Thermally Activated Delayed Fluorescence: Beyond the Single Molecule

Etherington, Marc K.

doi:10.3389/fchem.2020.00716

Cited by 24 publications

(20 citation statements)

References 82 publications

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“…Thus, more and more scientists have devoted themselves into the research of it in recent years. [82][83][84][85][86][87][88][89][90][91] Especially, Ruren Xu and coworkers proposed "Towards a new discipline of condensed matter chemistry" in 2018. [82,83] It is believed that after constant exploration, the molecular structure-packing property relationship could be revealed clearly and the adjustment of luminescence property in aggregation state could be easily realized from the source of molecular design.…”

Section: Summary and Perspectivesmentioning

confidence: 99%

Organic luminescent materials: The concentration on aggregates from aggregation‐induced emission

2020

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The research of organic luminescent materials in aggregate has drawn more and more attention for their wide applications. To adjust the luminescent properties for aggregates, a deep understanding of the corresponding internal mechanism is needed. In this short review, a brief introduction of aggregation‐induced emission (AIE) and some other solid state luminescence behaviors derived from or parallel to AIE is presented. Particularly, the relationship between emission property and intermolecular/intramolecular interactions is summarized, with the aim to guide the further development of organic optoelectronic materials in aggregate.

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Section: Summary and Perspectivesmentioning

confidence: 99%

Organic luminescent materials: The concentration on aggregates from aggregation‐induced emission

2020

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“…The exciplex formation between the host and the TADF emitter is an issue that should be taken into account. [127] As discussed, the purely organic TADF emitters are typically constructed based on a donor-acceptor structure. In this context, exciplex formation between the donor of the host and the acceptor of the TADF emitter (vice versa) is possible in the solid film, whether the host is unipolar or bipolar.…”

Section: Exciplex Formation Between the Host And Tadf Emittermentioning

confidence: 99%

Host‐Dopant Interaction between Organic Thermally Activated Delayed Fluorescence Emitter and Host Material: Insight into the Excited State

et al. 2021

Advanced Optical Materials

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rapidly, and the products based on OLEDs including smartphones, televisions, monitors, etc. are being commercialized.The utilization mechanism of the excitons determines the quantum efficiency of the devices. [13][14][15] OLEDs based on the conventional fluorescent materials can only harvest the singlet excitons for light emission, which results in an upper limit of only 25% for internal quantum efficiency (IQE). The phosphorescent OLEDs incorporating transition metals into the molecular framework of organic emitters represent a huge breakthrough, which demonstrated an IQE of nearly 100%. [16,17] However, phosphorescent emitters contain expensive transition metals, which increases the fabrication costs of the devices and limits their large-scale applications despite the high efficiency. Besides, the toxicity of heavy atoms is also a bothering issue. Thus, novel emission mechanisms are needed to improve both the efficiency and the cost issue. In this context, triplet-triplet annihilation (TTA, also known as P-type delayed fluorescence), [18] hybridized locally and charge transfer (HLCT, also known as the "hot exciton" mechanism), [19][20][21][22] and thermally activated delayed fluorescence (TADF) [23][24][25] are promising. Among them, TADF represents a successful mechanism for realizing high IQE up to 100% (Figure 1). In recent years, TADF emitters based on the multiresonance (MR-TADF) concept have drawn much research attention, which offer a perfect solution to achieving both high efficiency and high color purity. [1,3,6,26,27] Besides, TADF can be realized in purely organic emitters, which is merit for low-cost devices. In the TADF mechanism, the T 1 state can be converted to the S 1 state through a reserve intersystem crossing (RISC) facilitated by a small S 1 -T 1 energy gap (ΔE ST ). The fluorescence resulting from the S 1 on charge recombination is defined as prompt fluorescence with a short lifetime, while the fluorescence originating from the S 1 that is up converted from the T 1 state is defined as the delayed fluorescence with a long lifetime.TADF emitters are typically doped into a suitable organic matrix to address the quenching effects such as concentration quenching, triplet-triplet annihilation, singlet-triplet annihilation (STA), and triplet-polaron annihilation (TPA) to enhance the device efficiency and stability. [28][29][30][31][32][33] Thus, both host materials Organic light-emitting diodes (OLEDs) represent one of the most promising technologies for future displays and lighting sources, which have received extensive research attention. Purely organic thermally activated delayed fluorescence (TADF) emitters offer obvious advantages, including high efficiencies and low costs, and they are typically doped in host materials to achieve optimal device efficiencies. TADF emitters typically feature intramolecular charge transfer characteristics, and their excited states properties are sensitive to local environment, giving the implication that host materials can finely tune their emission properties...

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“…[20] In recent TADF literature on novel materials, a common motif is observed at higher emitter concentrations, the emission spectrum redshifts. [13] Contrasting explanations have been offered for the archetypical TADF emitter 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN), [1] which shows a similar redshift feature. Kim et al suggested that the observed effect is due to SSSE, [15] while Etherington et al followed up the study and revealed that dimer formations are the more likely reason.…”

Section: Steady-state Spectra and Plqymentioning

confidence: 99%

“…[ 20 ] In recent TADF literature on novel materials, a common motif is observed at higher emitter concentrations, the emission spectrum redshifts. [ 13 ] Contrasting explanations have been offered for the archetypical TADF emitter 1,2,3,5‐tetrakis(carbazol‐9‐yl)‐4,6‐dicyanobenzene (4CzIPN), [ 1 ] which shows a similar redshift feature. Kim et al.…”

Section: Photophysical Propertiesmentioning

confidence: 99%

“…[7] Recently, there have been investigations of concentrationinduced effects of TADF emitters. [8][9][10][11][12][13] Observed effects include changes in photophysical and electrical properties when increasing the emitter concentration in a matrix, leading to a shift in emission spectrum, photoluminescence quantum yield (PLQY), excited state lifetime, turn-on voltages, and external quantum efficiency (EQE) values in devices. A new pathway for device optimization should be considered, as a change in the host/guest ratio can influence the CT state energy in different ways.…”

Section: Introductionmentioning

confidence: 99%

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Dimers or Solid‐State Solvation? Intermolecular Effects of Multiple Donor–Acceptor Thermally Activated Delayed Fluorescence Emitter Determining Organic Light‐Emitting Diode Performance

Imbrasas

Lygaitis

Kleine

et al. 2021

Advanced Optical Materials

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Organic light‐emitting materials exhibiting thermally activated delayed fluorescence (TADF) show great promise for improving display applications. Recently, intermolecular effects between emitting molecules have been given more attention, revealing strong solid‐state solvation or aggregation induced changes of sample performance. Implications of this on device performance are not yet fully covered. In this work, a thorough investigation of a novel TADF emitter, methyl 2,3,4,5,6‐penta(carbazol‐9‐yl)benzoate (5CzCO2Me), is provided. Steady‐state emission spectra reveal a luminescence redshift with increasing emitter concentration in a small molecule host. In all investigated concentrations, the emission profile remains the same; thus, the redshift is attributed to the solid‐state solvation effect. The highest photoluminescence quantum yield (PLQY) is achieved in the 20 wt% sample, reaching 66%. The best organic light‐emitting diode (OLED) in terms of current–voltage–luminance and external quantum efficiency (EQE) parameters is the device with 60 wt% emitter concentration, reaching maximal EQE values of 7.5%. It is shown that the emitter transports holes and that charge‐carrier recombination does not take place on the bandgap of the host, but rather, a mixed host–guest concentration‐dependent recombination is seen. The hole‐transporting properties of 5CzCO2Me allow for a new dimension in tuning the device performance by controlling the emitter concentration.

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Thermally Activated Delayed Fluorescence: Beyond the Single Molecule

Cited by 24 publications

References 82 publications

Organic luminescent materials: The concentration on aggregates from aggregation‐induced emission

Organic luminescent materials: The concentration on aggregates from aggregation‐induced emission

Host‐Dopant Interaction between Organic Thermally Activated Delayed Fluorescence Emitter and Host Material: Insight into the Excited State

Dimers or Solid‐State Solvation? Intermolecular Effects of Multiple Donor–Acceptor Thermally Activated Delayed Fluorescence Emitter Determining Organic Light‐Emitting Diode Performance

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