Voltage-Tunable Dual Image of Electrostatic Force-Assisted Dispensing Printed, Tungsten Trioxide-Based Electrochromic Devices with a Symmetric Configuration

Electrostatic force-assisted dispensing (EFAD)-printed tungsten trioxide (WO₃)-based electrochromic devices (ECDs) displaying a dual image depending on the applied voltage are demonstrated. We first print WO₃ via EFAD printing, in which the width of the printed lines can be tuned by adjusting the printing speed. The performance of the ECDs is characterized while varying the thickness of the printed WO₃ film. It is determined that ∼550 nm thick WO₃ is the optimal film considering maximum transmittance contrast (ΔT_max), device dynamic responses, efficiency, and long-term coloration/bleaching cyclic stability. More significantly, the coloration of the devices in this work can alternatively appear due to the use of electrolyte-soluble anodic species (here, dimethyl ferrocene, dmFc), for which WO₃ films should be deposited on both electrodes and a part of the electrodes should be exposed to the electrolyte for the oxidation of dmFc. To take advantage of such features of the devices, we successfully demonstrate EFAD-printed, flexible WO₃ ECDs alternately displaying a dual image, which is expected to have high potential as a functional component of printed electronics.