Polymers from phenyl-substituted benzodithiophene and tetrafluoridequinoxaline with high open circuit voltage and high fill factor

A series of new copolymers from tetrafluoridequinoxaline (ffQx) and three distinctive phenyl (alkoxy-1-meta-fluorophenyl, alkoxyphenyl and alkylthiophenyl) substituted benzodithiophene (BDT), namely, PffQx-m-fPO, PffQx-PO and PffQx-PS, were designed and synthesized. Photophysical properties, charge mobilities and morphologies of the three polymers have been intensively investigated. Benefitted from the effects of phenyl and fluorine substituents on the backbone, all the polymers possess deep the highest occupied molecular orbital (HOMO) levels. In particular, PffQx-PS has a lower bimolecular recombination and deeper HOMO energy level, which contributes to the higher fill factor (FF, ca. 70%) and higher open-circuit voltage (V-oc, ca. 0.93 V) of the polymer solar cells (PSCs) with the polymer as donor and PC71BM as acceptor. All the PSCs with the ffQx-based polymers as donor exhibited VocS higher than 0.9 V and power conversion efficiencies over 7% (7.0% for PffQx-m-fPO, 7.4% for PffQx-PO and 8.0% for PffQx-PS). (C) 2016 Elsevier B.V. All rights reserved.