Amorphous molecular materials: charge transport in the glassy state of N,N′-di(biphenylyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamines

Charge transport in the glassy state of a new family of amorphous molecular materials, N,N′-di(biphenyl-2-yl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine (o-BPD), N,N′-di(biphenyl-3-yl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine (m-BPD), and N,N′-di(biphenyl-4-yl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine (p-BPD), has been studied. It was found that the molecular glass of p-BPD exhibits a high hole drift mobility of 1.0×10-3 cm2V-1s-1 at an electric field of 1.0×105 Vcm-1 at 293 K and that the hole drift mobility of m-BPD is more than one-order of magnitude smaller than those of o- and p-BPD. The analysis of the electric-field and temperature dependencies of the drift mobilities in terms of the disorder formalism shows that the difference in energetic disorder is responsible for the difference in the drift mobilities of these materials.