Charge transport in disordered molecular solids

Abstract

Hole mobilities have been measured in vapor deposited films of 1, I-bis ( di -4-toly laminopheny 1) cyclohexane (T APC) and T APC-doped bisphenol-A-polycarbonate (BPPC). Over an extended range of temperatures, the mobilities decrease with increasing field at low fields. At high fields, a log Jl a: E1!2 relationship is observed with a slope that approaches zero at high temperatures. The results are described within the framework of the disorder transport formalism. By comparison of the experimental results with Monte Carlo simulations, we show that the observed behavior is a signature of the simultaneous presence of diagonal and off-diagonal disorder. Agreement between simulation results and experiment is excellent. Generalizing these results provides a framework for determining the magnitude of the relevant diagonal and off-diagonal disorder parameters from an analysis of mobility measurements.

Effect of dipolar molecules on carrier mobilities in photorefractive polymers

“…The TOF technique and the method of extracting transit times were described in greater detail elsewhere. 11,20,39,44 IV. RESULTS…”

“…A more detailed description of the assumptions and predictions of the GDM have been given elsewhere. 14,20,26 25 attempt to increase the range of the exp(␤ͱE) dependence in these models.…”

“…14 Transport studies show that the carrier mobility is roughly proportional to 2 exp͓␤ͱE Ϫ⌬ 0 /TϪ2 / 0 ͔, [15][16][17] where is the average separation of transport sites, 0 is a constant, E is the electric field, T is the absolute temperature, T 0 is a constant, ␤ is the PooleFrenkel coefficient, and ⌬ 0 is the activation energy at zero field. Transport models are mostly distinguished by the form of charge transfer between transport molecules ͑e.g., small polaron 18 or adiabatic 19 hopping͒, by the distributions of site energies and positions, 20,21 and by the formalism for combining hopping events to calculate bulk transport. 20,22,23 Recent attention has been focused on reproducing the exp(␤ͱE) Poole-Frenkel form which the current models reproduce only over a limited range of electric fields, much more limited than the available data require.…”

“…Transport models are mostly distinguished by the form of charge transfer between transport molecules ͑e.g., small polaron 18 or adiabatic 19 hopping͒, by the distributions of site energies and positions, 20,21 and by the formalism for combining hopping events to calculate bulk transport. 20,22,23 Recent attention has been focused on reproducing the exp(␤ͱE) Poole-Frenkel form which the current models reproduce only over a limited range of electric fields, much more limited than the available data require. [23][24][25] Many recent results have been interpreted within the framework of the Gaussian disorder model ͑GDM͒ developed by Bässler and co-workers.…”

“…[23][24][25] Many recent results have been interpreted within the framework of the Gaussian disorder model ͑GDM͒ developed by Bässler and co-workers. 14,20,26 The GDM is based on the assumption that charge transport occurs by activated hopping with a Miller-Abrahams asymmetric hopping probability 19 through a manifold of localized states with superimposed energetic ͑diagonal͒ and positional ͑off diagonal͒ disorder with Gaussian distributions. Monte Carlo calculations with the GDM reproduce the Poole-Frenkel form over a limited range of fields and assume a variation of the activation energy form with 1/T 2 replacing 1/T.…”