Designing an All-Solid-State Tungsten Oxide Based Electrochromic Switch with a Superior Cycling Efficiency

There are ongoing efforts to integrate electrochromic device (ECD) technology with other electrochemical systems. ECDs made with safer solid polymer electrolytes (SPEs) are prone to performance degradations due to their high relaxation period that is detrimental to highly dynamic switching operations. Here, the fabrication of partially crystalline WO3 based all-solid-state mono-electrochrome switches is reported that shows outstanding optical and electrical stability under prolonged charge-discharge cycles. A free-standing SPE is specially designed by dispersing LiClO4 into polyvinyl alcohol followed by thermochemical cross-linking of the host. Continuous switching of the device shows two primary sources of performance degradations. One is associated with the polarization affecting both working and counter electrode interfaces (SPE-WE and SPE-CE), and the other is due to the irreversible redox reaction caused by total charge flow in the system that exceeds the double layer charge storage capacity of the CE. The conductivity and flexibility of the electrolyte are improved by adding glycerol as the plasticizer. In the CE, a nanocrystalline porous TiO2 buffer is used to avert the interface modifications. The performance of the switches is presented and compared using the spectro-electrochemical and cyclic voltammetry data.