Analysis of nondispersive time-of-flight transients

Non-dispersive carrier transport in molecularly doped polymers and the convection–diffusion equation

“…It is in this physical context that an attempt was made by Hirao and co-workers [12][13][14] to use a different CDE-inspired approach to explain unusual results concerning the field dependence of the mobility at applied fields that were relatively low (although still far from the Ohmic limit, which is generally inaccessible in MDPs). In that work, approximate expressions used in previous CDE-based studies were heuristically extended, to include the influence of diffusion currents.…”

“…[12][13][14] ignited a longlasting controversy regarding the applicability of the CDE to describe TOF transients in MDPs with flat plateaus but slowly decaying tails [32,33].…”

“…transport in the presence of a constant, spatially uniform electric field. Such an approach, stressing the importance of diffusion currents, was proposed by Hirao and co-workers for interpreting TOF results obtained at low electric fields [12][13][14]. Prior to that work, TOF experiments on MDPs had primarily been conducted at high fields, so the effect of diffusion currents could be largely ignored [1], although there was a general understanding that the wide, slowly-decaying tails of measured TOF current transients implied an enhanced spreading of the carrier packet as it drifted under the influence of the field.…”

“…In their diffusion-based analysis, however, Hirao et al [12][13][14] used a Green function approach to the CDE that was rigorously appropriate only to an unbounded medium, and was thus of questionable relevance to TOF experiments, which rely on carriers traversing a sample of finite width bounded by physical contacts with specific physical properties. In fact, for analyzing TOF experiments it is more appropriate to treat the CDE as boundary value problem, using, e.g., an eigenfunction expansion appropriate to actual boundary conditions relevant to TOF experiments.…”

Charge Mobility and Charge Traps in Conjugated Polymers

“…[7b] The analytical solution of the photocurrent transient equation (PTE) was proposed by Hirao et al [18] as:…”