging from −5.06 to −5.48 eV and LUMO energy levels ranging from −3.61 to −4.02 eV.