Line patterning for flexible and laterally configured electrochromic devices

Abstract

We have applied the line patterning method, which involves printing of patterns on a plastic or paper substrate using a commercial printer followed by coating of the non-printed areas by a conductive polymer, or metal conductor, to build laterally configured polymer and metallic interdigitated electrodes (IDEs) for electrochromic devices (ECDs). Selective deposition of transparent poly(3,4-ethylenedioxythiophene)–poly(styrene sulfonate) (PEDOT–PSS) or electroless gold films resulted in lateral electrode resolution values of ∼30 µm as determined by optical microscopy. These ECDs comprise complementary colored, dioxythiophene based electrochromic polymers deposited on alternating fingers of gold coated IDEs and a viscous electrolyte layer to enable ion transport between the polymers. The devices are switched by stepping the applied voltage between −1.2 V to +1.2 V and pass a maximum of 1.3 mA cm⁻² and a switching charge of 1.2 mC cm⁻² in ∼3 s to switch the device from a highly reflective gold state to an absorptive blue state. Three IDEs with different anode to cathode distances have been line patterned via electroless gold deposition. Electrochromic switching kinetics of 2-lane, 4-lane, and 6-lane ECDs have been studied by applying potential steps from −1.0 V to +0.8 V and monitoring the reflectance change as a function of time. The switching times to reach 85% of the full contrast are 4.3 s, 1.5 s, and 0.8 s for the 2-lane, 4-lane, and 6-lane devices, respectively. The extent of interdigitation noticeably improves the switching performance of lateral ECDs due to shorter diffusion distances for dopant ions and minimal electrolyte resistance.