Effect of Triplet Confinement on Triplet–Triplet Annihilation in Organic Phosphorescent Host–Guest Systems

Ligthart, Arnout; Vries, Xander de; Zhang, Le; Pols, Mike; Bobbert, Peter A.; Eersel, Harm van; Coehoorn, R.

doi:10.1002/adfm.201804618

Cited by 67 publications

(69 citation statements)

References 47 publications

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“…This is a clear direction for future research, as it can be used to unravel photochemical processes that are hard to describe with classical methods for which the size of the active spaces becomes prohibitive. This encompasses industrially relevant applications such as the development as OLED devices with improved phosphorescent emitters [130] as well as fundamental questions on how nature has evolved protection mechanisms to prevent damages caused by absorption of too many [131] or too energetic [132] photons. The new MO coefficients matrix C is then used to transform the one-and two-electron integrals in the new MO basis.…”

Section: Discussionmentioning

confidence: 99%

A state-averaged orbital-optimized hybrid quantum–classical algorithm for a democratic description of ground and excited states

Yalouz

Senjean

Jakob

et al. 2021

Quantum Sci. Technol.

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Section: Discussionmentioning

confidence: 99%

A state-averaged orbital-optimized hybrid quantum–classical algorithm for a democratic description of ground and excited states

Yalouz

Senjean

Jakob

et al. 2021

Quantum Sci. Technol.

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“…This requires efficient bimolecular recombination whereas monomolecular quenching of triplets at trap sites needs to be avoided [30,31]. Thus, in summary, TTA can be useful for solar energy conversion, photodynamic therapy, and understanding of triplet diffusivity and for the efficiency of OLEDs, and numerous studies have been devoted to improving these processes [9,13,32]. Nevertheless, a comprehensive study on how the bimolecular annihilation and monomolecular quenching processes compete with each other and the influence of material and film properties in controlling and modifying this competition is still lacking.…”

Section: Introductionmentioning

confidence: 99%

Kinetic Monte Carlo Study of Triplet-Triplet Annihilation in Conjugated Luminescent Materials

et al. 2020

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It is well known that in organic solids the collision of two excitons can give rise to delayed fluorescence (DF). Revived interest in this topic is stimulated by the current endeavor towards the development of efficient organic optoelectronic devices such as organic light-emitting diodes (OLEDs) and solar cells, or sensitizers used in photodynamic therapy. In such devices, triplet excitations are ubiquitously present but their annihilations can be either detrimental, e.g., giving rise to a roll-off of intensity in an OLED, or mandatory, e.g., if the sensitizer relies on up-conversion of long-lived low-energy triplet excitations. Since the employed materials are usually noncrystalline, optical excitations migrate via incoherent hopping. Here, we employ kinetic Monte Carlo simulations (KMC) to study the complex interplay of triplet-triplet annihilation (TTA) and quenching of the triplet excitations by impurities in a single-component system featuring a Gaussian energy landscape and variable system parameters such as the length of the hopping sites, i.e., a conjugated oligomer, the morphology of the system, the degree of disorder (σ ), the concentration of triplet excitations, and temperature. We also explore the effect of polaronic contributions to the hopping rates. A key conclusion is that the DF features a maximum at a temperature that scales with σ/k B T. This is related to disorder-induced filamentary currents and thus locally enhanced triplet densities. We predict that a maximum for the TTA process near room temperature or above requires typically a disorder parameter of at least 70 meV.

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“…This criterion for good confinement is similar to that for triplet deconfinement from Ir-cored phosphorescent emitter molecules to many host molecules, as obtained experimentally from electroluminescence, photoluminescence and triplet-triplet annihilation studies. [28][29][30][31] The effect of deconfinement on the PL decay decreases with increasing guest concentration, so that for c g ≥ 20% the same exciton occupation on guest sites can already be achieved for ∆E T ≥ 0.1 eV.…”

Section: Comparison With Experimentsmentioning

confidence: 99%

Effects of exciton deconfinement on the transient photoluminescence from thermally activated delayed fluorescence host–guest systems

Hauenstein

Gottardi²,

Bobbert

et al. 2020

Journal of Applied Physics

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For thermally activated delayed fluorescence (TADF) host-guest systems used in organic light-emitting diodes (OLEDs), understanding of the transient photoluminescence (PL) measurements is crucial for accurate determination of the photophysical rates of the emitter. Here, we study how the PL is affected by triplet exciton deconfinement from the guest to the host molecules. This deconfinement can complicate the analysis of the PL decay and potentially lead to a loss of efficiency. From an analytical model we find that the transient PL intensity remains bi-exponential in the presence of exciton deconfinement for the case of fast triplet diffusion, albeit with a longer decay time of the delayed component. Deconfinement might therefore not always be recognizable from a single transient PL measurement. The role of deconfinement depends on the energetic disorder, the guest concentration, and the energy difference ∆E T between triplet exciton energies on the host and guest molecules, and is effectively suppressed for ∆E T > 0.2 eV. We find from analytical modelling and kinetic Monte Carlo simulations that the decay can become non-bi-exponential and even show a distinct third decay step. The shape of the decay curves depends on the characteristic times for guest-host transfer and host diffusion, relative to the prompt and delayed decay times of the TADF emitter. A comparison with available experimental data is included, finding qualitative agreement with dedicated deconfinement studies and indicating the influence of other processes for the often observed power-law decay at long time scales.

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Effect of Triplet Confinement on Triplet–Triplet Annihilation in Organic Phosphorescent Host–Guest Systems

Cited by 67 publications

References 47 publications

A state-averaged orbital-optimized hybrid quantum–classical algorithm for a democratic description of ground and excited states

A state-averaged orbital-optimized hybrid quantum–classical algorithm for a democratic description of ground and excited states

Kinetic Monte Carlo Study of Triplet-Triplet Annihilation in Conjugated Luminescent Materials

Effects of exciton deconfinement on the transient photoluminescence from thermally activated delayed fluorescence host–guest systems

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