p-Doping of polystyrene polymers with attached functional side-groups from solution

Electrically doped buffer layers are often employed in organic optoelectronic devices to improve charge carrier injection or extraction. We study p-doping of non-conjugated polymers with attached hole transport moieties by intermixing strong molecular acceptors. Polymers and dopants are processed from solution and their electrical properties are benchmarked against non-polymerized, p-doped molecular materials. The equilibrium charge carrier density is estimated by electron paramagnetic resonance (EPR) measurements that show an increased number of unpaired spins upon doping. We find an increase in the conductivity of the electrically doped polymer and the corresponding molecular materials by several orders of magnitude by studying hole-only devices and employing charge extraction by linearly increasing voltage (CELIV). Altogether, the increased number of unpaired spins and the enhanced conductivity indicate the presence of free holes. The p-doping of the polymers with attached hole transport moieties is equally efficient as the p-doping of the corresponding molecular materials.