A BIPOLAR CHARGE-TRANSPORT MOLECULE

Hole and electron mobilities have been measured in vapor deposited lay ers of dimethylpropyl)-1,4,5,8-naphthalenetetracarboxylic diimide (TAN D). The TAND molecule contains a naphthalene diimide acceptor function ality and a triarylamine donor functionality. The mobilities are of co mparable magnitude and show similar held and temperature dependencies. The results are described within the framework of a formalism based o n disorder. The formalism is premised on the assumption that charge tr ansport 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 a re 0.110 and 0.091 eV for hole and electron transport, respectively. T he 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.