Liquid-Phase Electrochemically Autooxidized Doping of PEDOT Enabling Fabry–Pérot Electrochromic Pixels

Fabry-Pérot (F-P) resonators enhance light-matter interactions and are sought to incorporate stable, flexible poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). However, existing additives for PSS phase separation to enhance conductivity lack the ability to modify optical dielectric properties of PEDOT for augmenting optical resonation. Here, we developed a synergistic strategy that combines electrochemical autooxidized doping with phase separation through simple solution mixing of polyoxometalates. The approach reduces the band gap of PEDOT and significantly enhances the conductivity from 1.03 to 360 S cm^-1. Thus, the F-P resonators extend PEDOT's single blue state to multicolor variations. The autooxidized PEDOT was also employed as the electrochemical active layers for organic electrochemical transistors (OECTs) and electrochromic (EC) F-P array pixels (1 × 1 mm). The OECTs with a 1000-fold on/off ratio can control the color changes of EC pixels with a low gate voltage of only ±0.8 V.