Tuning joint sequence for donor-acceptor polymers based on fluorinated benzothiadiazole with thiophene/furan bridecakes

Three new donoreacceptor (DeA) polymers, PTBDT-ffBT-FT12, PTBDT-ffBT-TT12 and PTBDT-ffBT-T12T, based on thiophene substituted benzene[1,2-b:4,5-b'] thiophene (TBDT) and fluorinated benzothiadiazole (ffBT) with thiophene/furan conjugated bridges were prepared. The joint sequence of alkyl thiophene/furan bridges has significant influence on the energy levels, band-gap and molecule stacking of the copolymers. All copolymers show broad absorption bands, and the energy level and band gap could be well fine-tuned by the introduction of thiophene/furan bridges to polymer backbone. The small atomic radius of oxygen atom on furan bridges resulted in the inferior co-planarity and torsion backbone for PTBDT-ffBT-FT12 with furan bridges, while the adjacent dodecyl on thiophene bridges close to TBDT led to a big steric hindrance. As a result, the polymer solar cell (PSC) based on PTBDT-ffBT-T12T achieves the better efficiency compared to PTBDT-ffBT-FT12 and PTBDT-ffBT-TT12. (C) 2015 Elsevier Ltd. All rights reserved.