Benzimidazobenzothiazole‐Based Bipolar Hosts to Harvest Nearly All of the Excitons from Blue Delayed Fluorescence and Phosphorescent Organic Light‐Emitting Diodes

Cui, Lin‐Song; Kim, Jong Uk; Nomura, Hiroko; Nakanotani, Hajime; Adachi, Chihaya

doi:10.1002/anie.201601136

Cited by 125 publications

(57 citation statements)

References 44 publications

(14 reference statements)

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“…Notably, using 4CzPNPh [15a] as the yellow TADF dopant, a record high EQE of 22.5% was obtained, much higher than the 9.9% EQE obtained using mCP as the host. Cui et al reported two benzimidazobenzothiazole‐based hosts, 29Cz‐BID‐BT and 39Cz‐BID‐BT , (Figure ). These hosts possessed high triplet energies (>3.0 eV) and favor ambipolar charge transport.…”

Section: Development Of Host Materials For Tadf Devicesmentioning

confidence: 99%

Purely Organic Thermally Activated Delayed Fluorescence Materials for Organic Light‐Emitting Diodes

2017

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The earliest account of electroluminescence, the process of converting electrical energy into light, using organic materials can be traced back to 1963 when Pope et al. applied a direct current to an anthracene single crystal under a bias of 400 V using silver-paste electrodes. [3] Although anthracene fluorescence was observed, a driving voltage of 400 V is evidently not viable in practical applications. The seminal breakthrough in the development of OLEDs appeared in 1987 when Tang and Van Slyke reported a double-layered device using tris(8-hydroxyquinoline)aluminum (Alq 3 ) as the emitting and electron-transporting layer. [1] The green-emitting device showed an external quantum efficiency (EQE) of about 1% when driven at less than 10 V. This marked the dawn of OLED development and tremendous interest and effort from both academia and industry have followed subsequent to this pioneering work, resulting in the ultimate wide-scale commercialization of OLEDs, particularly for display applications.In order to make OLEDs commercially viable for lighting applications, where the cost per unit must be competitive with presently used technology, there are a number of challenges that must be overcome aside from reducing the production cost. The organic emitters should have high photoluminescence quantum yields (PLQYs), which directly impact the device efficiency. The energy levels of the frontier molecular orbitals (i.e., highest occupied and lowest unoccupied molecular oribitals (HOMOs and LUMOs)) of each of the layers in the device should be optimally relatively aligned in order to: i) minimize the barrier to charge injection, and ii) control the recombination region within the device, which greatly affects both the device efficiency and lifetime. [4] The organic materials must demonstrate sufficient thermal stability to be compatible with their vacuum deposition during device fabrication or produce thin films of suitable morphology when spin-coated during solution processing. Regardless of the fabrication method, the organic material must be morphologically stable during device operation when Joule heat is produced in the device. [5] Aside from the aforementioned challenges, another key issue to address is the management of hole and electron recombination within the device, each possessing their own spin. Unlike photoexcitation, in which mainly singlet excited states are produced in the organic emitters, exciton formation through charge (hole and electron) recombination in OLED devices results in 25% singlets and 75% triplets, according to The design of thermally activated delayed fluorescence (TADF) materials both as emitters and as hosts is an exploding area of research. The replacement of phosphorescent metal complexes with inexpensive organic compounds in electroluminescent (EL) devices that demonstrate comparable performance metrics is paradigm shifting, as these new materials offer the possibility of developing low-cost lighting and displays. Here, a comprehensive review of TADF materials is presented, with a...

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Section: Development Of Host Materials For Tadf Devicesmentioning

confidence: 99%

Purely Organic Thermally Activated Delayed Fluorescence Materials for Organic Light‐Emitting Diodes

2017

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“…Bipolar charge transport is also needed for high emission efficiency and ensuring low efficiency roll-off. Thus, a disruption of the p-conjugation-based connectivity between the donor and acceptor units by insulating, saturated atoms (sp 3 -hybridized C or Si) or a twisted p-conjugated spacer is favorable 154 for maintaining a triplet energy level and blocking of intramolecular electronic coupling, yet negatively effects carrier transport properties. 155 The role of the host specifically serves to separate the emitting species to reduce the concentration of high energy excited state species to reduce loss processes through photophysical processes, notably triplet-triplet annihilation, 19,136 and device efficiency, i.e.…”

Section: Carbazole-based Materials As Tadf Emittersmentioning

confidence: 99%

Perspective on carbazole-based organic compounds as emitters and hosts in TADF applications

2017

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“…An ideal host material for yellow‐to‐red TADF yellow emitters should have: (1) sufficiently high singlet and triplet state energies for exciton confinement; (2) appropriate highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels to avoid charge trapping on the emitter and to facilitate charge transport through the device; (3) broad spectral overlap with the emitters for efficient Förster energy transfer; and (4) ambipolar character to facilitate charge transport and carrier injection . To satisfy these requirements, the choice of building segments and the connectivity of the host should be carefully considered.…”

Section: Introductionmentioning

confidence: 99%

Bipyridine‐Containing Host Materials for High Performance Yellow Thermally Activated Delayed Fluorescence‐Based Organic Light Emitting Diodes with Very Low Efficiency Roll‐Off

Chen

Rajamalli

Tenopala‐Carmona

et al. 2019

Advanced Optical Materials

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Two bipolar host materials 3‐CBPy and 4‐mCBPy are reported. These hosts are structural analogs of the common host materials CBP and mCBP wherein the phenyl rings have been replaced with pyridines. The two materials possess deep highest occupied molecular orbital (HOMO) and shallow lowest unoccupied molecular orbital (LUMO) levels along with sufficiently high energy S1 and T1 states that make them suitable hosts for yellow emitters in electroluminescent devices. Yellow‐emitting thermally activated delayed fluorescence organic light‐emitting diodes are fabricated using 2,4,6‐tris (4‐(10H‐phenoxazin‐10‐yl)phenyl)‐1,3,5‐triazine (tri‐PXZ‐TRZ) as the dopant emitter with either 3‐CBPy or 4‐mCBPy employed as the host. Their device performance is compared to analogous devices using CBP and mCBP as host materials. The pyridine‐containing host devices show markedly improved external quantum efficiencies (EQE) and decreased roll‐off. The 7 wt% tri‐PXZ‐TRZ‐doped device exhibits very low turn‐on voltage (2.5 V for both 3‐CBPy and 4‐mCBPy) along with maximum external quantum efficiencies (EQEmax) reaching 15.6% (for 3‐CBPy) and 19.4% (for 4‐mCBPy). The device using 4‐mCBPy also exhibits very low efficiency roll‐off with an EQE of 16.0% at a luminance of 10 000 cd m−2.

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Benzimidazobenzothiazole‐Based Bipolar Hosts to Harvest Nearly All of the Excitons from Blue Delayed Fluorescence and Phosphorescent Organic Light‐Emitting Diodes

Cited by 125 publications

References 44 publications

Purely Organic Thermally Activated Delayed Fluorescence Materials for Organic Light‐Emitting Diodes

Purely Organic Thermally Activated Delayed Fluorescence Materials for Organic Light‐Emitting Diodes

Perspective on carbazole-based organic compounds as emitters and hosts in TADF applications

Bipyridine‐Containing Host Materials for High Performance Yellow Thermally Activated Delayed Fluorescence‐Based Organic Light Emitting Diodes with Very Low Efficiency Roll‐Off

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