Quantifying Exciton Annihilation Effects in Thermally Activated Delayed Fluorescence Materials

Thakur, K. B.; Zee, Bas van der; Wetzelaer, Gert‐Jan A. H.; Ramanan, Charusheela; Blom, Paul W. M.

doi:10.1002/adom.202101784

Cited by 14 publications

(14 citation statements)

References 35 publications

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“…Moreover, it corresponds very well to the k TTA of 8 × 10 −18 m 3 s −1 found in our recent TrPL study on CzDBA. [27] Surprisingly, we find that a single k TTA value fits the entire investigated temperature range (295-215 K). Recently, a kinetic Monte Carlo study of TTA in conjugated organic semiconductors found that the temperature dependence of TTA is weak in our investigated temperature range, given that the energetic disorder is small.…”

Section: Photophysical Parametersmentioning

confidence: 63%

“…We note that the role of SSA is controversial, either being considered a significant contribution to the roll-off, [41][42][43] whereas other works deem SSA unimportant, [20,37] making it necessary to consider its significance in this study. In our recent TrPL study on CzDBA neat films we found that SSA was not a major decay process, [27] which justifies neglecting it in our OLED analysis. Turning our attention to SPQ, the triplet density exceeds the singlet density often by more than an order of magnitude under steady state conditions, making TPQ a far more relevant process than SPQ.…”

Section: Effect Of Various Quenching Processes On the Efficiencymentioning

confidence: 77%

“…The rate equations can be solved in steady state to obtain [S(x)] and [T(x)] at every voltage, using values for k (r)ISC and other photophysical parameters published previously, [27] but for completeness we present them here again in Table 2. The steady-state local singlet concentration [S(x)], as derived in Section 1 of the Supporting Information, is given by…”

Section: Charge-transport Parametersmentioning

confidence: 99%

“…[16] A discussion of the Table 2. Photophysical parameters obtained from the photoluminescence decay of CzDBA, [27] as used in the simulation.…”

Section: Charge-transport Parametersmentioning

confidence: 99%

“…[16] However, a recent TrPL study done on CzDBA neat films showed that the reported k ISC was overestimated since in the analysis of the PL decay annihilation processes as TTA were not incorporated. [27] Taking these processes into account a k ISC of to 1 × 10 6 s −1 was obtained and also used in this work. To further illustrate the sensitivity of k TTA to ISC and rISC we plot in Figure S3, Supporting Information the normalized efficiency versus voltage of a 300 nm OLED at 295 K for the earlier reported values of k ISC as well as the currently used values obtained from PL decay.…”

Section: Comparison Tadf Model To Analytical Formulasmentioning

confidence: 99%

See 4 more Smart Citations

Numerical Device Model for Organic Light‐Emitting Diodes Based on Thermally Activated Delayed Fluorescence

Zee

Wetzelaer

et al. 2022

Adv Elect Materials

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have the drawback of using expensive, environmentally unfriendly heavy-metal complexes. In 2012, a new class of fully organic OLED materials emerged using thermally activated delayed fluorescence (TADF). [3,4] Here, the small singlet-triplet energy gap allows for efficient conversion from triplets to singlets on the same molecule, i.e., efficient reverse intersystem crossing (rISC) prompted by thermal energy. Therefore, while retaining the theoretically achievable 100% IQE, the necessity of an added toxic heavy-metal element was eliminated. Consequently, TADF materials are being treated as promising candidates for highly efficient OLEDs and have therefore gained considerable scientific attention in recent years. [5][6][7][8] High efficiencies have been demonstrated for TADF devices employing host-guest systems in multilayer architectures, similar to phosphorescent OLEDs. However, due to the many variables induced by multilayer architectures, such as the individual transport properties of the layers and illdefined barriers at the heterojunctions, a quantitative understanding of the device operation of TADF OLEDs is hampered. For this reason, a comprehensive device model for TADF OLEDs is presently lacking. In contrast, singlelayer polymer LEDs (PLEDs) have been successfully modeled with a well-established numerical drift-diffusion simulation program. [9][10][11][12] Also for TADF OLEDs, a simplified device structure would strongly benefit the development of a quantitative device model for TADF OLEDs.Recently, an efficient TADF OLED (EQE ≈ 19% at 500 cd A −1 ) was demonstrated based on a single TADF emitting layer of pristine 9,10-bis(4-(9H-carbazol-9-yl)−2,6-dimethylphenyl)−9,10diboraanthracene (CzDBA), [13] of which the chemical structure is shown in Figure 1a. A photoluminescence quantum yield (PLQY) of >90% in the neat film, low electron-and hole-trap densities combined with balanced bipolar transport [14] and efficient charge injection via Ohmic electron and hole contacts, [15] make these single-layer CzDBA OLEDs an ideal model system to uncover the device physics of OLEDs based on TADF emitters. In a recent study, the efficiency decrease at high voltage (rolloff) of a single-layer CzDBA OLED was studied using analytical formulas, [16] and triplet-triplet annihilation (TTA) was identified to be the origin of the roll-off in EQE at high voltages. However, in this analytical approach a number of assumptions were made by neglecting the following features: the effect of intersystem crossing (ISC), the effect that TTA generates singlets, In organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF), non-emissive triplet excitons are converted to emissive singlet excitons via reverse intersystem crossing (rISC). To model the operation of TADF-based OLEDs, quantification of the triplet population is therefore a prerequisite. A numerical drift-diffusion model is presented for TADF OLEDs that next to singlet and triplet generation also includes the positional dependence of intersyste...

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Section: Photophysical Parametersmentioning

confidence: 63%

Section: Effect Of Various Quenching Processes On the Efficiencymentioning

confidence: 77%

Section: Charge-transport Parametersmentioning

confidence: 99%

“…[16] A discussion of the Table 2. Photophysical parameters obtained from the photoluminescence decay of CzDBA, [27] as used in the simulation.…”

Section: Charge-transport Parametersmentioning

confidence: 99%

Section: Comparison Tadf Model To Analytical Formulasmentioning

confidence: 99%

See 3 more Smart Citations

Numerical Device Model for Organic Light‐Emitting Diodes Based on Thermally Activated Delayed Fluorescence

Zee

Wetzelaer

et al. 2022

Adv Elect Materials

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Boosting the Efficiency of Organic Solid‐State Lasers by Solvato‐Tailored Assemblies

Man

Bao

et al. 2022

Adv Funct Materials

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The photophysical properties of pure organic materials in solid-state are widely related to the crystal's arrangements. Herein, 4,6-bis((E)-4-(dibenzothiophene) styryl)-5(ethoxycarbonyl)-2,2-difluoro-2H-1,3,2-dioxaborinin-1-ium-2-uide (BBSF) is employed as a mode molecule to explore the relationship between molecular arrangement and performance. Three elegant crystals (solventfree-J-aggregation of EA-crystal, solvent-J-aggregations of CB-crystal, and FB-crystal) are obtained by solvato-tailored strategy. Detailed single crystal structures and photophysical data reveal that all the three crystals adopt a J-type aggregation model. EA-crystal does not involve solvent molecular while the CB-and FB-crystals involve chlorobenzene (CB) and fluorobenzene (FB) molecules, respectively. Solvent molecules can effectively separate the two columns of BBSF molecules, resulting in high brightness emission. Laser behaviors indicate that the solvent-microcrystals display higher brightness, lower threshold, as well as higher quality factor than solvent-free-microcrystal due to the weakened bimolecular exciton annihilation process. This strategy not only paves an intriguing way to the construction and preparation of pure organic J-aggregation laser materials but also offers a guideline for suppressing bmEA process through introducing solvent molecules.

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Electron Donor‐Functionalized Pyrenes with Amplified Spontaneous Emission for Violet–Blue Electroluminescent Devices Beyond the Spin Statistical Limit

Welscher,

Straub,

Stümpges

et al. 2024

Adv Funct Materials

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Direct electrically pumped organic lasers remain inaccessible to date, due to an interplay of different adverse effects. The most important of these effects are insufficient charge carrier mobility in the organic material, accumulation of triplet excitons upon charge injection, and absorption from the electrodes in the device. While triplet state management can be achieved using molecules that recycle triplet states into emissive singlet states, these molecules rarely support amplified emission. Pyrene derivatives not only show excellent charge transport properties, but their rigid π‐conjugated structure also entails excellent electro‐ and photoluminescence efficiency. Pyrenes exhibit very low‐lying first excited triplet states, rendering this class of molecules interesting for ultrafast upper‐level reverse intersystem crossing. This process counteracts the triplet accumulation in organic lasers. Here, pyrenes are functionalized with electron‐rich moieties of different donor strengths. Through comprehensive spectroscopic and quantum chemical analysis, the character of the charge transfer excited state is correlated with optical properties, excited state lifetimes, amplified spontaneous emission, and triplet recycling. Two donor functionalized pyrenes are reported with violet–blue emission that overcome the spin‐statistical limit of conventional organic emitters with spin factors ηST of up to 0.43 and low thresholds for amplified spontaneous emission Eth down to 1.73 µJ cm−2.

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Quantifying Exciton Annihilation Effects in Thermally Activated Delayed Fluorescence Materials

Cited by 14 publications

References 35 publications

Numerical Device Model for Organic Light‐Emitting Diodes Based on Thermally Activated Delayed Fluorescence

Numerical Device Model for Organic Light‐Emitting Diodes Based on Thermally Activated Delayed Fluorescence

Boosting the Efficiency of Organic Solid‐State Lasers by Solvato‐Tailored Assemblies

Electron Donor‐Functionalized Pyrenes with Amplified Spontaneous Emission for Violet–Blue Electroluminescent Devices Beyond the Spin Statistical Limit

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