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shows energy-level diagrams of white OLED structures studied and the chemical structures of the materials used. Each device comprises 10 / sq indium tin oxide glass, 70 nm hole-injection layer of 4 , 4 ,4trisN-2-naphthyl-N-phenylamino-triphenylamine, 20 nm hole-transport layer HTL of NPB, 7 nm yellow-emission
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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<sup>′</sup> diphenyl- N,N<sup>′</sup> -bis-(1-naphthyl)- 1,1<sup>′</sup> -biphenyl- 4-4<sup>′</sup> -diamine (NPB) and 50% 2-( t -...
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This work reports our effort on understanding the efficiency roll-off in
bilayer blue phosphorescent organic light emitting diodes (OLEDs), based on a
blue phosphorescence from
bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl)-iridium (FIrpic) doped
4,4-N,N-dicarbazole-biphenyl (CBP) emissive layer. The luminous efficiency of a
set of blue ph...
An improved concentration of phosphorescent dopant for highly-efficient hybrid white organic light-emitting diodes based on a high radiative exciton ratio (80%) deep-blue emitter has been developed. The high radiative exciton ratio for the deep-blue emitter was found to be the transfer from the higher triplet (T5) to the lowest singlet state (S1) b...
Phosphorescent white organic light-emitting diodes (PhWOLEDs) based on blue (Firpic) and yellow [(t-bt)2Ir(acac)] phosphorescent emitters with various doping concentration were reported. A PhWOLED with high performance characteristics has been obtained when the doping concentration for Firpic and (t-bt) 2Ir (acac) is 8 wt% and at 6 wt%, respectivel...
Two blue fluorophores with excellent hybridized local and charge-transfer (HLCT) and "hot exciton" properties were developed as the blue emitter and the host for orange-red phosphor to achieve highly efficient fluorescent/phosphorescent (F/P) hybrid white organic light-emitting diodes (WOLEDs) in a single-emissive-layer single-dopant (SEML-SD) arch...
We demonstrate high-efficiency white phosphorescent organic light-emitting diodes with low efficiency roll-off. The feature of the device concept is employing two phosphorescent emission layers (EMLs) separated by a mixed interlayer. Both the EMLs are doped by two phosphorescent dyes. The resulting white device with the optimized doping concentrati...
Citations
... Thus, the exciton formation is dominated by the host, and variousk inds of hosts have been used.A mong the many hostt ypes,b ipolar hosts and mixedh osts have been popularb ecause of balancedc arrier transporta nd wider ecombination zone for high external quantum efficiency( EQE) andl ong lifetime. [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] In particular, the mixed host has been provent ob ee ffective to upgrade the device performances. However,i nt he case of deep blue OLEDs, it has been challenging to develop mixed hosts because of difficulty of the design of high triplet energye lectron transport( n-type) host for phosphors or TADF emitters. ...
N‐type hosts for long lifetime in sky‐blue thermally‐activated delayed fluorescence (TADF) organic light‐emitting diodes (OLEDs) were investigated by synthesizing four hosts with zig‐zag‐type backbone structure for high triplet energy. The four hosts had two CN units at different positions of the zig‐zag‐type backbone structure and two dibenzofuran units through either the 2 or 4‐position of dibenzofuran. The position of the CN unit was controlled at the meta and para‐positions in the zig‐zag‐type backbone to study the relationship between material parameters and lifetime of the TADF OLEDs. It was revealed that the meta‐orientation of the CN units in the backbone was advantageous to extend device lifetime of the sky‐blue TADF OLEDs.
... The second EML comprised yellow and blue phosphorescent materials doped in MCP. A mixed interlayer was introduced to separate the two EMLs, which facilitates the transport of charge carriers [18,19]. By further optimizing the concentration of blue phosphorescent dye, which shows excellent electron transporting property, balanced carrier distribution and extended recombination zone were achieved. ...
We demonstrate high-efficiency white phosphorescent organic light-emitting diodes with low efficiency roll-off. The feature of the device concept is employing two phosphorescent emission layers (EMLs) separated by a mixed interlayer. Both the EMLs are doped by two phosphorescent dyes. The resulting white device with the optimized doping concentration shows a maximum efficiency of 31.0 cd/A with extremely low efficiency roll-off of 30.7 cd/A at 1000 cd/m2, 27.2 cd/A at 5000 cd/m2, and 25.5 cd/A at 10,000 cd/m2, respectively, without any outcoupling structures. This is enabled by the balanced charge carrier transport in EMLs, leading to broader exciton recombination zone.
... More importantly, these remarkable discoveries have revolutionized our understanding of organic semiconductors and optoelectronics. For commercial application, three primary colors of red, green and blue are required [21]. Up to now, the efficiency and brightness of green and blue TADF OLEDs have been rapidly developed. ...
... 61 Intrinsic deteriorations involve problems in the stability of organic thin fi lm, interface between anode and organic layer, excited state stability, movement of ionic impurity, diffusion of transparent electrode metal into emission layer (indium migration mechanism), cation instability, large energy barrier for charge carriers, positive charges accumulation, and width of recombination zone. 56,57,61,63,69,70,[72][73][74][75][76][77] Adachi's group has reported that a large energy barrier for hole injection at the interface of ITO/HTL (hole transporting layer) would lead to large joule heat generation. The produced heat would steadily cause local aggregation of organic molecules such as dimerization and crystallization of an amorphous HTL. ...
... Jou et al. 74 have reported a long-lifetime, high effi ciency white OLED with a mixed host in one of the double EMLs. These enhancements were attributed to a mixed-host structure, which effectively dispersed the carriers in a broad recombination zone and provided good thermal stability. ...
... .13 Effect of a mixed-host ratio on the OLED device lifetime.74 ...
... To realize full color and white OLED, various color mixing structures, including multiple dopant emissive layers and multiple emissive layers, and down conversion in the optical microcavity, have been utilized with various degrees of success [4][5][6][7][8][9][10]. Some methods for generating white color emission from OLED have been developed, such as the method of partial energy transfer in which the OLED materials are doped with fluorescent/phosphorescent dyes [11][12][13][14][15][16][17][18][19][20]. The mixing of the EL from the host molecules with excimer/ exciplex emissions has also been found to yield white emission [21][22][23]. ...
This work reports the color-tunable mixed photoluminescence (PL) emission from an Alq3 organic layer in an Au-Alq3-Au plasmonic structure through the combination of organic fluorescence emission and another form of emission that is enabled by the surface plasmons in the plasmonic structure. The emission wavelength of the latter depends on the Alq3 thickness and can be tuned within the Alq3 fluorescent spectra. Therefore, a two-color broadband, color-tunable mixed PL structure was obtained. Obvious changes in the Commission Internationale d'Eclairage (CIE) coordinates and the corresponding emission colors of Au-Alq3-Au samples clearly varied with the Alq3 thickness (90, 130, and 156 nm).
... Many methods have been developed to generate the white light emission of OLED by the partial energy transfer, such as host materials that are doped with fluorescence/phosphorescence dyes [4][5][6][7][8][9][10][11][12][13]. Several researchers have developed the mixing of the EL from the host molecules with the excimer/exciplex emissions to yield white light emission [14][15][16]. ...
We demonstrate in this report a new constructive method of fabricating white organic light-emitting devices (OLEDs) with a flexible plastic film embedded with yellow phosphor. The flexible film is composed of polydimethylsiloxane (PDMS) and fabricated by using spin coating followed by peeling technology. From the results, the resultant electroluminescent spectrum shows the white OLED to have chromatic coordinates of 0.38 and 0.54 and correlated color temperature of 4200 K. The warm white OLED exhibits the yield of 10.3 cd/A and the luminous power efficiency of 5.4 lm/W at a luminance of 1000 cd/m
2
. A desirable Lambertian-like far-field pattern is detected from the white OLEDs with the yellow phosphor containing PDMS film. This method is simple, reproducible, and cost-effective, proving to be a highly feasible approach to realize white OLED.
... A layer using a host and a blue dye to obtain a film nonuniformity of ±2.7% was successfully achieved. Specifically, the film was prepared using the solvent premixing deposition method [16][17][18][19]. The film was deposited shot by shot by using the planar source. ...
Organic light-emitting diode fabrication is suffering from extremely high material wasting during deposition especially using a typical point or even line source. Moreover, the need of depositing a high number of emitters and host(s) with a precise composition control in a single layer makes traditional vapor codeposition systems nearly impossible, unless otherwise with a very low yield. To improve, we have developed a novel thin-film deposition system with a planar source loadable with any premetered solvent-mixed organic compounds, plausibly with no component number limitation. We hence demonstrate experimentally, along with a Monte Carlo simulation, in the report the feasibility of using the technique to deposit on a large area-size substrate various organic materials with a relatively high material utilization rate coupling with high film uniformity. Specifically, nonuniformity of less than ±5% and material utilization rate of greater than 70% have been obtained for the studied films.
... The structure of the hole-only devices is as follows: indium-tinoxide (ITO) anode/4,4 -bis[ cathode. The energy levels of these materials were obtained from the literature [9,111213. All layers were prepared with thermal evaporation onto UV-O 3 treated ITO substrates except the PEDOT : PSS layers, which were prepared by spin-coating at 4000 rpm and drying under vacuum of about 10 −3 Torr for 30 min. ...
We have fabricated white organic light emitting diodes (OLEDs) with multi-emitting layer (EML) structures in which 4,4'-N,N'-dicarbazole-biphenyl (CBP) layers doped with the phosphorescent dopants fac-tris(2-phenylpyridine) iridium (Ir(ppy)3) and bis(2-(2'-benzo[4,5-a]thienyl)pyridinato-N,C3')iridium(acetylacetonate) (btp2Ir(acac)) and the fluorescent dopant 4,4'-bis[2-{4-(N,N-diphenylamino) phenyl}vinyl]biphenyl (DPAVBi) were used as green (G), red (R) and blue (B) EMLs, respectively. A higher efficiency was expected with the R/G/B EML sequence from the hole transport layer interface than with the G/R/B sequence because of the differences in the charge carrier conduction properties of the EMLs doped with phosphorescent dopants and the luminance balance between the phosphorescent and fluorescent emissions. A high efficiency of 18.3 cd A−1 (an external quantum efficiency of 8.5%) at 100 cd m−2 and good colour stability were achieved with the R/G/B EML sequence as expected, with an additional non-doped CBP interlayer used between the G and B EMLs. In addition, the OLED with this sequence was found to have the longest lifetime of the white devices we tested.
Developing new host materials is crucial to enhance the performance of blue organic light‐emitting diodes (OLEDs), but achieving long operational lifetimes for OLEDs has been challenging. In this study, boron‐ and silane‐based electron transport–type (n‐type) host materials, 5,9‐dioxa‐13b‐boranaphtho[3,2,1‐de]anthracen‐7‐yltriphenylsilane (BO‐pSi) and 2,12‐bis(triphenylsilyl)‐5,9‐dioxa‐13b‐boranaphtho[3,2,1‐de]anthracene (BO‐2mSi), derived from boron‐ and oxygen‐based 5,9‐dioxa‐13b‐boranaphtho[3,2,1‐de]anthracene (DOBNA) are developed. The DOBNA derivatives are modified with a triphenylsilyl blocking group to alleviate intermolecular interactions arising from the planar structure of DOBNA. The DOBNA derivatives maintain high triplet energy even in the solid state and show thermally activated delayed fluorescence features with electron transport properties. BO‐pSi is used as an n‐type host and exhibits a long operational lifetime of ≈5000 h up to 50% of the initial luminance of blue phosphorescent OLEDs. Furthermore, BO‐2mSi demonstrates a high external quantum efficiency of 7.1%, a small full width at half maximum of 33 nm, and a pure‐violet color coordinate of (0.16, 0.02) while maintaining color purity even at high doping concentrations up to 50 wt%.
High triplet energy hosts for blue phosphorescent organic light-emitting diodes were developed by decorating a meta-linked bitriazine core with carbazole and tetraphenylsilyl functional groups. A symmetric host with two carbazole units as the two triazine units of the core and an asymmetric host with one carbazole unit and one tetraphenylsilyl unit as the two triazine units were prepared. The triplet energy of these two hosts was 2.97 eV, suitable for triplet exciton harvesting of blue phosphors. Comparing the two host designs, the asymmetric decoration of the two triazine units with carbazole and tetraphenylsilyl units was superior to the symmetric decoration of the two triazine units with two carbazoles in terms of high external quantum efficiency (EQE) and long-term device stability. A high EQE of 19.7% and a long device lifetime of 2093.6 h at 100 cd m-2 were achieved using the asymmetrical host.
