Multi-Cell Designs for Energy Efficient Electrochromic Devices

Electrochromism is a reversible phenomenon in which a material's electronic structure and optical properties undergo modulation, resulting in observable changes in color or transparency when subjected to electrical stimuli. Organic conducting and semiconducting polymers respond to electrochemical potential by undergoing reversible color changes, a property which can readily be leveraged in an electrochromic device. A major limitation in the practical application of electrochromic devices is their tendency to self-discharge under open circuit conditions, leading to the degradation of the desired color state without continuous energy input. The challenge of continuous energy input is particularly critical given the increasing global energy demands. We are developing methods to stabilize the electrochromic state of two popular electrochromic polymers, PEDOT:PSS and ProDOT. PEDOT:PSS transitions from transparent to blue upon reduction while ProDOT transitions from magenta to transparent upon oxidation. To stabilize the color state, we employ a design containing multiple cells. This design stabilizes both the reduced state of PEDOT:PSS and the oxidized state of ProDOT, offering a viable strategy to improve the performance of electrochromic devices in applications which demand energy efficiency. Characterization techniques, including cyclic voltammetry and UV-Visible spectroscopy were employed to investigate the electrochemical behavior and optical properties of the materials. The systems were able to maintain the desired color state without measurable electrochromic fade for several hours. This behavior will be described in terms of the Nernst equation, highlighting the importance of basic thermodynamics relative to polymer morphology in describing the electrochemical properties of conducting and semiconducting polymers.