THIN-FILM SOLID-STATE IONIC MATERIALS FOR ELECTROCHROMIC SMART WINDOW GLASS

The optical transmissivity (and especially the reflectivity) of a multilayer electrochromic smart window glass structure can be reversibly modulated by an electrical current pulse, and the modulation is spectrally selective. This is important for building and vehicle windows and for other electrooptical applications. Thin-film solid-state ionic materials are the key elements of such a structure. Their roles and some of their current states of development at Tufts (and particularly the state of development of the electrochromic layer) are discussed. Also discussed is the state of development of prototype all-solid electrochemically reversible, five-layer window devices. These devices employ: a lithium-insertable rf sputter-deposited polycrystalline WO3 film that exhibits reflection modulation as the electrochromic layer; a lithium-insertable rf sputter deposited in In2O3 film or a thermally deposited V2O5 film as the counterelectrode layer; an rf sputter deposited LiNbO3 film as the ion-conducting (solid electrolyte) layer; and rf sputter deposited ITO Sn-doped In2O3) or undoped In2O3 films as the transparent conducting layers. The devices exhibit useful operating characteristics and indicate that robust and economical practical smart window glass could soon become a commercial reality.