E. H. Magin

Hole transport in tri-p-tolylamine doped polymers: the role of the polymer dipole moment

Abstract Hole mobilities have been measured in tri-p-tolylamine (TTA) doped polymers with polymer dipole moments that range from near-zero to 1.7 debye. The results are described within the framework of a formalism based on disorder, due to Bassler and coworkers. The formalism is based on the assumption that charge transport occurs by hopping through a manifold of localized states with superimposed energetic and positional disorder. The key parameter of the formalism is σ, the variance of the hopping site energies. The principal observations of this work are: (1) σ increases with increasing intersite distance for all polymers studied, and (2) σ increases with increasing dipole moment of the polymer. The interpretation of the results leads to the conclusion that for weakly polar dopant molecules, a major contribution to the width of the distribution of hopping site energies is the component due to van der Waals forces. For TTA doped poly(styrene)s, the van der Waals component is estimated as between 0.074 and 0.116 eV, increasing with incresing intersite distance or decreasing TTA concentration.

Electron transport in N,N'-bis(2-phenethyl)-perylene-3,4:9,10-bis(dicarboximide)

By time‐of‐flight techniques, electron mobilities have been measured in vapor deposited films of the title compound. The results were compared to predictions of the disorder formalism, due to Bassler and co‐workers, and models based on polaron formation. The results lead to the conclusion that fluctuations in hopping site energies are the major contribution to the activation energy. For consistency between experiment and predictions of the formalism, however, an additional source of activation is required. The source of this activation is believed due to either polaron formation or trapping. The width of the hopping site manifold, σ, is determined as 0.080 eV and the positional disorder parameter, Σ, as 1.0. The interpretation of these results by a model in which transport occurs only by polaron displacement leads to inconsistencies with both the temperature and field dependencies of the mobility.

Hole transport in vapor deposited enamines and enamine doped polymers

Abstract Hole mobilities have been measured of a series of vapor deposited enamine glasses and enamine doped polymers. The enamines are weakly polar donor molecules with dipole moments between 0.38 and 0.66 debye. For the vapor deposited glasses, the room temperature mobilities approach 10 −2 cm 2 /V s at high fields. For the doped polymers, the mobilities are in excess of 10 −3 cm 2 /V s. The results are described by a formalism based on disorder. According to the formalism, charge transport occurs by hopping through a manifold of localized states that are distributed in energy and distance. The key parameters of the formalism are σ, the energy width of the hopping site distribution, Σ the degree of positional disorder, and μ 0 a prefactor mobility. The width of the hopping site manifold is described by a model of dipolar disorder. The model is premised on the assumption than the total width is comprised of a dipolar component and a van der Waals component. For weakly polar molecules, the dipolar component vanishes and the total width gives the van der Waals component directly. For the vapor deposited glasses, the van der Waals components are 0.075 eV. Values for the doped polymers are 0.082 eV. The prefactor mobilities for the vapor deposited glasses are approximately 0.20 cm 2 /V s while values for the doped polymers are between 2 and 4 × 10 −2 cm 2 /V s. Values of the positional disorder parameter are approximately 1.0 for the vapor deposited glasses and 1.7 to 2.0 for the doped polymers. The high mobilities in these materials are due to the low values of the van der Waals components and the high prefactor mobilities.

Hole transport in vapor-deposited triphenylmethane glasses

Hole mobilities have been measured in a series of vapor-deposited triphenylmethane (TPM) glasses with different dipole moments. The results are described by a formalism based on disorder, due to Bassler and coworkers. The formalism is premised on the assumption that charge transport occurs by hopping through a manifold of localized states with superimposed energetic and positional disorder. A key parameter of the formalism is the energy width of the hopping site manifold. For TPM glasses, the width is between 0.093 and 0.123 eV, increasing with increasing dipole moment. The width is described by a model based on dipolar disorder. The model assumes that the total width is comprised of a dipolar component and a van der Waals component. The dipolar components are between 0.037 and 0.089 eV, increasing with increasing dipole moment. The van der Waals components are approximately 0.085 eV, and independent of the dipole moment. The van der Waals components are significantly larger than literature values reported for a wide range of triarylamine (TAA) glasses. The difference between the van der Waals components is the principal reason for the differences in mobility between TPM and TAA glasses and is attributed to differences in charge delocalization of the TPM and TAA molecules.

Hole transport in bis(ditolylaminostyryl)benzene doped poly(styrene)

Hole mobilities have been measured in poly(styrene) (PS) doped with bis(ditolylaminostyryl)benzene (TASB). TASB is a weakly polar molecule that contains two aniline donor functionalities. The dipole moment is 0.54 D. The results are described by a formalism based on disorder, due to Bassler and coworkers. According to the formalism, charge transport occurs by hopping within a manifold of localized states that are subject to a distribution of energies. A key parameter of the formalism is the energy width of the hopping site manifold. The width is described by a model based on dipolar disorder. The model is based on the assumption that the total width is comprised of a dipolar component and a van der Waals component. For TASB, with a near-zero dipole moment, the dipolar component vanishes and the total width becomes equal to the van der Waals component. For TASB, the van der Waals component is 0.102 eV and is independent of concentration. The absence of a concentration dependence is attributed to an intramolecular interaction between the two aniline functionalities associated with each TASB molecule.

The role of dipole moments on hole transport in triphenylamine‐doped polymers

Hole mobilities were measured in a series of triphenylamine (TPA) molecules with different dipole moments doped into apolar and highly polar poly(styrene)s. The results are described by a formalism based on disorder, due to Bassler and coworkers. The formalism is premised on the assumption that charge propagation occurs by hopping through a manifold of localized states with superimposed energetic and positional disorder. A key parameter of the formalism is the energy width of the hopping site manifold, or DOS. For the apolar poly(styrene), the width of the DOS increases with increasing dipole moment of the TPA molecule, whereas for the highly polar poly(styrene), the width is independent of the dipole moment. The results are explained by an argument based on dipolar disorder. The argument is premised on the assumption that the total width is determined by dipolar components due to the dopant molecule and the polymer repeat unit, and a van der Waals component. For the apolar poly(styrene), the width is determined by a TPA dipolar component that increases with increasing dipole moment of the TPA molecule and a van der Waals component of 0.077 eV. For the highly polar poly(styrene), the total dipolar component is 0.090 eV, independent of TPA dipole moment, and the van der Waals component 0.090 eV.

Hole trapping in molecularly doped polymers

Hole mobilities have been measured in di-p-tolylphenylamine-doped poly(styrene) containing 1-phenyl-3-p-diethylaminostyryl-5-p-diethylamino-phenylpyrazoline (DEASP), an 0.38 eV trap. For molar concentrations of less than a few multiples of 10−7, DEASP has no effect on the mobility. For concentrations in excess of 10−6, the mobility decreases with concentration as c−1.5. A concentration of 10−3 suppresses the trap-free mobility by approximately 5 orders of magnitude. The results are described within the framework of a formalism due to Hoesterey–Letson and the recent simulations of Wolf et al. and Borsenberger et al.

The Concentration Dependence of the Hole Mobility of a Hydrazone Doped Polymer

Hole mobilities of 4-diethylaminobenzaldehyde diphenylhydrazone (HDZ-F) doped poly(styrene) have been measured over a wide concentration range. The results have been described by a formalism based on disorder. The formalism is premised on the argument that charge transport occurs by hopping through a manifold of localized states that are distributed in energy and distance. The key parameter of the formalism is σ, the energy with of the hopping site manifold. For HDZ-F doped PS, σ is concentration-dependent. The maximum value is 0.121 eV and occurs at approximately 15% HDZ-F. The width decreases sharply for concentrations above and below. The concentration dependence is described by a model of dipolr disorder. The model is based on the assumption that the total widths are comprised of a dipolar component and a van der Waals component. The interpretation of the experimental results leads to the conclusion that the concentration dependence of the total width is largely determined by the van der Waals component.

HOLE TRANSPORT IN TRIPHENYLMETHANE DOPED POLYMERS

Hole mobilities have been measured in poly(styrene) (PS) doped with a series of triphenylmethane (TPM) derivatives with different dipole moments. The results are described within the framework of a formalism based on disorder, due to Bassler 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. The key parameter of the formalism is the energy width of the hopping site manifold. For TPM doped PS, the widths increase with increasing TPM concentration and increasing dipole moment. The 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, while 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 (T AA) molecules. The difference in the van der Waals components is the principal reason for the difference in mobility of TPM and T AA doped polymers.

Hole transport in vapor deposited bis(ditolylaminostyryl)benzene

Hole mobilities have been measured in vapor deposited bis(ditolylaminostyryl)benzene (TASB). TASB is a weakly polar molecule that contains two aniline donor functionalities. The results are described by a formalism based on disorder, due to Bassler and coworkers. The formalism is based on the assumption that charge transport occurs by hopping through a manifold of localized states that are distributed in energy. The key parameter of the formalism is the energy width of the hopping site manifold. The width is described by a model based on dipolar disorder. According to the model, the total width is comprised of a dipolar component and a van der Waals component. For TASB, the dipolar component is 0.012 eV and the van der Waals component 0.091 eV. The van der Waals component is considerably larger than values reported for other triarylamine donor glasses. This is attributed to differences in stereochemistry of the aniline donor functionalities.