Ambipolar Doping in -Conjugated Polymers

The realization of ambipolar (n- and p-type) doping within a single organic semiconductor is highly desirable for a variety of applications but has rarely been demonstrated in solution-processed pi-conjugated polymers. This work reports ambipolar doping in donor-acceptor-based pi-conjugated naphthalenediimide-diketopyrrolopyrrole (p(gNDI-TDPP)) polymers. Optical, electrical, electron spin resonance, and photoelectron spectroscopy measurements show evidence of the successful chemical doping of p(gNDI-TDPP) with the n-dopant 4-(2,3-dihydro-1,3-dimethyl-1H-benzimidazol-2-yl)-N,N-dimethylbenzenamine (N-DMBI-H) as well as the related dimer (N-DMBI)(2) and the p-dopant tris(4-bromophenyl)ammoniumyl hexachloroantimonate. Temperature-dependent conductivity shows that the barrier for charge transport is decreased at higher doping levels. We observed that the dimer (N-DMBI)(2) dopes more efficiently than N-DMBI-H as it reacts rapidly with NDIs and can contribute two electrons per dimer molecule. Comparable charge transport and charge-carrier concentrations in both n- and p-doped polymers were observed. Moreover, while the conductivity of the n-doped material drops on exposure to air, it can be largely recovered upon annealing, indicating that air exposure does not lead to the extensive irreversible chemical decomposition of the doped polymer.