Effects of disorder on the current density and recombination profile in organic light-emitting diodes

Coehoorn, R.; Mensfoort, van Slm Siebe

doi:10.1103/physrevb.80.085302

Cited by 43 publications

(41 citation statements)

References 46 publications

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“…Moreover, "behind" the recombination zone the mobility of charge carriers of one type decreases further due to their now very strongly reduced density. 27 According to the present work, an additional reduction in the carrier mobilities in and behind the recombination zone should occur by the increased effective disorder due to the random Coulomb field of the carriers of the opposite sign. This should lead to a further reduction in the calculated width of the recombination zone.…”

Section: Discussionmentioning

confidence: 99%

Electron-hole recombination in disordered organic semiconductors: Validity of the Langevin formula

et al. 2009

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Accurate modeling of electron-hole recombination in organic light-emitting diodes ͑OLEDs͒ is essential for developing a complete description of their functioning. Traditionally, the recombination rate is described by the Langevin formula, with a proportionality factor equal to the sum of the electron and hole mobilities. In the disordered organic semiconductors used in OLEDs these mobilities have been shown to depend strongly on the carrier densities and on the electric field. Moreover, the energetic disorder leads to percolating pathways for the electron and hole currents, which may or may not be correlated. To answer the question whether the Langevin formula is still valid under such circumstances we perform Monte Carlo simulations of the recombination rate for Gaussian energetic disorder. We vary the disorder energy, the temperature, the densities, and mobility ratio of electrons and holes, the electric field, and the type of correlation between the electron and hole energies. We find that at zero electric field the Langevin formula is surprisingly well obeyed, provided that a change in the charge-carrier mobilities due to the presence of charge carriers of the opposite type is taken into account. Deviations from the Langevin formula at finite electric field are small at the field scale relevant for OLED modeling.

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Section: Discussionmentioning

confidence: 99%

Electron-hole recombination in disordered organic semiconductors: Validity of the Langevin formula

et al. 2009

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“…The recombination rate at zero field is described by the Langevin formula, whereas for finite fields an extension of that formula as described in Ref. 39 is used. Based on the results obtained in Refs.…”

Section: Introductionmentioning

confidence: 99%

“…For calculating the current density and the exciton-formation profile, we employ a recently developed one-dimensional drift-diffusion OLED device model. 39 The model is based on the experimentally determined (unipolar) hole 40 and electron 41 mobility functions. The recombination rate at zero field is described by the Langevin formula, whereas for finite fields an extension of that formula as described in Ref.…”

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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“…8 In order to investigate the effect of this space charge on the EA signal, as a first step the position-dependent electric field F͑x͒ is calculated as a function of the voltage, using the drift-diffusion model given in Ref. 29. Figure 4͑a͒ shows results for a 122 nm thick PF-TAA layer, for three values of the voltage.…”

Section: Experimental Results and Analysismentioning

confidence: 99%

Relation between the built-in voltage in organic light-emitting diodes and the zero-field voltage as measured by electroabsorption

et al. 2010

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For developing understanding of the current density onset voltage and injection barriers in organic lightemitting diodes ͑OLEDs͒, a precise determination of the built-in voltage, V bi , is of crucial importance. Commonly, V bi is assumed to be equal to the voltage V 0,EA at which in an electroabsorption ͑EA͒ experiment the reflection of light at the OLED is found to become insensitive to a small voltage modulation. However, this assumption is shown to lead to significant errors for devices with well-injecting contacts. From an analysis of EA experiments for hole-only devices containing a polyfluorene-based copolymer, it is shown that V 0,EA may be interpreted as an effective current density onset voltage, agreeing with the commonly accepted picture, but that for these devices V bi is ϳ0.5 V larger than V 0,EA . This is found to be consistent with predictions of V 0,EA from model calculations of the electric field and light-absorption profiles in the semiconducting layer.

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Effects of disorder on the current density and recombination profile in organic light-emitting diodes

Cited by 43 publications

References 46 publications

Electron-hole recombination in disordered organic semiconductors: Validity of the Langevin formula

Electron-hole recombination in disordered organic semiconductors: Validity of the Langevin formula

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

Relation between the built-in voltage in organic light-emitting diodes and the zero-field voltage as measured by electroabsorption

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