One-dimensional physical model for complementary electrochromic device

Abstract

Eletrochromic devices are electrochemical systems that can undergo the optical modulation in response to an applied electrical stimulus. In order to investigate the electrochromic (EC) process mechanism and predict the electrochromic behavior, this paper proposes a physical model that employs tungsten trioxide (WO3), nickel oxide (NiO) and LiClO4-propylene carbonate (PC) solution. Within electrochromic films, electrolytes can transport lithium ions and anions through porous layers of electrochromic films. At the interfaces between solution and porous layers, lithium-ion intercalation and deintercalation take place. Considering both ion diffusion and electromigration, ion transport kinetics is described by Nernst-Plank equation. The partial differential equations (PDEs) for potential consist of Poisson equations for electrolytes and Ohm’s law for WO3 and NiO films. Moreover, the ion injection behavior at the interface is governed by Frumkin-Butler-Volmer (FBV) equation and potential conditions of the stern layer. Finally, a modified Beer-Lambert law incorporating porosity is proposed to explain the mechanism of transmittance. Under constant step potential conditions, the state variables of multiphysics field can be tracked, and the dynamic process of the transmittance and electrode current can be accurately predicted. This physical model can be applied for parameter design and precise control of ECDs, based on the optimization of device characteristics.