Bending a ferroelectric polymer produces internal polarization that can lead to external electric fields. Both theoretical and experimental analyses have been carried out to predict the magnitudes of these fields, using flexible ferroelectric polymer materials based on polyvinylidenefluoride. The output depends on the thickness of the film, the bending radius, and a measured piezoelectric coefficient that is characteristic of the material. The electric field can exceed the levels now used in xerographic transfer and charging subsystems, suggesting that piezoelectric bending could replace conventional high-voltage power supplies and corona devices. Examples of applications to copier and printer subsystems are described.

For a variety of molecularly doped, pendant-, and main-chain polymers, and vapor-deposited molecular glasses, the mobility of photoinjected charges at high electric fields is described by the Poole-Frenkel law; μ = μ₀ exp (γ√E) . Apart from their organic constituents, the primary transport-related feature shared by these materials is the lack of a periodic structure. We review the relation between the √E-dependent mobilities and dispersive transport, as described by the theory of Scher and Montroll for hopping transport in a disordered medium. We show that with a small modification, the theory predicts dispersive transport below and nondispersive transport above a transition temperature T_c. We argue that the √E dependence of the mobility and the universality of the current-time curves may be retained above and below T_c if the bulk film behaves as a lattice of bonds of length L, where L is intermediate between the dopant spacing and the thickness of the sample.

The hole mobilities of molecularly doped polymer films containing p-diethylaminobenzaldehyde diphenylhydrazone (DEH) are measured before and after systematic UV irradiation. Ultraviolet exposure has been shown to induce a photochemical reaction of the DEH molecule. This reaction is known to reduce dramatically the molecule's capability to transport charge. Presumably the reduction in mobility is associated with the substantial increase (about 1 eV) in the ionization potential of the DEH molecule after photocyclization. We demonstrate that systematic UV irradiation of molecularly doped polymer films containing DEH provides a novel approach for diluting the dopant concentration and effectively increasing the intersite separation between “active” dopant molecules in situ. This photochemical process is exploited to study charge transport in DEH-doped polycarbonate films parametric in UV irradiation time. Transport parameters are determined from transient photocurrent measurements over a range of electric fields and temperatures. Our principal observations are: (1) UV irradiation of DEH-doped polycarbonate films results in a corresponding decrease in the effective hole mobility, and (2) despite the systematic drop in mobility, a consequence of the elimination of active hopping sites, the activation energy for hopping, Δ, and the energetic disorder parameter, σ, remain constant.

Negative field dependence of hole mobility was observed in poly(methylphenylsilane) (PMPS) films doped with a plasticizer, dioctyladipate (DOA). By analyzing the hole mobilities in the framework of Bässler's disorder formalism, the negative field dependence was found to be due to the large increase in the parameter Σ, the positional disorder of hopping site distance. Furthermore, we succeeded in measuring the hole mobility of DOA-doped PMPS film under elongation. In UV absorption and fluorescence spectrum measurements of the elongated film, a red shift of the absorption edge was observed only for the polarized light parallel to the elongation axis, and a new emission appeared at the longer wavelength, suggesting that the molecular orientation and the extension of σ-conjugation length occurred with film elongation. The effect of film elongation was well reflected in the parameters in the charge transport expression for amorphous materials based on Bässler's disorder formalism.

Hole and electron mobilities have been measured in ternary solid solutions containing an electron acceptor, 4H-1,1-dioxo-4-dicyanomethylidene-2-p-tolyl-6-phenylthiopyran, and an electron donor, tri-p-tolylamine, in a polyester host. The results are discussed by a model based on disorder, due to Bässler and coworkers. The key result of this study is that the presence of the donor has no effect on electron transport, nor does the presence of the acceptor have any effect on hole transport. The interpretation of the experimental results leads to the conclusion that the electron and hole manifolds are independent and are not influenced by the presence of the transport states of the oppositely charged carriers.

An unambiguous experimental procedure is illustrated for characterizing the behavior of electrical contacts on unipolar transport active molecular solids devoid of deep traps. Such polymeric media, originally developed to serve as the transport layer in bilayer electrophotographic receptors, are now under wider investigation for use in organic electronic and photoelectronic devices. The technique is illustrated for two types of carbon contact on the trap-free hole transport polymer PTPB. First, a carbon-filled polymer is shown to be operationally ohmic for hole injection. To account for current-voltage characteristics over a wide temperature range, it is necessary to consider explicitly the field dependence of the drift mobility in computing the trap-free space-charge limited current. Using the same procedure, glassy carbon is clearly demonstrated to be emission limiting. Injection in this case is shown to conform to a model in which carrier supply to the film bulk is controlled by thermally assisted tunneling from metal to discrete transport-active states in polymer, including those not immediately adjacent to the contact interface. The technique described has also been used to demonstrate time-dependent changes in contact behavior. An illustration of this contactforming phenomenon following thermal deposition of Au on PTPB is included.

The structure of the electrostatic latent image formed by exposure of a corona-charged photoreceptor must be maintained prior to development. To meet this requirement, useful photoreceptors have high dark resistivities. If the photoreceptor surface is conductive, the electrostatic latent image will degrade with time. The time-dependent changes in the structure of an electrostatic latent image are analyzed, using a model with surface resistivity as the only adjustable parameter. The analysis offers a method for determining the surface resistivities of thin polymer films. Surface resistivities are reported for photoreceptors that have been modified by various surface treatments.