Negative electric field dependence of mobility in TPD doped Polystyrene

Abstract

A total negative field dependence of hole mobility down to low temperature was observed in N,N'-diphenyl-N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'diamine (TPD) doped in Polystyrene. The observed field dependence of mobility is explained on the basis of low values of energetic and positional disorder present in the sample. The low value of disorder is attributed to different morphology of the sample due to aggregation/crystallization of TPD. Monte Carlo simulations were also performed to understand the influence of aggregates on charge transport in disordered medium with correlated site energies. The simulation supports our experimental observations and justification on the basis of low values of disorder parameters.

The Sensitivity of Hopping Transport in Dipolar Glasses and Molecularly Doped Polymers to Localised Dipole Ordering

“…However, as previously noted from Figure 3(a) the response of σ GDM is not as sensitive as σ DOS to the introduction of local order where it is typically found that to achieve a 50% reduction in σ GDM relative to the DG reference magnitude it is necessary for C to exceed about 0.9 for n/N > 0.3. Similar behaviour has been reported in independent Monte Carlo studies [13][14][15] which was attributed to weakly percolating transport where the majority of carriers follow low-mobility paths through NOC sites. The preference to hop via the NOC sites is clearly understood with reference to Figure 4 where it is noted that after the injected carriers have had an opportunity to thermalise they will tend to occupy the lowest energy states associated with the σ DOS (NOC) tail.…”

“…Simulations with local ordering have been performed to model both DGs and MDPs. This work extends independent previous Monte Carlo studies which have either considered short-range order in MDPs using non-correlated random orientation vectors [12], or have examined the effect of introducing ordered regions into DG energy landscapes by using pre-determined Gaussian distributions to perform the allocation of site energies [13][14][15]. By contrast the generation of energy landscapes in the present study has been achieved using a fundamental electrostatic calculation of the dipole potential, where local variations of the potential have been introduced using dipoles that are locally ordered within cubic regions that have a specified volume.…”

Monte Carlo Simulation of Carrier Diffusion in Organic Thin Films with Morphological Inhomogeneity

“…One of the prime motives behind tailoring the film morphology is to incorporate more structural order in an otherwise highly disordered homogeneous system for providing percolation pathways and thereby enhancing the charge carrier mobility [25][26][27][28] . These morphologically tailored films contain a blend of ordered regions and disordered regions, where the energetic disorder is low and high respectively [25][26][27][28][29][30][31][32] . Hence, these morphologically tailored films cannot be treated as homogeneous rather they are inhomogeneous [25][26][27][28][29][30][31][32] .…”

“…These morphologically tailored films contain a blend of ordered regions and disordered regions, where the energetic disorder is low and high respectively [25][26][27][28][29][30][31][32] . Hence, these morphologically tailored films cannot be treated as homogeneous rather they are inhomogeneous [25][26][27][28][29][30][31][32] . The charge transport in such system occurs through a mixture of ordered and less ordered regions.…”

“…The charge transport in such system occurs through a mixture of ordered and less ordered regions. In such cases, the energetic disorder seen by the carrier changes intermittently and the influence of energetic disorder on charge transport become complex [25][26][27][28][29][30][31][32] .…”