Home About us Contact
|
Home About us Contact | ||
|
|
||
White Organic Light-emitting Diodes (white + organic_light-emitting_diode)
Selected AbstractsTriplet Harvesting in Hybrid White Organic Light-Emitting DiodesADVANCED FUNCTIONAL MATERIALS, Issue 9 2009Gregor Schwartz Abstract White organic light-emitting diodes (OLEDs) are highly efficient large-area light sources that may play an important role in solving the global energy crisis, while also opening novel design possibilities in general lighting applications. Usually, highly efficient white OLEDs are designed by combining three phosphorescent emitters for the colors blue, green, and red. However, this procedure is not ideal as it is difficult to find sufficiently stable blue phosphorescent emitters. Here, a novel approach to meet the demanding power efficiency and device stability requirements is discussed: a triplet harvesting concept for hybrid white OLED, which combines a blue fluorophor with red and green phosphors and is capable of reaching an internal quantum efficiency of 100% if a suitable blue emitter with high-lying triplet transition is used is introduced. Additionally, this concept paves the way towards an extremely simple white OLED design, using only a single emitter layer. [source] Harvesting Excitons Via Two Parallel Channels for Efficient White Organic LEDs with Nearly 100% Internal Quantum Efficiency: Fabrication and Emission-Mechanism AnalysisADVANCED FUNCTIONAL MATERIALS, Issue 1 2009Qi Wang Abstract By incorporating two phosphorescent dyes, namely, iridium(III)[bis(4,6-difluorophenyl)-pyridinato-N,C2,]picolinate (FIrpic) for blue emission and bis(2-(9,9-diethyl-9H -fluoren-2-yl)-1-phenyl-1H -benzoimidazol-N,C3)iridium(acetylacetonate) ((fbi)2Ir(acac)) for orange emission, into a single-energy well-like emissive layer, an extremely high-efficiency white organic light-emitting diode (WOLED) with excellent color stability is demonstrated. This device can achieve a peak forward-viewing power efficiency of 42.5,lm,W,1, corresponding to an external quantum efficiency (EQE) of 19.3% and a current efficiency of 52.8,cd,A,1. Systematic studies of the dopants, host and dopant-doped host films in terms of photophysical properties (including absorption, photoluminescence, and excitation spectra), transient photoluminescence, current density,voltage characteristics, and temperature-dependent electroluminescence spectra are subsequently performed, from which it is concluded that the emission natures of FIrpic and (fbi)2Ir(acac) are, respectively, host,guest energy transfer and a direct exciton formation process. These two parallel pathways serve to channel the overall excitons to both dopants, greatly reducing unfavorable energy losses. It is noteworthy that the introduction of the multifunctional orange dopant (fbi)2Ir(acac) (serving as either hole-trapping site or electron-transporting channel) is essential to this concept as it can make an improved charge balance and broaden the recombination zone. Based on this unique working model, detailed studies of the slight color-shift in this WOLED are performed. It is quantitatively proven that the competition between hole trapping on orange-dopant sites and undisturbed hole transport across the emissive layer is the actual reason. Furthermore, a calculation of the fraction of trapped holes on (fbi)2Ir(acac) sites with voltage shows that the hole-trapping effect of the orange dopant is decreased with increasing drive voltage, leading to a reduction of orange emission. [source] Versatile, Benzimidazole/Amine-Based Ambipolar Compounds for Electroluminescent Applications: Single-Layer, Blue, Fluorescent OLEDs, Hosts for Single-Layer, Phosphorescent OLEDsADVANCED FUNCTIONAL MATERIALS, Issue 16 2009Chih-Hsin Chen Abstract A series of compounds containing arylamine and 1,2-diphenyl-1H -benz[d]imidazole moieties are developed as ambipolar, blue-emitting materials with tunable blue-emitting wavelengths, tunable ambipolar carrier-transport properties and tunable triplet energy gaps. These compounds possess several novel properties: (1) they emit in the blue region with high quantum yields; (2) they have high morphological stability and thermal stability; (3) they are capable of ambipolar carrier transport; (4) they possess tunable triplet energy gaps, suitable as hosts for yellow-orange to green phosphors. The electron and hole mobilities of these compounds lie in the range of 0.68,144,×,10,6 and 0.34,147,×,10,6,cm2 V,1 s,1, respectively. High-performance, single-layer, blue-emitting, fluorescent organic light-emitting diodes (OLEDs) are achieved with these ambipolar materials. High-performance, single-layer, phosphorescent OLEDs with yellow-orange to green emission are also been demonstrated using these ambipolar materials, which have different triplet energy gaps as the host for yellow-orange-emitting to green-emitting iridium complexes. When these ambipolar, blue-emitting materials are lightly doped with a yellow-orange-emitting iridium complex, white organic light-emitting diodes (WOLEDs) can be achieved, as well by the use of the incomplete energy transfer between the host and the dopant. [source] Excimer-Based White Phosphorescent Organic Light-Emitting Diodes with Nearly 100,% Internal Quantum Efficiency,ADVANCED MATERIALS, Issue 2 2007L. Williams Efficient excimer emission is demonstrated in white organic light-emitting diodes (see figure) based on platinum(II)[2-(4,,6,-difluorophenyl)pyridinato-N, C2,)](2,4-pentanedionato) utilized in devices incorporating the novel host material 2,6-Bis(N -carbazolyl)pyridine (26mCPy). External quantum (power) efficiencies of 15.9,% (12.6,lm,W,1) are realized at 500,cd,m,2. [source] | ||||||||||