Flexible solid-state photoelectrochromic windows

Photoelectrochromic "smart" window technology is extended to include the us e of flexible substrates and solid-state electrolytes. This should facilita te their application as retrofit modifications of office windows, where, by blocking incoming solar irradiation, they could substantially lower air-co nditioning costs. These devices are based on a dye-sensitized TiO2 electrod e coupled with a 500 nm thick WO3 electrochromic counter electrode, separat ed by a cross-linked polymer electrolyte containing LiI. A novel method for preparing conducting nanoporous TiO2 films is described that allows for th e construction of these devices on flexible organic substrates. Colloidal s olutions of TiO2 free of surfactants were spin-coated onto indium-tin oxide coated polyester substrates, resulting in highly transparent films ranging from 100 nm to 1 pm in thickness. Upon annealing at 100 degrees C, these f ilms were strongly adherent and displayed excellent photoconductivity as sh own by their current-voltage characteristics. The devices typically transmi t 75% of visible light in the bleached state. After a few minutes of exposu re to white light (75 mW/cm(2)), the windows turn dark blue, transmitting o nly 30% of visible light. They spontaneously bleach back to their initial n oncolored state upon removal of the light source. (C) 1999 The Electrochemi cal Society. S0013-4651(99)99-03-065-7. All rights reserved.