A stretchable patch of multi-color electrochromic devices for driving integrated sensors and displaying bio-signals

We report a stretchable patch of multi-color electrochromic devices (ECDs) for powering integrated bio-sensors and visually displaying bio-signals. The fabricated ECD consists of a polyaniline cathode and an In-coated Zn anode, on transparent electrodes of Ti/Au grid, sandwiching poly(vinyl alcohol)/zinc chloride gel electrolyte in between. The ECD exhibits five colors, gray, light green, green, teal blue, and blue, depending on the applied bias voltage and shows a capacity of 64.1 mAh/m² with a driving voltage window of 1.3 V at a current density of 0.01 mA/cm². The ECDs, a temperature sensor, and a strain sensor are integrated on a stretchable elastomer film of Ecoflex/PDMS using patterned liquid metal galinstan interconnections, to form a skin-attachable patch device. Within this patch, the strain sensor is powered by the ECDs to detect the bending of wrist and the measured strains are displayed as different colors with the aid of an Arduino micro-controller. Simultaneously, the change in skin temperature and the extent of wrist bending are displayed as the changes in color of the corresponding ECD. This study clearly demonstrates that our flexible ECD can be used as both an integrated energy storage device and a display device, applicable to a wide range of wearable electronic systems.