Hole transport in PS and PC doped with low molecular-mass-dopants with dipole moments larger than 3D is investigated. Both near-surface and bulk charge-carrier generation techniques are used. There is good agreement between the experimentally measured values of hole mobility and the published data. It is shown that, for the investigated systems, the hole transport is none quilibrium and is well described by the multiple-trapping model with the Gaussian trap distribution over energy. The presence of a flat plateau on the time-of-flight curves does not necessarily mean establishment of the quasi-equilibrium hole transport in the system.29.19.23 Теория электрических свойств твердых тел
Abstract—General questions about hole transport and bimolecular recombination of charge carriers in molecularly doped polycarbonate with a low dopant concentration (10 wt %) are considered. The experiment is performed via a radiationinduced timeofflight technique with bulk generation of charge carriers. Tran sientcurrent curves are calculated numerically via a multipletrapping model. There is good agreement between the calculated and experimental results on the transientcurrent waveform. Nonequilibrium hole transport is observed in the studied molecularly doped polymer, and the bimolecular recombination is close to the Langevin recombination as described by the multipletrapping model.
The time-of-flight technique is used to measure hole mobility in molecularly doped polycarbonate and polystyrene that contain both polar and weakly polar additives. The two versions of the technique with the bulk and surface generation of charge carriers under small-signal conditions are employed. Numerical calculations show that the time dependence of the transient-current curves obtained with the first version of the technique is in agreement with the theory of multiple trapping for an exponential energy distribution of traps. In the case of time-of-flight curves with surface generation, the run of the post-transit branch is likewise consistent with the theory, whereas this consistency is often violated for the pretransit branch of the curves. This result is due to the effect of the defective surface layer of a polymer, which is not taken into account in numerical calculations. The results show that the hole transport in the studied molecularly doped polymers is dispersive. An increase in the polarity of the polymer matrix and the dopant drastically decreases the hole mobility and, at the same time, increases its field and temperature dependence.
A model of a polyelectrolyte solution has been formulated on the basis of the formalism of the thermodynamic perturbation theory. Macromolecules have been described in terms of the model of a flexible chain with an excluded volume and a variable electrical charge. During construction of the thermodynamic perturbation theory, a set of three independent subsystems—polyelectrolyte macromolecules placed in a structureless charge background of counterions, counterions placed in a structureless charge background of macromolecules, and Coulomb gas ions of a lowmolecularmass salt—has been taken as the reference sys tem. In the framework of this model, liquid–liquid phase separation due to strong correlationinduced attraction has been predicted. The behavior of the degree of ionization over a wide monomer concentration range, including the region of phase separation either in a saltfree solution or in the presence of univalent ions of a lowmolecularmass salt in the solution, has been studied. It has been shown that macromolecules in the coexisting phases should have different degrees of ionization. The occurrence of phase separation under normal conditions in the case when dimethylformamide is taken as a solvent and the nonoccurrence of this phase separation in the case of aqueous solutions of flexiblechain polyelectrolytes are predicted.