Influence of the intramolecular donor-acceptor distance on the performance of double-cable polymers

A series of double-cable polymers PFT-C₄-PDI, PFT-C₆-PDI and PFT-C₈-PDI, composed of the poly(fluorene-alt-thiophene) (PFT) backbone, the perylene diimide (PDI) pendants and the length-various (four-, six- and eight-carbon) covalent alkoxy linkers, were presented. The backbone polymer chain created the hole-transporting channel and the inner-chain aggregation of PDI units created the electron-transporting channel, but the aggregation became weaker along with the longer linker, as proven by the UV–Vis absorption and fluorescence quenching. The polymers were non-conducting, but functioned as efficient compatibilizers. The doping of the polymers induced the formation of the bi-continuous networks inside P3HT:PCBM blends, facilitated photo-generated exciton dissociation and charge transporting. PFT-C₄-PDI more efficiently increased the absorption coefficient and the charge-carrier mobility of the P3HT:PCBM film. The power conversation efficiency (PCE) of the P3HT:PCBM bulk-heterojunction solar cells with 3 wt% PFT-C₄-PDI, PFT-C₆-PDI and PFT-C₈-PDI doping were improved by 16.9%, 9.2% and 8.0%, respectively, relative to the non-doped reference device.