Deep Blue Phosphorescent Organic Light-emitting Diodes Research Articles

Control of Host-Matrix Morphology Enables Efficient Deep-Blue Organic Light-Emitting Devices.

Mixing a sterically bulky, electron-transporting host material into a conventional single host-guest emissive layer isdemonstratedtosuppress phase separation of the host matrix while increasing the efficiency and operational lifetime of deep-blue phosphorescent organic light-emitting diodes (PHOLEDs) with chromaticity coordinates of (0.14, 0.15). The bulky host enables homogenous mixing of the molecules comprising the emissive layer while suppressing single host aggregation; a significant loss channel of nonradiative recombination. By controlling the amorphous phase of the host-matrix morphology, the mixed-host device achieves a significant reduction in nonradiative exciton decay, resulting in 120 ± 6% increase in external quantum efficiency relative to an analogous, single-host device. In contrast to single host PHOLEDs where electrons are transported by the host and holes by the dopants, both charge carriers are conducted by the mixed host, reducing the probability of exciton annihilation, thereby doubling of the deep-blue PHOLED operational lifetime. These findings demonstrate that the host matrix morphology affects almost every aspect of PHOLED performance.

Superbly long lifetime over 13,000 h for multiple energy transfer channels in deep blue phosphorescence organic light-emitting diodes with Ir complex under CIEy of 0.17

Despite over two decades of relentless endeavor, the industrial application of blue phosphorescent organic light-emitting diodes (PhOLEDs) has not been realized due to extremely short lifetime. The degradation of PhOLEDs is generally accelerated at high current levels since high triplet energy with long exciton lifetime are mostly concentrated on host molecules and transferred to dopant via slow Dexter energy transfer (DET) processes rather than fast Förster resonance energy transfer (FRET) processes. Herein, we propose a novel device architecture that creates multiple energy transfer channels by employing an Ir-complex intermediate energy carrier (IEC). Unlike exciplex or electroplex, no excitons were generated between the host and the IEC even though the IEC also behaves as a p-type host. The most crucial role of the IEC is to diversify the energy transfer channels. By introducing the IEC in deep blue PhOLEDs, both FRET and DET channels were additionally created between the IEC and the host, and the IEC and the dopant. Consequently, an unprecedentedly long half luminance lifetime of 13,830 h at an initial luminance of 100 cd/m2 was obtained with a high efficiency of 14.4% and CIEy = 0.17. To our best knowledge, the lifetime in our report is the longest with a deep blue phosphorescent Ir complex.

Probing photophysical properties of isomeric N-heterocyclic carbene Ir(iii) complexes and their applications to deep-blue phosphorescent organic light-emitting diodes

The photophysical and electrochemical properties of the two isomeric N-heterocyclic carbene Ir(iii) complexes were investigated.

Recent Progress of Host Materials for Highly Efficient Blue Phosphorescent OLEDs

Phosphorescent organic light-emitting diodes (PHOLEDs) show a bright future for flat-panel displays and solid- state lighting due to higher quantum efficiencies compared with traditional fluorescent OLEDs. This review focuses on small-molecular organic host materials for blue PHOLEDs with external quantum efficiency higher than 20%. Hole transport-type, electron transport-type and bipolar transport hosts are introduced according to their charge transporting prop- erties. Their molecular structures and physical properties such as triplet energy, HOMO/LUMO energy levels and thermal stabilities, as well as device performances of host materials for blue and deep-blue PHOLEDs are comprehensively demon- strated. It is expected to provide reference value for the exploitation of new organic host materials and the commercialization of OLEDs.

Diphenylmethyl linked high-triplet-energy material as a host for deep-blue phosphorescent organic light-emitting diodes

A diphenylmethyl-linkage-based high-triplet-energy organic material, 3-(dibenzofuran-2-yldiphenylmethyl)-9-phenyl-9H-carbazole (TCDFCz), was synthesized as a host material for deep-blue phosphorescent organic light-emitting diodes (PHOLEDs). High-triplet-energy moieties, 9-phenylcarbazole and dibenzofuran, were connected through diphenylmethyl linkage, and high triplet energy of 2.97eV was obtained. TCDFCz was effective as the high-triplet-energy host material for deep-blue PHOLEDs, and a high quantum efficiency of 13.1% was achieved.

Synthesis of new bipolar materials based on diphenylphosphine oxide and triphenylamine units: efficient host for deep-blue phosphorescent organic light-emitting diodes

This paper reports the synthesis and physical properties of a series of bipolar host materials, using of a hole-transporting triphenylamine (TPA) monomer as a core incorporated with different numbers of diphenylphosphine oxide (PO) as electron-transporting moieties, 4-(diphenylphosphoryl)-N,N-diphenylaniline (DDPA), 4-(diphenylphosphoryl)-N-(4-(diphenylphosphoryl)phenyl)-N-phenylaniline (DDPP), and tris(4-(diphenylphosphoryl)phenyl)amine (TDPA), for solution-processed deep-blue phosphorescent organic light-emitting devices (PhOLEDs). With the increasing numbers of PO units, the glass-transition temperature of those compounds rise gradually. Moreover, the newly synthesized compounds all possess high triplet energies, which can prevent back energy transfer between the host and dopant molecules, and are expected to serve as appropriate hosts for iridium(III) tris(3,5-difluoro-4-cyanophenyl)pyridinato-N,C′ (FCNIrpic). The solution-processed devices using DDPP and TDPA as the hosts for the phosphorescence emitter FCNIrpic showed the maximum luminance efficiencies of 9.7 and 6.6cdA−1, respectively. The efficiency of TDPA based device shows nearly three times higher than the value of commonly used host material 1,3-bis(9-carbazolyl)benzene (mCP) with the same structure, which is outstanding with respect to other works related to the solution-processed deep-blue PhOLEDs based on small-molecule hosts.

Significance of irreversible formation of “electromer” in 1-bis[4-[N,N-di(4-tolyl)amino]phenyl]-cyclohexane layer associated with the stability of deep blue phosphorescent organic light emitting diodes

We demonstrate that injection of electrons in 1-bis[4-[N,N-di(4-tolyl)amino]phenyl]-cyclohexane (TAPC) layer irreversibly induces defect sites responsible for “electromer” emission. We also show that the defects alter the charge transporting properties of TAPC layer to influence the charge balance of iridium(III)[bis(4,6-difluorophenyl)pyridinato-N,C2′]tetrakis(1-pyrazolyl)borate (FIr6) based deep blue phosphorescent organic light emitting diodes (PHOLED). The present investigation implies that deep-blue PHOLEDs should be carefully designed for the emission zone to be located far enough from the TAPC layer so as to avoid or minimize the emission from TAPC layer.

Fused indole derivatives as high triplet energy hole transport materials for deep blue phosphorescent organic light-emitting diodes

High triplet energy hole transport materials based on novel fused indole core structure were synthesized and their device performances in deep blue phosphorescent organic light emitting diodes (PHOLEDs) were investigated. The fused indole based hole transport materials showed a high triplet energy over 2.90 eV and high glass transition temperature over 120 °C. The high triplet energy hole transport materials were used in deep blue PHOLEDs and gave a high external quantum efficiency of 24.7% with a color coordinate of (0.137,0.182).

Indolo Acridine-Based Hole-Transport Materials for Phosphorescent OLEDs with Over 20% External Quantum Efficiency in Deep Blue and Green

Thermally stable high-triplet-energy hole transport materials based on 8H-indolo[3,2,1-de]acridine core (FPC) were synthesized and the device performances of FPC-based phosphorescent organic light-emitting diodes (OLEDs) were investigated. The FPC-based hole transport materials showed a high triplet energy (above 2.90 eV) and high glass-transition temperature (above 140 °C). The FPC-based hole-transport materials (HTMs) were effective as the HTMs for green and deep-blue phosphorescent OLEDs, and a high quantum efficiency (over 20%) was achieved in both devices.

Solution processed deep blue phosphorescent organic light-emitting diodes with over 20% external quantum efficiency

Highly efficient solution processed deep blue phosphorescent organic light-emitting diodes (PHOLEDs) were developed using a solution processible high triplet energy host and deep blue dopant materials. Stable film morphology was observed from the spin coated deep blue emitting layer and a high quantum efficiency of 22.1% was achieved in the deep blue PHOLED with a color coordinate of (0.14, 0.19).

External Quantum Efficiency Above 20% in Deep Blue Phosphorescent Organic Light‐Emitting Diodes

Highly efficient deep blue phosphorescent organic light-emitting diodes (PHOLEDs) with external quantum efficiency above 20% are developed using a bipolar-type high-triplet-energy host material and a high-triplet-energy exciton blocking material. Maximum quantum efficiency of 25.1% and low roll-off (still 23.1% at 1000 cd m−2) are achieved in these deep blue PHOLEDs.

Dibenzothiophene derivatives as host materials for high efficiency in deep 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.

An ethylcarbazole based phosphine oxide derivative as a host for deep blue phosphorescent organic light-emitting diode

Deep blue phosphorescent organic light-emitting diodes (PHOLEDs) were developed using a 9-ethylcarbazole based phosphine oxide material (EPO1). A high triplet energy of 3.01 eV was obtained from the EPO1 host material and efficient energy transfer from the host to the deep blue emitting phosphorescent dopant was observed. A high quantum efficiency of 7.9% with a color coordinate of (0.15, 0.17) was achieved in the deep blue PHOLED using the EPO1 host material.

Effects of charge balance on device performances in deep blue phosphorescent organic light-emitting diodes

The performances of deep blue phosphorescent organic light-emitting diodes (PHOLEDs) have been investigated by changing the combination and the composition of host materials in a mixed host emissive layer (EML). An electron transport-type host material of m-bis-(triphenylsilyl)benzene (UGH3), was combined with an hole transport-type host materials, N,N′-dicarbazolyl-3,5-benzene (mCP) or 4,4′,4′′-tris( N-carbazolyl)triphenylamine (TcTa) both doped with a deep blue electro-phosphorescent dopant of iridium(III)bis(4′,6′-difluorophenylpyridinato)tetrakis(1-pyrazolyl)borate (FIr6). We found that a mixed host structure was effective to control the charge carrier injection and transport in EML. Therefore, we obtained highly improved efficiency in deep blue PHOLEDs with peak external quantum and luminance efficiencies of 22.9% and 39.2 lm/W with maintaining Commission Internationale de L’Eclairage (CIE) coordinates of ( x = 0.163, y = 0.287).

Highly Efficient Deep-Blue Phosphorescent Organic Light-Emitting Diodes Using Iridium(III) Bis[(5-cyano-4-fluorophenyl)pyridinato-N,C2']picolinate as an Emitter

The authors have demonstrated highly efficient deep-blue phosphorescent organic light-emitting diodes (BPHOLEDs) using iridium(III) bis[(5-cyano-4-fluorophenyl)pyridinato-N,C2']picolinate (FCNIrpic) as a blue emitter. FCNIrpic has a deeper-blue color than iridium(III) bis[4,6-(difluorophenyl)pyridinato-N,C2']picolinate. The BPHOLEDs with FCNIrpic showed a maximum luminous efficiency of 19.00 cd/A, a maximum external quantum efficiency of 10.70%, and Commission Internationale de L'Eclairage coordinates (CIEx,y) of (0.16,0.26).

High efficiency deep blue phosphorescent organic light-emitting diodes using a double emissive layer structure

High efficiency deep blue phosphorescent organic light-emitting diodes (PHOLEDs) have been developed with a double emissive layer structure (D-EML). Using bis(4′,6′-difluorophenylpyridinato)tetrakis(1-pyrazolyl)borate (FIr6) as an electro-phosphorescent dopant, we achieved a maximum external quantum efficiency of 14.8% in the deep blue PHOLEDs with D-EMLs, which is 50% higher value than that of 9.76% with single emissive layer structure (S-EML). Moreover, the external quantum efficiency at high current density region of 10 mA/cm 2 was maintained up to 11.3% in this D-EML device. We attributed this enhancement to the expansion of carrier recombination region and the effective confinement of exciton within the emissive layer.

Adamantane Derivative as Host Material for Efficient Deep-Blue Phosphorescent Organic Light Emitting Diodes

AbstractWe report on a high efficiency deep-blue phosphorescent organic light-emitting diode (POLED) based on new electron-transporting host material. The new electron-transporting host material is an adamantane derivative with high triplet energy and high electron mobility. The deep blue POLED that we have developed utilizes a deep-blue phosphorescent guest material, iridium(III)bis(4’,6’,-difluorophenylpyridinato)tetrakis(1-pyrazolyl)borate, and exhibits a power efficiency of about 10.2 lm/W at luminance of 100 cd/m2 and maximum external quantum efficiency (EQE) of about 13 %. The power efficiency of our POLED is much higher than that of POLED using p–bis(triphenylsilyly)benzene (UGH2). The maximum EQE of our POLED was also slightly more than that of POLED using UGH2. The obtained difference in power efficiency originates from the new host material having higher electron mobility than that of UGH2.