Mesoporous ITO Electrodes as Optically Passive Counter Electrodes for Electrochromic Devices
D. Eric Shen, Divya B. Iyer, Abigail M. Dejneka, John R. Reynolds, Anna M. Österholm
Abstract
High Resolution Image Download MS PowerPoint Slide Thin films of ITO nanoparticles (nanoITO) are evaluated as optically inactive and purely capacitive charge storage layers in colored-to-clear switching electrochromic devices (ECDs). A commercially available nanoITO dispersion in isopropanol is used without further formulation, and a range of coating parameters and postprocessing heat treatments are evaluated for their impact on electrode transmittance, haze, stability, and capacitance. The nanoITO electrodes are highly transmissive throughout the entire visible range (84% T 380–780 nm ) despite being several micrometers thick. These electrodes also have a sufficiently high capacitance to charge balance a family of cathodically coloring conjugated polymer-based electrochromes via double-layer charging as a result of their mesoporous structure. In fact, the nanoITO electrodes have sufficient capacitance to afford ECDs with high optical density in the colored state (<1% T at λ max, OD > 2) while still being able to switch effectively to the colorless state at <1.5 V. We show that nanoITO films are simple to coat using a variety of deposition techniques and compatible with rigid glass and flexible plastic substrates alike. While a simple heat treatment does improve the optical transparency slightly, it is not a requirement for successful device integration. This work strives to continue to reduce the barriers to ECD fabrication with strategies compatible with high-throughput coating techniques and straightforward, low-cost processing conditions.