Host Materials For Phosphorescent OLEDs Research Articles

Spirobifluorene Trimers : High Triplet Pure Hydrocarbon Hosts for Highly Efficient Blue Phosphorescent Organic Light‐Emitting Diodes.

Pure aromatic hydrocarbon materials (PHC) represent a new generation of host materials for phosphorescent OLEDs (PhOLEDs), free of heteroatoms. They reduce the molecular complexity, can be easily synthesized and are an important direction towards robust devices. As heteroatoms can be involved in bonds dissociations in operating OLEDs through exciton induced degradation process, developing novel PHCs appear particularly relevant for the future of this technology. In the present work, we report a series of extended PHCs constructed on the assembly of three spirobifluorene fragments. The resulting positional isomers present a high triplet energy level, a wide HOMO/LUMO difference and improved thermal and morphological properties compared to previously reported PHCs. These characteristics are beneficial for the next generation of host materials for PhOLEDs and provide relevant design guidelines. Used as host in blue‐emitting PhOLEDs, which are still the weakest link of the field, a very high EQE of 24 % and low threshold voltage of 3.56 V were obtained with a low‐efficiency roll‐off. This high performance strengthens the position of PHC strategy as an efficient alternative for OLED technology and opens the way to a more simple electronic.

Spirobifluorene Trimers : High Triplet Pure Hydrocarbon Hosts for Highly Efficient Blue Phosphorescent Organic Light-Emitting Diodes.

Pure aromatic hydrocarbon materials (PHC) represent a new generation of host materials for phosphorescent OLEDs (PhOLEDs), free of heteroatoms. They reduce the molecular complexity, can be easily synthesized and are an important direction towards robust devices. As heteroatoms can be involved in bonds dissociations in operating OLEDs through exciton induced degradation process, developing novel PHCs appear particularly relevant for the future of this technology. In the present work, we report a series of extended PHCs constructed on the assembly of three spirobifluorene fragments. The resulting positional isomers present a high triplet energy level, a wide HOMO/LUMO difference and improved thermal and morphological properties compared to previously reported PHCs. These characteristics are beneficial for the next generation of host materials for PhOLEDs and provide relevant design guidelines. Used as host in blue-emitting PhOLEDs, which are still the weakest link of the field, a very high EQE of 24 % and low threshold voltage of 3.56 V were obtained with a low-efficiency roll-off. This high performance strengthens the position of PHC strategy as an efficient alternative for OLED technology and opens the way to a more simple electronic.

Are pure hydrocarbons the future of host materials for blue phosphorescent organic light-emitting diodes?

This Chemistry Frontiers deals with a new generation of host materials for phosphorescent OLEDs only constituted with carbon and hydrogen atoms, which can be beneficial for the future development of the OLED industry.

Multifunctional Materials Serving as Efficient Non‐Doped Violet‐Blue Emitters and Host Materials for Phosphorescence

Efficient multifunctional materials acting as violet-blue emitters, as well as host materials for phosphorescent OLEDs, are crucial but rare due to demand that they should have high first singlet state (S1 ) energy and first triplet state (T1 ) energy simultaneously. In this study, two new violet-blue bipolar fluorophores, TPA-PI-SBF and SBF-PI-SBF, were designed and synthesized by introducing the hole transporting moiety triphenylamine (TPA) and spirobifluorene (SBF) unit that has high T1 into high deep blue emission quantum yield group phenanthroimidazole (PI). As the results, the non-doped OLEDs based on TPA-PI-SBF exhibited excellent EL performance with a maximum external quantum efficiency (EQEmax ) of 6.76 % and a violet-blue emission with Commission Internationale de L'Eclairage (CIE) of (0.152, 0.059). The device based on SBF-PI-SBF displayed EQEmax of 6.19 % with CIE of (0.159, 0.049), which nearly matches the CIE coordinates of the violet-blue emitters standard of (0.131, 0.046). These EL performances are comparable to the best reported non-doped deep or violet-blue emissive OLEDs with CIEy<0.06 in recent years. Additionally, the green, yellow and red phosphorescent OLEDs with TPA-PI-SBF and SBF-PI-SBF as host materials achieved a high EQEmax of about 20 % and low efficiency roll-off at the ultra-high luminance of 10 000 cd m-2 . These results provided a new construction strategy for designing high-performance violet-blue emitters, as well as efficient host materials for phosphorescent OLEDs.

Oligomers containing pyridinyl-substituted carbazole rings as host materials for phosphorescent OLEDs

Two oligoethers containing electroactive pendent pyridinyl-carbazole moieties have been synthesized by the multi-step synthetic route. Full characterization of their structures is presented. The oligomers represent derivatives of very high thermal stability with initial thermal degradation temperatures exceeding 400 °C. Glass transition temperatures of the amorphous materials were also very high and reached values of 124 °C and 145 °C, respectively. Bipolar chemical structure having oligomer, i.e. poly{3-(2-methoxy-3-pyridinyl)-9-(3-methyloxetan-3-yl)methyl-carbazole} was tested as host material for green phosphorescent organic light emitting diode using tris(2-phenylpyridine)iridium(III) as a triplet emitter. A green device containing 10 wt% of the green guest demonstrated among all the devices the best performance with current efficiency of 8.8 cd/A and power efficiency of 5.1 lm/W at 100 cd/m2. At higher brightness, such as 1000 cd/m2, used for illumination applications, this PhOLED showed enhanced efficiency of 11.7 cd/A (5.4 lm/W) with brightness exceeding 4000 cd/m2.

Triarylboryl‐Functionalized Oxadiazole as a Host Material with Electron Transporting Property for Green PhOLEDs

A triarylboryl‐functionalized oxadiazole compound, 2,5‐bis‐(m‐dimesitylboryl‐phenyl)‐1,3,4‐oxadiazole (1) was prepared and characterized to investigate multi‐functional properties in phosphorescent OLEDs (PhOLEDs). X‐ray crystal structure revealed that two Mes2B groups are oriented toward the same side and the entire fragments of oxadiazole, phenylene, and trigonal boron are in a nearly coplanar arrangement. From the optical and electrochemical measurements, 1 was shown to possess high triplet energy (E T = 2.75 eV) and deep HOMO (E HOMO = 6.02 eV) and low LUMO levels (E LUMO = 2.53 eV), which are suitable for electron transporting (ETM) and/or host materials in PhOLEDs. Green PhOLED devices incorporating 1 as electron transporting material (ETM), host, or host/ETM were fabricated and compared their performance with that of the devices based on the well‐known CBP (9,9′‐(1,1′‐biphenyl)‐4,4′‐diylbis‐9H‐carbazole) host and TPBi (1,3,5‐tris(1‐phenyl‐1H‐benzimidazol‐2‐yl)benzene) ETM. Among them, the devices based on 1 as host/ETM showed the highest performance that is comparable to that of the reference device.

螺芴氧杂蒽(SFX)类有机半导体及其OLEDs

One-pot protocol to spiro-based organic semiconductors has several advantages such as low-cost stuffs available, pot-atom-step economic (PASE) procedures, and others over the conventional o -halobiaryl method, representing the paradigm of green organic semiconductors (GOS) with the application of information technology. Herein, this review traces back to the history of spiro-compounds, including synthesis, structures and the application of electronics, followed by the discovery on one-pot synthesis of spirocyclic arenes with the merit of tandem mechanism that involves three bonding at once. We demonstrated the SFX-based molecular design platform under the four-element theory to organic semiconductors, affording a chance to get insight into structure-parameter relationship. Finally, we highlighted the SFX-based electroluminescent materials, including various fluorescent materials, RGB phosphorescent host and guest materials as well as printable OLEDs materials. Among them, the best deep-blue fluorescent OLED exhibits the maximum current efficiency (CE), the maximum power efficiency (PE) and external quantum efficiency (EQE) of 7.4 cd/A, 4.1 lm/W, 4.6%, respectively; the obtained green phosphorescent OLED with the CE of 70.0 cd/A, PE of 77.0 lm/W, EQE of 19.2%, as well as universal host materials for phosphorescent OLEDs. Finally, we outlook the spiro-based GOSs, including the obstacle of synthetic methodology to spiro-arenes, application bottleneck for OLEDs display and lighting source, potential explorations in other electronics, molecular circuits as well as smart devices.

Twisted bimesitylene-based oxadiazoles as novel host materials for phosphorescent OLEDs

The D2d-symmetric bimesitylene core has been exploited for designing novel host materials required in the construction of phosphorescence-based organic light emitting devices. The oxadiazole-functionalized twisted bimesitylenes are found to exhibit high band gap (triplet energies), and excellent glass transition temperatures and thermal stabilities for ready exploitation as host materials. The electron-transporting ability and respectable luminance efficiencies with triplet dopants (up to 19.0cd/A) allow oxadiazole-functionalized bimesitylenes as promising materials for phosphorescence-based light emitting devices, namely PHOLEDs.

A m-Terphenyl-Modifed Sulfone Derivative as a Host Material for High-Efficiency Blue and Green Phosphorescent OLEDs

A m-terphenyl-modified sulfone derivative, BTPS was designed and prepared as a host material for phosphorescent OLEDs. By using BTPS, high power efficiencies of over 46 lm W1− (EQE 22%) for blue and 105 lm W1− (EQE 28%) for green were obtained at 100 cd m−2.

Phenylcarbazole-dipyridyl triazole hybrid as bipolar host material for phosphorescent OLEDs

Two bipolar host materials p-cbtz and m-cbtz, with both phenylcarbazole and 3,5-bis(2-pyridyl)-1,2,4-triazole moieties, were synthesized and tested for fabrication of various phosphorescent OLEDs. The sp3-hybridized nitrogen atom of the 1,2,4-triazole fragment disrupted the π-conjugation between the electron donating 9-phenylcarbazole and the electron accepting 3,5-bis(2-pyridyl)-1,2,4-triazole and, thus, exhibited promising properties such as bipolar charge transport feature (10−5–10−6 cm2V−1s−1) and with relatively high triplet energy gaps (ET = 2.82–2.75 eV). As a result, they were utilized as universal hosts for various phosphorescent OLEDs, showing high efficiencies and low efficiency roll-off. For example, the devices hosted by m-cbtz achieve maximum external quantum efficiencies (ηext) of 8.8% for blue, 16.7% for green, 17.5% for yellow and 16.7% for red-emitting OLEDs. In addition, we also fabricated dual-emitter WOLEDs with a co-doped single emissive layer, exhibiting satisfactory device efficiencies (12.4%, 25 cd A−1, 17 lm W−1) and with highly stable chromaticity (CIEx = 0.26–0.27 and CIEy = 0.38) at an applied voltage of 8 to 11 V. These results demonstrated that the newly synthesized, phenylcarbazole-dipyridyl triazole host materials are advantageous for fabrication of various highly efficient phosphorescent OLEDs.

Novel ZnII complexes of 2-(2-hydroxyphenyl)benzothiazoles ligands: electroluminescence and application as host materials for phosphorescent organic light-emitting diodes

A group of novel zinc complexes containing 2-hydroxyphenylbenzothiazole (BTZ) ligands were designed and synthesized, in which different substituents (OCH3, CH3, F, CF3, COOCH2CH3) were attached at the 6-position of the benzothiazole ring in the BTZ ligands. Both photoluminescence (PL) and electroluminescence (EL) behaviors of these zinc complexes were investigated. The emission colors of these zinc complexes were readily tuned from bluish-green to yellow by simply varying the substituent, with strong electron-withdrawing substituents being favorable for longer-wavelength fluorescence. Efficient EL was obtained when these zinc complexes were used as non-doped emitting layers in organic light-emitting diodes (OLEDs). Furthermore, these zinc complexes were proved to be capable of acting as triplet hosts for iridium phosphor in red phosphorescent OLEDs. A high external quantum efficiency of 17.5% was realized for the red phosphorescent OLED with the present zinc complexes as hosts and tris(2-phenylisoquinoline)iridium as doped emitter, which is greatly enhanced compared to that (12.6%) of the device with the traditional 4,4′-bis(N-carbazoly)biphenyl (CBP) as host. The present study successfully exploited novel zinc complexes as electron-transporting host materials for phosphorescent OLEDs.

Synthesis of novel twisted carbazole–quinoxaline derivatives with 1,3,5-benzene core: bipolar molecules as hosts for phosphorescent OLEDs

A series of carbazole/quinoxaline hybrids have been synthesized by classic Ullmann and Pd/Cu-catalyzed Sonogashira coupling reaction. Their photophysical, thermal, and electrochemical properties were investigated. The introduction of electron rich carbazole and electron deficient quinoxaline on to the 1,3,5-benzene center leads to a twisted structure with good glass forming property and imparts a bipolar character. The triplet energies in the range of 2.34–2.53eV indicate them as potential host materials in phosphorescent OLEDs.

Novel heterofluorene-based hosts for highly efficient blue electrophosphorescence at low operating voltages

A novel concept for molecular design of blue host materials for phosphorescent OLEDs (PHOLEDs) by combining carbazole and heterofluorene via structurally mimicking 4,4′-N,N′-dicarbazole-biphenyl (CBP) was presented. The carbazole end-capped heterofluorenes (CzHFs) prepared accordingly in high yields, were found to be ideal hosts for blue PHOLEDs. At the brightness level of 1000 and 5000 cd m −2, the driving voltages are still lower than 4.5 V with the external quantum efficiencies retain as high as 18.1% and 16.8% respectively.

Electro-active oligomers containing pendent carbazolyl or indolyl groups as host materials for OLEDs

Oligoethers containing electroactive carbazolyl, indolyl or 2-phenylindolyl fragments were synthesized and characterized by NMR spectroscopy, elemental analysis and gel permeation chromatography. The oligomers represent amorphous materials of high thermal stability with glass transition temperatures of 107–161°C. The electron photoemission spectra of layers of the synthesized oligomers showed ionization potentials of 5.9–5.95 eV. Some of the derivatives were tested as host materials in phosphorescent OLEDs with iridium(III) [bis(4,6-difluorophenyl)-pyridinato-N,C2′]picolinate as the guest. The device based on oligomer containing carbazolyl fragments exhibited the best overall performance with a turn-on voltage of 3.5 V, maximum power efficiency of 4.1 lm/W and maximum brightness of 937 cd/m2. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Branched diphenylsilane derivatives containing electronically isolated indolyl moieties as host materials for blue organic light emitting diodes

Branched diphenylsilane derivatives with pendent indolyl fragments were synthesized and characterized. The compounds show high thermal stability with thermal decomposition starting at temperatures above 367 °C and ability to form glasses with glass-transition temperatures of 53–58 °C. The electron photoemission spectra of the layers of the synthesized compounds showed ionization potentials of ca. 5.85 eV. The derivatives were tested as host materials in phosphorescent OLEDs with iridium(III)[bis(4,6-difluorophenyl)-pyridinato- N, C2′]picolinate as the guest. The device with the host derivative containing four electronically isolated indolyl fragments exhibited the best overall performance with maximum current efficiency of about 12 cd/A.

An α-Carboline-containing Host Material for High-efficiency Blue and Green Phosphorescent OLEDs

Abstract An α-carboline derivative, 9,9′-m-phenylenedi-α-carboline (mCaP) was designed and synthesized as a host material for phosphorescent OLEDs. By using a combination with phosphorescent emitters such as FIrpic and Ir(ppy)3, we have successfully developed high-performance OLEDs with a power efficiency (ηp,100) at 100 cd m−2 of 37 lm W−1 for blue, and 94 lm W−1 for green, respectively.

Diphenylsilanes containing electronically isolated carbazolyl fragments as host materials for light emitting diodes

Branched derivatives containing diphenylsilane core and pendent carbazol-9-yl fragments were synthesized and characterized. The compounds represent amorphous materials of high thermal stability with glass transition temperatures of 54–93°C and thermal decomposition starting at temperatures above 391°C. The electron photoemission spectra of layers of the synthesized compounds showed ionization potentials of ca 5.9eV. The derivatives were tested as host materials in phosphorescent OLEDs with iridium(III)[bis(4,6-difluorophenyl)-pyridinato-N,C2′]picolinate as the guest. The device with the host derivative containing four isolated carbazolyl fragments exhibited the best overall performance with maximum current efficiency of 16.4cd/A and maximum brightness exceeding 200cd/m2.

Polyethers containing 2-phenylindol-1-yl moieties as host materials for light emitting diodes

Oxetane monomers and polyethers containing electroactive 2-phenylindol-1-yl or 3-(2-phenylindol-1-yl)carbazol-9-yl fragments were synthesized and characterized by NMR spectroscopy and elemental analysis. The polymers represent amorphous materials of high thermal stability with glass transition temperatures of 94–179 °C and thermal decomposition starting at temperatures above 400 °C. The electron photoemission spectra of layers of the synthesized polymers showed ionization potentials of 5.7–5.8 eV. The polymers were tested as host materials in phosphorescent OLEDs with iridium(III)[bis(4,6-difluorophenyl)-pyridinato- N, C2′]picolinate as the guest. The device based on polymer containing 2-phenylindol-1-yl fragments exhibited the best overall performance with a driving voltage of 5.9 V, maximum power efficiency of 8.46 lm/W and maximum brightness of 718 cd/m 2.

23.4: Invited Paper: Ideal Host‐Dopant System for Highly Efficient Phosphorescent OLEDs

AbstractUsing a narrow band‐gap fluorescent host material with a phosphorescent red dopant, highly efficient red phosphorescent OLEDs (PHOLEDs) exhibiting an ideal external quantum efficiency with a doping concentration of 1% were developed. The origin of such a low doping is revealed by the ideal Dexter doping condition study for efficient energy transfer in PHOLEDs. Besides this cause, the strong fluorescent host materials function very well in phosphorescent OLEDs. Singlet excitons generated by fluorescent host materials in phosphorescent OLEDs can produce dopant triplet excitons via the efficient Förster energy transfer mechanism.

Bridged triphenylamines as novel host materials for highly efficient blue and green phosphorescent OLEDs

Two bridged triphenylamine-triphenylsilane (BTPASi) hybrids have been designed as host materials for phosphorescent OLEDs; devices with the novel host materials achieve maximum external quantum efficiencies as high as 15.4% for blue and 19.7% for green electrophosphorescence.