DISORDER-INDUCED TRANSITION FROM GAUSSIAN TO DISPERSIVE CARRIER TRANSPORT IN MOLECULARLY DOPED POLYMERS

Dynamics of hopping charge transport in a polymer matrix doped with two different charge-transport molecules was studied by means of time-of-flight (TOF) photoconductivity measurements. In polymers doped with two molecules of little different ionization potential, the Gaussian (near-rectangular) TOF signal was observed over all compositions and the tail of the Gaussian TOF signal is broadened by a wide distribution of hopping time among molecules due to off-diagonal disorder. On the other hand, in polymers doped with two molecules of different ionization potential, the transition from the Gaussian to the dispersive TOF signal was observed and this is mainly caused by diagonal disorder. It is found that the energetic and spatial distribution of hopping sites play a key role in carrier transport in molecularly doped polymers.