High Triplet Energy Host Materials Research Articles

High triplet energy host materials for blue phosphorescent organic light-emitting diodes derived from carbazole modified orthophenylene

Carbazole modified orthophenylene compounds, 9-([1,1′:2′,1′′-terphenyl]-3-yl)carbazole (Cz-Ter), 9-([1,1′:2′,1′′:2′′,1′′′-quaterphenyl]-3-yl)carbazole (Cz-Quat), 9-([1,1′:2′,1′′:2′′,1′′′:2′′′,1′′′′-quinquephenyl]-3-yl)carbazole (Cz-Quin), were synthesized as host materials for blue phosphorescent organic light emitting diodes. The carbazole modified orthophenylene based host materials showed high triplet energy of above 2.90 eV and there was no reduction of triplet energy according to the increase in the number of phenyl units of the orthophenylene moieties. Cz-Ter, Cz-Quat and Cz-Quin showed maximum quantum efficiencies of 16.2%, 17.3% and 20.9% in blue PHOLEDs, respectively.

Synthesis of phenylcarbazole–thiophene-based structural isomers as unipolar host materials for blue PHOLEDs and their device performance

New high triplet-energy host materials, which are symmetrically or asymmetrically designed by using phenylcarbazole and thiophene moieties, were synthesized by Suzuki–Miyaura cross-coupling reactions and their device performances of blue phosphorescent organic light-emitting diodes were also investigated. The synthesized compounds showed a high triplet energy (>2.84eV) and good thermal stability. Highly efficient blue PHOLEDs were obtained when employing the symmetric compounds having C2 symmetry as the host material and bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic) as the guest material. Their maximum external quantum efficiency of the device reached as high as 18.9% with blue color coordinate of (0.15, 0.35).

High triplet energy Al complex as a host material for blue phosphorescent organic light-emitting diodes

An Al complex, tris((2-(pyrazol-1-yl)pyridin-3-yl)oxy)aluminum (Al(pypy)3), was synthesized as a high triplet energy host material for blue phosphorescent organic light-emitting diodes. A high triplet energy ligand, 2-(1H-pyrazol-1-yl)pyridin-3-ol, was coordinated to the Al to develop the high triplet energy host material derived from Al. The Al(pypy)3 host showed a high triplet energy of 2.86eV for efficient energy transfer to blue triplet emitter. A maximum quantum efficiency of 20.5% was achieved in blue device using the Al(pypy)3 host material.

A six-carbazole-decorated cyclophosphazene as a host with high triplet energy to realize efficient delayed-fluorescence OLEDs

A high triplet energy (ET) host material, hexakis(9H-carbazol-9-yl)cyclotriphosphazene (PzCz), is used in high-efficiency organic light-emitting diodes (OLEDs). PzCz (ET = 3.00 eV) functions as an effective host for thermally activated delayed fluorescence (TADF) molecules. Highest external electroluminescence quantum efficiencies over 15% and 18% are achieved for blue-green and green TADF-OLEDs, respectively.

Solvent effect on device performances of small molecule based solution processed blue phosphorescent organic light-emitting diodes using aromatic and alcohol solvents

Device performances of solution processed blue phosphorescent organic light-emitting diodes were studied using a high triplet energy host material soluble both in alcohol and aromatic solvents. 6-(Carbazole-9-yl)benzofuro[2,3-b]pyridine was used as the alcohol and aromatic solvent compatible triplet host material and the effect of solvent on the device performances of blue phosphorescent organic light-emitting diodes was investigated. Toluene and 2-propanol were effective as the solvent materials for the host and high external quantum efficiencies of 11.0% and 11.1% were achieved in the blue devices processed from toluene and 2-propanol, respectively.

Carbazole modified terphenyl based high triplet energy host materials for blue phosphorescent organic light-emitting diodes

Carbazole modified terphenyl based high triplet energy host materials were developed for application as host materials for blue phosphorescent organic light-emitting diodes. Two terphenyl based materials, 9-(5″-phenyl-[1,1′:2′,1″:3″,1′′′-quaterphenyl]-3-yl)-9H-carbazole (CzTPPh) and 9-(3″,5″-di(pyridin-3-yl)-[1,1:2′,1″-terphenyl]-3-yl)-9H-carbazole (CzTPPy), were synthesized as the host materials with high triplet energies of 2.75 eV and 2.73 eV, respectively. The two host materials were evaluated as the host materials for blue phosphorescent organic light-emitting diodes and high quantum efficiencies of 20.2% and 15.7% were obtained in the CzTPPh and CzTPPy devices, respectively.

High quantum efficiency and color stability in white phosphorescent organic light-emitting diodes using carboline derivative as a host material

Highly efficient and color stable phosphorescent white organic light-emitting diodes were developed using a high triplet energy host material, 3,3′-bis(9H-pyrido[2,3-b]indol-9-yl)-1,1′-biphenyl (CbBPCb), derived from carboline. Two color phosphorescent white organic light-emitting diodes were fabricated by co-doping of blue and orange triplet emitters or double emitting layer structure of blue and orange emitting layers. High quantum efficiency above 20% and color stability were achieved in the white device by optimizing the doping concentration and emitting layer thickness.

High triplet energy Zn complexes as host materials for green and blue phosphorescent organic light-emitting diodes

Two Zn complexes, bis(2-(oxazol-2-yl)phenolate) zinc (ZnOx2) and bis(2-(1-methyl-1H-imidazol-2-yl)phenolate) zinc (ZnIm2), were synthesized as high triplet energy host materials for green and blue phosphorescent organic light-emitting diodes. High triplet energies of 2.71 eV and 2.84 eV were obtained for ZnOx2 and ZnIm2, respectively. Green and blue phosphorescent devices were fabricated using the ZnOx2 and ZnIm2 host materials and high quantum efficiencies of 23.5% and 20.1% were achieved in green and blue devices, respectively.

P.145L: Late‐News Poster: Synthesis and Device Application of Carboline Derivatives as High Triplet Energy Materials for Blue Phosphorescent OLEDs

AbstractThree carboline derivatives, 9,9′‐m‐phenylenedi‐α‐carboline (NmCP1), 9,9′‐m‐phenylenedi‐β‐carboline (NmCP2), 9,9′‐m‐phenylendi‐γ‐carboline (NmCP3) were synthesized as high triplet energy host materials for blue phosphorescent organic light‐emitting diodes (PHOLEDs). Three carboline derivatives had nitrogen atom at different positions of carboline and the nitrogen atom position was correlated with the photophysical properties and device performances of carboline derivatives.

A thermally stable bipolar host material for blue phosphorescent organic light-emitting diodes

A dibenzofuran based host material, 9,9′-(4-(diphenylphosphoryl)dibenzo[b,d]furan-2,8-diyl)bis(9H-carbazole) (DBFDCzPO), was developed as a thermally stable high triplet energy host material for blue phosphorescent organic light-emitting diodes (PHOLEDs). DBFDCzPO showed high triplet energy of 2.89eV and stable film morphology up to 130°C. DBFDCzPO was compared 2,8-di(9H-carbazol-9-yl)dibenzo[b,d]furan and exhibited better device performances. A high quantum efficiency of 17.6% was achieved in the blue PHOLEDs using the DBFDCzPO host material.

High quantum efficiency in blue phosphorescent organic light emitting diodes using ortho-substituted high triplet energy host materials

A high triplet energy material derived from carbazole and ortho terphenyl, 3,3′′-di(9H-carbazole-9-yl)-1,1′:2′,1′′-terphenyl (33DCTP), was synthesized as the host material for blue phosphorescent organic light-emitting diodes (PHOLEDs). The 33DCTP host showed high glass transition temperature of 110°C, high triplet energy of 2.77eV, the highest occupied molecular orbital of −6.12eV and the lowest unoccupied molecular orbital of −2.52eV. High efficiency blue PHOLEDs were developed using the 33DCTP host and bis((3,5-difluorophenyl)pyridine) iridium picolinate dopant material, and high quantum efficiency of 23.7% was achieved with a color coordinate of (0.14, 0.28).

A diphenyl ether bridged, high triplet energy host material for blue phosphorescent organic light-emitting diodes

Abstract A carbazole type, thermally stable, high triplet energy host material having a diphenylether linkage, 9,9′-(oxybis([1,1′-biphenyl]-4′,3-diyl))bis(9 H -carbazole), was synthesized and the device performances of blue phosphorescent organic light-emitting diodes were studied. The new host material exhibited a high glass transition temperature of 111 °C and a high triplet energy of 2.73 eV for energy transfer to blue triplet emitter. Blue devices were fabricated using the new host material and a high quantum efficiency of 23.5% was achieved.

High Quantum Efficiency Blue Phosphorescent Organic Light-Emitting Diodes Using 6-Position-Modified Benzofuro[2,3-b]pyridine Derivatives

High quantum efficiency blue phosphorescent organic light-emitting diodes were developed using 6- position modified benzofuro[2,3-b]pyridine derivatives as host materials. Two high triplet energy host materials derived from benzofuro[2,3-b]pyridine modified with carbazole or 9-phenylcarbazole were synthesized and the device performances of the host materials were investigated. A high quantum efficiency of 24.3% was achieved using the benzofuro[2,3-b]pyridine host materials due to good charge balance and energy transfer.

Effect of the position of nitrogen in pyridoindole on photophysical properties and device performances of α-, β-, γ-carboline based high triplet energy host materials for deep blue devices

Three carboline derivatives with nitrogen at different positions of the pyridoindole unit were synthesized and the effect of the position of nitrogen on the photophysical properties and device performances was investigated. β-Carboline was effective in obtaining high triplet energy and stabilizing energy levels, while α-carboline was better than other carbolines in terms of quantum efficiency. However, γ-carboline could not stabilize the LUMO level and low quantum efficiency was obtained.

Computational design of high triplet energy host materials for phosphorescent blue emitters

A series of host molecules for blue electrophosphorescence have been designed using density functional theory by incorporating electron donors (carbazole (cbz) and diphenylamine (tph)) and electron acceptors (benzimidazole (bzi) and diphenylphosphine oxide (pho)) into the p-bis(triphenylsilyl)benzene (UGH2) moiety. Results obtained from the electronic structure calculations show that the triplet energy (ET), HOMO and LUMO energy levels and HOMO–LUMO gap (Eg) of the designed hosts can be modulated through different linking topologies. Among the designed host molecules benzimidazole with an N-linkage exhibits a higher triplet energy, when compared to the same host with a C-linkage. Asymmetric substitution on an inert host (UGH2) more effectively tunes the charge injection barrier from neighboring layers, HOMO and LUMO energies and Eg than symmetric substitution. The electron injection barrier is substantially diminished when electron transporting units are substituted in the para-position of the core unit compared to the same in the meta-position. Among the newly designed host molecules mcbz–pN–bzi, pcbz–pN–bzi, and ptph–pN–bzi are found to be good host materials for blue emitting phOLEDs.

Synthesis of 2- and 4-substituted carbazole derivatives and correlation of substitution position with photophysical properties and device performances of host materials

A synthetic method to synthesize 4-substituted carbazole derivative was developed to study the effect of substitution position of carbazole on photophysical properties and device performances of host materials. Two high triplet energy host materials with substituents at 2- and 4-positions of carbazole were synthesized by the new synthetic approach. Substitution of electron withdrawing group at 2-position was better than the substitution at 4-position to stabilize energy levels and to improve hole transport properties. However, high glass transition temperature and high quantum efficiency were obtained in the carbazole based host material with substituent at 4-position.

High external quantum efficiency in deep blue phosphorescent organic light emitting diodes using a simple device structure

Simple high efficiency deep blue phosphorescent organic light-emitting diodes were developed using a mixed host of high triplet energy host materials. A hole transport type host was used both as the hole transport layer and host in the mixed host emitting layer and an electron transport type host was mixed with the hole transport type host in the emitting layer. A three organic layer device structure of the hole transport layer/emitting layer/electron transport layer gave high external quantum efficiency of 26.4% with a color coordinate of (0.14, 0.19).

57.3: Invited Paper: Host and Charge Transport Materials for High Efficiency Deep Blue Phosphorescent Organic Light‐Emitting Diodes

AbstractIn this paper, we describe the development of high efficiency deep blue phosphorescent organic light emitting diodes using high triplet energy host and charge transport materials. The quantum efficiency of deep blue phosphorescent organic light‐emitting diodes could be improved above 20% by using high triplet energy bipolar host materials, hole transport materials and electron transport materials.

Synthesis, photophysical and electro-optical properties of bis-carbazolyl methane based host material for pure-blue phosphorescent OLED

A new high triplet-energy host material, 9-(4-(bis(9-ethyl-9H-carbazol-3-yl)methyl)phenyl)-9H-carbazole (bis-CMPC), was synthesized and its device performance of phosphorescent organic light-emitting diode was investigated. This host material showed a high triplet energy (∼2.95eV) and good thermal stability. Highly efficient pure-blue PHOLED was obtained when employing bis-CMPC as the host material and bis((3,5-difluoro-4-cyanophenyl)pyridine) iridium picolinate as the guest material. The maximum external quantum efficiency of the device reached as high as 13.3% with a pure-blue color coordinate of (0.14, 0.21).

Dibenzofuran derivative as high triplet energy host material for high efficiency in deep blue phosphorescent organic light-emitting diodes

A high efficiency deep blue phosphorescent organic light-emitting diodes was developed using an weak electron transport type high triplet energy host material with dibenzofuran and phosphine oxide units. The host material showed a high triplet energy of 3.01eV and was effective as the host material for deep blue phosphorescent organic light-emitting diodes. The device performances could be optimized by managing the doping concentration of phosphorescent dopants and a high quantum efficiency of 25.9% with a color coordinate of (0.14, 0.22) was achieved.