Browsing by Author "Wang, Yu-Young"

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Direct encapsulation of organic light-emitting devices (OLEDs) using photo-curable co-polyacrylate/silica nanocomposite resin
(2007-08-01)
Wang, Yu-Young
;
Hsieh, Tsung-Eong
;
Chen, I-Ching
;
Chen, Chin-Hsin
;
材料科學與工程學系
Direct encapsulation of organic light-emitting devices (OLEDs) was realized by using highly transparent, photo-curable co-polyacrylate/silica nanocomposite resin. Feasibility of such a resin for OLED encapsulation was evaluated by physical/electrical property analysis of resins and driving voltage/luminance/lifetime measurement of OLEDs. Electrical property analysis revealed a higher electrical insulation of photocured nanocomposite resin film at 3.20 x 1012 9 in comparison with that of oligomer film at 1.18 x 10(12) Omega at 6.15 V to drive the bare OLED. This resulted a lower leakage current and the device driving voltage was efficiently reduced so that the nanocomposite-encapsulated OLED could be driven at a lower driving voltage of 6.09 V rather than 6.77 V for the oligomer-encapsulated OLED at the current density of 20 mA/cm(2). Luminance measurement revealed a less than 1.0% luminance difference of OLEDs encapsulated by various types of resins, which indicates that the photo-polymerization takes very little effect on the light-emitting property of OLEDs. Lifetime measurement of OLEDs found that t(80), the time span for the normalized luminance of device drops to 80%, for nanocomposite-encapsulated OLED is 350.17 h in contrast to 16.83 h for bare OLED and 178.17 h for the oligomer-encapsulated OLED. This demonstrates that nanocomposite resin with optimum properties is feasible to OLED packaging and a compact device structure could be achieved via the method of direct encapsulation.
Effect of UV curing on electrical properties of a UV-Curable co-Polyacrylate/Silica nanocomposite as a transparent encapsulation resin for device packaging
(2007-11-20)
Wang, Yu-Young
;
Hsieh, Tsung-Eong
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Electrical properties of UV-curable co-polyacrylate/silica nanocomposite resins prepared via sol-gel process for device encapsulation were investigated. It was found that, by appropriate UV curing process and the formation of nanoscale silica particles finely dispersed in the resin matrix, the leakage current density of the nanocomposite resin films decreases from 235 to 1.3 nA (.) cm(-2) at the applied electrical field of 10 kV (.) cm(-1). The silica nanoparticles also restricted the motions of polar functional groups in organic matrix that the nanocomposite films with satisfactory dielectric properties [dielectric constant (epsilon) = 3.93 and tangent loss (tan delta = 0.0472) could be obtained. Chemical structure analyses revealed that excessive UV curing results in photooxidation and/or photodegradation in resin samples, leading to the polar groups and ionic/radical segments in organic matrix as well as the -Si-O-Si- structure in the vicinity of silica nanoparticles. These organic/inorganic functional groups generated more permeation paths for charge carrier migration and hence deteriorated the electrical properties of the nanocomposite samples. Though post-baking treatment at 80 degrees C for 1 h followed by UV curing improved the rigidity of the resin sample, it brought the polar functional groups closer to each other and similarly degraded electrical properties of the nanocomposite resins.
Preparation of UV-curable intercalated/exfoliated epoxide/acrylateclays nanocomposite resins
(2007-06-01)
Wang, Yu-Young
;
Hsieh, Tsung-Eong
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Preparation of UV-curable intercalated/exfoliated epoxide/acrylateclays nanocomposite resins with the addition of specific monomers and solvent via the consideration of solubility parameter and chemical reactivity was carried out in this work. Due to the good compatibility with surfactant in acrylateclays and the cationic oligorner in resin matrix, the two additive monomers dispersed uniformly in resin matrix with the swollen acrylateclays before UV curing. As revealed by conversion ratio and DTG analyses, chemical bonds between the two additive monomers, the cationic oligomers and surfactant in acrylateclays were formed during UV irradiation. This, in turn, generated a hybrid acrylate-based/epoxy network and effectively enlarged the lamellae spacing of inorganic clays in nanocomposite resins prepared in this work. The XRD and TEM characterizations revealed that the intercalated clay domains containing exfoliated lamellae about 1 nm in thickness uniformly disperse in polymeric matrix. The nanocomposite resin containing 5 wt.% inorganic filler possessed the physical properties as follows: Td-5% = 213 degrees C, CTE = 80.5 ppm/degrees C, moisture absorption = 6.12%, average optical transmittance = 83.17%, and adhesion strength on glass substrate = 43.8 kgf/cm(2). The analyses above indicated that the formation of polymeric interpenetrating networks and nanometer-scale exfoliation of clay lamellae not only improve the thermal properties and resistance to moisture permeation, but also retain highly optical transmittance and satisfactory adhesion strength of nanocomposite resins prepared in this work. A better device lifetime property was hence achieved when the nanocomposite resins were applied to the packaging of OLEDs.
Transparent photo-curable co-polyacrylate/silica nanocomposites prepared by sol-gel process
(2007-08-15)
Chou, Yen-Chun
;
Wang, Yu-Young
;
Hsieh, T.-E.
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材料科學與工程學系
;
Department of Materials Science and Engineering
This work prepared the highly transparent photo-curable co-polyacrylate /silica nanocomposites by using sol-gel process. The FTIR and C-13 NMR analyses indicated that during the sol-gel process, the hybrid precursors transform into composites containing nanometer-scale silica particles and crosslinked esters/ anhydrides. Transmission electron microscopy (TEM) revealed that the silica particles within the average size of 11.5 nm uniformly distributed in the nanocomposite specimen containing about 10 wt% of Si. The nanocomposite specimens exhibited satisfactory thermal stability that they had 5% weight loss decomposition temperatures higher than 150 degrees C and coefficient of thermal expansion (CTE) less than 35 ppm/degrees C. Analysis via derivative thermogravimetry (DTG) indicated that the crosslinked esters /anhydrides might influence the thermal stability of nanocomposite samples. The UV-visible spectroscopy indicated that the nanocomposite resins possess transmittance higher than 80% in visible light region. Permeability test revealed a higher moisture permeation resistance for nanocomposite samples, which indicated that the implantation of nano-scale silica particles in polymer matrix forms effective barrier to moisture penetration. Adhesion test of nanocomposite samples on glass substrate showed at least twofold improvement of adhesion strength compared with oligomer. This evidenced that the silica and the hydrophilic segments in nanocomposite resins might form interchains hydrogen bonds with the -OH groups on the surface of glass so the substantial enhancement of adhesion strength could be achieved. (c) 2007 Wiley Periodicals, fnc.