Physical, chemical, theoretical aspects of conducting polymer electrochromics in the visible, IR and microwave regions

Conducting polymers (CPs) display strong electrochromism across the visible, near-IR (NIR), IR and even microwave spectral regions. Applications range from military to space. However, a fundamental understanding of the phenomena behind this electrochromism, the charge carrier(s) responsible, and the relation of nanoscopic morphology and electrochemical properties to the electrochromism, still remains lacking. This paper takes a first step at such a correlation, mining a wealth of data accumulated over the course of many years by our group. Expected findings are that certain population states contribute predominantly to certain spectral regions (e.g. bipolaron states to the IR, the valence band to the visible and other mid-gap states to the microwave). Among more specific findings, a prominent 7 μm (0.16 eV) peak in LWIR devices is ascribed to bipolarons, whilst a low-energy transition at 0.054 eV is ascribed to inter/intra-chain transitions. Other findings point to the potential design of very broad-band electrochromic systems encompassing the visible through microwave regions.