Reversibly controlled infrared transparency of conjugated polymer films incorporated into a compact electrochemical...

We demonstrate a reversible control of the mid-infrared (mid-IR) transparency of conjugated polymer films in a compact electrochemical cell structure with planar IR-transparent electrodes. The mid-IR absorbance of up to more than 1.0 is observed when a 1.0 µm thick polythiophene layer is electrochemically doped with an ionic liquid under variable bias voltage. Furthermore, the doping and dedoping processes can be repeated with reproductive absorbance spectra, in contrast to the conventional one-way chemical doping. Our device structure works for actively variable attenuation filters in the mid-IR region and can also be extended potentially to the terahertz region.