Robust, Fast Switching, Black Electrochromic Windows Based on Transparent Mixed Conductor n-Doped Poly(Benzodifurandione) (n-PBDF)

Organic electrochromic (EC) requires efficient ion/electron transport and coupling in thin-film electrodes. However, most soft organic EC materials, despite relatively high ionic conductivity and solubility derived from sidechains, have low electronic conductivity, causing uneven coloration, delayed redox reactions, and reduced electrochemical stability. Achieving deep colors like black requires thicker electrodes, which diminishes ion/electron transport, reducing overall device efficiency and durability. Herein, we present an n-doped poly(benzodifurandione) (n-PBDF) redox electrode that functions as a black EC active layer with high electronic/ionic conductivity and efficient ion-electron coupling. To overcome the solvent incompatibility and processing limitations of sidechain-free n-PBDF colloids, we develop an on-demand eco-friendly ink formulation, combined with ultrasonic spray-coating to achieve uniform and scalable film deposition at low temperatures. The n-PBDF redox electrodes, due to their microstructural properties, offer enhanced ionic diffusion and stability, maintaining performance even under harsh environmental conditions. This extends the application potential of functional EC devices, such as smart windows, and suggests promising avenues for sustainable advancements in organic electrochemical materials and their scalable processes.