A regioregular head to tail thiophene based “double-cable” polymer with pendant anthraquinone functional groups: Preparation, spectroscopy and photovoltaic properties

We present an investigation into the electronic, photophysical and photovoltaic properties of a π-conjugated “double-cable” polymer based on regioregular head to tail poly(3-functionalized thiophene) with pendant anthraquinone acceptor groups (PT-AQ). This material was compared with model blends composed of a mixture of regioregular head to tail poly(3-hexylthiophene) (P3HT) as the polymer donor and anthraquinone-2-carboxylic acid octyl ester (AQ) as a small-molecule acceptor. We find that PT-AQ shows complete quenching of fluorescence whilst the donor/acceptor blend shows residual fluorescence emission and both phase separation and crystallization of the acceptor component. The operation of the double-cable based devices is however, dominated by geminate recombination and poor charge transport and extraction. Nevertheless, we show that the PT-AQ devices have a higher efficiency than devices based on representative bulk-heterojunction AQ:P3HT blends as the very coarse phase separation and crystallization is suppressed.