High-efficiency White Organic Light-emitting Diodes Research Articles

Multiple strategies towards high-efficiency white organic light-emitting diodes by the vacuum deposition method

This review summarizes the progress in WOLEDs in recent years including all phosphorescent WOLEDs, hybrid WOLEDs, all fluorescence WOLEDs, doping-free WOLEDs, and single-emitter WOLEDs.

Structural design for highly efficient pure fluorescent warm WOLEDs by employing TADF molecule as blue emitter and exciplex donor

Abstract In this work, highly efficient pure fluorescent white organic light-emitting diodes (WOLEDs) are realized through the structural design by employing thermally activated delayed fluorescence (TADF) molecule of mSOAD as blue emitter and exciplex donor, respectively. The combination of mSOAD: PO-T2T exhibits yellow-green exciplex emission with high EQE of 9.7%. Based on the application of this exciplex as the host, the high efficiency WOLEDs with current efficiency, power efficiency and external quantum efficiency (EQE) of 30.2 cd A−1, 28.0 lm W−1 and 11.6%, respectively, are achieved finally. Meantime, stable warm white emission spectra with Commission Internationale de l'Eclairage (CIE) coordinates change as low as (0.030, 0.008) from 5 V to 8 V are also realized. The reasonable structural design and double functions application of TADF molecule are responsible for the high performances fluorescent WOLEDs.

高效率双发光层结构白色有机电致发光器件

高效率双发光层结构白色有机电致发光器件

ChemInform Abstract: Yellow/Orange Emissive Heavy‐Metal Complexes as Phosphors in Monochromatic and White Organic Light‐Emitting Devices

AbstractReview: 215 refs.

High-efficiency white organic light-emitting diodes using thermally activated delayed fluorescence

White organic light-emitting diodes (WOLEDs) have attracted much attention recently, aimed for next-generation lighting sources because of their high potential to realize high electroluminescence efficiency, flexibility, and low-cost manufacture. Here, we demonstrate high-efficiency WOLED using red, green, and blue thermally activated delayed fluorescence materials as emissive dopants to generate white electroluminescence. The WOLED has a maximum external quantum efficiency of over 17% with Commission Internationale de l'Eclairage coordinates of (0.30, 0.38).

The influence of type-I and type-II triplet multiple quantum well structure on white organic light-emitting diodes.

We demonstrate high-efficient white organic light-emitting diodes (WOLEDs) based on triplet multiple quantum well (MQW) structure and focus on the influence on WOLEDs through employing different potential barrier materials to form type-I and type-II MQWs, respectively. It is found that type-I MQW structure WOLEDs based on 1,3,5-tris(N-phenyl-benzimidazol-2-yl)benzene as potential barrier layer (PBL) offers high electroluminescent (EL) performance. That is to say, maximum current efficiency and power efficiency are achieved at about 1,000 cd/m2 with 16.4 cd/A and 8.3 lm/W, which increase by 53.3% and 50.9% over traditional three-layer structure WOLEDs, respectively, and a maximum luminance of 17,700 cd/m2 is earned simultaneously. The achievement of high EL performance would be attributed to uniform distribution and better confinement of carriers within the emitting layer (EML). However, when 4,7-diphenyl-1,10-phenanthroline or 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline is used as PBL to form type-II MQW structure, poor EL performance is obtained. We attribute that to improper energy level alignment between the interface of EML/PBL, which leads to incomplete confinement and low recombination efficiency of carriers, a more detailed mechanism was argued.

Novel dibenzothiophene based host materials incorporating spirobifluorene for high-efficiency white phosphorescent organic light-emitting diodes

Two host materials, DBTSF2 and DBTSF4, were designed and synthesized, incorporating dibenzothiophene (DBT) and spirobifluorene (SF) blocks. Their thermal, electrochemical and photo-physical properties were fully characterized. DBTSF4, which adopted an ortho-linkage between DBT and SF moieties, showed a significantly higher T1 energy of 2.82eV as compared to its para-linkage analogue DBTSF2 (2.49eV). Their applications as host for green, blue and white phosphorescent organic light-emitting diodes (PHOLEDs) were explored. The DBTSF4 based blue PHOLED has a highest current efficiency of 23.5cdA−1. And using DBTSF4 as a single host, two-color based white PHOLEDs were achieved from cold white emission with CIE coordinate of (0.31, 0.43) to yellowish warm white emission (0.44, 0.49) with maximum current efficiencies varying from 35.8 to 52.3cdA−1 and maximum external quantum efficiencies from 13.1% to 16.9% respectively. The white PHOLED devices also showed a low efficiency roll-off even at 10,000cdm−2.

High color rending index and high-efficiency white organic light-emitting diodes based on the control of red phosphorescent dye-doped hole transport layer

We have investigated the transport characteristics of red phosphorescent dye bis(1-(phenyl)isoquinoline) iridium (III) acetylanetonate (Ir(piq)₂acac) doped 4,4',4"-tri(N-carbazolyl)triphenylamine (TCTA), and found that the increasing doping ratio was facilitated to improve the ability of hole transporting. A high color rendering index (CRI) and high-efficiency WOLED was achieved by employing Ir(piq)₂acac doped TCTA film as an effective red emissive layer due to the generation of charge transfer complex (CTC) at the interface. The relative proportion in red: green: blue emission intensity can be controlled by the CTC concentration to obtain high CRI WOLEDs. The WOLED with an optimal red dye doping concentration of 5 wt% exhibits a high CRI of 89 and a power efficiency of 31.2 lm/W and 27.5 lm/W at the initial luminance and 100 cd/m², respectively. The devices show little variation of the Commission Internationale de I'Eclairage coordinates in a wide range of luminance.

High efficient and high color rendering index white organic light-emitting diodes

We have fabricated high-efficient white organic light-emitting diodes (WOLEDs) using two types of electron transport materials with different electron mobility. The effect of the electron mobility on the device performance is discussed. In addition, to generate the desired white emission and high color rendering index, we perform the structure design of OLED, in which the functions of co-host of blue and green dopants on chromatic-stability are investigated. Experimental results find that the maximum color rendering index reaches as high as 91 at the voltage of 8 V.

Reduced efficiency roll-off in highly efficient and color-stable hybrid WOLEDs: The influence of triplet transfer and charge-transport behavior on enhancing device performance

By wisely utilizing combinations of exciton-managed orange-phosphorescence/sky blue-fluorescence, we report on high-efficiency white organic light-emitting diodes (WOLEDs) with high color-stability together with reduced efficiency roll-off. Two WOLEDs with the peak current efficiencies of 34.5 and 42.5 cd A −1 which slightly shift to 34.2 and 40.0 cd A −1 at 1000 cd m −2 are demonstrated. Systematic investigations focused on the effects of hole-injection buffer layer, thickness of emitting-layer (EML) and the stepwise-doping profile of orange phosphorescent EML on the device performance have been performed. It is evidently shown that careful management of the triplet/singlet excitons and charge-carriers is key to realizing such high performance of the devices. The results will beyond doubt be helpful to the design of both material and device structure for high-performance WOLEDs and next-generation solid-state lighting sources.

High-Efficiency White Organic Light-Emitting Diodes Using Codoped Blue-Light-Emitting Layers with Different Functional Materials

We have demonstrated high-efficiency white organic light-emitting diodes (WOLEDs) using codoped blue-emitting layers with three light emitters, 4''-(2,2-diphenylvinyl)-1-[4-(N,N-diphenylamino)-styryl]-terphenyl, fac-tris(2-phenypyridine) iridium(III), and bis(5-benzoyl-2-phenylpyridinato-C,N)iridium(III) (acetylacetonate). Blue-emitting layers (BEMLs) were codoped with the different functional materials, N,N'-bis(1-naphyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine and 4,7-diphenyl-1,10-phenanthroline, which are used as charge-transporting materials in OLEDs. An optimized device with centralized carriers in emitting layers showed a maximum luminance of 19 710 cd/m2 at 12 V, a maximum luminous efficiency of 23.20 cd/A at 0.14 mA/cm2, and an external quantum efficiency of 10.20% at 32.19 cd/m2.

High-Efficient White Organic Light-Emitting Diodes Using the Two Different Blue Fluorescent Emitters

The authors have demonstrated white organic light-emitting diodes (WOLEDs) using the two blue fluorescent emitters, 4"-(2,2-diphenylvinyl)-1-[4-(N,N-diphenylamino)-styryl]-terphenyl (PVAS-tPh) and 1,4-Bis[2-(7-N-diphenyamino-2-(9,9-diethyl-9H-fluoren-2-yl)) vinyl] benzene (DAF-ph) and the red and green phosphorescent emitters, bis(5-benzoyl-2-phenylpyridinato-C,N)iridium(III) (acetylacetonate) ((Bzppy)1Ir(III)acac) and fac-tris(2-phenypyridine) iridium(III) (Ir(ppy)3), respectively. The two blue emitters were constituted for high-efficient WOLEDs. The structure optimized device showed power efficiency of 2.3 times higher than that of control device and had the maximum luminance of 36300 cd/m2 at 13 V and the maximum power efficiency of 32.2 Im/W at 0.017 mA/cm2 respectively.

High-Efficiency White Organic Light-Emitting Diodes Using Blue and Red Phosphorescent Materials with Exciton Blocking Layer

High-efficiency white organic light-emitting diodes (WOLEDs) were fabricated with two emissive layers and an exciton blocking layer (EBL) was sandwiched between two phosphorescent dyes, bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl) iridium III (Flrpic) as the blue emission and iridium(III) bis(5-acetyl-2-phenylpyridinato-N,C2') acetylacetonate ((acppy)2Ir(acac)) as the red emission. This EBL effectively prevented a triple-triple energy transfer between the two phosphorescent emissive layers with blue and red emission. The white device showed Commission Internationale De L'Eclairage (CIE(x, y)) coordinates of (0.33, 0.42) at 22400 cd/m2, a maximum luminance of 27300 cd/m2 at 13.2 V, and a maximum luminous efficiency of 26.9 cd/A.

High Efficient White Organic Light-Emitting Diodes Using BCzVBi as Blue Fluorescent Dopant

Efficiency improvement and color optimization of white organic light-emitting diodes (WOLEDs) were achieved via employing blue host DPVBi doped with blue fluorescent, BCzVBi. The structure of high efficient WOLED device was composed of ITO/NPB/DPVBi:BCzVBi-6%/MADN:DCM2-0.5%/Bphen/Liq/Al. WOLED doped by blue fluorescent BCzVBi exhibits 6.19 cd/A of luminous efficiency and 15400 cd/m2 of maximum luminescence. It also performs 480 cd/m2 of luminance at 5.7 V and 15400 cd/m2 at 12.9 V with CIE(x,y) coordinates of (0.33, 0.32) and (0.32, 0.32), respectively. Hole carrier and energy transfer from DPVBi to BCzVBi are proposed to explain the observed phenomena.

Hybrid spacer for high-efficiency white organic light-emitting diodes

High-efficient white organic light-emitting diodes (WOLEDs) were fabricated by using the following three different emitting materials: 4″-(2,2-diphenylvinyl)-1-[4-(N,N-diphenylamino)-styryl]-terphenyl for blue emission, fac-tris(2-phenypyridine) iridium(III) for green emission, and bis(5-benzoyl-2-phenylpyridinato-C,N)iridium(III) (acetylacetonate) for red emission. For higher efficiency, a hybrid spacer (HS) was inserted between each emissive layer (blue-red, red-green, and green-blue emissive layers). It was found that the WOLEDs using HS showed maximum power efficiency of 28.69lm∕W, maximum external quantum efficiency of 13.1%, and Commission Internationale de I’Eclairage coordinates (CIEx,y) of (x=0.37,y=0.37).

White Organic Light Emitting Diodes using Red and Blue Phosphorescent Materials with Blocking Layer

High-efficiency white organic light-emitting diodes(WOLEDs) were fabricated with two emissive layers and an blocking layer was sandwiched between two phosphorescent dopants, bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl) iridium III(FIrpic) as the blue emission and a newly synthesized red phosphorescent material guest, bis(5-acetyl-2-phenylpyridinato-N,C2`) acetylacetonate(). This blocking layer prevented a T-T annihilation in a red emissive layer, and balanced with blue and red emission as blocking of hole carriers. The white device showed Commission Internationale d`Eclairage() coordinates of (0.317, 0.425) at 22400 , a maximum luminance of 27300 at 268 , a maximum luminous efficiency and power efficiency of 26.9 cd/A and 18.6 lm/W.

High-efficiency White Phosphorescent Organic Light-Emitting Diodes

High-efficiency white organic light-emitting diodes (WOLEDs) based on phosphorescent dye bis[2-(4-tert- butylphenyl)benzothiazolato-N,C 2′]iridium (acetylacetonate) [(t-bt) 2Ir(acac)] phosphor doped 4,4′-bis(carbazol-9-yl) biphenyl (CBP) as a yellow emitting layer were fabricated. The structure of the devices is indium-tin oxide (ITO)/ N, N′-bis-(1-naphthyl)- N, N′-biphenyl-1,1′-biphenyl-4,4′-diamine (NPB)/CBP:(t-bt) 2Ir(acac)/NPB/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)/8- hydroxyquinoline aluminum (Alq 3)/Mg:Ag, and the second NPB layer from the anode was used as a blue fluorescent emitter and the first NPB layer was used as a hole transporting layer, the BCP and Alq 3 were used as hole blocking and electron transporting layers, respectively. The results showed that the turn-on voltage of the device was 3 V with a maximum luminance of 15460 cd·m −2 at 16.5 V and a maximum luminance efficiency of 7.5 lm·W −1 at 4 V, respectively. The Commission Internationale de l′Eclairage (CIE) coordinates located at (0.33, 0.32) remained stable at the driving voltage higher than 8 V, which is almost consistent with the optimum white CIE of (0.33, 0.33). The purity of white light could be adjusted by doping concentration. The effects of charge carrier trapping and energy transfer on the device performance were also discussed.

High-Efficiency White Organic Light-Emitting Diodes Based on Phosphorescent Iridium Complex and 4,4'-Bis[N-1-napthyl-N-phenyl-amino]biphenyl Emitters

High-efficiency white organic light-emitting devices (WOLEDs) based on phosphorescent dye bis[2-(4-tert-butylphenyl)benzothiazolato-N,C2']iridium (acetylacetonate) [(t-bt)2Ir(acac)] doped 4,4'-bis(carbazol-9-yl) biphenyl (CBP) as a yellow-emitting layer together with blue fluorescent emitter and hole-transporting material 4,4'-bis[N-1-napthyl-N-phenyl-amino]biphenyl (NPB) were fabricated. In those devices with a simple structure, 2,9-dimethyl,-4,7-diaphenyl,1,10-phenanthroline (BCP) and tris(8-quinolinolato) aluminum (Alq) were used as hole-blocking and electron-transporting layers, respectively. The purity of white light can be adjusted by doping concentration and bias voltage. The device shows a maximum luminance of 7580 cd/m2 with a luminance efficiency of 4.32 cd/A and Commission International De L'Eclairage (CIE) coordinates of (0.319,0.342) at 13.5 V. A maximum luminance efficiency of 10.2 cd/A at a current density of 0.026 mA/cm2 was achieved.

Long-lifetime, high-efficiency white organic light-emitting diodes with mixed host composing double emission layers

A long-lifetime, high-efficiency white organic light-emitting diode was fabricated with a mixed host in one of double emission layers. The first layer comprised yellow rubrene doped in a mixed host consisting of 50% N,N′diphenyl-N,N′-bis-(1-naphthyl)-1,1′-biphenyl-4-4′-diamine (NPB) and 50% 2-(t-butyl)-9,10-bis(2′-naphthyl)anthracene (TBADN). The second layer comprised blue 4,4′-bis[2-{4-(N,N-diphenylamino)phenyl}vinyl] biphenyl doped in TBADN. This device exhibited the longest lifetime, five times that of its pure NPB counterpart. The resulting efficiency was 6.0lm∕W (10.9cd∕A) at 10mA∕cm2, 33% better than that of the NPB counterpart. These improvements were attributable to the mixed-host structure, which effectively dispersed carriers and gave a good charge balance.

High Efficiency White Electrophosphorescence Mechanism with Two Phosphorescent Dopants

High efficiency white organic light emitting diodes (WOLED) have been expected for applications of lighting, illumination and back-light sources for LCD. Recently, since organic phosphors demonstrated very high electroluminescence (EL) quantum efficiency of ˜100%, high efficiency WOLED with the organic phosphors has been anticipated. In this study, we employed an emitter layer which is doped with blue and red phosphorescence molecules. In our optimized device structure, we obtained maximum EL quantum efficiency of 4%. However, the shapes of the EL spectrum were strongly dependent on current density. With analysis of exciton decay process under optical and electrical excitations, we conclude that triplet-triplet annihilation occurs in blue and red phosphors independently, resulted in a significant change of the EL spectrum. Thus, the coincidence of the lifetimes of the blue and red phosphors is indispensable to escape change of EL spectrum with current density.