A bipolar host based high triplet energy electroplex for an over 10 000 h lifetime in pure blue phosphorescent organic light-emitting diodes

Jung, Min Kyo; Lee, Jun Yeob; Kim, T.

doi:10.1039/c9mh01268k

Cited by 119 publications

(100 citation statements)

References 35 publications

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“…C3 is reported as a robust host even for pure blue phosphorescent OLEDs. 48 The superior molecular stability of C4 to A4 has been demonstrated above. Previously, we suggested that PO groups would undermine the molecular stability due to the low BDEf of C−P bonds.…”

Section: Implications For Rational Design Of Robust Oled Materialsmentioning

confidence: 82%

Negative Charge Management to Make Fragile Bonds No Longer Fragile towards Electrons for Robust Organic Optoelectronic Materials

Wang¹,

Meng²,

Wang³

et al. 2020

Preprint

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The development of robust organic (opto)electronic devices is mainly hindered by the chemical deterioration of organic materials on service. For organic light-emitting diode (OLED) materials, a key molecular parameter for intrinsic chemical stability is the bond-dissociation energy of the fragile bond (BDEf) with the lowest BDE in the molecule. Although rarely concerned, most OLED molecules have the lowest BDEf in negatively charged states (BDEf(−), ∼1.6−2.5 eV), which would be a fatal short-slab for device stability. Here, we confirmed the close correlation between BDEf(−), intrinsic material stability, and device lifetime. To make fragile bonds no longer fragile towards electrons, we found that introducing strong electron-withdrawing groups with delocalizing structures would be an effective and universal strategy, which was found in typical phosphine-oxide and carbazole module molecules and backed by comparisons in several reported and newly designed molecules. It not only substantially improves BDEf(−) by ∼1 eV, but revives the originally vulnerable building blocks, thus largely enriches available groups for rational design of robust OLED and other organic (opto)electronic materials.

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Section: Implications For Rational Design Of Robust Oled Materialsmentioning

confidence: 82%

Negative Charge Management to Make Fragile Bonds No Longer Fragile towards Electrons for Robust Organic Optoelectronic Materials

Wang¹,

Meng²,

Wang³

et al. 2020

Preprint

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“…Till date, several molecular design approaches have been reported for the development of stable and high E T hosts for blue PhOLEDs, in which the design featuring chemically stable and high E T building units with nonconjugative mode of connectivity is attractive. [ 24–35 ] Commonly, carbazole has been employed as an electron donor for constructing blue host materials due to its high E T , excellent hole transporting property, amorphous nature, good thermal stability, and wide scope for chemical modification. [ 4–6,24–35 ] As an electron acceptor units, aryltriazine, phosphine oxide, and cyano units have been widely used as the electron transporting units for blue hosts.…”

Section: Introductionmentioning

confidence: 99%

Molecular Engineering of Cyano‐Substituted Carbazole‐Based Host Materials for Simultaneous Achievement of High Efficiency and Long Lifetime in Blue Phosphorescent Organic Light‐Emitting Diodes

Konidena

Chung

Lee

2020

Adv Elect Materials

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quenching, triplet-triplet annihilation and exciton diffusion. [4][5][6] As the major component of the emitting layer (EML) is the host material, it plays a pivotal role in managing the carrier mobility, charge recombination zone and operational lifetime of the device. [11][12][13][14][15][16][17][18][19][20][21][22][23] Therefore, the host materials are equal important as the dopant materials in dictating the final device performance. Currently, efficient host materials with superior external quantum efficiency (EQE) and long operational lifetime for red and green PhOLEDs have been developed and the phosphors replaced the fluorescent emitters in commercial application. [4][5][6] However, the stable host materials for blue PhOLEDs with high E T over 3.0 eV and suitable frontier molecular orbital energy levels (highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO)) are scarcely reported, because it is challenging to achieve all these parameters together. [24][25][26][27][28][29][30][31][32][33][34][35] In addition, the device lifetime of blue PhOLEDs is far inferior to that of red and green counterparts and thus the further attention is highly needed to promote the lifetime of blue PhOLEDs to replace the blue fluorescent emitters in commercial applications. [29][30][31][32][33][34][35][36][37][38][39][40][41] In general, many factors affect the lifetime of the blue PhOLEDs and one of the key factors is the stability of the host material. [23,[29][30][31][32][33][34][35][36][37][38][39][40][41] On the other hand, it has been demonstrated that the mixed host systems are advantageous in improving the performance of PhOLEDs compared to single host systems due to balanced carrier density, broad recombination zone, and little charge leakage. [29,31,33,[42][43][44][45] Although several mixed host systems were reported for blue PhOLEDs, but many of them were mainly focused on improving the EQE rather than the lifetime because the high triplet energy electron transporting type host material design is difficult. [29,31,[41][42][43] Therefore, the development of electron transporting type hosts with high E T and long lifetime for blue PhOLEDs is highly desirable.Till date, several molecular design approaches have been reported for the development of stable and high E T hosts for blue PhOLEDs, in which the design featuring chemically stable and high E T building units with nonconjugative mode energy host materials named 1CNCzBN, 2CNCzBN, 3CNCzBN, and 4CNCzBN containing a cyanocarbazole and a benzonitrile for blue phosphorescent organic light-emitting diodes (PhOLEDs) is presented. The effect of the substitution position of the cyano unit in the carbazole core on physicochemical and electroluminescence characteristics is described. All the compounds show high triplet energy (E T ) of above 2.85 eV and the 3CNCzBN compound containing the cyano unit at C3 position of carbazole exhibits superior E T of 3.04 eV. Except for 1CNCzBN, all the compounds reveal good electron-transporting properties, ...

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“…As the exciton converting materials, phosphors and TADF emitters have been employed. [ 13,14 ] The phosphors can convert all excitons into radiative triplet excitons by intersystem crossing and the TADF emitters can transform all excitons into radiative singlet excitons by reverse intersystem crossing (RISC). The secondary phosphors and TADF emitters have been specified as an assistant dopant or sensitizer in the literatures.…”

Section: Introductionmentioning

confidence: 99%

High External Quantum Efficiency in Fluorescent OLED by Cascade Singlet Harvesting Mechanism

Lee

2020

Advanced Optical Materials

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the external quantum efficiency (EQE) of the fluorescent OLEDs has been actively explored.The basic insight of the EQE boosting device approach of the fluorescent OLEDs is to harvest singlet excitons of the fluorescent emitter by only Förster energy transfer process without any charge trapping or Dexter energy transfer process. [11] In order to reach the 100% IQE goal in the fluorescent OLEDs by Förster energy transfer, the host material has to completely harvest singlet excitons and triplet excitons in excited state and trigger radiative transition. [12] In general, common hosts can use only singlet excitons for the Förster energy transfer process. Therefore, the hosts need to be assisted by a secondary material converting the radiative singlet excitons and nonradiative triplet excitons of the host into radiative excitons. As the exciton converting materials, phosphors and TADF emitters have been employed. [13,14] The phosphors can convert all excitons into radiative triplet excitons by intersystem crossing and the TADF emitters can transform all excitons into radiative singlet excitons by reverse intersystem crossing (RISC). The secondary phosphors and TADF emitters have been specified as an assistant dopant or sensitizer in the literatures. [15] Several device structures have been exemplified as the singlet exciton harvesting approaches. The most common method is to mix a host, a TADF sensitizer, and a fluorescent emitter and the TADF sensitizer can be replaced with a phosphor. This approach realized high EQE between 15% and 25% in the fluorescent OLEDs. [16,17] In other approaches, an exciplex was used as the host instead of the material combination of host and TADF emitter because TADF type exciplex can have 100% exciton conversion efficiency by reverse intersystem crossing. [18,19] However, the EQE of the fluorescent OLEDs hiring the exciplex without any phosphor and TADF emitter as the host was inferior to that of the fluorescent OLEDs assisted by them. The main reason of the relatively low EQE was the loss mechanism triggered by Dexter energy transfer between the exciplex host and the fluorescent emitter. The intimate contact between the two materials facilitated the Dexter energy transfer because it induced molecular orbital overlap for electron exchange. Therefore, a device concept to circumvent the close contact between exciplex and fluorescent emitter is

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A bipolar host based high triplet energy electroplex for an over 10 000 h lifetime in pure blue phosphorescent organic light-emitting diodes

Abstract: Ultimate device performances of blue phosphorescent organic light-emitting diodes, an external quantum efficiency of 27.6%, a device lifetime over 10 000 h at 100 cd m−2, and CIE (0.12, 0.13), were achieved by employing an electroplex host.

Cited by 119 publications

References 35 publications

Negative Charge Management to Make Fragile Bonds No Longer Fragile towards Electrons for Robust Organic Optoelectronic Materials

Negative Charge Management to Make Fragile Bonds No Longer Fragile towards Electrons for Robust Organic Optoelectronic Materials

Molecular Engineering of Cyano‐Substituted Carbazole‐Based Host Materials for Simultaneous Achievement of High Efficiency and Long Lifetime in Blue Phosphorescent Organic Light‐Emitting Diodes

High External Quantum Efficiency in Fluorescent OLED by Cascade Singlet Harvesting Mechanism

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