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Research Papers

Effect of Additives on the Durability and Properties of Antireflective Films for Solar Glass Covers

[+] Author and Article Information
Gema San Vicente

 Departamento de Energía (CIEMAT), Unidad de Concentración Solar-Plataforma Solar de Almería, Avenida Complutense 22, E-28040 Madrid, Spaingema.sanvicente@ciemat.es

Rocío Bayón, Angel Morales

 Departamento de Energía (CIEMAT), Unidad de Concentración Solar-Plataforma Solar de Almería, Avenida Complutense 22, E-28040 Madrid, Spain

J. Sol. Energy Eng 130(1), 011007 (Dec 28, 2007) (4 pages) doi:10.1115/1.2804626 History: Received October 11, 2006; Revised May 17, 2007; Published December 28, 2007

Generally, single layer antireflective (AR) coatings are based on SiO2 for which the low refractive index is achieved by increasing the porosity of the films. On the other hand, the increase of porosity on any material results in a decrease of its mechanical properties. In addition to increasing the solar transmittance, it is equally important that the AR film is long-term stable for its application in solar collectors. In this sense, the objective of our work has been to develop a film that exhibits good AR properties and physical durability as well. In the present study, sol-gel silica films have been deposited on borosilicate glass. The effect of adding some organic compounds to the precursor solution in the properties of the films has been studied. Moreover, accelerated weathering tests have been performed in order to investigate the outdoor durability. A value of solar transmittance as high as 0.974 has been obtained by using a porosity promoter additive. However, the durability tests have shown the necessity of incorporating a hydrophobic additive to the precursor solutions in order to avoid the degradation of the optical properties of the films. 1.5% decrease in solar transmittance is observed after 1900h in the weathering chamber for films prepared with methyltriethoxysilane.

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Figures

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Figure 2

Effect of the solution additives on the DTA curves

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Figure 3

Transmittance spectra of uncoated borosilicate glass (a), polymeric SiO2 film on borosilicate glass (b), polymeric + triton SiO2 film on borosilicate glass (c), and polymeric + triton + MTES (10%) SiO2 film on borosilicate glass (d). The solar transmittance calculated values have been recorded for each sample.

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Figure 4

Transmittance spectra of modified silica films on borosilicate glass prepared at different withdrawal rates and global AM 1.5 solar photon spectral distribution

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Figure 1

Effect of the solution additives on the thermogravimetric curves

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Figure 5

Solar transmittance of silica films with different compositions as a function of the time in the weathering chamber

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