Papers by Keyword: OLEDs

Abstract: Organic-inorganic hybrid thin films were fabricated using the sol-gel method and applied to multi-layer organic light-emitting diodes (OLEDs) as an active layer. A polymer emissive material poly (9,9-dioctyl-fluorene-co-N-4-butylphenyl-diphenylamine) (TFB) was solved in a sol-gel reaction accelerator perhydropolysilazane (PHPS). The PHPS solution turned into SiO₂ by humidity treatment. Thus, the TFB:PHPS solution became SiO₂ thin films in which the organic emissive material TFB was dispersed. All the organic layers of OLEDs can be fabricated using solution-process because the organic-inorganic hybrid active layer is not soluble with the adjacent organic layers. Consequently, we successfully fabricated quintuple-layer OLEDs consisting of the following five organic films: hole-injection, hole-transporting, active (organic-inorganic hybrid) electron-transporting, and electron-injection layers. Electroluminescence (EL) was successfully observed.

Abstract: The four varied side chains of charged iridium(III) complexes were synthesized and characterized for organic light emitting diodes. The core materials were designed with 9,9-bis(4-methoxyphenyl)-4,5-diazafluorene as the bulky N^N ligand which prevent the π-π stacking interaction in the solid state. Their photophysical and electrochemical properties were investigated. OLEDs were fabricated with the structure ITO/PEDOT:PSS/ PVK:complex (10:7 by weight)/ TPBi/LiF/Al. The similar colors were obtained with varied OLEDs performances. We concluded that the long alkyl chains affected to the excellent film-forming property of emitting layer. Therefore, the device based on the n-octyl chain namely [(9,9-bis(4-octyloxyphenyl)-9H-cyclopentadipyridine-N-N′)-bis-(2-phenylpyridine-C^2′,N)-iridium(III)] haxafluorophosphate (C8) showed the maximum current efficiency and brightness of 11.37 cd/A and 3,926 cd/m², respectively.

Abstract: This paper presents the results of a combined analytical, computational and experimental study of adhesion and degradation of Organic Light Emitting Devices (OLEDs). The adhesion between layers that are relevant to OLEDs is studied using force microscopy during Atomic Force Microscopy. The interfacial failure mechanisms associated with blister formation in OLEDs and the addition of TiO₂ nanoparticles (into active regions) are then elucidated using a combination of fracture mechanics/finite element modeling and experiments. The blisters observed in the models are shown to be consistent with the results from adhesion and interfacial fracture mechanics models. The implications of the work are discussed for the future design of OLED structures with improved lifetimes and robustness.

Abstract: We examine the fundamental operation of an Organic Light Emitting Device with emphasis laid on the Hole Transport Layer (HTL) and the optoelectronic properties of the other layers that make up the device. Investigation of the adhesion properties together with surface morphology, electrical and optical characterization of the different layers of the device was carried out. Poly (3,4-ethylenedioxythiophene):poly (styrene sulfonate) (PEDOT: PSS) was used as the conventional HTL material in the first case. This yields the reference device or system under studies. In the second case, PEDOT: PSS was replaced by an inorganic material, molybdenum trioxide (MoO ₃ ). The device performance in case two (2) revealed an improvement in performance. A couple of deposition techniques were examined together with the analysis of their effect on the resultant device properties. With the aid of theoretical models, we quantified the results obtained in terms of average pull-off forces and corresponding adhesion energies. The Derjaguin-Muller-Toporov model was utilized to model the adhesion energies between interfaces of adjacent layers of the device. Results that delineate modeling of charge transport across device interfaces are shown including the effects of pressure on the device optoelectronic properties.

Abstract: The importance of artificial light has long been recognized as it extends the day. Copious corporations and academic institutions are investing cosmic treasures in tracking down the advanced artificial lighting applications with a vision towards energy efficient and eco-friendly solid state lighting. In this regard, organic light-emitting diodes (OLEDs) are going to change the human lifestyle, by offering a promising avenue to develop future energy saving solid-state lighting sources because of their intrinsic characteristics such as low driving voltage, high resolution, high brightness, large viewing angle, large color gamut, high contrast, less weight and size, efficiency etc., there by dictating their ability to reach the pinnacle in the field of flat panel displays and solid state lighting sources. With the goal towards future application, many design strategies like synthesis of novel materials, well judged anatomy of device configuration, development of refined and low cost fabrication techniques have been put forward to achieve high efficiency, good color stability and quality lighting. Practical applications, which enrich the ideas of the specialists in this field to develop new routes for future research development of OLEDs are enumerated and illustrated by specific examples. This chapter also integrates the novel approaches for energy efficient and eco-friendly solid state lighting as well as the limitations and global haphazards of currently used lighting systems. The current state of the art, ongoing challenges and future perspectives of this research frontier to reduce the driving voltage, minimization of degradation issues, enhance their life time are illustrated. Review on the status and future outlook of these OLEDs strongly reveals their emergence in the next few years.

Abstract: The paper presents some results of study based on applications of ZnS core shell quantum dots (QDs) doped with Cu. Keeping the luminous properties in focus we synthesized the core shell QDs by chemical precipitation route, resulting in formation of core@shell QDs with ZnS core doped with copper and ZnS shell on it, i.e. [ZnS:Cu@Zn. We focus the application of these particles in field of OLEDs (AMOLED) to address the performance deficiencies like varying brightness of the different wavelength emitting LEDs, called Green Window problem. Efforts have been done to address the problems by synthesizing highly luminescent green emitting copper doped ZnS, core@shell QDs. Further a monolayer of core shell quantum dots was deposited on ITO by spin coating for analyzing the photometric properties of the QDs.

Abstract: The effect of laser dye (Fluorol 7GA) content on the optoelectronic properties of Poly ( 9,9'-di-n-octylfluorenyl-2.7-diyl) conjugated polymer (PFO) based OLEDs has been investigated. The PFO/Fluorol 7GA hybrids with weight ratios between 0.1 and 5 wt. % were prepared using the solution blending method. The blends were deposited on ITO (Indium Tin Oxide) substrate using spin-coating technique. Thin layer of aluminum was deposited on top of the films to act as electrode. Absorption and photoluminescence techniques were used to investigate the energy transfer in the blend. The device performance was investigated in terms of electroluminescence, luminance, luminance efficiency and color measurements. The Förster energy transfer occurred in the blends as evidence from optical spectroscopy and average distance between donor and acceptor molecules. The optimum ratio was 0.5 wt. % where highest enhancement in OLEDs performance was observed. These were attributed to the synchronize effect of efficient energy transfer from PFO to Fluorol 7GA and carrier trapping processes.

Abstract: Two novel luminescent molecules based on tetrahedral silicon core with the carbazole and benzimidazole groups, bis(6-(1H-benzo[d]imidazol-1-yl)-9-ethyl-9H-carbazol-3-yl)dimethylsilane (1) and bis(6-(1H-benzo[d]imidazol-1-yl)-9-ethyl-9H-carbazol-3-yl)diphenylsilane (2), were designed, synthesized and fully characterized by IR, 1H NMR, 13C NMR and elemental analysis. Thermal results show that these compounds have high thermal stability and glass-transition temperature (Tg). The results based on the photophysical properties and molecular calculations reveal that they are fluorescent with emission in the region of violet to blue and own large HOMO-LUMO band gaps, making them potentials as blue emitters, host materials or charge blocking materials in organic light-emitting diodes (OLEDs) display.

Abstract: Organic semiconductor thin films of aluminum (III) bis(2-methyl-8-quninolinato)-4- phenylphenolate (BAlq), -naphthylphenylbiphenyl amine (NPB), and tris(8-hydroxy-quinoline) aluminum (AlQ) for organic light-emitting diodes (OLEDs) were deposited by the vacuum sublimation technique. The optical properties in the UV-visible region of the thin films were investigated by optical transmittance and absorption spectra. The band gaps were obtained from direct allowed transitions at room temperature by means of the Tauc plots. The Urbach energy and the slope of Urbach edge were evaluated, respectively according to the Urbach-edges method. The thin film devices of sandwich structure were fabricated using these organic semiconductor materials, in addition, the effective carrier mobility, free carrier density, and electrical conductivity of the thin films were calculated in terms of the measured current-voltage characteristics of the devices.

Abstract: A full color 2.2″ passive matrix organic light-emitting diodes (OLEDs) with 128 (RGB) * 160 pixels was developed. The display features that driving circuit can transform 18 bits gray-scale data from a PC to the OLED panel via a DVI channel. The size of the pixel was 240μm240μm, while that of mono sub-pixel is 190μm45μm. The lifetime of panel was estimated over 5000h because of the use of dual-scan driving technology, and the power consumption of the display was 300mw about when the average luminance of panel reach 40cd/m2.