Development of new hole-transporting amorphous molecular materials for organic electroluminescent devices and their charge-transport properties

New hole-transporting amorphous molecular materials with high glass-transition temperatures (Tgs) for organic electroluminescent (EL) devices, N,N,N′,N′-tetrakis(9,9-dimethyl-2-fluorenyl)-[1,1′-biphenyl]-4,4′-diamine (FFD) and N,N′-bis[9,9-dimethyl-2-fluorenyl]-N,N′-diphenyl-9,9-dimethylfluorene-2,7-diamine (PFFA), have been developed and their charge-transport properties investigated. These materials with Tgs of 165 and 135°C permitted the fabrication of thermally stable organic EL devices. It was found that both FFD and PFFA glasses exhibit high hole drift mobilities of 4.1×10−3 cm2 V−1 s−1 and 1.1×10−3 cm2 V−1 s−1 at an electric field of 1.0×105 V cm−1 at 293 K. The electric-field and temperature dependencies of the drift mobilities were analyzed in terms of the disorder formalism.