Accelerating PLQY and RISC rates in deep-blue TADF materials with the acridin-9(10<i>H</i>)-one acceptor by tuning the peripheral groups on carbazole donors

Mei, Yongqiang; Liu, Di; Li, Jiuyan; Wang, Jiahui

doi:10.1039/d2tc03448d

Cited by 11 publications

(4 citation statements)

References 48 publications

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“…A common strategy to prevent loss processes, such as concentration quenching or interactions between triplet and/or singlet excitons is the adjustment of the molecular structure in such way, that an increase in the intermolecular distance is achieved, e.g., by incorporation of bulkier side groups. [36] Although such strategies typically offer improvements in reduction of the concentration quenching and increase of the PLQY, a major downside is that a simple change in the molecular structure can have tremendous influence on the intrinsic charge transport. In our study, the incorporation of tert-butyl groups on the carbazole donor-part resulted in a large imbalance of the charge transport, with the hole-transport being almost 2 orders of magnitude higher than the electron-transport (Figure S1, Supporting Information).…”

Section: Resultsmentioning

confidence: 99%

Reduction of Non‐Radiative Losses in Trap‐Free Organic Light‐Emitting Diodes by Dilution with A Large Bandgap Host

Sachnik,

Zhou,

Nikan

et al. 2023

Advanced Optical Materials

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The emitter 9,9′,9′'‐(5‐(4,6‐diphenyl‐1,3,5‐triazin‐2‐yl)benzene‐1,2,3‐triyl)tris(9H‐carbazole) (3CzTRZ) seems an ideal candidate for efficient single‐layer blue organic light‐emitting diodes (OLEDs). It combines trap‐free electron and hole transport with thermally activated delayed fluorescence (TADF) for triplet harvesting. However, in spite of the absence of charge trapping defects, neat films of 3CzTRZ suffer from a low photoluminescence quantum yield (PLQY) of only 40%. Time‐resolved photoluminescence measurements reveal that the low PLQY results from the fact that next to fast intersystem crossing the rate for reverse intersystem crossing is very slow and nearly similar to the rate of non‐radiative recombination of triplet excitons to the ground state. This loss process of non‐radiative triplet decay is even more pronounced in OLEDs due to the 75% direct triplet‐exciton formation, resulting in a low external quantum efficiency (EQE) of 4.5%. By diluting 3CzTRZ in a large bandgap host, the triplet lifetime is increased by at least an order of magnitude, resulting in an enhanced PLQY of 70% and a more than three‐fold enhancement of the EQE to 15% in a single‐layer blue OLED. Device simulations confirm that the increased EQE can be ascribed to an elongated triplet lifetime upon dilution of the emitter in a host matrix.

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Section: Resultsmentioning

confidence: 99%

Reduction of Non‐Radiative Losses in Trap‐Free Organic Light‐Emitting Diodes by Dilution with A Large Bandgap Host

Sachnik,

Zhou,

Nikan

et al. 2023

Advanced Optical Materials

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“…Because the degree of twist between the ICz units and phenyl linker was high, HOMO and LUMO were well separated from each other in both emitters, and the Δ E ST values of ICzCN and ICzCYP were 0.01 and 0.03 eV. Therefore, we estimated an improvement in the up-conversion rate from the T 1 to the S 1 state [ 22 ].…”

Section: Resultsmentioning

confidence: 99%

Highly Effective Thermally Activated Delayed Fluorescence Emitters Based on Symmetry and Asymmetry Nicotinonitrile Derivatives

et al. 2022

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In this study, we developed two thermally activated delayed fluorescence (TADF) emitters, ICzCN and ICzCYP, to apply to organic light-emitting diodes (OLEDs). These emitters involve indolocarbazole (ICz) donor units and nicotinonitrile acceptor units with a twisted donor-acceptor-donor (D-A-D) structure for small singlet (S1) and triplet (T1) state energy gap (ΔEST) to enable efficient exciton transfer from the T1 to the S1 state. Depending on the position of the cyano-substituent, ICzCN has a symmetric structure by introducing donor units at the 3,5-position of isonicotinonitrile, and ICzCYP has an asymmetric structure by introducing donor units at the 2,6-position of nicotinonitrile. These emitters have different properties, such as the maximum luminance (Lmax) value. The Lmax of ICzCN reached over 10000 cd m−2. The external quantum efficiency (ηext) was 14.8% for ICzCN and 14.9% for ICzCYP, and both achieved a low turn-on voltage (Von) of less than 3.4 eV.

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“…For comparison, Fig. 1c shows the relation between J 90 and the EQE at 1,000 cd m − 2 (EQE 1,000 ) for TADF OLEDs 5 , 38 , 39 , 48 – 113 with representative fluorescent 28 , 114 – 129 and phosphorescent 86 – 88 , 128 – 155 devices across red, green and blue colours.…”

Section: Methodsmentioning

confidence: 99%

“…b , Schematic graph showing definition of J 90 . c , Graph of the relation between J 90 and EQE 1,000 for TADF 5 , 38 , 39 , 48 – 113 , fluorescent (Fluo.) 28 , 114 – 129 and phosphorescent (Phos.)…”

Section: Mainmentioning

confidence: 99%

A figure of merit for efficiency roll-off in TADF-based organic LEDs

Diesing,

Zhang,

Zysman-Colman

et al. 2024

Nature

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Organic light-emitting diodes (OLEDs) are a revolutionary light-emitting display technology that has been successfully commercialized in mobile phones and televisions1,2. The injected charges form both singlet and triplet excitons, and for high efficiency it is important to enable triplets as well as singlets to emit light. At present, materials that harvest triplets by thermally activated delayed fluorescence (TADF) are a very active field of research as an alternative to phosphorescent emitters that usually use heavy metal atoms3,4. Although excellent progress has been made, in most TADF OLEDs there is a severe decrease of efficiency as the drive current is increased, known as efficiency roll-off. So far, much of the literature suggests that efficiency roll-off should be reduced by minimizing the energy difference between singlet and triplet excited states (ΔEST) to maximize the rate of conversion of triplets to singlets by means of reverse intersystem crossing (kRISC)5–20. We analyse the efficiency roll-off in a wide range of TADF OLEDs and find that neither of these parameters fully accounts for the reported efficiency roll-off. By considering the dynamic equilibrium between singlets and triplets in TADF materials, we propose a figure of merit for materials design to reduce efficiency roll-off and discuss its correlation with reported data of TADF OLEDs. Our new figure of merit will guide the design and development of TADF materials that can reduce efficiency roll-off. It will help improve the efficiency of TADF OLEDs at realistic display operating conditions and expand the use of TADF materials to applications that require high brightness, such as lighting, augmented reality and lasing.

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Accelerating PLQY and RISC rates in deep-blue TADF materials with the acridin-9(10H)-one acceptor by tuning the peripheral groups on carbazole donors

Abstract: Blue thermally activated delayed fluorescence (TADF) emitters always suffer from poor color purity and low efficiencies, especially those deep blue emitters. Here, Acridin-9(10H)-one (i.e. acridone, AD) featuring orthogonal and highly...

Cited by 11 publications

References 48 publications

Reduction of Non‐Radiative Losses in Trap‐Free Organic Light‐Emitting Diodes by Dilution with A Large Bandgap Host

Reduction of Non‐Radiative Losses in Trap‐Free Organic Light‐Emitting Diodes by Dilution with A Large Bandgap Host

Highly Effective Thermally Activated Delayed Fluorescence Emitters Based on Symmetry and Asymmetry Nicotinonitrile Derivatives

A figure of merit for efficiency roll-off in TADF-based organic LEDs

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