The gravure printing technique is currently under investigation as a possible method for the roll-to-roll production of OLEDs in the 6th framework EU funded project entitled ROLLED - "Roll-to-roll manufacturing technology for flexible OLED devices and arbitrary size and shape displays". The objective in the project is to fabricate an entire OLED structure by using roll-to-roll manufacturing methods and to examine, how the commercial production could be set up and integrated into an existing printing process. In order to attain a roll-to-roll compatibility, all the materials, inks and device structures need to be suitable for printing. Since, such OLED device structures are very sensitive to moisture and oxygen, high barrier materials to be applied as wet chemical coatings on transparent polymer films such as PET by common roll-to-roll coating techniques have been investigated. The barrier films on their respective substrates act as front and back side encapsulation materials, where the front side encapsulation material is to be used as a transparent and flexible substrate for OLED fabrication. The transmission rates to be achieved for both front and back side encapsulation for oxygen and water vapour are 5 mg m-2day-1 (corresponding to 7 cm3m-2day-1 for O2). In this paper, we show how light-emitting devices manufactured by gravure printing operate compared to the ones manufactured by traditional methods. Furthermore, we present recent results on the development of ITO nanoparticle coatings, cathode inks and flexible barrier materials.
A new chemical nanotechnological route for the preparation of fully densified doped SiO2 coatings with thicknesses in the low µm-range on Si- and SiO2-wafers has been developed. Beside pure SiO2 coatings, that might be useful as a buffer layer on silicon, silicate layers with increased refractive index are needed for planar waveguide application. Therefore, a synthesis for the preparation of nano particulate sols was developed, thus allowing the incorporation of dopands like Al2O3, PbO and Er2O3 for passive and active layers. Alumina was incorporated for the improvement of the Erbium solubility in active components. The coating sols consist of an organic binder, dissolved in a suspension of nanoscaled silica particles (10 nm in diameter) and dopands and were applied on Si- and SiO2-wafers by spin coating. After removal of the binder at 500 °C, investigated by IR-spectroscopy, highly porous (nD = 1.23) but transparent doped silica layers were obtained. The densification of the layers was examined by measuring the refractive index by ellipsometry as a function of the densification temperature. Completely densified layers with thicknesses between 1.7 µm (doped SiO2) and 6.5 µm (doped SiO2) were obtained at temperatures between 1000 °C (doped SiO2) and 1100 °C) (pure SiO2). The layer thickness and unevenness was determined by interferometric measurements. The optical loss of Al2O3 and PbO doped layers was measured by prism coupling, the Er2O3 doped layers with Er3+ concentrations of up to 2.5 mole % show fluorescence around 1500 nm with a fluorescence lifetime of about 3.6 ms.
Optical sol-gel materials have been of interest for many years. The reason is that through the preparation of sold with nanoparticulate liquid structures, transparent coatings of many inorganic oxides can be produced. By using oxides for example, with different refractive indices, reflective or antireflective coatings can be fabricated. To obtain stable layers, the gel coating have to be densified at higher temperatures, in general between 400 and 600 degrees C. This may be suitable for glass surfaces, but not for temperature sensitive substrates like plastics. In addition to this, if multilayer coatings have to be produced, between each step a densification process has to be carried out before the net coating step takes place. This leads to an unsatisfying situation if industrial low cost processing is required. In addition to this, the dip coating process is not suitable for high speed or large area coating techniques. This is one of the reasons whey the sol-gel process never has gained a real high significance for industrial coatings on glass and is limited to special products so far.
A new synthesis route to organic-inorganic composites with low OH- and CH-content has been developed. Thus methacrylate- modified chlorosilanes were either homocondensed or cocondensed with fluoroalkyl-modified chlorosilanes by a non- hydrolytic reaction with 2-methyl-2-propanol under formation of an inorganic network and hydrogen chloride and tertiary butyl chloride as well. Remaining chlorosilane groups were reacted by a second alcohol treatment to obtain air-stable, highly condensed, and low OH-containing sols. The condensation was followed by 29Si-NMR-spectroscopy, showing T2- content of up to 60% and T3 content of up to 35% for trichlorosilanes and D2-content of more than 90% for dichlorosilanes respectively. The OH-content, which was estimated by FT-IR-spectroscopy, was lower than 10% referring to materials prepared by the conventional aqueous sol-gel process. For further decrease of the CH-content copolymerization with fluorinated methacrylates was investigated. After addition of a photoinitiator transparent bulk materials with a diameter of 1 cm and a length of 1.5 cm were obtained by photopolymerization in closed UV-transparent containers using a Beltronr UV apparatus with a low pressure Hg-Xe lamp. NIR-absorbance measurements were carried out and optical losses of bulk materials were determined. Cocondensed and copolymerized materials show low optical losses of 0.12 dB/cm at 1300 nm and 0.33 dB/cm at 1550 nm.
Multi-layer interference filters of surface modified SiO2- and TiO2-nanoparticles have been produced on polycarbonat (PC) and on scratch resistant film. AR-coatings (anti-reflex- coatings) were prepared from a dispersion of SiO2 and TiO2 colloidal nanoparticles in a hybrid inorganic organic matrix. The TiO2 particles have been synthesized by addition of HCl and H2O to a solution of titanium tetraisopropanolate in isopropanol. The SiO2 nanoparticles were synthesized by base catalyzed hydrolyses and condensation of tetraethoxysilane (TEOS) mixed with an aqueous solvent. The surface modification of the TiO2 and SiO2 nanoparticles with 3-glycidoxypropyltrimethoxysilane (GPTS) avoids the agglomeration of the nanoparticles and covalent bonds between the matrix and nanoparticles are formed during a photopolymerization step. The nanoparticles were dispersed in a hydrolyzed GPTS matrix and UVI Cygacure 6974 was added as a photoinitiator. The (lambda) /4 ((lambda) equals 550 nm) films of TiO2 and SiO2 sols were prepared on PC and on scratch resistant coated PC by spin-coating techniques. The refractive index of the SiO2/TiO2-coatings can be adjusted from 1.47 up to 1.94 depending on the SiO2 or TiO2 concentration. By the combination of index matching and photopolymerization, a low temperature interference filter can be realized for plastic substrates with reflection of 0.5% at 550 nm. The coatings show excellent adhesion to the substrates in the cross hatch test and promising mechanical properties.
A new synthesis and processing route for SiO2 glass like micropatterns with heights up to 30 micrometer by gel embossing and thermal densification has been developed. For this reason an organically modified nanoparticulate sol prepared by acid catalysis of methyl- and phenyl- triethoxysilane and tetraethyl orthosilicate in combination with colloidal silica sol was used. Sol coatings with thicknesses up to 15 micrometer are obtained by dipping of float glass substrates. After a predrying step of about 60 s micropatterns are obtained using a pressure of only 2.5 mN/mm2. Due to this low pressure, flexible and low cost silicon rubber stampers can be used. The gelation time of the sol can be extended from 5 d to 16 days and the working time for embossing can be extended from 60 s up to 100 s by a partial replacement of methyl silane by phenyl silane from 0 to 20 mole %. After embossing and drying at 50 degrees Celsius the patterned layer was densified at temperatures up to 500 degrees Celsius to 95% density as indicated by refractive index measurements. It is assumed that the densification process is strongly promoted by the used colloidal silica nano particles. The linear shrinkage of the micropatterns is limited to about 25% due to the high solid content of the sol and the high green density of the layers. Since the structures are densified at temperatures far below Tg sharp edged patterns can be obtained as shown by high resolution secondary electron microscopy. The capability of this technique is demonstrated by the fabrication of light trapping structures with pyramides of 7 micrometer in height and 10 micrometer in width on an area of 20 multiplied by 20 mm2 and micro lens arrays of lenses with 30 micrometer in height and 600 micrometer in diameter on an area of 20 multiplied by 30 mm2.
A photochromic dye, spirooxazine (SO), was incorporated in organic-inorganic composite (OIC) materials by the advantages of sol-gel processing. It has been found that the photochromic response is high enough and the fading rate is similar to the dye-in-ethanol solution while the photofatigue resistance is strongly dependent on the matrix composition and the starting compounds. In the present work, we present results on the effect of matrix composition and starting compounds as well as additives on the photofatigue resistance of SO- OIC photochromic coatings. Sol-gel coatings synthesized from methyltrimethoxysilane (MTMS) and glycidyloxypropyltrimethoxysilane (GPTMS) as starting compounds, and using 1H,1H,2H,2H-perfluoroalkyltrimethoxysilane (FAS) and 1-methylimidazole (MI) as additives provide the SO dye with a favorable matrix environment in terms of photofatigue, so that the overall photochromic performance of the dye can be optimized. The photofatigue resistance reaches the same level as, while both the photochromic response and fading rate are much better than the SO-PMMA coatings.
An organic-inorganic synthesis route to Au-colloid containing, transparent SiO2 coatings has been developed, using four different types of functionalized silanes as stabilizing ligands for the Au. By variation of the kind and the concentration of the stabilizing silane in the sol the onset temperature for the colloid formation varies between 100 and 300 degree(s)C and the final colloid radii can be controlled in a range between 3 and 30 nm after densification of the composite coatings on glass at 500 degree(s)C. The third order polarizability (Chi) m(3) in the metal particles is one order of magnitude higher than in glass composites and exhibits a strong dependence on the ligand.
A sol-gel method for the preparation of transparent copper nano particle-containing SiO2 coatings on glass has been developed. The sol is synthesized from alkoxysilanes and tetra ethyl orthosilicate with copper ammine complexes, prepared from Cu2+ salts and amino alkoxy silanes. Glass substrates are coated by dipping and layers up to 1 micrometers in thickness are obtained after thermal densification at temperatures between 200 degree(s) - 500 degree(s)C. The Cu colloid formation can be achieved using a reducing atmosphere during densification. Thus reddish-brown colored coatings on glass with optical densities between 0.5 and 2 are obtained. Under ambient air the color turns from reddish-brown to dark green. This process is reversible and by re-heating under reducing conditions the reddish-brown color can be re- established. UV-VIS absorbance measurements and structural investigations by WAXS, TEM, ESCA and SNMS show that the green color is due to an oxide layer at the colloidal interface.
The sol-gel method which features a low-temperature wet-chemical process opens vast possibilities to incorporating organic dyes into solid matrices for various optical applications. In this paper we present our experimental results on the sol-gel derived photochromic organic- inorganic composite (Ormocer) materials following an introductory description of the sol-gel process and a brief review on the state of the art of the photochromic solids prepared using this method. Our photochromic spirooxazine-Ormocer gels and coatings possess better photochromic response and color-change speed than the corresponding photochromic polymer coatings and similar photochemical stability to the latter. Further developments are proposed as to tackle the temperature dependence problem and further tap the potentialities of the photochromic dye-Ormocer material for practical applications.
A sol-gel derived photochromic glass coating of about 1.5 micrometers in thickness is synthesized by infiltration of Ag+ into a predried Na-Al-B-Si gel layer. The formation of small Ag colloids is initiated by a soft heat treatment and the colloids are converted by a HCl vapor treatment into AgCl crystallites of about 40 nm in diameter. The coating darkens by UV irradiation, forming Ag crystallites of about 5 nm in size. This process is completely reversible at 400 degree(s)C and no decay is observed in numerous cycles. An amplitude hologram which acts as a diffraction grating with a grating period of about 10 micrometers can be produced within this layer by a two-wave mixing experiment with laser light of 351 nm wavelength. The diffraction efficiency of this grating is determined to 0.11%. After thermal erasing the diffraction pattern can be rewritten and erased repeatedly without any loss of efficiency.
The preparation of crackfree and transparent SiO2 coatings on soda lime glass with thicknesses of about 8 micrometers after densification at 500 degree(s)C is presented. The high thickness can be obtained by using an 80:20 mixture of methyltriethoxysilane and tetraethyl orthosilicate as alkoxide precursors in combination with an aqueous colloidal SiO2 sol with particle sizes of about 7 nm. This principle of synthesis is also applied to ZrO2 containing coatings yielding to thicknesses of about 3 micrometers . Refractive index measurements indicate that the coatings are nearly completely densified. At higher temperatures tensile stresses appear within the layers and are transmitted to the substrate, increasing its thermal stability.
AgCl/AgBr crystallites with diameters of about 40 nm were synthesized within a sodium alumo borosilicate glass matrix by the sol-gel process. Ag was introduced into the sol through the addition of an ethanolic AgN03 solution. After gelation, AgClxBr1- x was generated by treating the gel with NaCl and CuBr solutions. The gel can be densified to a glassy powder that shows a darkening effect with a saturation behaviour after UV irradiation and recovers at elevated temperatures (> 150 °C) . The best recovery kinetics were obtained for a silver halide content of about 12 mole/g.
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