Mixed Host Research Articles

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).

33.3: Distinguished Student Paper: Improved Blue Phosphorescent OLEDs with a Linearly‐Graded Mixed Host Architecture

AbstractA blue PhOLED with a linearly‐graded mixed host architecture is compared to a uniformly‐mixed host device. We show that the recombination region is moved into the interior of the emissive layer and results in higher efficiency through avoiding quenching of the phosphor by species in the electron transporting layer.

Highly efficient white phosphorescent organic light emitting diodes using a mixed host structure in deep blue emitting layer

Highly efficient phosphorescent white organic light-emitting diodes (PHWOLEDs) were developed using a deep blue phosphorescent emitter doped into a mixed host of high triplet energy host materials. The deep blue emitting layer was combined with a red:green emitting layer to fabricate PHWOLEDs. A high quantum efficiency of 19.5% with a color coordinate of (0.29,0.38) and 19.8% with a color coordinate of (0.39,0.46) were achieved in the PHWOLEDs using the mixed host emitting layer doped with a deep blue phosphorescent dopant. In addition, a low optimum doping concentration below 5% in red, green and blue dopants was realized in the PHWOLEDs.

Single crystal Ce doped scintillator material with garnet structure sensitive to gamma ray and neutron radiation

A mixed garnet scintillator host material is obtained from the melt—Yttrium Gadolinium Gallium Aluminum Garnet (YGGAG). In addition to the high thermal and chemical stability and radiation hardness found in garnet crystals, it offers sensitivity to neutrons due to the presence of Gd atoms, has lower melting temperature than yttrium aluminum garnet, and similar crystallization behavior suitable for growth of large volume crystals. Crystals of YGGAG doped with Ce of 10×10×10mm3 have already demonstrated energy resolution of 10% at 662keV.

High Efficiency Simple White Phosphorescent Organic Light-Emitting Diodes Using a Phosphine Oxide Host

Highly efficient simple white organic light-emitting diodes (WOLEDs) were fabricated using a mixed host of 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) and 2,7-bis(diphenylphosphoryl)-9,9'-spirobi[fluorene] (SPPO13) in the light-emitting layer. A two layer WOLED structure of TAPC hole transport layer and TAPC:SPPO13 emitting layer was developed. Red and blue phosphorescent emitters were doped in the TAPC:SPPO13 mixed host emitting layer and a high quantum efficiency of 16.0% was obtained. In addition, the maximum power efficiency of the WOLEDs was 37.5 Im/W and color coordinate was (0.43, 0.41). The color coordinate could be kept stable irrespective of the luminance of the device.

Carrier Transport Mechanisms of Phosphorescent Organic Light-Emitting Devices Fabricated Utilizing a N,N′-Dicarbazolyl-3,5-Benzene: 1,3,5-Tri(Phenyl-2-Benzimidazole)-Benzene Mixed Host Emitting Layer

The electrical and the optical properties of phosphorescent organic light-emitting devices (PHOLEDs) fabricated utilizing a mixed host emitting layer (EML) consisting of N,N'-dicarbazolyl-3,5-benzene (mCP) and 1,3,5-tri(phenyl-2-benzimidazole)-benzene (TPBi) were investigated to clarify the carrier transport mechanisms of PHOLEDs. While the operating voltage of the PHOLEDs with a mixed host EML significantly decreased due to the insertion of TPBi with a high electron mobility, the quantum efficiency of the PHOLEDs decreased due to the hindrance of the exciton energy transfer by TPBi molecules. The electroluminescence spectra for the PHOLEDs with an tris(2-phenylpyridine)iridium-doped mixed host EML showed that the TPBi molecules in the mixed host EML increased the electron injection into the mixed host EML, resulting in a decrease of the shift length of the recombination zone in comparison with a single host EML.

Soluble processed low-voltage and high efficiency blue phosphorescent organic light-emitting devices using small molecule host systems

We report low voltage driving and highly efficient blue phosphorescence organic light emitting diodes (PHOLEDs) fabricated by soluble process. A soluble small molecule mixed host system consisting of hole transporting 4,4’,4’’ tris(N-carbazolyl)triphenylamine (TCTA) and bipolar carrier transporting 2,6-bis(3-(carbazol-9-yl)phenyl)pyridine (26DCzPPy) exhibits high solubility with smooth surface properties. Moreover, this small molecule host shows the smoothest morphological property similar to a vacuum deposited amorphous film. A low driving voltage of 5.4V at 1000cd/m2 and maximum external quantum efficiency 14.6% obtained in the solution processed blue PHOLEDs are useful for large area low cost manufacturing.

The impact of uniform and mixed species blood meals on the fitness of the mosquito vector Anopheles gambiae s.s: does a specialist pay for diversifying its host species diet?

We investigated the fitness consequences of specialization in an organism whose host choice has an immense impact on human health: the African malaria vector Anopheles gambiae s.s. We tested whether this mosquito's specialism on humans can be attributed to the relative fitness benefits of specialist vs. generalist feeding strategies by contrasting their fecundity and survival on human-only and mixed host diets consisting of blood meals from humans and animals. When given only one blood meal, An.gambiae s.s. survived significantly longer on human and bovine blood, than on canine or avian blood. However, when blood fed repeatedly, there was no evidence that the fitness of An.gambiae s.s. fed a human-only diet was greater than those fed generalist diets. This suggests that the adoption of generalist host feeding strategies in An.gambiae s.s. is not constrained by intraspecific variation in the resource quality of blood from other available host species.

Enhanced enantioselectivity of 3-methylcyclohexanone by mixed diol host compounds

3-Methylcyclohexanone is only partially resolved by crystallisation with a chiral diol host compound (ee 40%), but when recrystallised from an equimolar mixture of the chiral diol host and a similar but achiral host we obtain complete resolution. The latter host acts as a nucleation inhibitor and the enhanced resolution is attributed to kinetic effects.

Sequential energy and charge transfer processes in mixed host–guest complexes of subphthalocyanine, porphyrin and phthalocyanine chromophores

Porphyrins, phthalocyanines and subphthalocyanines are three attractive classes of chromophores with intriguing properties making them suitable for the design of artificial photosynthetic systems. The assembly of these components by a supramolecular approach is of particular interest as it provides a facile means to build multi-chromophoric arrays with various architectures and tuneable photophysical properties. In this paper, we show the formation of mixed host-guest supramolecular complexes that consist of a β-cyclodextrin-conjugated subphthalocyanine, a tetrasulfonated porphyrin and a series of silicon(IV) phthalocyanines substituted axially with two β-cyclodextrins via different spacers. We found that the three components form supramolecular complexes held by host-guest interactions in aqueous solution. Upon excitation of the subphthalocyanine part of the complex, the excitation energy is delivered to the phthalocyanine unit via excitation energy transfer and the porphyrin chromophore acts as an energy transfer bridge enabling this process. It was shown that photo-induced charge transfer also takes place. A sequential electron transfer process from the porphyrin unit to the phthalocyanine moiety and subsequently from the subphthalocyanine moiety to the porphyrin unit takes place, and the probability of this process is controlled by the linker between β-cyclodextrin and phthalocyanine. The lifetime of the charge-separated state was found to be 1.7 ns by transient absorption spectroscopy.

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.

Solution-Processed Electrophosphorescent Devices Based on Small-Molecule Mixed Hosts

Highly efficient electrophosphorescent organic light-emitting diodes (PHOLEDs) containing mixed hosts of bis(3,5-di(9H-carbazol-9-yl)phenyl)diphenylsilane (SimCP2) and 1,3-bis[(4-tert-butylphenyl)-1,3,4-oxadiazolyl]phenylene (OXD-7) and a soluble derivative of the green emitter fac-tris(2-phenylpyridine)iridium (III) [(Ir(ppy)3 ] have been demonstrated. All organic layers were mixed in a single layer for solution processing during the fabrication of the PHOLEDs. The amorphous mixed host of SimCP2:OXD-7:Ir(ppy)3 exhibited ambipolar charge transport as well as high hole and electron mobilities on the order of 10-7 cm2 /Vs from space-charge-limited current measurement. The values of both the hole and electron mobilities were 100 times greater than that of the widely used poly(9-vinylcarbazole) (PVK):OXD-7:Ir(ppy)3 host, resulting in efficient charge balance in the SimCP2 host. Based on a simple fabrication process of single-layer PHOLED, a green device with the maximum luminous and power efficiencies of 42 cd/A and 20 lm/W, respectively, was obtained at 600 cd/m2.

High Power Efficiency in Blue Phosphorescent Organic Light-Emitting Diodes Using a Spirobifluorene Phosphine Oxide Compound

High power efficiency blue phosphorescent organic light-emitting diodes (PHOLEDs) were fabricated using a mixed host of 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) and 2,7-bis(diphenylphosphoryl)-9,9’-spirobi[fluorene] (SPPO13) in the emitting layer. A maximum power efficiency of 33.7 lm/W and a high power efficiency of 28.4 lm/W at 1,000 cd/m2 were achieved in the blue PHOLED with the mixed host emitting layer of TAPC and SPPO13. The efficiency roll-off of the device was also reduced by using the mixed host emitting layer.

Enhancement Mechanisms of the Color Purity in Blue Organic Light-Emitting Devices Fabricated Utilizing an Emitting Layer Containing Mixed Fluorescence and Phosphorescence Host Materials

The electrical and optical properties of blue organic light-emitting devices (OLEDs) containing a mixed host emitting layer (EML) consisting of a 1,3-bis(carbazole-9-yl)benzene (mCP) layer and a 3-tert-butyl-9,10-di(naphtha-2-yl)anthracene (TBADN) layer were investigated. The driving voltage of the OLEDs with a mixed host EML was smaller than that of the OLEDs with a single EML. The electroluminescence spectra for OLEDs containing a mixed host EML showed a dominant peak related to the mCP or the TBADN layer. The color coordinates of the OLEDs containing a 5% TBADN-doped mCP EML were (0.146, 0.091), indicative of the deep blue color coordinates.

Ce3+ and Eu3+ activtated Na2Sr2Al2PO4F9 nanophosphor

A halophosphate based nanophosphor has been synthesized by wet chemical method. XRD confirms the preparation of nanophosphor and this article presents the luminescence properties of Ce 3+ and Eu 3+ activated Na2Sr2Al2PO4F9 under UV/NUV excitation. The photoluminescence spectrum comprises of a main peak in the range 270–350 nm with a shoulder in the range 350–370 nm, which may be ascribed to transitions from 5d–4f levels of cerium in the mixed host lattice (Na2Sr2Al2PO4F9). In Na2Sr2Al2PO4F9: Eu 3+ nanophosphor, orange/red luminescence under the near ultraviolet excitation of 393 nm, attributed to the transitions from 5D0 excited states to 7FJ (J=0–4) ground states of Eu 3+ ions.

Fabrication of a blue organic light-emitting diode with a novel thermal deposition boat

A highly efficient blue phosphorescent organic light emitting diode (PhOLED) is fabricated by using a novel thermal deposition boat. The boat has two unique features: indirect deposition rate control and fast rate response. With these features, a compact combinatorial evaporation source module is constructed, which utilizes only limited space and enables the fabrication of OLED devices of complex architectures. The deposition rate using this newly designed boat can be controlled within 5% accuracy and the rate response is sufficiently fast that it is particularly useful for producing emitting layers with a linearly graded composition. Two blue PhOLED devices with different architecture in the emitting layer are fabricated with the new boat. The device with a linearly graded mixed host shows higher efficiency than the device with a uniformly mixed one, indicating the advantage of gradual interface change.

The relationship between the device performance and hole mobility of host materials in mixed host system for deep blue phosphorescent organic light emitting devices

We report on the systematic investigation of the relationship between hole mobility of host materials and device performance to maximize the power efficiency. Three different materials with different hole mobility were used as host materials of iridium(III)[bis(4,6-difluorophenyl)pyridinato-N,C 2′]tetrakis(1-pyrazolyl)borate (FIr6) based deep blue phosphorescent organic light-emitting device (PHOELD). Host material, tris(4-( N-carbazolyl)phenyl)methylsilane (MCBP), with higher hole mobility (1.1 × 10 −3 cm 2 V −1 s −1), can accommodate more electron current carried by an n-type host, bis(4-(4,5-diphenyl-4H-1,2,4-triazol-3-yl)phenyl)dimethylsilane (SiTAZ), than the other p-type hosts with lower hole mobility, maintaining the charge balance between hole and electron current. As a result, the optimized device shows high external quantum efficiency (EQE) of 19.0%, high power efficiency of 23.5 lm/W, low efficiency roll off, and deep blue color coordinates of (0.15, 0.23).

Controlling the Recombination Zone of White Organic Light‐Emitting Diodes with Extremely Long Lifetimes

AbstractThe lifetime of the organic devices remains a major challenge that must be overcome before the wide application of white organic light‐emitting diodes (WOLEDs) technology. In this work, we present a new strategy to achieve WOLEDs with an extremely long lifetime by wisely control of the recombination zone. A blue emitting layer of 6,6′‐(1,2‐ethenediyl)bis(N‐2‐naphthalenyl‐N‐phenyl‐2‐naphthalenamine doped 9‐(1‐naphthyl)‐10‐(2‐naphthyl)‐anthracene was deposited on top of the mixed host blue emitting layer to prevent hole penetration into the electron transporting layer and to attain better confinement of carrier recombination. In this way, we obtained a WOLED with a record high lifetime of over 150 000 hours at an initial brightness of 1000 cd m−2, 40 times longer than the conventional bilayer WOLED. The electroluminescent spectra of the long‐lived WOLED showed almost no color‐shifting after accelerated aging. It is anticipated that these results might be a starting point for further research towards ultrastable OLED displays and lightings.

Pure White Organic Light-Emitting Diode with Lifetime Approaching the Longevity of Yellow Emitter

A high-efficiency pure white organic light-emitting diode was fabricated with lifetime approaching that of the low-excitation-energy (yellow) emitter containing counterpart, or six times that of the deep-blue counterpart. The white device was composed of two emission layers with mixed hosts of different compositions. They were respectively doped with yellow rubrene and deep-blue 4,4'-bis-[4-{N,N,N',N'- tetrakis-(4-fluoro-diphenylamino)-phenyl}-vinyl]-biphenyl. The resulting efficiency was 6.0 lm/W (12.4 cd/A) at 20 mA/cm(2). The long device lifetime may be attributed to the double mixed-host architecture employed that effectively dispersed the injected carriers into three different recombination zones and consequently diluted the damaging effect arising from the accumulated charge from un-recombined carriers, hence leading to a markedly improved lifespan.

High power efficiency in single layer blue phosphorescent organic light-emitting diodes

High efficiency single layer blue phosphorescent organic light-emitting diodes (PHOLEDs) without any charge transport layer were developed. A mixed host of spirobifluorene based phosphine oxide (SPPO13) and 1, 1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) was used as the host in the emitting layer. A high maximum external quantum efficiency of 15.8% and a quantum efficiency of 8.6% at 1000 cd/m 2 were achieved in the single-layer blue PHOLEDs without any charge transport layer. The maximum power efficiency and power efficiency at 1000 cd/m 2 were 31.4 and 16.9 lm/W, respectively.