Synthesis and Photovoltaic Characterization of Dithieno[ 3,2-b: 2', 3'-d] thiophene-Derived Narrow-Bandgap Polymers

Three novel dithieno[3,2-b:2',3'-d]thiophene-based low-bandgap polymers are synthesized by a Suzuki-Miyaura coupling reaction or by direct arylation polycondensation. The polymers present a high molecular weight (26-32 kDa) and narrow polydiversity (1.3-1.7). With a highest occupied molecular orbital (HOMO) energy level around -5.20 eV, these polymers exhibit a narrow bandgap of 1.75-1.87 eV. All the polymers display strong absorption in the range of 350-700 nm. Bulk-heterojunction (BHJ) solar cells are further fabricated by blending the as-prepared polymer with (6,6)-phenyl-C-61-butyric acid methyl ester (PC61BM) at different weight ratios. The best devices contribute a power conversion efficiency (PCE) of 0.73% under AM 1.5 (100 mW cm(-2)).