We report on a photorefractive polymer composite that shows an initial rise time of 4 ms at a grating spacing of 3.1 μm. A systematic characterization of the ionization potential of a series of chromophores used in photorefractive applications is presented. No obvious correlation between material response time and ionization potential is found in PVK:ECZ:TNFDM composites doped with chromophores with an ionization potential higher or comparable to that of carbazole. All the chromophores under investigation are found to form a charge-transfer complex with the sensitizer TNFDM and a correlation between the spectral position of this band and the value of the ionization potential of the chromophore is demonstrated.

We present the exact computer simulation of transient space-charge limited transport under double injection in disorder materials. In this study, we focus on the phenomena related to the application of electro luminescence. We studied both the transport, i.e., charge carrier generation, their delocalized transport, trapping and detrapping, and the recombination currents, where we concentrated on the energy, time and spatial dependence of the recombination. In connection with the experiment, we modeled a situation after excess carriers generated by short pulses of a strongly absorbed light in a sandwich sample. An implicit (backward) Euler numerical method is utilized to obtain the transient solution of the nonlinear partial differential equations that describe charge carrier transport, trapping and recombination processes. We used amorphous hydrogenated silicon (a–Si:H) as an example material for the application of this method.

Reported here are novel submicron diameter crystals of titanium oxide phthalocyanine (TiOPc) and the electrophotographic properties of photoreceptors that employ them. The use of triether solvents such as diethylene glycol dimethylether and dimethoxy tetrahydrofuran produces five times smaller TiOPc crystals than the phase 3 TiOPc crystals produced in tetrahydrofuran. The photosensitivity of these smaller TiOPcs is as high as that of the tetrahydrofuran produced phase 3 TiOPc crystals, which have been a source for one of the most photosensitive charge generation materials used in electrophotographic photoreceptors.

Free charge carrier generation which is photoinduced by excitation of charge transfer complexes or by formation of exciplexes has often been interpreted in terms of large “initial” separations between geminate carrier pairs. Such large separations are in contrast to the contact geometry of ground state charge transfer complexes and the relatively short range electron transfers expected in exciplex formation. The large separations appear to be required by Onsager analysis of the electric field dependence of the free carrier yield. Almost invariably the analysis is made under the assumption that the initial distribution of pair radii with respect to the applied field is spherically symmetric. Here we propose the possibility that the angular distribution function might be nonspherical and suggest a simple modification of the Onsager analysis to include a field-dependent angular distribution of pair radii that is Boltzmann-weighted. The resulting electric field dependence is shown to be much steeper than for the corresponding spherical distribution and provides the opportunity to interpret experimental data in terms of substantially smaller initial separations.

Polarizabilities and dipole moments of hole transport molecules with different mobilities were measured. The zero-field mobilities of the molecularly-doped polymers increase with increasing polarizabilities and decrease with increasing dipole moments of the dopants. Concerning molecules with similar dipole moments, mobilities correlate well with polarizabilities. Also concerning molecules whose polarizabilities are almost equal, the correlation between mobilities and dipole moments is clear. The 3-D plot of the mobility as a function of the polarizability and the dipole moment is nearly coplanar. Within a framework of the small polaron formalism, polarizabilities are good indices to evaluate the degree of electron cloud extension that affects transfer integral J. On the other hand, the magnitude of the polaron binding energy E_p is macroscopically influenced mostly by the intramolecular structural relaxation. However, we propose that the E_p has a distribution caused by intermolecular interactions, which is not considered in the small polaron formalism. Such distributions, which have recently been discussed within a framework of the disorder formalism, are due to the random internal field caused by the local charge-dipole interaction. These analyses support the experimental data that the logarithm of mobility is described as a linear combination of the polarizability and the dipole moment.

That energetic disorder is the key behind the Poole-Frenkel mobility of photoinjected charges in molecularly doped polymers has always been suspected. In recent years, considerable experimental evidence for the importance of group dipoles has led to the realization that the charge-dipole interaction provides an important contribution to the Gaussian density of states. Here we discuss how the peculiarities of dipolar-disorder, in particular, the manner with which the dipolar disorder is spatially correlated, lead directly to the facts that (i) the mobility in these systems is strongly field-dependent at relatively low fields, (ii) the mobility increases exponentially with √E , and (iii) the field-dependence of the mobility is relatively insensitive to the nature of the underlying hopping rates.

Recently an unusual dependence of the charge carrier drift mobility in molecularly doped polymers on the concentration of traps has been reported. This dependence differs from the expected inverse proportionality that should be valid for trap-controlled transport. Using the results of computer simulation we argue that the reason for this dependence is different regimes of charge carrier transport for layers with different trap concentrations, i.e., dispersive transport for small trap concentrations and nondispersive transport for high trap concentrations. Our results also show that mobility, as estimated from the time of intersection of the asymptotes to the plateau and trailing edge of the photocurrent transient, is very sensitive to variations of its shape and, in some cases, effectively masks the real concentration and field dependence of the true mobility.

The field, temperature and concentration dependence of the dark injection of holes and electrons from metal electrodes into molecular dispersions of respectively 5′-[4-[bis(4-ethylphenyl)amino]phenyl]-N,N,N',N'-tetrakis(4-ethylphenyl)-[1,1′:3′,1′'- terphenyl]-4,4′'-diamine and 1,3-bisdicyanomethylene-2-methyl-allyl-indane in polymers has been investigated. All results point to a two step process: in a first step charge carriers are injected to the bottom of the potential well created by an image potential between the charge transport material and the electrode. The competition between escape of the charge carriers from this well and recombination with empty levels in the electrode governs the final rate of charge carrier injection. While in a qualitative way this approach resembles an extension to doped polymers of the Willig-Gerischer model, developed for organic single crystals, a quantitative description of this system requires us to consider also the diagonal and non-diagonal disorder of the hole transport material.

Surface state models of tribocharging have been successful in explaining many features of the charging of two-component electrophotographic developers. In this paper a new approach for constructing triboelectric series is presented based on surface state models. This method of analysis has several advantages: it requires only limited experimental data, allows the construction of triboelectric series, and makes it possible to separate the effects of the concentration of charging sites and differences in work function on charging. The method was used to analyze tribocharging data recently published by K.-Y. Law and co-workers. Both the work functions and charging site densities of toners treated with various silicas and ionic charge control agents are shown to depend on the surface composition of the toner. Surface treatment with silica causes the work function to increase, shifting the treated toner lower in the triboelectric series. The greater the surface area of the silica, the greater the shift. Hydrophobic silicas cause a greater shift than hydrophilic silicas. For toner surface treated with a set of negative charge control agents (3,5-di-tbutylsalicylic acid and its salts with Li, Na, K, and Rb) it was found that, with the exception of Cs and H, the binding energy of the ions decreases as the ions become heavier, while the concentration of charging sites increases. The results show that the high density of states limit does not apply to all of these materials.