Hole mobilities have been measured for a series of triphenyl-methane (TPM) derivatives with different dipole moments doped into poly(styrene) (PS). The results are described within the framework of a formalism based on disorder, due to Bässler and coworkers. The formalism is premised on the assumption that transport occurs by hopping through a manifold of localized states that are subject to a distribution of energies and distances. The key parameters of the formalism are the energy width of the hopping site manifold, the degree of positional disorder, and a prefactor mobility. For TPM-doped PS, the widths are between 0.104 and 0.124 eV, increasing with increasing TPM concentration and increasing dipole moment. Values of the positional disorder parameter are between 2.0 and 4.5, increasing with increasing dilution. The prefactor mobilities decrease with increasing dilution and can be described by wavefunction decay constants of approximately 1.0 Å. The energy widths are described by a model based on dipolar disorder. According to the model, the widths are comprised of a dipolar component and a van der Waals component. The dipolar components are between 0.012 and 0.067 eV, and the van der Waals components are 0.104 eV. The van der Waals components are significantly larger than literature values for PS doped with a wide range of triarylamine (TAA) molecules. The difference in the van der Waals components is the principal reason for the very considerable difference in mobility of TPM- and TAA-doped polymers. For constant dopant concentrations, the degree of positional disorder and the prefactor mobilities are essentially the same for all TPM- and TAA-doped polymers.
This review traces the history and development of organic photoconductors (OPCs), the multilayer thin film photosensitive element in electrophotographic printers, from Chester Carlson's 1938 demonstration of xerography to the present. A brief discussion of the history of electrophotography is followed by a review of OPC basics and the development of specific charge generating materials (CGMs) and charge transporting materials (CTMs). Next is a discussion of OPC commercialization and the last section demonstrates the cycle of OPC research and development by the number of OPC presentations at international conferences.
Hole transporting properties of tris-(8-hydroxyquinolinato) aluminum (Alq) were investigated using time-of-flight (TOF) photocurrent transients and photoinduced discharge techniques. A thin layer of Alq was inserted between two hole transporting layers. Within the time domain of the photocurrent transients,the fraction of holes escaping from one side of the Alq layer to the other side is strongly field, temperature, and Alq thickness dependent. The results of photoinduced discharge experiments indicate that eventually the holes escaped the trilayer samples. The injection barrier is estimated to be approximately 0.12 eV. The hole penetration range is estimated to be 10-30 angstrom in the range of field strengths studied, therefore suggesting the recombination zone of electrons and holes in Alq-containing electroluminescent (EL) devices is confined close to the interface of Alq and the hole transporting layer. The results demonstrate the importance of the hole injection barriers and hole trapping to the performance of organic EL devices using Alq as the electron transporting and emissive layer.
Xerographic photoreceptors charge acceptance and potential discharge models experimental methods photogeneration theories photogeneration charge transport theories hole transport electron and bipolar transport photoreceptors summary and concluding remarks. Appendices: polymers generation materials transport materials.
