High efficiency blue phosphorescent organic light-emitting diode using tetraphenylsilane core molecule as host material

An effective thermally activated delayed fluorescence host material for highly efficient blue phosphorescent organic light-emitting diodes with low doping concentration

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

Three bicarbazole based host materials with different interconnect positions between carbazole units, 3,3'-(9,9'-[3,3'-bicarbazole]-9,9'-diyl)dibenzonitrile (3CN33BCz), 3,3'-(9,9'-[3,4'-bicarbazole]-9,9'-diyl)dibenzonitrile (3CN34BCz), and 3,3'-(9,9'-[4,4'-bicarbazole]-9,9'-diyl)dibenzonitrile (3CN44BCz), were developed and their synthesis, material characterization, and device characterization were reported. Two carbazole units were connected via 3,3'-, 3,4'-, and 4,4'-positions to correlate the interconnect positions with photophysical properties and device performances. The linkage via 4,4'-position increased triplet energy and thermal stability of the host materials, while the linkage via 3,3'-position enhanced current density. All bicarbazole host materials showed good device performances and high quantum efficiency above 25% was attained using the biscarbazole derivatives for green and blue phosphorescent organic light-emitting diodes. In particular, the bicarbazole host materials with a linkage via 4-position showed high quantum efficiency above 30% in the green devices.

Two diphenylphosphine oxide modified phenylcarbazole host materials with substituents at 2,7 (PPO27) and 3,6 (PPO36) positions were synthesized and their device performances were correlated with the chemical structure of the host materials. Low driving voltage was obtained in the PPO27host with two diphenylphosphine oxides at 2,7 positions due to reduced band gap. The PPO27 showed better performances in sky blue phosphorescent organic light-emitting diodes, while the PPO36 showed better performances in deep blue phosphorescent organic light-emitting diodes. A high quantum efficiency of 23.9% and power efficiency of 37.5 lm W−1 were achieved in the blue device with PPO27host.

We demonstrate a multiple quantum well (MQW) structure with charge control layers (CCLs) to produce highly efficient blue phosphorescent organic light-emitting diodes (OLEDs). Three types of devices (A, B, and C) were fabricated with the following emitting layer structures while maintaining the thickness of the EMLs: host-emitter doping layers, nondoping layers, and CCLs. Triplet energies in such MQW devices were confined at the EMLs. The properties of a device with an MQW demonstrated a maximum luminous efficiency and external quantum efficiency of 18.33 cd/A and 9.47%, respectively. The device also showed a reduction in the turn-on voltage from 3.5 V to 2.5 V and an enhancement of the power efficiency. The described MQW device concept is considered to be useful for future OLED displays and light applications.

Steric modulation of thermally activated delayed fluorescence-type host for high quantum efficiency in blue phosphorescent organic light-emitting diodes

Spatial separation of two blue triplet emitters for improved lifetime in blue phosphorescent organic light-emitting diodes by confining excitons at the interface between two emitting layers

Exciton stabilizing high triplet energy n-type hosts for blue phosphorescent organic light-emitting diodes

Bipolar host materials with carbazole and dipyridylamine groups showing high triplet energy for blue phosphorescent organic light emitting diodes

Various dibenzothiophene derivatives were synthesized as high triplet energy host materials for deep blue phosphorescent organic light-emitting diodes (PHOLEDs) and their device performances were investigated. Dibenzothiophene host materials with a hole transport type carbazole and electron transport type phosphine oxide moieties showed high quantum efficiency and low driving voltage due to balanced charge injection and transport. A high quantum efficiency of 20.2% and only 10% reduction of quantum efficiency at 1000 cd m−2 were demonstrated from the deep blue PHOLEDs with the dibenzothiophene based high triplet energy host materials.

1,2,4-Triazole-Ligand-based Iridium(III) complex and its use in blue phosphorescent organic light-emitting diodes

We have investigated a relationship between device performances and host properties in the emissive layer (EML) of iridium(III) bis(4′,6′-difluorophenylpyridinato)tetrakis(1-pyrazolyl)borate doped blue phosphorescent organic light-emitting diodes (PHOLEDs). We found that the recombination zone as well as charge carrier injection properties of the EML could be systematically engineered through a mixed host system. Therefore, light-emitting performances of blue PHOLEDs were greatly improved with external quantum and power efficiencies of 20.5% and 43.5 lm/W at a luminance of 56 cd/m2, respectively.

Highly efficient blue phosphorescent organic light-emitting diodes are investigated using iridium(Ill) bis[(4,6-di-fluorophenyl)-pyridinato-N,C2']picolinate doped in N,N'-dicarbazolyl-3,5-benzene (mCP) with a charge control layer (CCL) as the dual recombination zone (DRZ) system. DRZ with CCL was used to form a broad recombination zone and exciton confinement within each emission zone. Holes and electrons can be easily transported through the CCL, which were a mixed p-type mCP and n-type 2,2',2"-(1,3,5-benzenetryl) tris(1-phenyl)-1H-benzimidazol, for controlling the carrier movement. The CCL can play a role in triplet exciton blocking as expected from high triplet energy levels as well. Additionally, a white organic light-emitting diode was fabricated using a new phosphorescent orange emitter: bis[2-(2,4-difluorophenyl)pyridinato]iridium 2-(2-hydroxyphenyl)benzothia zolate doped in DRZ. The white device showed a maximum luminous efficiency of 23.15 cd/A, a maximum external quantum efficiency of 9.56%, and a maximum power efficiency of 13.37 lm/W. It also showed white emission with CIEx,y coordinates of (x = 0.33, y = 0.41) at 8 V.

Triplet emitter doped exciton harvesting layer for improved efficiency and long lifetime in blue phosphorescent organic light-emitting diodes

Up to now, the most efficient blue phosphorescent organic light-emitting diode (PhOLED) was achieved with a maximum external quantum efficiency (ηext) of 34.1% by using an exciplex cohost. It still remains a challenge to obtain such high efficiencies using a single-host matrix. In this work, a highly efficient sky-blue PhOLED is successfully fabricated using a newly developed bipolar host material, namely 5-(2-(9H-[3,9'-bicarbazol]-9-yl)phenyl)nicotinonitrile (o-PyCNBCz), which realizes a ηext of 29.4% at a practical luminance of 100 cd m-2 and a maximum ηext of 34.6% (at 23 cd m-2). The present device is characterized by simple configuration with a single host and single emitting layer. o-PyCNBCz also reveals high efficiency of 28.2% (94.8 cd A-1) when used as the host for green PhOLED. Under identical conditions, o-PyCNBCz always outperforms than its isomer 3-PyCNBCz (5-(9-phenyl-9H-[3,9'-bicarbazol]-6-yl)nicotinonitrile) in terms of more balanced charge transportation, higher photoluminescent quantum yields of over 90%, and higher horizontal orientation ratio of the emitting dipole for the host-dopant films, which finally lead to its superior performance in PhOLEDs. It is observed that all these merits of o-PyCNBCz benefit from its ortho-linking style of carbazole (p-type unit) and cyanopyridine (n-type unit) on the phenylene bridge and the resultant molecular conformation.