Oxide-based chromogenic coatings and devices for energy efficient fenestration: Brief survey and update on thermochromics and electrochromics

Abstract

Modern buildings often have large windows and glass facades in order to achieve good day-lighting and desirable indoors–outdoors contact. These glazings are challenging with regard to the buildings' energy efficiency and frequently let in or out too much energy; this phenomenon has to be balanced by energy guzzling cooling or heating. In particular, the cooling requirement has grown strongly in recent years. Chromogenic glazings, based on thermochromism or electrochromism, are emerging technologies that can regulate the inflow of visible light and solar energy between widely separated limits and create better energy efficiency than is possible with static solutions. Thermochromic thin films—in practice based on vanadium dioxide—have a transmittance of infrared solar radiation that is smaller at high temperature than at low temperature. Electrochromic multilayer structures—often incorporating nanoporous thin films of tungsten oxide and nickel oxide—are able to vary the transmittance of visible light and solar energy when a low voltage is applied for a short time so as to shuttle charge between the two oxide films. Furthermore, and importantly, the new chromogenic fenestration technologies are able to improve indoor comfort. This brief tutorial review surveys the fields of oxide-based thermochromics and electrochromics with particular attention to recent advances.