“Dark-to-Warm” Smart Windows Enabled by Black-to-Black Electrochromic Copolymers with Minimal Visible and Remarkable NIR Modulation

Conducting polymers, despite their promising electrochromic properties, face limitations in smart windows due to their inverse modulation in visible and near-infrared (NIR) regions. In this study, we introduce novel “black-to-black” electrochromic copolymers, synthesized through direct arylation polymerization (DArP) of tris(thienothiophene) (TTT), 3,4-dialkylthiophene (DKTh), and benzo[c][1,2,5]thiadiazole (Tz) monomers. These copolymers demonstrate minimal visible impact (<5%) and broad NIR modulation (>60%). The resulting electrochromic devices seamlessly transition between “Warm” mode (low visible and high NIR transmittance) and “Dark” mode (low visible and NIR transmittance), showcasing high switching stability, open-circuit memory, and coloration efficiency. The synthesized copolymers and devices surpass conventional “color-to-transmissive” conducting polymers, exhibiting significant solar heat gain coefficient (SHGC) modulation and high optical contrast. This discovery prompts further exploration of dual-band electrochromic materials, particularly those featuring a “Warm” mode based on conducting polymers.