Effect of triplet confinement on triplet–triplet annihilation in organic phosphorescent host–guest systems

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Abstract

The efficiency of phosphorescent organic light emitting diodes (OLEDs) shows a decrease with increasing luminance (“roll-off”). One of the contributions to the roll-off is triplet–triplet annihilation (TTA). TTA is the process of energy transfer from one triplet exciton to another, after which the excited exciton decays nonradiatively to the lowest triplet state. In this study, the TTA-rate is measured for a large number of emissive materials consisting of a small concentration of phosphorescent “guest” molecules, with emission colors across the entire visible range, embedded in various host materials. It is found that the TTA-rate does not only depend on the direct interaction rate between the excitons on the guest molecules, but also on the difference in triplet energy ΔE T of the host and guest molecules: when ΔE T is smaller than about 0.20 eV, diffusion of excitons via the host molecules leads to a significant enhancement of the TTA-rate. By varying the guest concentration and using kinetic Monte Carlo simulations, the roles of the direct interaction, guest-mediated diffusion, and host-mediated diffusion are disentangled.

Original languageEnglish
Article number1804618
Number of pages10
JournalAdvanced Functional Materials
Volume28
Issue number52
DOIs
Publication statusPublished - 27 Dec 2018

Fingerprint

Excitons
excitons
Molecules
molecules
Organic light emitting diodes (OLED)
luminance
Energy transfer
atomic energy levels
Luminance
light emitting diodes
energy transfer
interactions
Color
color
Kinetics
LDS 751
augmentation
kinetics
decay
simulation

Keywords

  • exciton confinement
  • exciton diffusion
  • kinetic Monte Carlo simulations
  • organic light-emitting diodes
  • triplet–triplet annihilation

Cite this

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title = "Effect of triplet confinement on triplet–triplet annihilation in organic phosphorescent host–guest systems",
abstract = "The efficiency of phosphorescent organic light emitting diodes (OLEDs) shows a decrease with increasing luminance (“roll-off”). One of the contributions to the roll-off is triplet–triplet annihilation (TTA). TTA is the process of energy transfer from one triplet exciton to another, after which the excited exciton decays nonradiatively to the lowest triplet state. In this study, the TTA-rate is measured for a large number of emissive materials consisting of a small concentration of phosphorescent “guest” molecules, with emission colors across the entire visible range, embedded in various host materials. It is found that the TTA-rate does not only depend on the direct interaction rate between the excitons on the guest molecules, but also on the difference in triplet energy ΔE T of the host and guest molecules: when ΔE T is smaller than about 0.20 eV, diffusion of excitons via the host molecules leads to a significant enhancement of the TTA-rate. By varying the guest concentration and using kinetic Monte Carlo simulations, the roles of the direct interaction, guest-mediated diffusion, and host-mediated diffusion are disentangled.",
keywords = "exciton confinement, exciton diffusion, kinetic Monte Carlo simulations, organic light-emitting diodes, triplet–triplet annihilation",
author = "Arnout Ligthart and {de Vries}, Xander and Le Zhang and Pols, {Mike C.W.M.} and Bobbert, {Peter A.} and {van Eersel}, Harm and Reinder Coehoorn",
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Effect of triplet confinement on triplet–triplet annihilation in organic phosphorescent host–guest systems. / Ligthart, Arnout; de Vries, Xander; Zhang, Le; Pols, Mike C.W.M.; Bobbert, Peter A.; van Eersel, Harm; Coehoorn, Reinder.

In: Advanced Functional Materials, Vol. 28, No. 52, 1804618, 27.12.2018.

Research output: Contribution to journalArticleAcademicpeer-review

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AU - Ligthart, Arnout

AU - de Vries, Xander

AU - Zhang, Le

AU - Pols, Mike C.W.M.

AU - Bobbert, Peter A.

AU - van Eersel, Harm

AU - Coehoorn, Reinder

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N2 - The efficiency of phosphorescent organic light emitting diodes (OLEDs) shows a decrease with increasing luminance (“roll-off”). One of the contributions to the roll-off is triplet–triplet annihilation (TTA). TTA is the process of energy transfer from one triplet exciton to another, after which the excited exciton decays nonradiatively to the lowest triplet state. In this study, the TTA-rate is measured for a large number of emissive materials consisting of a small concentration of phosphorescent “guest” molecules, with emission colors across the entire visible range, embedded in various host materials. It is found that the TTA-rate does not only depend on the direct interaction rate between the excitons on the guest molecules, but also on the difference in triplet energy ΔE T of the host and guest molecules: when ΔE T is smaller than about 0.20 eV, diffusion of excitons via the host molecules leads to a significant enhancement of the TTA-rate. By varying the guest concentration and using kinetic Monte Carlo simulations, the roles of the direct interaction, guest-mediated diffusion, and host-mediated diffusion are disentangled.

AB - The efficiency of phosphorescent organic light emitting diodes (OLEDs) shows a decrease with increasing luminance (“roll-off”). One of the contributions to the roll-off is triplet–triplet annihilation (TTA). TTA is the process of energy transfer from one triplet exciton to another, after which the excited exciton decays nonradiatively to the lowest triplet state. In this study, the TTA-rate is measured for a large number of emissive materials consisting of a small concentration of phosphorescent “guest” molecules, with emission colors across the entire visible range, embedded in various host materials. It is found that the TTA-rate does not only depend on the direct interaction rate between the excitons on the guest molecules, but also on the difference in triplet energy ΔE T of the host and guest molecules: when ΔE T is smaller than about 0.20 eV, diffusion of excitons via the host molecules leads to a significant enhancement of the TTA-rate. By varying the guest concentration and using kinetic Monte Carlo simulations, the roles of the direct interaction, guest-mediated diffusion, and host-mediated diffusion are disentangled.

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