VO2-based Thermochromic and Nanothermochromic Materials for Energy-Efficient Windows: Computational and Experimental Studies
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
VO2-based ﬁlms are thermochromic and exhibit high or low infrared transmittance when the temperature is below or above a critical temperature. The thermochromic switching is passive and reversible, and therefore VO2 based ﬁlms are promising for energy-efﬁcient window applications. However the practicaluse of VO2 for energy-efﬁcient windows has long been hampered by low luminous transmittance and low solar energy transmittance modulation. The main goal of this dissertation work is to address these issues.
The ﬁrst half of the work proposes the concept of nanothermochromics for simultaneous improvement of luminous transmittance and modulation of solar energy throughput. nanothermochromics considers VO2 nanoparticle composite layers, whose optical properties were modeled by effective medium theories. Calculations on VO2 spheroids have shown that VO2 nanoparticles, especially nanospheres, can offer dramatically improved luminous transmittance and solar transmittance modulation that are not possible for ﬁlms. Calculations done on coreshell nanoparticles showed comparable improvements and offer an opportunity to reduce the material costs. It was also found that the composite of In2O3:Sn (ITO) and VO2 can yield moderately high luminous transmittance, solar transmittance modulation and low-emittance properties.
In the second half of the dissertation work, Mg-doped VO2 ﬁlms were sputter deposited. Their band gaps and Mg-content were investigated by means of optical absorption measurement and Rutherford backscattering spectrometry, respectively. The band gaps of VO2 were found to increase by ∼3.9±0.5 eV per unit of atom ratio Mg/(Mg+V) for 0<Mg/(Mg+V)<0.21. Computations based on effective medium theory were done to estimate the performance of Mg-doped VO2 ﬁlms and nanoparticle composite layers. The results suggest that moderately doped VO2 ﬁlms with 0<Mg/(Mg+V)<0.06 perform better than un-doped ﬁlms and that the performance can be further enhanced with one layer of antireﬂection coating. The best results were achieved by un-doped VO2 nanospheres, closely followed by the VO2 nanospheres with low Mg-content.
Furthermore, the an experimental study on sputter deposited VO2 nanorods has identiﬁed the geometry of the oxygen gas inlet, the type of substrate, the substrate temperature and the layer thickness as important factors that inﬂuence the growth morphology.
Taken as a whole, nanothermochromics offered by VO2 nanoparticles was shown to be the best solution for VO2 based thermochromic energy-efﬁcient window coatings.
Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. , 143 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1095
VO2, thermochromism, nanothermochromics, energy efficient windows, optical modeling, effective medium theory, thin film characterization, doping
Condensed Matter Physics
IdentifiersURN: urn:nbn:se:uu:diva-210016ISBN: 978-91-554-8801-7OAI: oai:DiVA.org:uu-210016DiVA: diva2:660598
2013-12-13, Häggsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala University, Polacksbacken, Uppsala, 13:15 (English)
Parkin, Ivan, Professor
Granqvist, Claes-Göran, ProfessorNiklasson, Gunnar, Professor
FunderSwedish Research Council
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