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Photovoltaic organic light-emitting diodes (PVOLEDs) that have dual functions of organic light-emitting diodes and organic solar cells have been studied. Using the structure of glass/ITO anode/hole transporting layer (HTL)/5,6,11,...
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Photovoltaic organic light-emitting diodes (PVOLEDs) that have dual functions of organic light-emitting diodes and organic solar cells have been studied. Using the structure of glass/ITO anode/hole transporting layer (HTL)/5,6,11,12-tetraphenylnaphthacene (rubrene)/C_(60)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)ILiFIAl, we examined the dependence of properties for PVOLEDs on HTL materials. Using N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)-benzidine (NPB) with high hole mobility and high lowest-unoccupied molecular orbital (LUMO) level as a HTL material, we obtained the PVOLED that operated as an organic solar cell with 1.86% power conversion efficiency under reverse bias and as an organic light-emitting diode under forward bias with approximately 700 cd/m~2 luminance at 7 V.
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Synthesis of new PVK and 1H-pyrazolo[3,4-b]quinoline based copolymers for electro-optic applications is described. Both copolymers are soluble and can be processed into thin films. A single layer OLED structure was fabricated and ...
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Synthesis of new PVK and 1H-pyrazolo[3,4-b]quinoline based copolymers for electro-optic applications is described. Both copolymers are soluble and can be processed into thin films. A single layer OLED structure was fabricated and a blue light emission was observed. Although devices were not optimized, the "turn-on bias voltage was relatively low, ca. 12 V.
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Flexible top-emission organic light-emitting diodes (TOLEDs) with a thin-film encapsulation (TFE) are of increasing attention to improve the flexibility of foldable smartphone organic light-emitting diode (OLED) displays. There ar...
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Flexible top-emission organic light-emitting diodes (TOLEDs) with a thin-film encapsulation (TFE) are of increasing attention to improve the flexibility of foldable smartphone organic light-emitting diode (OLED) displays. There are inevitable issues to achieve foldable display with smaller folding radius for the future portable display. Herein, the device flexibility is investigated with infolding and outfolding tests with the curvature radius from 2.5 to 0.32 mm. Parylene (1 mu m)/silicon nitride (SiNx) (X nm)/parylene (1 mu m)/SiNx (X nm) (X = 100, 70, 50, and 30 nm) of TFEs are applied on the TOLEDs. It is found that stable device performances can be achieved at the curvature radius of 0.32 mm after 100 000 cycles infolding testing when the SiNx thickness is 30 nm. The device has significant degradation upon outfolding of 5000 cycles at the same radius of 0.32 mm. Note that, the water vapor transmission rate (WVTR) of the TFT with 30 nm SiNx is higher than the TFE with thicker SiNx (e.g., 50 nm). The flexibility and WVTR can be much improved using four-stacked TFE with 30 nm SiNx for foldable active-matrix OLED displays.
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Mixed-ligand terbium carboxylates-Tb(Carb)_3(TPPO)_2 (HCarb = HSaI (salicylic acid), Hpobz (2-phenoxybenzoic acid); TPPO = triphenylphosphine oxide) and zinc complexes with tetradentate Schiff bases-ZnSB (H_2SB = H_2SAL1, H_2SAL_2...
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Mixed-ligand terbium carboxylates-Tb(Carb)_3(TPPO)_2 (HCarb = HSaI (salicylic acid), Hpobz (2-phenoxybenzoic acid); TPPO = triphenylphosphine oxide) and zinc complexes with tetradentate Schiff bases-ZnSB (H_2SB = H_2SAL1, H_2SAL_2 (derivatives of salicylic aldehyde); H_2MO1, H_2MO2 (derivatives of o-vanillin)) were used as electroluminescent (EL) layers in organic light emitting diodes (OLEDs). These devices have undergone reversible and irreversible mechanisms of EL degradation. The reversible one is mainly associated with charge carrier trap filling. At the same time several mechanisms of irreversible degradation were observed under UV light irradiation, heating and ageing in ambient conditions. The degradation mechanisms of OLEDs under heating from 293 K to 320 K were related to the changes in the interface regions. The initial degradation was eliminated by (1) an application of alternating bias voltage; (2) a decrease of the substrate temperature and the velocity of the thermal evaporation of materials. The degradation of OLEDs was not observed under low UV irradiation that is promising for OLEDs operation under day light.
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Colloidal CdSe semiconductor nanoplatelets with characteristic longitudinal sizes of 20–70 nm and thicknesses of several atomic layers are synthesized. The spectra and kinetics of the photoluminescence of these quasi-two-dimensio...
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Colloidal CdSe semiconductor nanoplatelets with characteristic longitudinal sizes of 20–70 nm and thicknesses of several atomic layers are synthesized. The spectra and kinetics of the photoluminescence of these quasi-two-dimensional nanostructures (quantum wells) at room and cryogenic temperatures are investigated. A hybrid light-emitting diode with the electron and hole transport layers based on TAZ and TPD organic compounds, respectively, and the active “emissive” element based on a layer of such single-component nanoplatelets is designed. The spectral and electrical characteristics of the fabricated device, emitting at a wavelength of λ = 515 nm, are determined. The use of quasi-two-dimensional nanostructures of this kind (nanoplatelets) is promising for the fabrication of hybrid light-emitting diodes with pure colors.
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A bis-sulfone small molecule, 4,4'-bis(phenylsulfonyl)biphenyl has been evaluated as a host for the phosphor iridium(III) bis(2-(4,6-difluorophenyl)pyridinato-JV,C2 )picolinate in blue-green organic light-emitting devices. In addi...
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A bis-sulfone small molecule, 4,4'-bis(phenylsulfonyl)biphenyl has been evaluated as a host for the phosphor iridium(III) bis(2-(4,6-difluorophenyl)pyridinato-JV,C2 )picolinate in blue-green organic light-emitting devices. In addition, a poly(norbornene)-based polymer functionalized with a 3,6-bis(carbazol-9-yl)carbazole moiety as a side group is utilized as a solution-processible hole-transport layer; comparison is made to the widely-used hole-transport polymer poly(N-vinylcarbazole) (PVK). At 100cd/m2, the highest efficiency device incorporating the new polymer achieved an external quantum efficiency (EQE) of 6.9% (12.9 cd/A) with a turn-on voltage of 4.3 V. In comparison, the highest efficiency device using PVK achieved an EQE of 6.4% (11.3 cd/A) with a turn-on voltage of 6.0 V.
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Purpose: In contrast to the dominant medical liquid crystal display (LCD) technology, organic light-emitting diode (OLED) monitors control the display luminance via separate light-emitting diodes for each pixel and are therefore s...
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Purpose: In contrast to the dominant medical liquid crystal display (LCD) technology, organic light-emitting diode (OLED) monitors control the display luminance via separate light-emitting diodes for each pixel and are therefore supposed to overcome many previously documented temporal artifacts of medical LCDs. We assessed the temporal and luminance characteristics of the only currently available OLED monitor designed for use in the medical treatment field (SONY PVM2551MD) and checked the authors' main findings with another SONY OLED device (PVM2541). Methods: Temporal properties of the photometric output were measured with an optical transient recorder. Luminances of the three color primaries and white for all 256 digital driving levels (DDLs) were measured with a spectroradiometer. Between the luminances of neighboring DDLs, just noticeable differences were calculated according to a perceptual model developed for medical displays. Luminances of full screen (FS) stimuli were compared to luminances of smaller stimuli with identical DDLs. Results: All measured luminance transition times were below 300 μs. Luminances were independent of the luminance in the preceding frame. However, for the single color primaries, up to 50.5% of the luminances of neighboring DDLs were not perceptually distinguishable. If two color primaries were active simultaneously, between 36.7% and 55.1% of neighboring luminances for increasing DDLs of the third primary were even decreasing. Moreover, luminance saturation effects were observed when too many pixels were active simultaneously. This effect was strongest for white; a small white patch was close to 400 cd/m2, but in FS the luminance of white saturated at 162 cd/m2. Due to different saturation levels, the luminance of FS green and FS yellow could exceed the luminance of FS white for identical DDLs. Conclusions: The OLED temporal characteristics are excellent and superior to those of LCDs. However, the OLEDs revealed severe perceptually relevant artifacts with implications for applicability to medical imaging.
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This work gives a summary of organic optoelectronic device research at HKU. At present, there is ongoing research on organic light emitting diodes (OLEDs) and organic solar cells. For OLEDs, the research efforts have been focused ...
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This work gives a summary of organic optoelectronic device research at HKU. At present, there is ongoing research on organic light emitting diodes (OLEDs) and organic solar cells. For OLEDs, the research efforts have been focused on studying how ITO treatments and deposition conditions affect the OLED performance, as well as development of the novel materials for OLED applications. For solar cells, effects of ITO treatments and some novel materials and device structures have been investigated.
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We fabricated an 8/spl times/9 (3RGB) passive matrix of organic light-emitting diodes (OLED's) and operated it at a video-rate to simulate NTSC signals. The color purity of red emission was improved by controlling the depth distri...
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We fabricated an 8/spl times/9 (3RGB) passive matrix of organic light-emitting diodes (OLED's) and operated it at a video-rate to simulate NTSC signals. The color purity of red emission was improved by controlling the depth distribution of DCM in the Alq/sub 3/ layer. A newly synthesized binuclear metal complex compound was incorporated for blue emission and provided good chromaticity. We found that the rectification property of the OLED is important to drive a passive matrix and about 10/sup 5/ OLED pixels can be driven when aluminum is used as the cathode material.
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