Annealing Effect on Small Molecules Blend Organic Light-Emitting Diodes (original) (raw)
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Organic light-emitting diodes (OLEDs) were fabricated containing guest molecule of Tris(8-hydroxyquinoline) aluminum (Alq 3 ) blend with host molecules of N,N'-diphenyl-N,N'-bis(3methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) and 2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole (PBD) small molecules. Optical, photoluminescence (PL) and electroluminescence (EL) properties were investigated with respect to blend systems. The obtained optical energy gap and PL intensity in the blend systems increased due to the transfer of high energy from the host to guest molecules. Luminance and current efficiency were enhanced for blended OLEDs as compared to that of pure Alq 3 , related to high exiton recombination in guest caused by high injection and accumulation of charge carrier.
Blending effect on small molecule based OLED
Optoelectronics And Advanced Materials – Rapid Communications (ISI-cited)
Organic light-emitting diodes (OLEDs) were fabricated containing guest molecule of Tris(8-hydroxyquinoline) aluminium (Alq3) blend with host molecules of N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) and 2-(4biphenylyl)-5-phenyl-1,3,4-oxadiazole (PBD) small molecules. Optical, photoluminescence (PL), electroluminescence (EL) and impedance properties were investigated with respect to blend systems. Optical energy gap and PL intensity obtained increased in blend systems attributed to high energy transfer from host to guest molecules. Luminance and current efficiency were enhanced for blended OLEDs as compared to that of pure Alq3, related to high accumulation of charge carrier and exciton recombination in guest. Impedance spectra show conductivity of OLEDs was improved by blending technique.
Nanomaterials
Obtaining white light from organic LEDs is a considerable challenge and, to realize white light emission, many studies have been conducted, primarily addressing two- or three-color blend systems as a promising strategy. In this work, pristine films, grown by spin coating, consisting of commercial blue Poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO), green Poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT), and red spiro-copolymer (SPR) light-emitting materials, were studied as reference materials. Afterward, binary (SPR doped in host PFO) and ternary (SPR and F8BT doped in host PFO) thin films were successfully prepared with various ratios. The characterization of the as-grown and thermally-treated blend films was focused on their optical and photophysical properties. After, the fabrication of OLED devices on glass substrates was carried out for the evaluation of a blend’s composition and annealing in terms of the devices’ electrical characteristics and electro-emission properties i...
Bulletin of Materials Science. (Accepted) (ISI-cited)
Ternary system of single layer organic light-emitting diodes (OLEDs) were fabricated containing Tris(8-hydroxyquinoline) aluminum (Alq3) blended with N,N'-diphenyl-N,N'bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) and 2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole (PBD) small molecules. Electroluminescence (EL) properties were investigated with respect to blend systems. Significant improvement in turn-on voltage and luminance intensity was observed by employing the blends technique. Negative differential resistance (NDR) characteristics observed at a low voltage region in blended OLED is related to the generation of guest hopping side (GHS) and phonon scattering phenomenon. However, luminescence of the devices is not altered by the NDR effect.
The light-emitting layer (EML) is generally prepared by mixing the host and dopant to realize an organic light-emitting diode (OLED). However, phase separation is often observed during the fabrication process to prepare OLEDs, depending on the structure of the host materials. In particular, phase separation because of π−π stacking is frequently observed during thermal annealing for the solution process. The annealing process is required for solvent removal and complete relaxation of the molecule. Hence, the materials with a high glass transition temperature (T g) are ideal because phase separation occurs because of π−π stacking during the annealing process, if T g is too low. To understand this phenomenon, we compared two host materials with similar molecular weights but different threedimensional connectivity, which causes different rotational freedom. Then, we investigated the effect on the device properties, depending on the annealing conditions. In both materials, when the annealing temperature rises above 120°C, the dopant completely escaped from the EML. However, the material that does not disturb the molecular stacking order by annealing because of its limited free rotation through the internal bond shows much better device characteristics even after annealing at a higher temperature than T g. The results show that interdiffusion at the interface and unstable internal density distribution with annealing temperature are responsible for the device degradation behavior.
American Journal of Applied Sciences, 2010
ABSTRACT Problem statement: How the thickness of the tris (8-hydroxyquinolinato) Aluminum (Alq3) effect the optical and electrical properties of organic light emitting diode. Approach: The optimum thickness, photoluminescence and current-voltage characteristic of Alq3 layer on N, N-bis (inaphthyl)- N,N-diphenyl-1,1-biphenyl-4,4-diamine (55 nm) layer in Organic Light-Emitting Devices (OLED) structure are reported. Alq3 and NPB organic layers are used as Electron Transport Layer (ETL) and as Hole Transport Layer (HTL) in Organic Light-Emitting Devices (OLED). The thin layers of the NPB and Alq3 were prepared by thermal evaporation method. Results: The Alq3 layer was evaporated on the NPB layer for thickness ranging from 16 to 134 nm and photoluminescence and I-V characteristic were studied using fiber optics spectrophotometer (Ocean Optics- USB 2000 FLG) and current-voltage source (Keithley, model 2400). Conclusion: It was found that the Alq3 with 84 nm thicknesses gives the highest photoluminescence peak at 520 nm wavelengths, as well as the lowest turn on voltage of the device. The optical reflectance spectra for every sample were also reported.
In this article we report electroluminescence (EL) from double and single layer thin film devices comprising poly(N-vinylcarbazole) (PVK) films doped with various new emitter molecules (dyes). The structure of the single layer device is doped PVK sandwiched between indium tin oxide (ITO) and aluminum (Al) layers as anode and cathode, respectively. We have used 2% concentration of Rhodamine 6G, carbocyanine, 1,2,4 oxadiazole, and fluroscein dyes. The double layer device has the structure ITO/PVK/8- hydroxyquinoline aluminum (Alq3)/Al. We have studied the IV characteristics as well as the variations of the EL with voltage and current of these devices.
Journal of Materials Science: Materials in Electronics, 2020
Organic light-emitting diodes (OLEDs) play a key role in modern display devices and systems. A highly desirable material for fabricating OLEDs is tris(8hydroxyquinoline)aluminum (Alq 3). In this work, a highly efficient OLED based on dysprosium (Dy)-incorporated Alq 3 (Alq 3-Dy) was fabricated. The fabricated OLED had four layers, namely, those of indium tin oxide (ITO), N, N 0-Di(1naphthyl)-N, N 0-diphenyl-(1,1 0-biphenyl)-4,4 0-diamine (NPB), Alq 3-Dy, and aluminum (Al). The ITO and Al layers were used as electrodes, while the NPB was selected as a hole transport layer. All the layers were deposited sequentially on a glass substrate. The surface morphologies of these layers clarified that the materials were deposited as nanosphere particles. The OLED performance showed significant improvement in terms of the operating voltage, current efficiency, and luminance of the fabricated Alq 3-Dy OLED compared with that of the pure Alq 3 OLED device. The luminance value was significantly enhanced from approximately 250 cd/m 2 for the pure Alq 3 OLED to approximately 5000 cd/m 2 for the Alq 3-Dy OLED. Moreover, the electroluminescence (EL) intensity of the Alq 3-Dy OLED was 20 times higher than that of the Alq 3 OLED. These findings may have a significant impact on the fabrication of the OLEDs and display devices.