Bandgap Engineering of Indenofluorene-Based Conjugated Copolymers with Pendant Donor-π-Acceptor Chromophores for Photovoltaic Applications

Three narrow-band-gap conjugated copolymers based on indenofluorene and triphenylamine with pendant donor-pi-acceptor chromophores were successfully synthesized by post-functionalization approach. All the polymers have good solubility in common solvents and excellent thermal stability. The photophysical properties, energy levels and band gaps of the polymers were well manipulated by introducing different acceptor groups onto the end of their conjugated side chains. By using different acceptor groups, the band gaps of the polymers were narrowed from 1.86 to 1.53 eV by lowering their lowest unoccupied molecular orbital levels, whereas their relatively deep highest occupied molecular orbital levels of approximately -5.35 eV were maintained. Bulk-heterojunction solar cells with these polymers as electron donors and (6,6)-phenyl-C-71-butyric acid methyl ester as acceptor showed power conversion efficiencies as high as 3.1% and high open circuit voltages more than 0.88 eV. The relationships between the performance and film morphology, energy levels, charge mobilities were discussed. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 4406-4415, 2011