Andreas Gier

Sol—gel coatings for light trapping in crystalline thin film silicon solar cells

Abstract An increase of light absorption by light trapping is a key issue for the design of thin film solar cells from crystalline silicon. According to our numerical work, the deposition of crystalline silicon layers of thickness, W = 4 μ m, on textured glass substrates doubles the cell current for facet angles, α = 75°, and texture periods p μ m, without the need for anti reflection coatings. We demonstrate the fabrication of such micron-sized light traps by embossing of sol—gel glasses.

Development of organic-inorganic coatings for strength-preserving of glass bottles

An amino-epoxy-silane based coating system (GAMAL) for glass surfaces was developed, which can efficiently protect bottles from the damages of a bottling plant. Testing bottles with a ramp pressure tester show an identical value of about (40±4) bar for conventionally hot- and cold-end coated bottles and bottles coated with the developed organic-inorganic composite (GAMAL) system. After already 2 min of wet line-simulation testing, all species of a conventionally coated probe fall short of the critical limit of 16 bar, whereas bottles coated with GAMAL (thickness about 7 μm) show a value of (21±3) bar. Coating is possible by dip and spray application on cold or hot (80°C) substrates, the coating is cured at 120°C for 5 to 10 min. Additional functions such as colour or UV protection can be added easily, without reduction of the protection potential. The low content of carbon (about 0.5 g per 1l soft drink bottle) should not disturb the recycling process of such coated bottles.

Preparation of micropatterns with profile heights up to 30 microns from silica sols

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.

Coatings for increasing and preserving the bending strength of glass

The practical strength of glass with a value of about 100 MPa is approximately 100 times smaller than its theoretical ones [1]. This is due to micro flaws on the glass surface, which amount up to 50.000 on one cm2[2]. During the handling of glass externals stresses are amplified by these flaws, like clefts, pores or inclusions [3]. The degree of amplification depends on the geometry of the crack tip, which can be strongly influenced by chemical interactions with the surroundings. Depending on the intensity of these external influences, a rather slow crack propagation is observed under subcritical load (static fatigue). However, when the applied tensile stress exceeds a critical value (Kic-factor) the crack grows spontaneously with almost the speed of sound [4,5], leading essentially to the breaking of the glass.

Zum Einfluß von Sol-Gel-Beschichtungen auf die Spannungsrißkorrosion an Floatglasoberflächen

Einleitung und Zielsetzung: Obwohl Glas einer der chemisch resistentesten Werkstoffe ist, treten beim Kontakt mit unterschiedlichen Medien chemische Wechselwirkungen auf. Wie Untersuchungen von Wiederhorn gezeigt haben, wird die Spannungsriskorrosion und damit die statische Ermudung von Glas durch das Zusammenwirken von mechanischer Belastung und Wasser aus der Umgebung begunstigt. Aus dem Stand der Technik ist bekannt, das bei der Herstellung von Glasfasern organische Polymerbeschichtungen eingesetzt werden, um die Diffusion von Wasser und Wasserdampf an die Glasoberflache zu vermeiden. Daneben sind viele Arbeiten aus der Sol-Gel-Chemie bekannt, die sich mit dem Einflus von organischen Beschichtungen auf die Spannungsriskorrosion beschaftigen. Die durchgefuhrten Untersuchungen verfolgten das Ziel, die Mikrorisse in Glasoberflachen durch naschemische Behandlung vor einem korrosiven Angriff durch Wasser zu schutzen. Die Beeinflussung der Lebensdauer sollte anhand von Zeitstandversuchen an geschadigten Glasern nachgewiesen werden, sowie durch Bestimmung der Bruchfestigkeit als Funktion der Lastauftragsrate.