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

Coehoorn, R.; Zhang, Le; Bobbert, Peter A.; Eersel, Harm van

doi:10.1103/physrevb.95.134202

Cited by 35 publications

(42 citation statements)

References 37 publications

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“…That may be viewed as a result of a "competition" between polarons that can each quench the nearby triplet. An analogous effect has been theoretically predicted [16] and experimentally found [13,17] for the case of TTA at high initial triplet volume densities and from a KMC simulation study of NN-type TPQ [8].…”

Section: A No-diffusion and Strong-diffusion Limitssupporting

confidence: 69%

“…For the case of immediate NN-type TPQ, a significant enhancement of the rate with increasing field was found [8]. The enhancement is due to a "polaron wind effect," which is analogous to the effect of electric fields on the rate of diffusion-controlled reactions between ions in solution [26].…”

Section: B Simulation Results and Analysismentioning

confidence: 95%

“…The approach has been described extensively in Ref. [8]. In short, the systems considered are 100 × 100 × 100 nm 3 boxes in which the molecular sites reside on a simple cubic lattice with a lattice constant a = 1 nm.…”

Section: A Methodsmentioning

confidence: 99%

“…Table I in Ref. [8] contains an overview of the dependence of the diffusion coefficient on the disorder parameter and the carrier density.…”

Section: A Methodsmentioning

confidence: 99%

“…Within such analyses, it is assumed that the rate coefficient is independent of the local polaron density and the local electric field. However, we have recently shown that for the specific case of TPQ occurring immediately when a polaron has diffused to a nearest-neighbor (NN) site of the triplet, the effective rate coefficient can show in organic materials a distinct carrier density and electric field dependence [8]. Such an immediate NN-type TPQ mechanism may be viewed as resulting from a Dexter-type short-range quantum-mechanical tunneling process.…”

Section: Introductionmentioning

confidence: 99%

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Förster-type triplet-polaron quenching in disordered organic semiconductors

Coehoorn

Bobbert

Eersel³

2017

Phys. Rev. B

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Triplet-polaron quenching (TPQ) is a major cause of the efficiency loss at large current densities in phosphorescent organic light-emitting diodes. The nature of the interaction process is presently not well understood. In this paper, we study TPQ due to Förster-type triplet-polaron interactions in energetically disordered organic semiconductors with a Gaussian polaron density of states. A continuum theory, which neglects the spatial inhomogeneity and energetic disorder, is from a kinetic Monte Carlo approach shown to correctly predict that the effective steady-state TPQ rate coefficient k TPQ,eff depends only sensitively on the polaron diffusion in a rather narrow range of diffusion coefficients. However, in this regime, significant discrepancies between the two approaches are found, in particular for realistic values of the TPQ-Förster radius, around 3 nm, and for systems with strong energetic disorder. Both approaches show that k TPQ,eff is not constant but can depend on the polaron density and the electric field. Various methods for deducing the TPQ mechanism from experiment are discussed, including an approach which utilizes the shape of the time-dependent photoluminescence after pulsed illumination.

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Section: A No-diffusion and Strong-diffusion Limitssupporting

confidence: 69%

Section: B Simulation Results and Analysismentioning

confidence: 95%

Section: A Methodsmentioning

confidence: 99%

“…Table I in Ref. [8] contains an overview of the dependence of the diffusion coefficient on the disorder parameter and the carrier density.…”

Section: A Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Förster-type triplet-polaron quenching in disordered organic semiconductors

Coehoorn

Bobbert

Eersel³

2017

Phys. Rev. B

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Investigating Free Charge‐Carrier Recombination in Organic LEDs Using Open‐Circuit Conditions

Fischer

Reineke

2019

Advanced Optical Materials

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Although organic light‐emitting diodes (LEDs) are widely used in commercial applications, a comprehensive knowledge about the occurring recombination pathways is still absent. Especially access to the bandgap is needed to figure out which path the charge carriers take, key to further understand and optimize the latest generations of thin film LED technology. Here, state‐of‐the‐art organic LEDs are treated like solar cells by measuring the open‐circuit voltage under UV illumination. A variation of the illumination intensity and temperature gives access to the effective bandgap, the ideality factor and the recombination strength. A differential evaluation approach is implemented, yielding the full temperature and intensity dependence of these parameters. A radiative and a non‐radiative recombination process are identified and used to reconstruct the current density dependence of the external quantum efficiency. All recombination events are related to an effective bandgap that suggests free charge recombination between the guest and the host material of the emission layer. This approach will thus help to identify and eliminate non‐radiative recombination losses in LEDs based on other type of molecules emitters and materials, such as perovskites or quantum dots, as well. Knowing the effective bandgap will also be essential to realize LEDs with the lowest possible driving voltages.

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Tracking Exciton Diffusion and Exciton Annihilation in Single Nanoparticles of Conjugated Polymers by Photon Correlation Spectroscopy

Schedlbauer

Streicher

Förster

et al. 2022

Advanced Optical Materials

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emission color of an organic light-emitting diode (OLED), for example, arises primarily from the electronic structure of the individual molecular building block making up the thin film of the device, implying that single-molecule fluorescence techniques are ideal probes of the underlying intrinsic electronic structure. [1] Intermolecular interactions can, conceivably, arise between polymer chains, inducing H-and J-type aggregation effects, [2] but such coupling is usually effectively suppressed by resorting to molecules with bulky sidechains. [3] A π-conjugated polymer material that has proven particularly interesting in this regard is ladder-type poly(para-phenylene) (LPPP). [4] This compound not only displays a remarkable structural rigidity, minimizing excited-state relaxation and therefore making absorption and luminescence spectra near-perfect mirror images of each other. [5] It also shows well-resolved vibronic transitions, attesting to the low degree of intermolecular disorder. Interchain electronic aggregation effects are virtually absent, so that ensemble absorption and emission spectra are almost identical in the dissolved form and in bulk films. [5] In fact, intermolecular interactions are so weak that the sum of single-molecule luminescence spectra almost perfectly replicates the bulk-film ensemble spectrum. [6] At the same time, LPPP-based materials have a high fluorescence quantum yield and exhibit substantial photostability, making them ideal for applications involving large excitation densities. [5] Feldmann and Lemmer pioneered the use of LPPP in low-threshold mechanically flexible laser structures, [7] a feat that received widespread attention culminating in the award of the Philip-Morris Research Prize. [8] To this day, a photograph of the far-field intensity pattern generated by such a plastic laser [9] decorates the cover of the journal "Organic Electronics". [10] More recently, the unique characteristics of LPPP have been exploited in optical microcavities to create exciton-polariton condensates by strong light-matter coupling, [11] which can even enable optical transistor-like action [12] and single-photon optical nonlinearities at room temperature. [13] Inferring polymer aggregation effects from spectral signatures alone can be challenging and requires a detailed understanding A fundamental question relating to the nature of light emission and absorption in organic semiconductors is the dimension of the domain within a bulk material responsible for the interaction of light and matter. How large can a nanoparticle become to retain the quantized nature of light emission? Excitons are only a few nanometers in size, but because they diffuse in space, they probe a much larger volume than the single molecule. When excitons meet, they may decay non-radiatively by singlet-singlet or singlet-triplet annihilation (SSA or STA). Fluorescence photon statistics reveal whether single photons are emitted (photon antibunching) or arrive in randomly spaced packets (photon bunching), offering direct insight ...

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

Cited by 35 publications

References 37 publications

Förster-type triplet-polaron quenching in disordered organic semiconductors

Förster-type triplet-polaron quenching in disordered organic semiconductors

Investigating Free Charge‐Carrier Recombination in Organic LEDs Using Open‐Circuit Conditions

Tracking Exciton Diffusion and Exciton Annihilation in Single Nanoparticles of Conjugated Polymers by Photon Correlation Spectroscopy

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