Mixed Host Research Articles

Host engineering for improving the performance of blue phosphorescent organic light-emitting devices

We report an effective means to greatly improve the performance of blue phosphorescent organic light-emitting devices by doping well-known electron- or hole-transporting triplet host material, specifically, 3-(4-biphenyl)-4-phenyl-5-(4- tert-butylphenyl)-1,2,4-triazole (TAZ) or 4,4′,4′′-tris( N-carbazolyl)triphenylamine (TCTA), into emissive layer to form mixed host structures. A superior device performance with high current and power efficiencies of 47.4 cd/A and 37.3 lm/W, respectively, and more importantly, a theoretical maximum of external quantum efficiency of 21.9%, can be achieved for an optimized TCTA-doped device. On the other hand, doping of TAZ into hole-transporting host material would degrade device performance. It is found that, in addition to the well-known effects of charge carrier balance, both energy levels and triplet energies of mixed host materials play crucial roles in determining the device performance. As confirmed by the time-resolved phosphorescence decay studies, the lifetime of FIrpic is strongly dependent on the triplet energy of host materials and the shorter lifetime of triplet excitons with high Stern–Volmer quenching constant of 0.1564% −1 in TAZ-doped films is the origin of the low electroluminescence efficiency of the TAZ-doped devices.

Complete sequence of raptor adenovirus 1 confirms the characteristic genome organization of siadenoviruses

Currently, the family Adenoviridae contains five genera, out of which Siadenovirus is one of the two least densely populated ones. A new member representing a new species in this genus has been detected in various birds of prey. The virus, named raptor adenovirus 1 (RAdV-1), could not be isolated, probably because no appropriate permissive cell-line was available. Partial genomic sequences, obtained by PCR and suggesting that the virus is a new siadenovirus species, have been published earlier. In the present paper, determination and analysis of the complete RAdV-1 genome are reported. This is the first complete genome sequence acquired from a non-isolated adenovirus (AdV). The sole source was a mixture of the internal organs of the diseased and dead birds. Until now, the genomic organization considered characteristic to siadenoviruses had been deduced from the detailed study of only two virus species, one of which originated from birds and the other from a frog. The present analysis of RAdV-1 confirmed the genus-specific genetic content and genomic features of siadenoviruses, and a putative novel gene was found as well. In general, AdVs and most of the AdV genera are thought to be strictly host specific. In the genus Siadenovirus, however, two virus species of rather divergent (avian and amphibian) host origin were present when the genus was found. Although by now the greatest number of known siadenoviruses infect birds, the original hosts of the genus remain unknown.

Enhanced efficiency in mixed host red electrophosphorescence devices

Enhanced efficiency of red phosphorescent organic light-emitting devices is observed by using a bis[2-(2′-benzothienyl)pyridinato-N,C3′] iridium(acetylacetonato) doped 4,4′-N,N′-dicarbazole-biphenyl (CBP) and 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBI) mixed host emitting layer. The CBP:TPBI mixed host device shows a maximum external quantum efficiency of 9.1%, which is dramatically improved compared to that of the CBP (6.6%) and TPBI (5.4%) single host devices. Such a mixed host strategy can also be exploited in red phosphor dibenzo[f,h]quinoxaline iridium (acetylacetonate) doped devices. Investigations reveal that the position of charge carrier recombination zone of the mixed host devices predominantly locates in the electron blocking layer/emitting layer interface. The efficiency enhancement is attributed to the optimized hole and electron injection balance and hence increased charge carrier recombination rate in the emitting layer.

The relationship between the host structure and optimum doping concentration in red phosphorescent organic light-emitting diodes

The effect of the host structure on the optimum doping concentration in red phosphorescent organic light-emitting diodes (PHOLEDs) was investigated. A mixed host of the phosphine oxide derivative (SPPO21) and 4,4′,4″-tris(N-carbazolyl)triphenylamine (TCTA) was used as the host in the red PHOLED and the device performances were studied according to the doping concentration. The device performance of the red PHOLED was optimized at a doping concentration of 2% in the SPPO21 rich red PHOLED, while the device performance was optimized at a doping concentration of 6% in the device with 50% TCTA content. It was found that the optimum doping concentration was determined by the energy transfer and charge trapping.

The Timing of Alemtuzumab Significantly Impacts Mixed Chimerism and Acute Graft Versus Host Disease

The Timing of Alemtuzumab Significantly Impacts Mixed Chimerism and Acute Graft Versus Host Disease

Combination of heterojunction and mixed-host structures in one blue fluorescent organic light emitting diode to improve the power efficiency

High power efficiency blue organic light-emitting diode (OLED), based on 2-methyl-9,10-di(2-naphthyl) anthracene (MADN) and p-bis(p-N,N-diphenyl-amino-styryl) benzene (DSA-ph), has been realized by combining heterojunction (HJ) structure and mixed host (MH) structure in one device. This combination resulted in both high current efficiency and low driving voltage, and thus highly efficient blue OLED with peak power efficiency of 5.0lm/W was achieved, which is approximately five times higher than 1.1lm/W in the MH control device and 56% higher than 3.2lm/W in the HJ control device.

Luminescence characteristics of Ca1−xSrxS:Ce nanophosphors

Luminescence characteristics of Ca1−xSrxS:Ce (x=0, 0.25, 0.50, 1) nanophosphors have been investigated. XRD of all the samples show a single cubic phase of Ca1−xSrxS:Ce. TEM micrographs exhibit the rod like structure of the samples with a decrease in diameter with decreasing amount of Ca. The results of TEM were found to be in good agreement with the XRD results. The photoluminescence spectrum comprises of a main peak in the range 480–510nm with a shoulder in the range 530–565nm, which may be ascribed to transitions from 5d–4f levels of cerium in the mixed host lattice. The red shift in the emission wavelength with increasing Ca content may be correlated with the change in crystal field of mixed host lattice for different Ca and Sr concentrations. We have also investigated TL response of Ca1−xSrx:Ce to 60Co-γ rays. All the samples with different Sr and Ca contents show different TL response. TL response for the sample with x=0.75 shows the simplest TL glow curve with the maximum TL intensity, for which we have calculated the activation energy using glow curve deconvolution functions.

Host Plant Effects on Development and Reproduction of the Glassy-Winged Sharpshooter,Homalodisca vitripennis(Homoptera: Cicadellidae)

Development, survivorship, longevity, reproduction, and life table parameters of the glassy-winged sharpshooter, Homalodisca vitripennis (Germar), were examined in the laboratory using three host plants, sunflower (Helianthus annuus L.), Chrysanthemum morifolium L., and euonymus (Euonymus japonica Thurb.). Females deposited similar-sized egg masses on all three plants. Hatching was highest with eggs deposited on euonymus and lowest for those deposited on sunflower. Embryonic development time among host plants was similar while nymph development time was shortest on sunflower and longest on euonymus. Nymph survival to adulthood ranged from 32% on euonymus to 82% for those reared on sunflower. Adult females had similar life spans on sunflower and chrysanthemum. H. vitripennis completed a lengthy egg-to-adult development on euonymus, however, mating did not occur. The onset of mating was contingent on maturation of adult females. The majority of mating activity occurred within the first three days after onset. Premating periods ranged from 6 to 7 d on sunflower to 27 d on chrysanthemum, with overall mating rates of 77.4 and 19.8%, respectively. Females typically mated more than once and they had the longest oviposition period and highest egg production on sunflower; ≈ 50 and 67% of total number of eggs were deposited within first 45 d after the start of oviposition on sunflower and chrysanthemum, respectively. Adult size and weight related to which host plant was consumed throughout development. Greater intrinsic and finite rates of increase and net reproduction rate, and shorter population doubling time occurred when the sharpshooters were allowed to develop on sunflower. The overall developmental and reproductive parameters obtained in this study indicate that a mixed host plant system, composed of sunflower and euonymus or chrysanthemum plants, is an efficient means for optimizing egg production and colony maintenance of the glassy-winged sharpshooter.

High efficiency and low roll-off blue phosphorescent organic light-emitting devices using mixed host architecture

We report high efficiency and low roll-off for blue electrophosphorescent organic light emitting devices based on a mixed host layer architecture. The devices were fabricated using a mixed layer of di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane, a hole transport material, and 2,8-bis(diphenylphosphoryl)dibenzothiophene, an electron transport material, as the host layer doped with the blue phosphor iridium (III) bis[(4,6-difluorophenyl)-pyridinato-N,C2′]picolinate. Using a mixed layer as the host allowed us to achieve high power efficiency (59 lm/W at 100 cd/m2), low turn-on voltage (2.7 V for >10 cd/m2), and low roll-off in these devices.

Highly Luminescent Tetradentate Bis-Cyclometalated Platinum Complexes: Design, Synthesis, Structure, Photophysics, and Electroluminescence Application

N,N-Di(6-phenylpyridin-2-yl)aniline (L1), N,N-di(6-(2,4-difluorophenyl)pyridin-2-yl)aniline (L2), N,N-di(3-(pyridin-2-yl)phenyl)aniline (L3), N,N-di(3-(1H-pyrazol-1-yl)phenyl)aniline (L4), N,N-di(3-(3-methyl-1H-pyrazol-1-yl)phenyl)aniline (L5), and N,N-di(3-(4-methyl-1H-pyrazol-1-yl)phenyl)aniline (L6) undergo cyclometalation to produce two types of tetradentate bis-cyclometalated platinum(II) complexes: C--N*N(wedge)C platinum complexes 1 and 2 and N--C*C--N platinum complexes 3-6, respectively, where an "X--Y" (X, Y = C or N) denotes a bidentate coordination to the platinum to form a five-membered metallacycle and "X*Y" denotes a coordination to form a six-membered metallacycle. The crystal structures of 1, 3, and 5 were determined by the single-crystal X-ray diffraction analysis, showing distorted square-planar geometry, that is, two C--N coordination moieties are twisted. Complex 5 showed much greater distortion with largest deviation of 0.193 A from the mean NCCNPt coordination plane, which is attributed to the steric interaction between the two 3-methyl groups on the pyrazolyl rings. Density functional theory (DFT) calculations were carried out on the ground states of 1 and 3-6. The optimized geometries are consistent with the crystal structures. The highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) of the molecules displayed a localized characteristic with the contribution (18-45%) of the platinum metal to the HOMOs. All complexes are emissive at ambient temperature in fluid with quantum yields of 0.14 to 0.76 in 2-methyltetrahydrofuran. The emission of the complexes covers from blue to red region with lambda(max) ranging from 474 to 613 nm. Excimer emission was observed for 1 and 2 at high concentration of the complexes. The emission lifetime at infinite dilution for 1 and 2 was determined to be 7.8 and 11.4 micros, respectively. Concentration quenching was observed for 3 and 4, but the excimer emission was not observed. The life times for 3-6 were determined to be in the range of micro seconds, but those of 4-6 (3.4-5.7 micros) were somewhat shorter than that of 3 (7.6 micros). The highly structured emission spectra, long life times, and DFT calculations suggested that the emissive state is primarily a (3)LC state with metal-to-ligand charge-transfer (MLCT) admixture. The ZFS of 23 cm(-1) for the emissive triplet state was observed directly by high resolution spectroscopy for 1 in a Shpol'skii matrix, which also suggested an emission from a triplet ligand centered ((3)LC) state with admixture of MLCT character. Complex 1 was incorporated into an organic light-emitting diode (OLED) device as an emitter at 4 wt % in the mixed host of 4,4',4''-tris(N-carbazolyl)triphenylamine (TCTA) and 2,2',2''-(1,3,5-benzenetriyl)tris(1-phenyl-1-H-benzimidazole) (TPBI) and demonstrated excellent performance with maximum external quantum efficiency of 14.7% at the current density of 0.01 mA/cm(-1).

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).

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

High power efficiency blue phosphorescent organic light-emitting diodes (PHOLEDs) with only two organic layers were developed using a spirobifluorene based phosphine oxide (SPPO13) host material. Two layer blue PHOLEDs with only 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) hole transport layer and TAPC:SPPO13:blue dopant mixed host emitting layer were fabricated. A high power efficiency of 26.0 lm/W at 1000 cd/m2 were achieved in the simple blue device due to the high quantum efficiency of 17.5% and a low driving voltage of 4.1 V at 1000 cd/m2. In addition, a maximum power efficiency of 48.5 lm/W and a high quantum efficiency of 19.6% were demonstrated from the simple blue PHOLEDs with only two organic layers.

White organic light-emitting devices fabricated by spin-coating molecular materials

White organic light-emitting device (WOLEDs) employing molecular mixed host (MH) is demonstrated by spin-coating. The spin-coated film functions as light-emitting layer and hole transporting layer, with the former formed by spin-coating solution containing MH of NPB (N.N′-Bis(naphthalene-1-yl)-N,N′-bis(phenyl)-benzidine) and MADN (2-methyl-9,10-di(2-naphthyl) anthracene), blue dye (4,4′-bis[2-(4-(N,N-diphenylamino)phenyl)vinyl]biphenyl) and yellow dye (5,6,11,12-tetraphenylnaphacene). The performances of the devices made with different mixed ratio of MH are investigated. It is found that the device performances depends on the MH ratio, and under the optimal NPB:MADN ratio (60:40), the WOLEDs show a maximum luminance of 24 671 cd/m2 and a current efficiency of 5.8 cd/A for the practical luminance of 1000 cd/m2. The effect of MH ratio on device performances can be attributed to the difference of hole mobility between the NPB and MADN.

Improved electrophosphorescence efficiency for organic light-emitting diodes using the cohost with stepwise blending profile

A tris(2-phenylpyridine) iridium doped phosphorescent organic light-emitting diode using a mixed host with stepwise blending profile was demonstrated. We adopted the mixture of 4,4′,4″-tris(N-carbazolyl) triphenylamine and 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene as the host in the emitting layer. By using a stepwise blending ratio profile of the two host materials, a peak external quantum efficiency of 17.7% and a peak power efficiency of 45.7 lm/W were attained, which increased by 59.5% and 60.9% relative to the optimal uniform blending ratio profile based device, respectively. The efficiency improvement was attributed to the multiple exciton formation interfaces, which could expand the recombination regions.

A very high efficiency electrophosphorescent device doped with short triplet lifetime phosphor using multi-recombination zones

We have demonstrated a high-efficiency electrophosphorescent device doped with bis(2-phenyl-benzoimidazole) iridium (III) acetylacetonate with a triplet lifetime in the range of nanoseconds. Then the doped mixed host was sandwiched by two doped single-host layers. Multi-recombination zones were formed in the emission layer. Such a structure could increase the proportion of recombined carriers to injected carriers and extend the recombination zone. As a result, a maximum external quantum efficiency of 18.6% was attained due to the presence of multi-recombination zones. The mechanism of improving the electroluminescence performance was also discussed.

Recombination zone study of phosphorescent organic light-emitting diodes with triplet mixed host emitting structure

Recombination zone of green phosphorescent organic light-emitting diodes (PHOLEDs) with triplet mixed host was studied using red sensing layer. Recombination zone of triplet mixed host device with 4,4′,4″-tris( N-carbazolyl)triphenylamine and 1,3,5-tris( N-phenylbenzimidazole-2-yl)benzene as hosts was rather dispersed compared with that of single host device with recombination zone near charge transport layer. The recombination zone was shifted to hole transport side at high driving voltage.

Polymer-induced improvements in ferroelectric liquid crystal

The chevron geometry in the SmC* phase of ferroelectric liquid crystals (FLC) has been a major obstacle in the use of FLC in displays as it results in poor electro-optical performance. The present paper reports a novel method to overcome this problem, by doping a small amount of polymer in the FLC matrix. In addition to the improvement in smectic ordering, polymer doping is also found to be useful in improving the vital electro-optical properties. The various electro-optical parameters like switching time, tilt angle, contrast ratio etc. show improvement in polymer mixed guest host mixture of FLC samples. POLYM. COMPOS., 31:1776–1781, 2010. © 2010 Society of Plastics Engineers.

Small molecule host system for solution-processed red phosphorescent OLEDs

We demonstrate high efficiency solution-processed red phosphorescent OLEDs with small molecule mixed host systems. 2-TNATA (4,4′,4″-tris(N-(2-naphthyl)-N-phenyl-amino)triphenylamine):TPBI (2,2′,2″-(1,3,5-phenylene)tris(1-phenyl-1H-benzimidazole)) and m-MTDATA (4,4′,4″-tri-(N-3-methylphenyl-N-phenylamino)triphenylamine):TPBI host systems are reported as good soluble mixed host systems. A doping level of 3% bis(2-phenylquinoline)(acetylacetonate)iridium (Ir(phq) 2acac) dopant in the 2-TNATA:TPBI (1:1 ratio) mixed host produces the best quantum efficiency and driving voltage. This fabricated red phosphorescent OLED has a driving voltage of 5.2 V and maximum current and power efficiencies of 17.8 cd/A and 11.3 lm/W, respectively. Minimal electron or hole trapping in the phosphorescent dopant molecules and prevention of self quenching by the low doping technique appear to be the key reasons for good device performance.

Solution-processed organic films of multiple small-molecules and white light-emitting diodes

We investigated characteristics of solution-processed films of 4,4′-bis(2,2-diphenylvinyl)-1,1′-bibenyl (DPVBi), N,N′-bis(naphthalene-1-yl)- N,N′-bis(phenyl)-benzidine (NPB), and their blends, and it was found that the spin-coated films of NPB, and blends of NPB and DPVBi, though having lower densities, were more uniform than their vacuum-deposited counterparts. Using the spin-coated films of NPB:DPVBi as mixed host, doped with blue dye (4,4′-bis[2-(4-( N,N-diphenylamino)phenyl)vinyl]biphenyl) and yellow dye (5,6,11,12-tetraphenylnaphacene), new white organic light-emitting devices (WOLEDs) were demonstrated. The luminance (maximum luminance of 35822 cd/m 2), efficiency (5.3 lm/W (100 cd/m 2) and 8.3 cd/A (1000 cd/m 2)) and stability of these solution-processed devices are better than or equivalent to the vacuum-deposited one, which was expected as an alternative route to the fabrication of small-molecular WOLEDs, reducing the cost of devices and avoiding the complexities of the co-evaporation of multiple dopants and host materials in the vacuum deposition.

Effect of 13 single and eight mixed host plant diets on survival, post-embryonic development and morphology of variegated grasshopper in laboratory

Zonocerus variegatus (Orthoptera: Pyrgomorphidae) is known as an agricultural pest in West and Central Africa. In this study, the effects of 13 single and eight mixed host plant diets on the survival, post-embryonic development and morphology of Z. variegatus in the laboratory were investigated. In each cage, 20 one-day larvae were provided with these diets and their survival monitored every two days, from August 2000 to September 2002, until all individuals died. Results showed that the number of larval stages varied from six to eight according to the diet. Six larval stages were most frequent. Development to the adult stage (complete development) was only noted with 52% of diets. All the mixed host plant diets induced complete development of Z. variegatus except that of Cajanus cajan + Synedrella nodiflora + Chromolaena odorata. Complete development was observed with four single host plant diets: Lablab purpurea, C. cajan, Manihot esculenta and S. nodiflora. Compared to leguminous species and Asteraceae, M. esculenta (Euphorbiaceae) was the species that resulted in the highest level of survival and development of Z. variegatus. Chromolaena odorata and S. nodiflora (Asteraceae) induced late appearance of the different Z. variegatus nymphal instars and the appearance time was shorter on legumes. The supernumerary stage 7 has the same color as the larva in stages 1–6, but this larva was significantly larger than stage 6 and smaller than the adult stage. These results indicate that legumes for short fallows affected the survival and post-embryonic development of Z. variegatus in the laboratory.