Hole Transport Type Host Material Research Articles

Highly Twisted Donor-Acceptor Boron Emitter and High Triplet Host Material for Highly Efficient Blue Thermally Activated Delayed Fluorescent Device.

New highly efficient thermally activated delayed fluorescence (TADF) dopant materials (PXB-DI and PXB-mIC) for blue organic light-emitting diodes are reported. These materials were designed by combining highly conjugated rigid ring donor moieties and a boron acceptor with a highly twisted configuration to have high TADF performance and minimized self-quenching properties. In addition, a new high triplet energy and hole transport-type host material, 5-(5-(2,4,6-triiso-propylphenyl)pyridin-2-yl)-5 H-benzo[ d]benzo[4,5]imidazo[1,2- a]imidazole (PPBI), is also reported. This host represents deeper blue color owing to keeping the original spectra of emitters. A fabricated blue TADF device with PXB-mIC in the PPBI host exhibited maximum external quantum efficiency (EQE) of 12.5% with a CIE of (0.15, 0.08), which is close to that of the National Television System Committee blue color. The blue TADF device performances of the PPBI host was compared with the electron transport-type 2,8-bis(diphenylphosphine oxide)dibenzofuran (DBFPO) host. The blue TADF device with PXB-DI in the DBFPO host exhibited a maximum EQE of 37.4% in the sky blue region. This study demonstrates that our molecular design concept of new emitters and host is beneficial for future high-efficiency deep-blue TADF devices.

Development of solution-processable blue/hybrid-white OLEDs based on thermally activated delayed fluorescence

In this work, hybrid-WOLEDs are fabricated by employing single emitting layers (S-EMLs), which consist of 5-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-10,10-diphenyl-5,10-dihydrodibenzo[b,e][1,4]azasiline (DTPDDA) as a blue thermally activated delayed fluorescent (TADF) emitter and bis(2-methyldibenzo[f,h]quinoxaline) (acetylacetonate)iridium(III) (Ir(MDQ)2acac) as a phosphorescent red emitter. This architecture employs EMLs of a blue exciplex-forming co-host, which are hole transport type host material was 1,3-bis(N-carbazolyl) benzene (mCP) and the electron transport type host material was diphenylphosphine oxide-4-(triphenylsilyl)phenyl (TSPO1). The resulting hybrid-WOLEDs showed maximum external quantum efficiency (EQE) of 6.16% and current efficiency (CE) of 11.58cd/A with Commission Internationale de L’Eclairage coordinates of (0.32, 0.33).

High triplet energy exciplex hosts for deep blue phosphorescent organic light-emitting diodes

High triplet energy exciplex hosts for deep blue phosphorescent organic light-emitting diodes were developed by synthesizing a high triplet energy hole transport type host material designed for exciplex formation with a high triplet energy electron transport type host material derived from a diphenyltriazine.

A strong hole transport type host material for high quantum efficiency blue phosphorescent organic light-emitting diodes

A strong hole transport type host material derived from bicarbazole and ditolylamine, 4,4′-(9H,9′H-[2,3′-bicarbazole]-9,9′-diyl)bis(N,N-di-p-tolylaniline) (BCTA), was synthesized as the host material of blue emitting tris[1-(2,4-diisopropyldibenzo[b,d]furan-3-yl)-2-phenylimidazole] (Ir(dbi)3) triplet emitter. The strong hole transport character of BCTA compensated hole trapping effect of Ir(dbi)3 and optimized charge balance in the emitting layer, delivering 17.8% external quantum efficiency in the blue phosphorescent organic light-emitting diodes.

Effect of a broad recombination zone with a triple-emitting layer on the efficiency of blue phosphorescent organic light-emitting diodes

The device characteristics of blue phosphorescent organic lightemitting diodes (PHOLEDs) with a broad recombination region within emitting layers (EMLs) were investigated by changing the combination and the composition of the host materials. Six types of devices were fabricated with the novel host material 9-(4-(triphenylsilyl)phenyl)-9H-carbazole, hole transport-type host material N,N′-dicarbazolyl-3,5-benzene, and electron transporttype host material 2,2′,2″-(1,3,5-benzenetriyl)tris-[1-phenyl-1H-benzimidazole] as diverse EML structures. Balanced chargecarrier injection and a distributed recombination zone within EMLs were achieved through a triple-emitting layer (T-EML). The properties of a device with a T-EML using a stepwise structure without any mixed host system were found to be superior to the other PHOLEDs. This can be explained in terms of improved charge balance and triplet-exciton confinement within the broad recombination region. Open image in new window

Improved efficiency of red phosphorescent organic light-emitting diodes with combination of heterojunction and mixed host structure.

We report an improvement of efficiency in red phosphorescent organic light-emitting diodes (PHOLEDs) based on a combination of heterojunction (HJ) structure and mixed host (MH) system using a phosphorescent red emitter: bis(2-phenylquinolinato)-acetylacetonate iridium III [Ir(pq)2(acac)] doped in 4,4,N,N'-dicarbazolebiphenyl (CBP) of hole transport type host material and 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi) of electron transport type host material. This combination device resulted in an effective electron and hole balance and distribution of the recombination zone. Therefore, highly efficient red PHOLEDs with maximum luminous efficiency and external quantum efficiency of 21.93 cd/A and 14.09% were achieved. Moreover, the combination device showed a power efficiency of 9.51 lm/W, which is higher than 7.61 lm/W in the control device at a luminance of 1000 cd/m2.

Enhanced efficiency of blue phosphorescent organic light-emitting diode base on triple-emitting layer with mixed host system.

We report an improvement of efficiency in blue phosphorescent organic light-emitting diodes (PHOLEDs) based on triple-emitting layer (T-EML) with mixed host (MH) system using a phosphorescent blue emitter: iridium(III)bis[(4,6-di-fluoropheny)-pyridinato-N,C2]picolinate (Flrpic) doped in N,N'-dicarbazolyl-3,5-benzene (mCP) of hole transport-type host material and 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi) of electron transport-type host material. This T-EML device resulted in both an effective electron and hole balance and efficient distribution of the recombination zone. As a result, the property of T-EML device which demonstrated a maximum luminous efficiency of 24.45 cd/A and a external quantum efficiency of 10.9%. It also showed a high maximum power efficiency of 13.82 lm/W, which is approximately two times higher than that of the control device.

Electroluminescence enhancement in blue phosphorescent organic light-emitting diodes based on different hosts

Blue phosphorescent organic light-emitting diodes (OLEDs) are fabricated by utilizing the hole transport-type host material of 1,3-bis(carbazol-9-yl)benzene (MCP) combined with the electron transport-type host material of 1,3-bis (triphenylsilyl) benzene (UGH3) with the ratios of 1:0, 8:2 and 6:4, and doping with blue phosphorescent dopant of bis(4,6-difluorophenylpyridinato-N,C2)picolinatoiridium (FIrpic). The device with an optimum concentration proportion of MCP:UGH3 of 8:2 exhibits the maximum current efficiency of 19.18 cd/A at luminance of 35.71 cd/m2 with maintaining Commission Internationale de L’Eclairage (CIE) coordinates of (0.1481, 0.2695), which is enhanced by 35.7% compared with that of 1:0 with (0.1498, 0.2738). The improvements are attributed to the effective carrier injection and transport in emitting layer (EML) because of mixed host materials. In addition, electron and exciton are confined in the EML, and 4,4′,4″-Tris(carbazol-9-yl)-triphenylamine (TCTA) and Di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane (TAPC) have the high lowest unoccupied molecular orbital (LUMO) energy level and triplet exiton energy.

High efficiency deep blue phosphorescent organic light-emitting diodes using a tetraphenylsilane based phosphine oxide host material

High efficiency deep blue phosphorescent organic light-emitting diodes (PHOLEDs) were fabricated using a tetraphenylsilane based phosphine oxide derivative, bis(4-(diphenylphosphoryl)phenyl)diphenylsilane (BDDS), as the electron transport type host material. The BDDS was effective as the host material for deep blue PHOLED and a mixed host of the BDDS with hole transport type host material further improved the quantum efficiency of deep blue PHOLEDs. A maximum quantum efficiency of 18.1% and a quantum efficiency of 12.2% at 1000cd/m2 with a color coordinate of (0.137, 0.191) were achieved.

Simplified white phosphorescent organic light-emitting diodes without any charge transport layer

High efficiency simple white phosphorescent organic light-emitting diodes without any charge transport layer were developed using an electron transport type high triplet energy host material. A red emitting layer/interlayer/blue emitting layer stack structure was inserted between an anode and a cathode. The electron transport type host material was used as the host for the blue emitting layer and it was mixed with a hole transport type host material in the red emitting layer. A high current efficiency of 16.2 cd/A and a maximum power efficiency of 16.5 lm/W could be obtained from the simple white device.

Host Engineering for High Efficiency in Phosphorescent White Organic Light-Emitting Diodes

High efficiency phosphorescent white organic light emitting diodes (PHWOLEDs) were fabricated by controlling the charge transport properties of host materials. Blue/red/blue stack structure was used and the use of hole transport type host material in red emitting layer was effective to improve the quantum efficiency of PHWOLEDs. High quantum efficiency of 12.2% was obtained in PHWOLEDs.

Improved efficiency in solution processed green phosphorescent organic light-emitting diodes using a double layer emitting structure fabricated by a stamp transfer printing process

A high efficiency soluble green phosphorescent organic light-emitting diode (PHOLED) was developed using a double layer emitting structure fabricated by a stamp transfer printing process. One green emitting layer with a hole transport type host material was coated on a hole transport layer and the other green emitting layer with an electron transport type host material was stamp transfer printed on the green emitting layer. The efficiency of solution processed green PHOLEDs was more than quadrupled using the double layer emitting structure fabricated by the stamp transfer printing method.