Yellow Organic Light-emitting Devices Research Articles

High-efficiency organic light-emitting diodes based on ultrathin blue phosphorescent modification layer**Project supported by the National Natural Science Foundation of China (NSFC) (Grant Nos. 61675041 and 61605253), the Foundation for Innovation Research Groups of the NSFC (Grant No. 61421002), and the Fund from the Science & Technology Department of Sichuan Province, China (Grant No. 2016HH0027).

Yellow organic light-emitting devices (YOLEDs) with a novel structure of ITO/MoO3(5 nm)/NPB(40 nm)/TCTA(15 nm)/CBP:(tbt)2Ir(acac)(x%(25 nm)/FIrpic(y nm)/TPBi(35 nm)/Mg:Ag are fabricated. The ultrathin blue phosphorescent bis[(4,6-difluorophenyl)-pyridi-nato-N,C2′](picolinate) iridium (III) (FIrpic) layer is regarded as a high-performance modification layer. By adjusting the thickness of FIrpic and the concentration of (tbt)2Ir(acac), a YOLED achieves a high luminance of 41618 cd/m2, power efficiency of 49.7 lm/W, current efficiency of 67.3 cd/A, external quantum efficiency (EQE) of 18%, and a low efficiency roll-off at high luminance. The results show that phosphorescent material of FIrpic plays a significant role in improving YOLED performance. The ultrathin FIrpic modification layer blocks excitons in EML. In the meantime, the high triplet energy of FIrpic (2.75 eV) alleviates the exciton energy transport from EML to FIrpic.

High efficiency yellow organic light-emitting diodes with optimized barrier layers

High efficiency Iridium (III) bis (4-phenylthieno [3,2-c] pyridinato-N,C2′) acetylacetonate (PO-01) based yellow organic light-emitting devices are fabricated by employing multiple emission layers. The efficiency of the device using 4,4′,4″-tris(N-carbazolyl) triphenylamine (TCTA) as potential barrier layer (PBL) outperforms those devices based on other PBLs and detailed analysis is carried out to reveal the mechanisms. A forward-viewing current efficiency (CE) of 65.21cd/A, which corresponds to a maximum total CE of 110.85cd/A is achieved at 335.8cd/m2 in the optimized device without any outcoupling enhancement structures.

Integration of organic LEDs with inorganic LEDs for a hybrid lighting system

We demonstrate that a surface-emitting hybrid light source can be realized by a combination of organic and inorganic light-emitting devices (LEDs). To this end, a blue inorganic LED bar is deployed at one side of a transparent light guide plate (LGP), and a yellow organic LED (OLED) is in contact with the rear surface of the LGP. In such a configuration, it is found that the overall luminance is almost equivalent to the sum of the luminances measured from each light source, and the overall luminance uniformity is determined mainly by the luminance uniformity of the OLED panel at high luminances. We have achieved a white color showing the Commission Internationale d'Eclairage (CIE) chromaticity coordinates of (x = 0.34, y = 0.33), the power efficiency of 9.3 lm/W, the luminance uniformity of 63% at the luminance of 3100 cd m–2, the color rendering index as high as 89.3, and the correlated color temperature finely tunable within the range between 3000 and 8000 K. Such a system facilitates color tuning by adjusting their luminous intensities and hence the implementation of the emotional lighting system.

Highly efficient and solution-processed iridium complex for single-layer yellow electrophosphorescent diodes

A novel electrophosphorescent material based on a biscyclometalated iridium(III) complex of the N,N-diphenyl-4′′-(1-phenyl-1H-benzo[d]imidazol-2-yl)-[1,1′:4′,1′′-terphenyl]-4-amine ligand, named Ir(TPABPBI)2(acac), has been synthesized and its application in organic light emitting devices (OLEDs) was studied. Highly efficient, solution-processed, single-layer, electrophosphorescent diodes utilizing the complex have been prepared and characterized. In these devices, the high triplet energy poly(9-vinylcarbazole) (PVK) is used as a host polymer doped with 2-(4-biphenylyl)-5-(4-tert-butyl-phenyl)-1,3,4-oxadiazole (PBD) employed for electron transport. When the doping concentration of Ir(TPABPBI)2(acac) is up to 4%, devices with a current efficiency of 30.0 cd A−1 corresponding to an EQE of 15% can thus be achieved, along with the Commission de l'Eclairage 1931 chromaticity coordinates of (0.507, 0.486). More importantly, the yellow phosphorescence can be achieved without the generation of excimer emission. Such devices exhibit a very broad and featureless peak at ca. 568 nm with a wide full spectral width at half maximum (FWHM) of 83 nm. These results render Ir(TPABPBI)2(acac) a promising organic phosphor for applications in yellow OLEDs, especially for large-area, highly efficient and cheap yellow PhOLEDs.

基于NPBX掺杂CzHQZn的黄色有机电致发光器件

The performance of yellow organic light-emitting devices(OLEDs) based on a novel material [(E)-2-(2-(9-ethyl-9H-carbazol-3-yl)vinyl) quinolato-zinc(CzHQZn)] with an emitting/hole-transporting layer as an acceptor was investigated.These devices were fabricated as follows: ITO/2T-NATA(30 nm)/NPBX∶25% CzHQZn(x nm)/BCP(10 nm)/Alq3(60-x) nm/LiF(0.5 nm)/Al(x: the thickness of doping layer).The x is 15,20,25,30 nm,respectively,the thickness of Alq3 is correspondingly changed,the total thickness of doping layer and Alq3 is a constant of 60 nm.When x is 20 nm,the thickness of Alq3 is 40 nm,a yellow OLED can be obtained with the CIE coordinates of(0.514 6,0.470 5),the luminance of 1.078 cd/m2 at 4 V.The maximum luminance is 449 0 cd/m2 at 14 V,and the maximum luminous efficiency is 0.98 cd/A.

Highly efficient pure yellow electrophosphorescent device by utilizing an electron blocking material

Yellow organic light-emitting devices (OLEDs) are not easy to obtain since yellow emissive materials are rare and the color purity is often perturbed by the emission from the carrier transport layer. A high-efficiency yellow-emission phosphorescent complex, iridium(III) bis(2-(9,9′-spirobi[fluorene]-7-yl)pyridine-N,C2′) acetylacetonate ((SBFP)2Ir(acac)), is selected as the dopant material for yellow phosphorescent OLEDs (PHOLEDs). An electron blocking material, Ir(ppz)3 (ppz = phenylpyrazole), is utilized to restrain the blue emission from the hole transport layer and improve the color purity of yellow devices. The optimized device shows stable pure yellow electrophosphorescence with the Commission Internationale de l'Eclairage (CIE) coordinates of (0.46, 0.53), and the spectra are largely insensitive to the driving voltages. A maximum luminance of 37219 cd m−2, a maximum luminous efficiency of 50.6 cd A−1 and a maximum external quantum efficiency of 15.4% are obtained.

Highly Efficient Organic Light-emitting Devices based on a New Yellow Fluorescent Dopant

We have fabricated yellow organic light-emitting devices (OLEDs) with a new fluorescent small molecules, 3-(N,N-bis(9,9,9',9'-tetraethyl-2,2'-difluorene-7-yl))aminoperylene 1. The yellow dopant 1 was doped into the host material, tris(8-hydroxyquinolinolato) aluminum (Alq3), with various doping concentration. At 1wt% of the concentration, the device showed the highest efficiency 4.05 % at 100 cd/m2. Commission Internationale de I'Ecairage chromaticity coordinates (CIE) of the yellow emission of the device at 100 cd/m2 was (0.42, 0.55).

High-efficiency orange and yellow organic light-emitting devices using platinum(II) complexes containing extended π-conjugated cyclometalated ligands as dopant materials

Two luminescent platinum(II) complexes 1 and 2 containing extended π-conjugated cyclometalated ligands have been used as dopant materials for the construction of two high-efficiency organic light-emitting devices I and II. Device I (containing dopant 1) emits orange emission and exhibits a maximum external quantum efficiency of 12.4%, a maximum luminous efficiency of 32.3cd∕A, and a maximum power efficiency of 11.2lm∕W. Device II (containing dopant 2) emits yellow light and exhibits a maximum external quantum efficiency of 16.1%, a maximum luminous efficiency of 51.8cd∕A, and a maximum power efficiency of 23.2lm∕W.

High performance yellow light-emitting organic electrophosphorescent devices based on Re(I) complex

Yellow organic light-emitting devices (OLEDs) with (2,3-diphenylpyrazino [2,3-f] [1, 10] phenanthroline) Re(CO)3Br (Re-Dppp) doped CBP as emissive layer were studied. It is found experimentally that Re-Dppp based yellow OLEDs possess high electroluminescent efficiency and brightness: a maximum brightness of 6249 cd/m2 at 15 V and a highest current efficiency of 14.2 cd/A with a brightness of 180 cd/m2 occurring at 1.3 mA/cm2 are achieved, which indicate that Re(I) complexes have a potential application in commercialized PMOLEDs.

Efficiency Enhancement Mechanism in Yellow Organic Light-Emitting Devices with Multiple Heterostructures Acting as an Emitting Layer

The electrical properties of organic light-emitting devices (OLEDs) with multiple heterostructures consisting of N,N'-bis-(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB)/5,6,11,12-tetraphenylnaphthacene (rubrene) emitting layers were investigated. The efficiencies of the OLEDs were significantly affected by the number of heterostructures. Although the turn-on voltage of the OLEDs increases with increasing number of NPB/rubrene heterostructures owing to an increase in the number of trapped holes, the efficiency of the OLEDs increases with increasing driving voltage and increasing number of heterostructures. The efficiency enhancement mechanism in the OLEDs with multiple heterostructures is described on the basis of the electrical results.

Electroluminescence Mechanism for the Efficiency Enhancement and the Color Stabilization of Yellow Organic Light-Emitting Devices with a Mixed Layer

The luminous efficiency of the organic light-emitting devices (OLEDs) with a mixed layer in a hole transport layer (HTL) and an emitting layer (EML) was highest among the fabricated OLEDs, and the luminous efficiency of the OLEDs with a mixed layer at 10 mA/cm2 was 6.5 cd/A. The Commission Internationale de l'Eclairage (CIE) chromaticity coordinates of the OLEDs fabricated utilizing a mixed layer became stabilized, and the CIE chromaticity coordinates of the OLEDs at 15 V was (0.457, 0.510), indicative of a deep yellow color. The efficiency enhancement and the color stabilization of the OLEDs with a mixed layer were attributed to the exciplex emission process.

Bright red-to-yellow organic light-emitting devices based on polarization-induced spectral shifts and broadening

We demonstrated red and yellow organic light-emitting devices (OLEDs) with the structure of ITO/NPB/AlQ:DCJTB/AlQ/LiF/Al, where the NPB, AlQ and DCJTB are 4, 4′-bis[ N-(1-naphthyl)- N-henylamino] biphenyl, tris(8-quinolinolato)aluminum and 4-(dicyanomethylene)-2- t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran, respectively. Electroluminescent (EL) behaviors of these devices have been examined with different concentrations of DCJTB doped into AlQ matrix. The emission color of the devices depends on the doping concentrations of DCJTB. For red and yellow OLEDs, a maximum luminescence of 2750 cd/m 2 and 21,700 cd/m 2 was obtained, respectively. The peak emission wavelength shift of DCJTB was found to be due to the polarization effects. It is of particular interest that the EL spectrum of DCJTB got broadening with the doping concentrations and current densities of the devices in our experiments.

High-efficiency yellow double-doped organic light-emitting devices based on phosphor-sensitized fluorescence

We demonstrate high-efficiency yellow organic light-emitting devices (OLEDs) employing [2-methyl-6-[2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene] propane-dinitrile (DCM2) as a fluorescent lumophore, with a green electrophospho- rescent sensitizer, fac tris(2-phenylpyridine) iridium [Ir(ppy)3] co-doped into a 4,4′-N,N′dicarbazole-biphenyl host. The devices exhibit peak external fluorescent quantum and power efficiencies of 9%±1% (25 cd/A) and 17±2 lm/W at 0.01 mA/cm2, respectively. At 10 mA/cm2, the efficiencies are 4.1%±0.5% (11 cd/A) and 3.1±0.3 lm/W. We show that this exceptionally high performance for a fluorescent dye is due to the ∼100% efficient transfer of both singlet and triplet excited states in the doubly doped host to the fluorescent material using Ir(ppy)3 as a sensitizing agent. These results suggest that 100% internal quantum efficiency fluorescent OLEDs employing this sensitization process are within reach.

Bright, saturated, red-to-yellow organic light-emitting devices based on polarization-induced spectral shifts

We demonstrate red, orange, and yellow organic light-emitting devices (OLED) with the electroluminescent layer consisting of aluminum tris(8-hydroxyquinoline) (Alq 3) doped with laser dye DCM2, with the emission color dependent on the concentration of DCM2. A peak emission wavelength shift of up to 50 nm is found to be due to strong polarization effects. For red and yellow–orange OLEDs, a maximum luminance of 1400 cd/m 2 and 15200 cd/m 2 is measured, with a luminance of 100 cd/m 2 attained at 100 mA/cm 2 (14 V) and 10 mA/cm 2 (12 V), respectively. The current versus voltage dependencies of these devices are consistent with trap-limited conduction, unaffected by the presence of DCM2.