Nanostructured Coatings on Glazing for Active Solar Facades

Thin films on glazing play an important role in the design of solar energy conversion systems as thermal collectors or photovoltaic panels. Antireflective coatings based on porous silicon dioxide are well established in the field of solar collector glazing. Regarding architectural integration of thermal collectors, colored glass panes based on multilayer interference stacks of dielectric thin films offer a smart alternative to the coloration of the absorber sheets. Materials with tunable refractive index are highly desirable in such coatings in order to give access to optimised designs. Thin films of silicon titanium mixed oxides TixSi1-xO2 have been deposited in a particle free atmosphere by a sol-gel dip-coating process. Optical properties of thin films have been characterized by spectrophotometry and spectral ellipsometry. A nanocomposite structure has been evidenced by Transmission Electron Microscopy (TEM). As low tunable refractive index material, novel nanocomposite thin films based on the elements Mg, F, Si and O have been deposited. Transparent and homogenous thin layers were achieved with variable Mg:Si molar ratios. Surprisingly low refractive index values have been found, reaching desired values for anti- reflective applications. Broad spectral transmittance maxima are observed with values up to 99.8 %. The nanostructure of quaternary Mg-F-Si-O thin films has been investigated by TEM, showing evidence of embedded crystalline nanoparticles. In comparison to existing anti- reflective materials, the novel quaternary thin films might be highly interesting regarding improvement of hardness and improved aging stability with respect to pores filling by hydrocarbons. Intermediate size A4 colored glazing based on TixSi1-xO2 films have been produced exhibiting 14.0 and 12.6 % visible reflectance and only small energy losses (1.4 and 3.4 % with respect to the uncoated substrate) showing the high potential of such materials for colored solar facades. A real-sized prototype of colored thermal solar collector has been realized, providing a convincing demonstration device.

Sol-gel deposition and characterization of low refractive index nanocomposite Mg:F:Si:O thin films for solar and protective coatings

Estelle De Chambrier, Dipanwita Dutta, Christian Roecker, Jean-Louis Scartezzini, Josef Andreas Schuler

Coatings for thermal solar energy conversion have to be abrasion-resistant, stable at elevated temperatures, and often have to protect the substrate against corrosion. Due to the conditions of refractive index matching between the substrate and the ambient air, low refractive index materials are desired regarding a large variety of optical applications. Novel nanocomposite thin films based on the elements Mg, F, Si and O have been deposited by a sol-gel dip-coating process starting from trifluoroacetic acid, magnesium acetate and alcoxide precursors. Optical properties of this new material have been characterised by spectrophotometry and spectral ellipsometry, and show surprisingly low refractive index values. The experimental data obtained for varying chemical composition have been compared to the optical properties as predicted by Bruggeman and Ping-Sheng effective medium theories. Strong deviations from both theories are reported, suggesting modifications of the involved crystalline phases and/or formation of nanopores. Evidence for embedded crystalline nanoparticles has been found by Transmission Electron Microscopy (TEM). Compared to well known existing low refractive index materials such as porous SiO2 and MgF2, the quaternary Mg:F:Si:O thin films can be expected to show higher hardness and improved aging stability with respect to pore filling by hydrocarbons. The novel thin film material opens promising perspectives for new solar and protective coatings.

2007

Air cooling powered by façade integrated coloured opaque solar thermal panels

Stefan Mertin, Andreas Schueler

For building integration of solar-powered energy systems, aesthetic aspects play an importantrole. Covering a standard solar collector with a coloured glazing, opaque to the human eye but highly transparent to solar energy, permits a perfect architectural integration of solar thermal panels into glazed building façades. The thermal energy produced can be used for both solar heating and cooling, as well as for domestic hot water. The principle of the coloured appearance is based on interference in the thin-film coating on the reverse side of the cover glass. Different interference filters based on nano-composite materials deposited by the solgel method were presented at CISBAT 2007 [1]. Currently, we are developing new plasma-deposition processes, which are more suitable for industrial large-scale production. A new state-of-the-art ultra-high vacuum (UHV) system for magnetron sputtering deposition of novel nano-composite solar coatings has recently been designed, constructed, and installed at the Solar Energy and Building Physics Laboratory (LESO-PB). Up to five different magnetron sources can be used simultaneously, in reactive and non-reactive mode. The geometric configuration of the chamber has been optimised for best film homogeneity and allows the deposition on substrates up to 100 mm in diameter. The optical and electronic properties of thin films are closely interrelated and highly relevant for solar coatings. Photoelectron spectroscopy provides information on the coating structure, the deposited material and its chemical state inside the coating, as well as the nature of the interface between different layers. A system for ESCA analysis (Electron Spectroscopy for Chemical Analysis) has recently been installed and put into operation at LESO-PB. By ellipsometry and spectrophotometry, we can determine exactly the different optical properties of the coating, such as layer thickness, refractive index, or absorption coefficient. This provides best conditions for highly efficient research and development on new materials for further optimisation of the coloured interference filters.First results have been obtained with our new experimental infrastructure and will be presented in this contribution.

EPFL2011

Coloured coatings for glazing of active solar thermal façades by reactive magnetron sputtering

Martin Joly, Stefan Mertin, Jean-Louis Scartezzini, Andreas Schueler

For building integration of solar-powered energy systems, aesthetic aspects play an important role. Covering a standard solar collector with a coloured glazing, opaque to the human eye but highly transparent to solar energy, permits a perfect architectural integration of solar thermal panels into glazed building façades. The thermal energy produced can be used for both solar heating and cooling, as well as for domestic hot water. The principle of the coloured appearance is based on interference in the thin-film coating on the reverse side of the cover glass. Different interference filters based on nano-composite materials deposited by the solgel method were presented at CISBAT 2007 [1]. Currently, we are developing new plasma-deposition processes, which are more suitable for industrial large-scale production. A new state-of-the-art ultra-high vacuum (UHV) system for magnetron sputtering deposition of novel nano-composite solar coatings has recently been designed, constructed, and installed at the Solar Energy and Building Physics Laboratory (LESO-PB). Up to five different magnetron sources can be used simultaneously, in reactive and non-reactive mode. The geometric configuration of the chamber has been optimised for best film homogeneity and allows the deposition on substrates up to 100 mm in diameter. The optical and electronic properties of thin films are closely interrelated and highly relevant for solar coatings. Photoelectron spectroscopy provides information on the coating structure, the deposited material and its chemical state inside the coating, as well as the nature of the interface between different layers. A system for ESCA analysis (Electron Spectroscopy for Chemical Analysis) has recently been installed and put into operation at LESO-PB. By ellipsometry and spectrophotometry, we can determine exactly the different optical properties of the coating, such as layer thickness, refractive index, or absorption coefficient. This provides best conditions for highly efficient research and development on new materials for further optimisation of the coloured interference filters. First results have been obtained with our new experimental infrastructure and will be presented in this contribution.

EPFL2011

Air cooling powered by façade integrated coloured opaque solar thermal panels

Stefan Mertin, Andreas Schueler

EPFL2011

Coloured coatings for glazing of active solar thermal façades by reactive magnetron sputtering

Martin Joly, Stefan Mertin, Jean-Louis Scartezzini, Andreas Schueler

For building integration of solar-powered energy systems, aesthetic aspects play an important role. Covering a standard solar collector with a coloured glazing, opaque to the human eye but highly transparent to solar energy, permits a perfect architectural integration of solar thermal panels into glazed building façades. The thermal energy produced can be used for both solar heating and cooling, as well as for domestic hot water. The principle of the coloured appearance is based on interference in the thin-film coating on the reverse side of the cover glass. Different interference filters based on nano-composite materials deposited by the solgel method were presented at CISBAT 2007 [1]. Currently, we are developing new plasma-deposition processes, which are more suitable for industrial large-scale production. A new state-of-the-art ultra-high vacuum (UHV) system for magnetron sputtering deposition of novel nano-composite solar coatings has recently been designed, constructed, and installed at the Solar Energy and Building Physics Laboratory (LESO-PB). Up to five different magnetron sources can be used simultaneously, in reactive and non-reactive mode. The geometric configuration of the chamber has been optimised for best film homogeneity and allows the deposition on substrates up to 100 mm in diameter. The optical and electronic properties of thin films are closely interrelated and highly relevant for solar coatings. Photoelectron spectroscopy provides information on the coating structure, the deposited material and its chemical state inside the coating, as well as the nature of the interface between different layers. A system for ESCA analysis (Electron Spectroscopy for Chemical Analysis) has recently been installed and put into operation at LESO-PB. By ellipsometry and spectrophotometry, we can determine exactly the different optical properties of the coating, such as layer thickness, refractive index, or absorption coefficient. This provides best conditions for highly efficient research and development on new materials for further optimisation of the coloured interference filters. First results have been obtained with our new experimental infrastructure and will be presented in this contribution.

EPFL2011