Fully visible-light-harvesting conjugated polymers with pendant donor-π-acceptor chromophores for photovoltaic applications

Toward fully visible light absorbing conjugated polymers, two narrow-band-gap conjugated polymers PFMIX and PCzMIX were synthesized by attaching two different acceptor groups malononitrile and 2-(1,2-dihydro-1-oxoinden-3-ylidene)malononitrile (DCNIO) onto the same polymer main chain via Knoevenagel condensation from the corresponding aldehyde-functionalized precursor polymers. For comparison, the polymers with DCNIO acceptor, PFDCNIO and PCzDCNIO were also developed. The optical properties, energy levels, hole transporting abilities and photovoltaic properties of the resulting polymers were investigated in detail. The absorption spectra of PFMIX and PCzMIX were greatly extended by simultaneously using acceptors with different electron-withdrawing ability. The resulting polymers exhibited promising photovoltaic properties, and the maximum of power conversion efficiency of 2.83% could be achieved for the device based on PFMIX when blended with (6,6)-phenyl-C71-butyric acid methyl ester.