Modeling of the transient mobility in disordered organic semiconductors with a Gaussian density of states

Germs, WC Wijnand; Holst, van der Jjm Jeroen; Mensfoort, van Slm Siebe; Bobbert, PA Peter; Coehoorn, R.

doi:10.1103/physrevb.84.165210

Cited by 50 publications

(34 citation statements)

References 48 publications

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“…18 A fair description of the frequency-and voltage-dependent capacitance could be obtained within a one-dimensional (1D) multiple-trapping model for carrier relaxation. 18 In that study, the following approach was used: (1) three-dimensional (3D) Monte Carlo (MC) calculations were carried out to obtain the time-dependent mobility after a sudden very small increase of the charge density, providing the (complex) frequency-dependent mobility after a Fourier transformation, and (2) this result was included in a 1D calculation of the (complex) frequency-dependent current density. Because this approach is indirect and rather involved, it is of interest to analyze the results of transient current-density measurements using a more direct fully 3D approach.…”

Section: Introductionmentioning

confidence: 99%

Charge-carrier relaxation in disordered organic semiconductors studied by dark injection: Experiment and modeling

et al. 2013

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Understanding of stationary charge transport in disordered organic semiconductors has matured during recent years. However, charge-carrier relaxation in nonstationary situations is still poorly understood. Such relaxation can be studied in dark injection experiments, in which the bias applied over an unilluminated organic semiconductor device is abruptly increased. The resulting transient current reveals both charge-carrier transport and relaxation characteristics. We performed such experiments on hole-only devices of a polyfluorene-based organic semiconductor. Modeling the dark injection by solving a one-dimensional master equation using the equilibrium carrier mobility leads to a too-slow current transient, since this approach does not account for carrier relaxation. Modeling by solving a three-dimensional time-dependent master equation does take into account all carrier transport and relaxation effects. With this modeling, the time scale of the current transient is found to be in agreement with experiment. With a disorder strength somewhat smaller than extracted from the temperature-dependent stationary current-voltage characteristics, also the shape of the experimental transients is well described.

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Section: Introductionmentioning

confidence: 99%

Charge-carrier relaxation in disordered organic semiconductors studied by dark injection: Experiment and modeling

et al. 2013

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“…At least three potentially relevant timescales can therefore be identified, first, the single particle relaxation time τ rel , describing the relaxation of a single hole or electron in the density of states of the semiconductor. Although this time can be up to seconds at low charge densities due to the high degree of disorder in organic semiconductors, 10 the experimental results presented below do not seem to carry any features that are related to this timescale, and in the numerical modeling we shall assume the charge carrier distribution to be always in local thermal equilibrium. The second anticipated timescale is the transit time, i.e.…”

Section: Introductionmentioning

confidence: 99%

Scaling of characteristic frequencies of organic electronic ratchets

et al. 2012

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The scaling of the characteristic frequencies of electronic ratchets operating in a flashing mode is investigated by measurements and numerical simulations. The ratchets are based on organic field effect transistors operated in accumulation mode. Oscillating potentials applied to asymmetrically spaced interdigitated finger electrodes embedded in the gate dielectric create a time-dependent, spatially asymmetric perturbation of the transistor channel potential. As a result, a net dc current can flow between source and drain despite zero source-drain bias. The frequency at current maximum is linearly dependent on the charge carrier density and the charge carrier mobility and inversely proportional to the squared length of the ratchet period, which can be related to the RC time of one asymmetric unit. Counterintuitively, it is independent of driving amplitude. Furthermore, the frequency at current maximum depends on the asymmetry of the ratchet potential, whereas the frequency of maximum charge pumping efficiency does not.

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“…Formally, it would be possible to express all simulation results in terms of a fundamental length unit, e.g., the nearestneighbor distance a, and a fundamental time unit, e.g., the average hopping time t 0 between two nearest-neighbor sites with equal hole energies. However, in order to help the reader to readily see the relevance of the results to realistic materials, we present the simulation results for concrete values of these time and length scales: a = 1 nm, so that N t = 10 −27 m −3 , a value typical for small-molecule materials used in OLEDs, and t 0 = 3.0 × 10 −11 s, a value typical for hole transport in the often-used material α − NPD [21,33] …”

Section: A Simulation Approachmentioning

confidence: 99%

Effect of polaron diffusion on exciton-polaron quenching in disordered organic semiconductors

et al. 2017

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Exciton-polaron quenching (EPQ) is a major efficiency loss process in organic optoelectronic devices, in particular at high excitation densities. Within commonly used models, the rate is assumed to be given by the product of the exciton density, the polaron density, and a constant EPQ rate coefficient, which is proportional to the polaron diffusion coefficient and an EPQ capture radius. In this work, we study the effects of polaron diffusion on the EPQ rate in energetically disordered materials with a Gaussian density of states using kinetic Monte Carlo simulations, and show that the effective rate coefficient can depend strongly on the polaron concentration and on the electric field. We furthermore find that under realistic conditions, the effective value of the capture radius can exceed the expected value of ∼1 nm by up to two orders of magnitude. To a first approximation, the simulation results can be understood from macroscopic diffusion theory, adapted at finite electric fields to include the observed "polaron wind" effect. However, for strongly disordered systems we find distinct deviations from that theory, related to the very small time and spatial scales involved in the capture process.

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Modeling of the transient mobility in disordered organic semiconductors with a Gaussian density of states

Cited by 50 publications

References 48 publications

Charge-carrier relaxation in disordered organic semiconductors studied by dark injection: Experiment and modeling

Charge-carrier relaxation in disordered organic semiconductors studied by dark injection: Experiment and modeling

Scaling of characteristic frequencies of organic electronic ratchets

Effect of polaron diffusion on exciton-polaron quenching in disordered organic semiconductors

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