Showing papers by "Claes-Göran Granqvist published in 2009"

Mg doping of thermochromic VO2 films enhances the optical transmittance and decreases the metal-insulator transition temperature

Abstract: Thermochromic films of MgxV1−xO2 were made by reactive dc magnetron sputtering onto heated glass. The metal-insulator transition temperature decreased by ∼3 K/at. %Mg, while the optical transmittance increased concomitantly. Specifically, the transmittance of visible light and of solar radiation was enhanced by ∼10% when the Mg content was ∼7 at. %. Our results point at the usefulness of these films for energy efficient fenestration.

Advances in Chromogenic Materials and Devices

Abstract: Abstract Chromogenic materials allow the transmittance of visible light and solar energy to be varied under the action of an external stimulus. This paper first discusses buildings related energy savings that can be accomplished by chromogenic technologies, and their beneficial effects on comfort issues. We then summarize recent work on thermochromic VO 2 -based thin films with particular attention to multi-layers of VO 2 and TiO 2 and to new VO 2 :Mg films for which the doping gives significantly lowered absorption of visible light. The final part covers electrochromic materials and devices with foci on coloration efficiency and on durability issues for foil-type constructions based on films of WO 3 and NiO.

Thermochromic VO2‐based multilayer films with enhanced luminous transmittance and solar modulation

Abstract: Vanadium dioxide (VO2) shows an abrupt and reversible change in optical and electrical properties when the temperature is raised beyond a critical point of similar to 68 degrees C. Films made from this material have a potential to be used in energy efficient "smart" windows with temperature-dependent throughput of solar radiation. Two of the drawbacks of this material have been its low luminous transmittance and limited solar modulation of transmittance during switching. In this work we report calculations and experiments on multilayers Of VO2 and TiO2, produced by reactive DC magnetron sputtering, that significantly improve the luminous transmittance and solar modulation of the films during switching. We also explore the angular-dependent transmittance of five-layer TiO2/VO2/TiO2/VO2/TiO2 films and demonstrate that the modulation of luminous and solar transmittance can be enhanced at non-normal angles of incidence.

Gas sensing response of NiO nanoparticle films made by reactive gas deposition

Abstract: Nanocrystalline films comprised of NiO particles were prepared by advanced reactive gas evaporation and were investigated for gas sensing applications, specifically for detecting reducing (H2S) and oxidizing (NO2) species. The films were studied in as-deposited state and after annealing at temperatures up to 400 °C, and the sensors were operated from room temperature to 325 °C. The optimal operating temperature was in the 150–162 °C range for H2S and in the 100–125 °C range for NO2. We believe that this is the first report of high-sensitivity detection of H2S with NiO-based sensors, as well as the first proof that such sensors can work at room temperature.

Coloration Mechanism in Proton-Intercalated Electrochromic Hydrated NiOy and Ni1-xVxOy Thin Films

Abstract: Electrochromic (EC) films of nickel oxide, with and without vanadium, were prepared by reactive dc magnetron sputtering. They were characterized by electrochemical and optical measurements and ...

Thermochromic VO2-based multilayer applications an materials sciences films with enhanced luminous transmittance and solar modulation

Abstract: Vanadium dioxide (VO 2 ) shows an abrupt and reversible change in optical and electrical properties when the temperature is raised beyond a critical point of ~68°C. Films made from this material have a potential to be used in energy efficient "smart" windows with temperature-dependent throughput of solar radiation. Two of the drawbacks of this material have been its low luminous transmittance and limited solar modulation of transmittance during switching. In this work we report calculations and experiments on multilayers of VO 2 and TiO 2 , produced by reactive DC magnetron sputtering, that significantly improve the luminous transmittance and solar modulation of the films during switching. We also explore the angular-dependent transmittance of five-layer TiO 2 /NO 2 /TiO 2 /NO 2 /TiO 2 films and demonstrate that the modulation of luminous and solar transmittance can be enhanced at non-normal angles of incidence.

Transparent conductors for solar energy and energy efficiency: a broad-brush picture

Abstract: Transparent conductors (TCs) have numerous and diverse applications for solar energy applications and for energy efficiency. The largest of these applications, in terms of area, are based on the fact that the TCs have low infrared emittance and can be used to improve the thermal properties of modern fenestration. Depending on whether the TCs are reflecting or not in the near infrared pertinent to solar irradiation, the TCs can serve in 'solar control' or 'low-emittance' windows. Other applications rely on the electrical conductivity of the TCs, which render them useful as current collectors in solar cells and for inserting and extracting electrical charge in electrochromic 'smart windows' capable of combining energy efficiency and indoor comfort in buildings. This paper ventures to give a broad-brush picture of TCs and discuss their properties from the perspective of the radiative properties in our ambience. This approach leads naturally to considerations of spectral selectivity, angular selectivity, and temporal variability of TCs. The spectrally selective materials are thin films based on metals (normally silver) or wide band gap semiconductors with heavy doping (normally based on indium, tin, or zinc). The potential importance of carbon-based TCs is emphasised. Angular dependent TCs, especially those for which the properties are governed by inclined columnar nanostructures, are introduced. A discussion of TC-like materials with thermochromic and electrochromic properties is included, especially with regard to vanadium-dioxide-based films and electrochromic multilayer structures embracing tungsten oxide and nickel oxide.

Thermochromic material and fabrication method

Abstract: In a method for manufacturing of thermochromic material, a target increased luminous transmittance level for the thermochromic material is determined (210). The luminous transmittance level is defined within a predetermined wavelength region. Preferably, this predetermined wavelength region at least partly comprises visible light. A concentration level of a first dopant element is determined (212) for generating the luminous transmittance level of the thermochromic material. The first dopant element is capable of forming an oxide having a high bandgap in its electronic structure, and in a specific embodiment is Al and/or Mg. A VO2-based thermochromic material is doped (214) with the determined concentration level of the first dopant element. At least one second dopant may also be employed.

Optical modeling of spectrally selective reflectors based on TiO2:Nb transparent conducting oxide films for silicon solar cell applications

Abstract: A spectrally selective reflector (SSR) can be fabricated by depositing a transparent conducting oxide on a reflective substrate. SSRs can be incorporated in concentrating solar cells in order to minimize the heating. We deposited TiO 2 :Nb thin films on glass by DC magnetron sputtering, extracted optical constants, and used those to model an optimized SSR. Corresponding films were then successfully produced. The best wavelength-integrated reflectance values were 79 % and 31 % in the ranges 300 < λ < 1100 nm and 1100 < λ < 2500 nm, respectively. These data are better than those previously achieved using SnO 2 :F.