Correlation between structure and photovoltaic performance of a series of furan bridged donor–acceptor conjugated polymers

Abstract

A series of donor–acceptor (D–A) polymers based on furan-bridged benzodithiophene and different acceptor blocks were designed and synthesized. By incorporating various acceptors with differing electron-withdrawing abilities into the same polymer backbone, we were seeking to reveal the correlation between molecular structures and the corresponding film morphology as well as photovoltaic performance. The experimental results and theoretical calculations indicate that the selection of acceptor units has significant impacts on the polymer energy levels and backbone coplanarity, leading to differing intermolecular packing. By using atomic force microscopy and transmission electron microscopy, we also observed that the size and topology of the alkyl-chains on acceptors can tune the polymer solubility and result in different film morphology. As a result of optimized morphology, we demonstrated power conversion efficiencies over 5% for the new polymer based devices, which are among the highest efficiencies of reported furan bridged D–A polymers.