John A. Sinicropi

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.

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 transport in poly(styrene) doped with p-diarylaminostilbene molecules

Abstract Hole mobilities have been measured in poly(styrene) (PS) doped with a series of p -diarylaminostilbene molecules (DAS) with different dipole moments. At room temperature, the mobilities vary by a factor of approximately 20, decreasing with increasing dipole moment. The results are described by a model based on disorder, due to Bassler and coworkers. The model is based on the argument that charge transport occurs by hopping through a manifold of localized states that are distributed in energy. The key parameter of the model is the energy width of the hopping site manifold. For DAS doped PS, the energy widths are between 0.092 and 0.107 eV, increasing with increasing dipole moment and increasing DAS concentration. The width is described by a model based on dipolar disorder. According to the model, the width is comprised of a dipolar component and a van der Waals component. Describing the dipolar component by the expression due to Young leads to the conclusion that the van der Waals component is 0.092 eV, and independent of the DAS concentration. A comparison of these results with literature results for a wide range of doped polymers suggests that differences in the van der Waals component is the principal reason for the very considerable differences in mobility of these materials.

Hole transport in enamine-doped polymers

Hole mobilities of a series of enamine (ENA) derivatives doped into poly(styrene) (PS) have been measured over a wide concentration range. At high fields and high ENA concentrations, the room temperature mobilities are in excess of 10-3 cm2/Vs. These are the highest of any doped polymers described in the literature. The results are described by a model based on disorder. According to the model, charge transport occurs by hopping through a manifold of localized states that are distributed in energy and distance. The key parameters of the model are a, the energy width of the hopping site distribution, the degree of positional disorder, and μ0, 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 that 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 is determined only by the van der Waals component. The values for ENA doped PS are betweeen 0.077 and 0.103 eV, increasing with increasing dilution. The prefactor mobilities are between 10-6 and 10-1 cm2/Vs, increasing with increasing concentration. Values of the positional disorder parameter are between 1.6 and 4.8. The high mobilities in these materials are due to the low values of the van der Waals components and the high prefactor mobilities.