99 Mater. Res. Soc. Symp. Proc. Vol. 1492 © 2013 Materials Research Society DOI: 1 557/op 013 0.1 l.2 . Progress in Chromogenic Materials and Devices: New Data on Electrochromics and Thermochromics C. G. Granqvist, S.-Y. Li, . Bayrak Pehlivan, and G. A. Niklasson Department of Engineering Sciences, The Ångström Laboratory, Uppsala University, P. O. Box 534, SE-75121 Uppsala, Sweden ABSTRACT Electrochromic (EC) and thermochromic (TC) materials are of much interest for “smart” windows which combine energy efficiency with the provision of indoor comfort. This paper summarizes results from several recent studies related to nanoparticles of transparent and electrically conducting ITO (i.e., In 2 O 3 :Sn) and of thermochromic VO 2 . Specifically, we consider (i) the use of ITO nanoparticles in polaronic EC devices in order to suppress near-infrared solar transmittance, (ii) performance limits for plasmonic EC devices embodying ITO nanoparticles, and (iii) ITO-VO 2 -based nanocomposites with joint low thermal emittance and TC properties, and with Mg-doping of the VO 2 as a means for boosting the luminous transmittance. Both experimental and theoretical results are presented. INTRODUCTION Windows are necessary elements in buildings where people live and work, and they give visual indoors-outdoors contact along with day-lighting. However, the windows usually let in or out too much energy, which must be balanced by energy guzzling space heating or space cooling. Multiple glazing is necessary to diminish heat losses and provide energy efficiency, and a transparent low-emittance coating on one of the surfaces enclosing a gas-filled gap between two neighboring panes can bring down the heat transfer to roughly half of what it would be in the absence of the coating [1]. A further significant improvement of the window can be achieved if it also is “smart”, meaning that it admits solar energy into a room when there is a heating demand and prevents the solar energy inflow—but keeps unimpeded indoors-outdoors contact—when there is a cooling demand. The “smartness” can be accomplished by chromogenic fenestration [2] involving electrochromic (EC) thin films, allowing electrically controlled inflow of visible light and solar energy, or a thermochromic (TC) thin film which limits the solar energy inflow above a certain “comfort temperature”. This paper summarizes some recent studies of ours which involve nanoparticles of transparent and electrically conducting tin doped indium oxide (In 2 O 3 :Sn, known as ITO) and of thermochromic VO 2 , sometimes with varying degrees of Mg doping. The first study regards a standard (“polaronic”) EC device incorporating a transparent polymer electrolyte and demonstrates experimentally and theoretically that the near-infrared (NIR) part of the solar irradiation—with about half of the solar energy—can be absorbed very efficiently by ITO nanoparticles dispersed in the electrolyte, and that this functionality does not interfere much with an EC modulation of visible light [3]. The second study considers a new type (“plasmonic”) EC device, which embodies ITO nanoparticles, and presents computed performance limits on the optical modulation [4]. Thirdly we regard nanocomposites of ITO and thermochromic VO 2 and demonstrate that a temperature-dependent modulation of the near-infrared transmittance can be 155