Bipolar transport in a molecularly doped polymer containing a bifunctional dopant molecule

Hole and electron mobilities have been measured in N-[p-(di-p-tolylamino)phenyl]-N'-(1,2-dimethylpropyl)-1,4,5,8-naphthalenetetracarboxylic diimide (TAND)-doped polycarbonate (PC). The TAND molecule contains a naphthalene diimide acceptor functionality and a triarylamine donor functionality. Both electron and hole transport are observed in TAND-doped PC with comparable mobilities. To our knowledge, this is the first literature report of bipolar transport in a doped polymer containing a bifunctional dopant molecule. The results are described by a model based on disorder, due to Bassler and coworkers. The model is premised on the assumption that charge transport occurs by hopping through a manifold of localized states with superimposed energetic and positional disorder. The key parameters of the formalism are σ, the energy width of the hopping site manifold, and Σ, the degree of positional disorder. For TAND-doped PC, the widths are 0.130 and 0.137 eV for hole and electron transport, respectively. The corresponding values of the positional disorder are 3.7 and 3.4. The results suggest that the hole and electron transport manifolds are each independent and not influenced by the transport states of the oppositely charged carriers.