LOW-VOLTAGE ELECTROCHROMIC DEVICE FOR PHOTOVOLTAIC-POWERED SMART WINDOWS

We report the properties of an all-solid-state electrochromic (EC) dev ice that can be switched over a useful range of optical transmissions with voltages below 1 V. This switching voltage is smaller than requir ed by other solid-state EC devices reported to date. Ww attribute the lower-than-normal switching voltage so the use of a thermally evaporat ed MgF2 thin film as the lithium ion conducting layer. Electrochemical impedance spectroscopy studies show that high lithium ion conductivit y and low interfacial barriers for lithium exchange with the adjacent electrochromic and ion storage layers make MgF2 a good choice for the ion conductor in EC devices. This reduction in switching voltage is a first step toward powering an EC device by an integrated semitranspare nt single-junction photovoltaic (PV) cell. In a side-by-side bench tes t, where the EC device is connected to a semitransparent a-SiC:H PV ce ll having on open circuit voltage of 0.87 V, a relative transmission c hange in the EC device of 40% is achieved in less than 60 s. (C) 1996 American Institute of Physics.