Intramolecular Donor-Acceptor Regioregular Poly(3-hexylthiophene)s Presenting Octylphenanthrenyl-Imidazole Moieties Exhibit Enhanced Charge Transfer for Heterojunction Solar Cell Applications

Intramolecular donor–acceptor structures prepared by covalently binding conjugated octylphenanthrenyl‐imidazole moieties onto the side chains of regioregular poly(3‐hexylthiophene)s exhibit lowered bandgaps and enhanced electron transfer compared to the parent polymer, e.g., conjugation of 90 mol% octylphenanthrenyl‐imidazole moieties onto poly(3‐hexylthiophene) chains reduces the optical bandgap from 1.91 to 1.80 eV, and the electron transfer probability is at least twice as high as that of pure poly(3‐hexylthiophene) when blended with [6,6]‐phenyl‐C61‐butyric acid methyl ester. The lowered bandgap and the fast charge transfer both contribute to much higher external quantum efficiencies, thus much higher short‐circuit current densities for copolymers presenting octylphenanthrenyl‐imidazole moieties, relative to those of pure poly(3‐hexylthiophene)s. The short‐circuit current density of a device prepared from a copolymer presenting 90 mol% octylphenanthrenyl‐imidazole moieties is 13.7 mA · cm−2 which is an increase of 65% compared to the 8.3 mA · cm−2 observable for a device containing pure poly(3‐hexylthiophene). The maximum power conversion efficiency of this particular copolymer is 3.45% which suggest that such copolymers are promising polymeric photovoltaic materials. Regioregular copolymers of poly(3‐hexylthiophene) side chain‐tethered with octylphenanthrenyl‐imidazole moieties exhibit lowered bandgaps and enhanced charge transfer properties that make them suitable for application in heterojunction polymer/PCBM solar cells. Both short‐circuit current density and power ‐conversion efficiency of the copolymers are greatly improved over those of the parent polymer.