Ultrahigh Optical Contrast Electrochromic Polymers

Electrochromic materials undergo reversible color changes upon application of an external potential bias. P-type cathodically coloring electrochromic materials absorb in the visible region in the neutral state, and the oxidized state absorbs in the NIR to IR region appearing transmissive by eye. However, the oxidized species exhibit an absorbance tailing into the visible region, thus never reaching a fully transparent state. In this work, we report a new concept for the design of p-type anodically coloring electrochromic polymers. The neutral states of these polymers are UV absorbing and completely transparent in the visible region. The color of the polymer in oxidized state is controlled by tuning the conjugation length. These polymers are mixed to create transparent-to-black electrochromic device. The device exhibits an ultrahigh optical contrast up to 95%, the highest value reported in literature.