Synthesis and Characterization of New Poly(thieno[3,4-d]thiazole) Derivatives for Photovoltaic Applications

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.