Spatially dispersive transport: A mesoscopic phenomenon in disordered organic semiconductors

Rappaport, Noam; Preezant, Yevgeni; Tessler, Nir

doi:10.1103/physrevb.76.235323

Cited by 22 publications

(28 citation statements)

References 22 publications

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“…However, for devices with a thickness of the order of or smaller than this typical length scale, the concept of a local mobility breaks down. 23 The presence of current filaments from the injecting to the collecting elec trode then leads to a higher net current than obtained with a 085203-6 M ODELING AND ANALYSIS OF THE THREE-... PHYSICAL REVIEW B 79, 085203 (2009) 1D continuum model; the effect becoming larger for larger electric field. This is the reason for the discrepancies found in Figs.…”

Section: Three-dimensional Structure Of the Current Distribution:mentioning

confidence: 94%

Modeling and analysis of the three-dimensional current density in sandwich-type single-carrier devices of disordered organic semiconductors

et al. 2009

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We present the results of a modeling study of the three-dimensional current density in single-carrier sandwich-type devices of disordered organic semiconductors. The calculations are based on a master-equation approach, assuming a Gaussian distribution of site energies without spatial correlations. The injection-barrier lowering due to the image potential is taken into account, so that the model provides a comprehensive treatment of the space-charge-limited current as well as the injection-limited current (ILC) regimes. We show that the current distribution can be highly filamentary for voltages, layer thicknesses, and disorder strengths that are realistic for organic light-emitting diodes and, that, as a result, the current density in both regimes can be significantly larger than as obtained from a one-dimensional continuum drift-diffusion device model. For devices with large injection barriers and strong disorder, in the ILC transport regime, good agreement is obtained with the average current density predicted from a model assuming injection and transport via one dimensional filaments [A. L. Burin and M.

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Section: Three-dimensional Structure Of the Current Distribution:mentioning

confidence: 94%

Modeling and analysis of the three-dimensional current density in sandwich-type single-carrier devices of disordered organic semiconductors

et al. 2009

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“…[46,47] Instead of suggesting that the charge-energy distribution is a function of time, it was argued that for thin films the energy distribution of the charges is different across the plane of the film, and hence is a function of xy spatial coordinate. If the theory by Scher and Montroll led us to the notion that to reach equilibrium one needs to let the measurement span a long enough time window, or that the film needs to be thick enough, now Rappaport suggests that the film width is a critical factor as well.…”

Section: Non-averaging Approachmentioning

confidence: 99%

Charge Transport in Disordered Organic Materials and Its Relevance to Thin‐Film Devices: A Tutorial Review

et al. 2009

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In this review, we describe a variety of models or theoretical approaches to transport in disordered media and discuss the implication to modern organic devices. There are far too many models or variations, so our aim is not to try to cover them all. Instead, we show that when the different models are presented along with the assumptions included while being developed, they can all teach us and help us to develop some intuition regarding what goes on in nonordered materials. One may encounter debates regarding a model being wrong, but it is our belief that only when the models are used out of context (not within their basic assumptions) the obtained results could be false.One of the things one encounters while starting to study organic semiconductors is that the textbook models taught in semiconductor-device courses have to be revisited, and one has to look for ''old'' books that were written before silicon technology took over. With this spirit, we start a few years back, or a century ago. In 1900, three years after the discovery of the electron by Thomson, Drude proposed a model that explained the known conductivity phenomenon in metals and other types of materials.[1] This model was based on the assumption that electrons classically accelerate under an applied electric field and collide with the lattice's heavy positive ions. Upon collision, the electrons were assumed to scatter into a random angle and at a speed that was on average consistent with the local temperature. It would then go on accelerating until the next scattering event. This model, although erroneous in the assumption that the basic scattering centers were the lattice ions, was able to physically explain the already known Ohm's law and the Joule heating effect. Along with the debut of quantum mechanics came the quantum mechanical description of matter and the realization that in a well-ordered lattice electrons should be mathematically described as Bloch waves, and that the scattering was not the result of collisions with any lattice ion but rather scattering from defects, contaminations, and phonons. Nevertheless, the Drude model, under the semiclassical approximation, is conceptually appropriate for describing electron transport through crystal lattices, that is, freely roaming charge carriers that scatter upon collisions with defects, contaminations, and phonons. The carriers earn the name ''free'' whenever the material properties are such that the mean free path between collisions, L, is much longer than the typical carrier's Bloch wavelength, thus the carriers have very broad wavefunctions extending over many lattice units.However, as was historically elucidated by Anderson, [2] introducing disorder into the lattice and breaking the crystal symmetry results in the wavefunctions becoming localized and in the formation of energy states in the forbidden band-gap. The Drude concepts, and others deriving on its intuitive approach, can no longer serve us in explaining transport under such circumstances. Since the materials we are interested in a...

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“…the effect on the recombination rate of a mobility anisotropy 31 and the effect of correlation or anticorrelation between the electron and hole state energies on the same molecular site. 32 Finally, one might raise the question whether, in view of the disorderinduced filamentary of the current density in actual OLEDs, [33][34][35][36][37][38] the Langevin formula can still be applicable. One of the assumptions which leads to that formula is that the charge carrier transport occurs homogeneously across the device.…”

Section: Introductionmentioning

confidence: 99%

Predictive modeling of the current density and radiative recombination in blue polymer-based light-emitting diodes

Mensfoort

Billen

Carvelli

et al. 2011

Journal of Applied Physics

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The results of a combined experimental and modeling study of charge transport, recombination and light emission in blue organic light-emitting diodes (OLEDs) based on a polyfluorene derivative are presented. It is shown that the measured temperature-dependent current-voltage curves and the voltage-dependent current efficiency are accurately described using an OLED device model that is based on the separately determined unipolar electron and hole mobility functions. The recombination rate is calculated using the Langevin formula, including recombination of holes with free as well as trapped electrons. The light emission is obtained from the exciton formation profile using independently determined values of the exciton radiative decay probability, the average dipole orientation, and assuming a fraction of singlet excitons ηS =(22±3)%, close to the quantum-statistical value. No additional free parameter is used. This shows that predictive one-dimensional device modeling of OLEDs is feasible.

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Spatially dispersive transport: A mesoscopic phenomenon in disordered organic semiconductors

Cited by 22 publications

References 22 publications

Modeling and analysis of the three-dimensional current density in sandwich-type single-carrier devices of disordered organic semiconductors

Modeling and analysis of the three-dimensional current density in sandwich-type single-carrier devices of disordered organic semiconductors

Charge Transport in Disordered Organic Materials and Its Relevance to Thin‐Film Devices: A Tutorial Review

Predictive modeling of the current density and radiative recombination in blue polymer-based light-emitting diodes

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