Quinoxaline-Based D-A Conjugated Polymers for Organic Solar Cells: Probing the Effect of Quinoxaline Side Chains and Fluorine Substitution on the Power Conversion Efficiency

Abstract

We describe the successful synthesis of four novel donor-acceptor (D-A) type copolymers, referred to as PQxBT, PQxFBT, TQxBT, and TQxFBT. The effects of using a fluorinated bithiophene (FBT) and varying the side-chain moieties tethered to the quinoxaline (Qx) unit (electron-withdrawing group in the polymer backbone) on the physical properties and photovoltaic performance were investigated. Specifically, the four polymers were synthesized using either alkoxyphenyl (P) or alkylthiophene (T) units anchored to the quinoxaline in the polymer backbone. The FBT-bearing polymers, PQxFBT and TQxFBT, displayed more redshifted absorption spectra and higher crystallinity owing to the greater planarity of their polymer backbone as compared to the non-fluorinated polymers. The TQxFBT copolymer, equipped with both the alkylthiophene side chains and FBT, exhibited face-on orientation in film state and a well-mixed nanophase morphology in TQxFBT:PC71BM blend films. The photovoltaic device fabricated from TQxFBT:PC71BM exhibited the highest power conversion efficiency of 4.18%. (c) 2016 Wiley Periodicals, Inc.