Blue Fluorescent Devices Research Articles

Spin-Flip-Restricted Multiple-Resonance Emitters for Extended Device Lifetime in Indolocarbazole-Based Blue Organic Light-Emitting Diodes.

In this study, a multiple-resonance (MR) core structure is developed with a spin-flip-restricted emission mechanism based on a fused indolo[3,2,1-jk]carbazole (ICz) framework as emitters to improve the lifetime of blue organic light-emitting diodes. The molecular skeleton modulation approach applied to the conjugated π-system effectively stabilizes the triplet energy of the fused ICz emitters and narrows the full-width-at-half maximum (<20nm). In addition, the emitters exhibit higher exciton stability than conventional boron-based MR emitters. The fused ICz-based blue fluorescent device exhibits a high external quantum efficiency of 7.2%, a blue index of 68.6cd A-1 at a Commission internationale de l'éclairage y coordinate (CIEy) of 0.075, and a device lifetime 1.8 times longer than that of a boron-based emitter. In addition, a phosphor-sensitized fluorescent device based on the ICz emitter exhibited an improved external quantum efficiency of 20.6% with a CIEy coordinate of 0.076.

Spirobifluorene-based hole-blocking material with enhanced efficiency through hole and exciton confinement in blue fluorescent OLEDs

A new hole-blocking material, 2-(9,9′-spirobi[fluoren]-5-yl)-4-phenylbenzo [4,5]thieno[3,2-d]pyrimidine (SBF-BTPym), was designed and synthesized using spirobifluorene and electron transport moieties. The high triplet energy and high thermal stability of the spirobifluorene moiety were suitable for designing the hole-blocking material for blue fluorescent organic light-emitting diodes (OLEDs). The electron deficiency of benzothienopyrimidine allowed good electron transport properties, and a deep highest occupied molecular orbital energy level of −6.55 eV suppressed leakage of the holes from the emitting layer (EML) to the adjacent layer. Blue fluorescent OLEDs consisting of a triplet-triplet annihilation–induced host were fabricated using SBF-BTPym. The maximum external quantum efficiency of the blue fluorescent device was 7.2%, which was higher than that of the device without a hole-blocking layer by 10%. According to transient electroluminescence analysis, exciton confinement in the EML is mainly responsible for the improved efficiency.

Study on n-type GaN based organic-inorganic hybrid light emitting heterojunction

The organic-inorganic hybrid light-emitting devices have become research hotspot for combining both the high electron mobility of inorganic semiconductors and the extraordinary optoelectronic properties of organic semiconductors. In the research, an organic-inorganic hybrid blue fluorescent device was fabricated by employing n-type GaN on a sapphire substrate as an electron injection layer of blue organic electroluminescent device. The GaN-based device emitted blue electroluminescence at 472 nm with the maximum luminance of 36333 cd/m2 and a turn-on voltage of 3.8 V. The maximum power efficiency, current efficiency, and external quantum efficiency of 2.24 lm/W, 5.93 cd/A and 2.93% have been achieved for GaN-based device, which is comparable to ITO-based organic light emitting diode with the identical configuration. Finally, thermal simulation results showed that GaN-based device exhibited better heat dissipation than ITO-based one, which is beneficial to reduce the device aging and improve operation lifetime.

Highly Efficient Soluble Blue Delayed Fluorescent and Hyperfluorescent Organic Light-Emitting Diodes by Host Engineering.

Solution-processed high-efficiency fluorescent organic light-emitting diodes with an external quantum efficiency over 18% were developed by engineering a host material and device structure designed for solution process. A high triplet energy host material designed for the solution process, (oxybis(3-(tert-butyl)-6,1-phenylene))bis(diphenylphosphine oxide) (DPOBBPE), worked efficiently as the host of blue fluorescent devices because of good solubility, high photoluminescence quantum yield, and good film properties. The DPOBBPE host enabled a high external quantum efficiency of 18.8% in the fluorescent organic light-emitting diodes by the solution process. Moreover, 25.8% external quantum efficiency in the soluble blue thermally activated delayed fluorescent devices was also realized. The 25.8% external quantum efficiency of the DPOBBPE delayed fluorescent device and 18.8% external quantum efficiency of the fluorescent device are the highest efficiency values achieved in the solution-processed blue fluorescent organic light-emitting diodes. Moreover, the solution-processed fluorescent device showed an improved blue color coordinate of (0.14, 0.20) compared to (0.17, 0.31) of the delayed fluorescent device.

Unconventional Molecular Design Approach of High-Efficiency Deep Blue Thermally Activated Delayed Fluorescent Emitters Using Indolocarbazole as an Acceptor.

Unconventional blue thermally activated delayed fluorescent emitters having electron-donating type indolocarbazole as an acceptor were developed by attaching carbazolylcarbazole or acridine donors to the indolocarbazole acceptor. Three compounds were derived from the indolocarbazole acceptor. The indolocarbazole-acridine combined products showed efficient delayed fluorescent behavior and a high quantum efficiency of 19.5% with a color coordinate of (0.15, 0.16) when they were evaluated as thermally activated delayed fluorescent emitters in deep blue fluorescent devices. This is the first demonstration of the use of electron-donating carbazole-derived moieties as efficient acceptor units of blue thermally activated delayed fluorescent emitters.

High-efficiency blue fluorescent devices with simple structure

Thermally activated delayed fluorescence (TADF) materials can harvest both singlet and triplet excitons for light emission without the utilization of heavy metal elements such as iridium and platinum and become the third generation organic optoelectronic materials after fluorescent and phosphorescent materials. TADF material bis[4-(9,9-dimethyl-9, 10-dihydroacridine)phenyl]sulfone (DMAC-DPS) shows high photoluminescence quantum yield in solid films, rendering it as a suitable emitter for non-doped organic light emitting diodes. We optimize the hole transport layer, electron transport layer and emission layer thickness for the none-doped DMAC-DPS devices to pursuit high luminance efficiency. We compare the properties of the devices using indium tin oxide (ITO)/MoO3 hole injection contact with either a 40 nm mCP or 30 nm NPB/10 nm mCP hole transport layer and the results indicate (1) the former devices show larger current than the latter devices for there is a large energy barrier of ca. 0.7 eV for hole injection from NPB into mCP in the latter devices; (2) Both of the devices show similar luminance efficiency and the underlying reason is that the small modulation of the dominant hole current slightly affects the device efficiency. In order to investigate the influence of different electron transport layers on the device performance, we have prepared the devices with either 10 nm DPEPO/40 nm TmPyPB, 50 nm TmPyPB or 50 nm SPPO13 electron transport layer and find out (1) the devices with DPEPO electron transport layer show the highest EQE of 16.2% due to the fact that DPEPO with triplet energy of 3.3 eV can confine excitons inside the emisson layer effectively; (2) The devices with SPPO13 possess the highest current density at certain voltage among the devices and the maximum external quantum efficiency and power efficiency for the SPPO13 based devices are 14.3% and 26.8 lm W - 1, which are higher than 13.8% and 22.2 lm W - 1 for the TmPyPB based devices. The possible reason is that highly polarized phosphorus oxygen groups of SPPO13 greatly improve the electron injection and as a result improve the carrier balance in the devices. Moreover, we compare the properties of the devices with a 15 and 30 nm emission layer and find that the devices with a 30 nm emission layer have slightly better luminance efficiency. High efficiency of the DMAC-DPS devices can be attributed to the effective conversion of triplet excited states to singlet excited states via reverse intersystem crossing (RISC) process. TADF sensitized fluorescence devices can achieve high luminance efficiency by using the well-established fluorescent materials with the advantages such as the superior stability, versatility and abundance. We report highly efficient blue TADF sensitized devices using DMAC-DPS as the host material and the traditional fluorescence blue-emitting material 2,5,8,11-tetra-tert-butylperylene (TBPe) as the guest material. The devices with 1.0% TBPe show the maximum external quantum efficiency and power efficiency of 12.7% and 22.9 lm W - 1, which are about 3 times higher than those of the conventional 2-methyl-9,10-bis(naphthalen- 2-yl)anthracene (MADN): TPBe devices. This can be attributed to the effective use of triplet excited states for light emission via RISC process and highly efficient Forster energy transfer process from DMAC-DPS to TBPe. Utilization of a TADF material as host material and sensitizer and a traditional fluorescence material as emitting dopant serves as a novel approach to achieve high-efficiency organic light emitting diodes.

P-159: Electron Transporting Materials for Highly Efficient and Long Lifetime Blue OLED Devices for Display and Lighting Applications

A series of new electron transporting (ET) materials with deep HOMO levels more than 6.2 eV were designed and developed. These electron transporting materials, applied in blue fluorescent devices, exhibited high efficiency and long lifetime with efficiency of 9.7 cd/A and 33902 hrs half-lifetime under 1000 cd/m2.

24-4: Investigation of Effect of Triplet-Triplet Annihilation and Molecular Orientation on External Quantum Efficiency of Ultrahigh-Efficiency Blue Fluorescent Device

The effects of triplet-triplet annihilation (TTA) and molecular orientation were quantitatively investigated for a high-efficiency blue fluorescent organic light-emitting diode. Both the efficient TTA generation by improving carrier balance and the horizontal orientation of the transition dipole moment of the blue dopant realized ultrahigh external quantum efficiency (approximately 12%).

Pure blue and white light electroluminescence in a multilayer organic light-emitting diode using a new blue emitter

We characterized the 6,12-bis{[N-(3,4-dimethylphenyl)-N-(2,4,5-trimethylphenyl)]amino} chrysene (BmPAC), which has been proven to be a blue fluorescent emission with high EL efficiency. The blue fluorescent device exhibits good performance with an external quantum efficiency of 5.8% and current efficiency of 8.9 cd/A, respectively. Using BmPAC, we also demonstrate a hybrid phosphorescence/fluorescence white organic light-emitting device (WOLED) with high efficiency of 36.3 cd/A. In order to improve the relative intensity of blue light, we plus a blue light-emitting layer (BEML) in front of the orange light emitting layer (YEML) to take advantage of the excess singlet excitons. With the new emitting layer of BEML/YEML/BEML, we demonstrate the fluorescence/phosphorescence/fluorescence WOLED exhibits good performance with a current efficiency of 47 cd/A and an enhanced relative intensity of blue light.

A new multifunctional fluorenyl carbazole hybrid for high performance deep blue fluorescence, orange phosphorescent host and fluorescence/phosphorescence white OLEDs

A new multifunctional host material, 3,3′-(2,7-di(quinolin-8-yl)-9H-fluorene-9,9-diyl)bis(9-phenyl-9H-carbazole) has been designed, synthesized and used in high performance OLEDs. This tetrasubstituted fluorene was found to have good morphological and thermal stability with a high glass transition temperature of 192 °C and a decomposition temperature of 480 °C. A non-doped tri-layer blue fluorescent device based on this tetrasubstituted fluorene shows a deep blue emission with a Commission Internationale de L’Eclairage coordinates of (0.16, 0.10) and a maximum power efficiency of 1.1 lm/W. An orange phosphorescent device using this tetrasubstituted fluorene as a host in conjunction with an iridium complex as dopant exhibits a maximum power efficiency of 21.0 lm/W, which is much higher than that of a biscarbazolylbiphenyl-based control device (11.5 lm/W) with the same device structure. Furthermore, by using the tetrasubstituted fluorene as a blue florescent emitter and a host for phosphorescent dopant, a white emitting OLED with a maximum power efficiency of 22.5 lm/W and CIE coordinates of (0.38, 0.33) were obtained. These results show that this tetrasubstituted fluorene is a versatile multifunctional material for OLED applications.

Synthesis of Diimidazolylstilbenes as n‐Type Blue Fluorophores: Alternative Dopant Materials for Highly Efficient Electroluminescent Devices

Two new n-type diimidazolylstilbenes as blue-fluorescent dopant materials are synthesized and characterized. Blue-fluorescent devices based on these two compounds as the dopants reveal outstanding external quantum efficiencies (EQEs) (current efficiencies) of 7.8% (10.4 cd A(-1) ) and 7.7% (7.9 cd A(-1) ) with Commission internationale de l'Eclairage (CIE) co-ordinates of (0.14, 0.15) and (0.15, 0.11).

Chromatic-stable white organic light-emitting devices incorporating red color conversion layers

Chromatic-stable white organic light-emitting devices (WOLEDs) are reported by combining simple blue fluorescent devices based on a new kind of blue emitter TC-1759 (derivation of N6,N6,N12,N12-tetrap-tolylchrysene-6,12-diamine) with red color conversion layer (DCJTB). By adjusting the thickness of color conversion layers (CCLs), a very pure white light emission with CIE coordinates of (0.34, 0.33) is obtained at the fixed bias of 8V, and its color temperature is 5036K. The chromaticity of the device shows a good stability with a slight offset of (0.03,0.02) at the driving voltage varied from 6V to 10V. The maximum luminance and maximum current efficiency achieved 1348cd/m2 (12V), and 1.37cd/A at 3.52mA/cm2.

33.1: Invited Paper: A Novel Triplet Green Host System and Charge Balance Tuning for High Performance Singlet Blue Devices

AbstractOur former findings on the charge balance in blue fluorescent devices show a clear connection between the basic performance parameters: Efficiency and lifetime both show an optimum with respect to voltage. Unfortunately, for devices using a conventional hole injection and NPB as hole transport material, the optimum values do not occur at the same voltage. Moreover, the optimum voltage for lifetime is much higher than that for optimum efficiency. After investigating the underlying charge balance issues, we developed new stack layouts and hole transport materials to shift the lifetime optimum to lower voltage values. Using an appropriate hole injection layer and one of our latest hole transport materials, we can now combine excellent lifetime, low voltage and good efficiency in one fluorescent blue device. In addition, we obtain 10% EQE by carefully tuning the hole transport side in fluorescent blue devices. No special hole blocking layer is required to obtain this high efficiency.For green phosphorescent devices, we developed a thermally stable co‐host material which allows for the use of low emitter concentrations in the range of 5% without sacrificing device performance. We combine this material with an electron transporting host that shows a slight initial rise in lifetime when a low emitter concentration is employed. Due to these features, the tuning of the host mixing ratio results in excellent LT95 values in combination with good voltage, efficiency and low efficiency rolloff for high luminance.

Multifunctional electron-transporting indolizine derivatives for highly efficient blue fluorescence, orange phosphorescence host and two-color based white OLEDs

In this work, derivatives of indolizine are first used as electron-transporting host materials for hybrid fluorescence/phosphorescence white organic light-emitting devices (F/P-WOLED). Of the indolizine derivatives, a blue fluorescent material BPPI (3-(4,4′-biphenyl)-2-diphenylindolizine) was found to have: (1) blue emission with high quantum yields, (2) good morphological and thermal stabilities, (3) electron-transporting properties, and (4) a sufficiently high triplet energy level to act as a host for red or yellow-orange phosphorescent dopants. The multifunctional BPPI enables adaptation of several simplified device configurations. For example, a non-doped blue fluorescent device exhibits good performance with an external quantum efficiency of 3.16% and Commission Internationale de l'Eclairage coordinates of (0.15, 0.07). A high-performance orange phosphorescent device was found to have a high current efficiency of 23.9 cd A−1. Using BPPI, we also demonstrate a F/P-WOLED with a simplified structure, stable emissions and respectable performance (current and external quantum efficiencies of 17.8 cd A−1 and 10.7%, respectively).

ChemInform Abstract: Synthesis and Photo‐ and Electroluminescence Properties of 3,6‐Disubstituted Phenanthrenes: Alternative Host Material for Blue Fluorophores.

Three deep-blue fluorescent 9,10-bis(4-tert-butylphenyl)phenanthrenes with diphenyl, -naphthyl, and -pyrenyl moieties at C3 and C6 positions were synthesized and used as the host for doped blue fluorescent devices; one of these devices reveals excellent external quantum efficiency of 7.7% and current efficiency of 9.8 cd A−1 with low efficiency roll-off, deep-blue color coordinates (0.14, 0.14) and long operational lifetime.

Novel transport materials for high-performance fluorescent and phosphorescent OLEDs

To improve the performance of blue fluorescent and green phosphorescent organic light-emitting diode devices, Merck developed novel green phosphorescent host and electron-transporting materials. The newly developed electron-transporting material improves the external quantum efficiency of blue fluorescent devices up to 8.7%, with an excellent lifetime. In combination with the newly developed host materials, the efficiency of green phosphorescent devices can be improved by a factor of 1.7, and the lifetime by a factor of 7.

Synthesis and photo- and electroluminescence properties of 3,6-disubstituted phenanthrenes: alternative host material for blue fluorophores

Three deep-blue fluorescent 9,10-bis(4-tert-butylphenyl)phenanthrenes with diphenyl, -naphthyl, and -pyrenyl moieties at C3 and C6 positions were synthesized and used as the host for doped blue fluorescent devices; one of these devices reveals excellent external quantum efficiency of 7.7% and current efficiency of 9.8 cd A(-1) with low efficiency roll-off, deep-blue color coordinates (0.14, 0.14) and long operational lifetime.

39.4: Highly Efficient Fluorescent Blue OLEDs with Efficiency‐enhancement Layer

AbstractWe found a new device structure which has an efficiency‐ enhancement layer between emitting layer and electron transporting layer. We applied the structure to a pure blue fluorescent device with a CIE1931 coordinate of (0.14, 0.12) and successfully obtained very high EQE of over 10% with low driving voltage of 3.7 V at 10 mA/cm2 and long lifetime of 10,000 hrs at an initial luminance of 1,000 cd/m2. Results of transient EL measurements indicated the contribution of triplet excitons to the high EQE.