A Bipolar Charge Transport Molecule

Hole and electron mobilities have been measured in vapor deposited layers of N-(p-(di-p-tolylamino)phenyl)- N'-(1,2-dimethylpropyl)-1,4,5,8-naphthalenetetracarboxylic diimide (TAND). The TAND molecule contains a naphthalene diimide acceptor functionality and a triarylamine donor functionality. The mobilities are of comparable magnitude and show similar field and temperature dependencies. The results are described within the framework of a formalism based on disorder. The formalism is premised on the assumption that charge transport occurs by hopping through a manifold of localized states with superimposed energetic disorder. The key parameter of the formalism is the energy width of the hopping site manifold. For TAND, the widths are 0.110 and 0.091 eV for hole and electron transport, respectively. The result leads to the conclusion that the hole and electron transport manifolds are independent and not influenced by the transport states of the oppositely charged carriers.