Submicronic VO 2 –PVP composites coatings for smart windows applications and solar heat management I.G. Madida a,b , A. Simo a,b , B. Sone a,b , A. Maity a,c , J.B. Kana Kana a,b,d , A. Gibaud a,b,e , G. Merad a,b , F.T. Thema a,b , M. Maaza a,b,⇑ a UNESCO–UNISA Africa Chair in Nanosciences/Nanotechnology, College of Graduate Studies, University of South Africa, Muckleneuk Ridge, PO Box 392, Pretoria, South Africa b Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation, 1 Old Faure Road, Somerset West 7129, PO Box 722, Somerset West, Western Cape Province, South Africa c Council for Scientific and Industrial Research, PO Box 395, Pretoria 0001, South Africa d Department of Materials Science & Engineering, University of Arizona, Tucson, AZ 85721, USA e Laboratoire de Physique de L’Etat Condense ´, (UMR 6087) Universite ´ du Maine, 72085 Le Mans, France Received 5 February 2014; received in revised form 17 June 2014; accepted 18 June 2014 Communicated by: Associate Editor Matheos Santamouris Abstract Large surface and chemically stable thermochromic composite coatings consisting of IR active sub-micron VO 2 particles embedded in a passive polymeric host matrix of Polyvinylphenol were synthesized by dip and spin coating process. The hybrid composite coatings are IR transparent and IR reflective below and above the switching temperature of 68 °C. Although these cost effective hybrid composite coatings are two-dimensional morphologically (1–3 nonpercolated submicron VO 2 crystallites within the coating thickness), they exhibit a significant reversible IR transmission modulation with temperature of 45% between 25 °C and 100 °C at 1 mm. This satisfactory reproducible thermochromic optical switching characteristic could address the impediment to greater market penetration of thermochro- mic VO 2 based technology relatively to the high cost coatings engineered by vacuum technologies. From technological applications per- spective, the global production of glass which could regulate solar heat by using such hybrid thermochromic coatings, could be part of 1 billion m 2 /year with 25% for building sector and about 11% for the automotive industry. Likewise, such cost effective hybrid ther- mochromic coatings could play a significant role in the minimization of air conditioning load and thus energy consumption in both build- ing and automotive sectors. As hinted to in its 2012 annual report, the International Energy Council’s predictions have estimated that with 2 billions m 2 of coated windows worldwide with smart coatings, energy saving in the building and automotive economic fields is equivalent of CO 2 reduction by about 100 millions of tons. Ó 2014 Elsevier Ltd. All rights reserved. Keywords: Smart windows; IR modulation; Thermochromism; Overheating; Vanadium dioxide; Composite 1. Introduction In parallel to the expansion of advanced technologies in the solar energy photo-conversion; namely Photovoltaics (PV) and Concentrated Solar Power (CSP), there is a fast growing sector of smart windows for air-conditioning http://dx.doi.org/10.1016/j.solener.2014.06.025 0038-092X/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Nanosciences African Network (NANOAF- NET), iThemba LABS-National Research Foundation, 1 Old Faure Road, Somerset West 7129, PO Box 722, Somerset West, Western Cape Province, South Africa. Tel.: +27 218431018; fax: +27 218433543. E-mail address: Maaza@tlabs.ac.za (M. Maaza). www.elsevier.com/locate/solener Available online at www.sciencedirect.com ScienceDirect Solar Energy 107 (2014) 758–769