On the transport of excess charge carriers in polymers
A. P. Tyutnev, J. Kundin, V. S. Saenko, E. D. Pozhidaev.
Polymer Science Series B, 44, 77-85, (2002)
The general aspects of the transport of excess charge carriers in polymers are considered. Published data on transient radiation-induced conductivity of polymers, including the model polymer poly(vinylcarbazole), are analyzed. It was shown that these data provide evidence of the nonequilibrium (dispersive) transport of charge carriers over the entire experimentally accessible range of observation time (from tens of nanoseconds to tens of minutes at room temperature). Using poly(vinylcarbazole) as an example, it was found that the dispersive transport of holes is also supported by time-of-flight measurements, provided, however, that special precautions are taken to exclude undesirable methodological effects. The generally accepted treatment of charge transport as a quasi-equilibrium phenomenon for which the plateau on the time-of-flight current transient is treated in terms of the Gaussian disorder model requires substantial revision. More detailed analysis over a broader time interval, especially for long times, and the involvement of data on radiation-induced conductivity in molecularly doped polymers in consideration evidently show the dispersive nature of charge carrier transport in such polymer systems as well. The formation of the plateau on the time-of-flight curve seems to be due to the effect of the near-surface polymer layer whose role in the radiation-induced conductivity is reduced to a minimum because of the bulk generation of charge carriers. The transport parameters are given for some polymers and the drift displacements of the majority carriers in them are calculated for several time intervals. Reasons for the unique photoelectric properties of poly(vinylcarbazole) are discussed.