Thermally Crosslinked Triphenylamine-Fluorene Conjugated Polymers: A Strategy for Stable and Efficient Electrochromic Materials.

A series of thermally crosslinkable triphenylamine-fluorene conjugated polymers (MeVb1, MeVb2, and MeVb3) with varying crosslinking densities are synthesized and systematically studied. Upon thermal crosslinking, these polymers exhibit enhanced solvent resistance and uniform film morphology. All films demonstrate stable electrochromic behavior, with tunable color transitions from transmissive yellow to deeper color. All-solid-state electrochromic devices incorporating these polymers and WO₃ exhibit excellent reversibility. Among them, the MeVb3-X-based device, which has the highest crosslinking density, achieves the best solvent resistance and a high optical contrast (ΔT%) of 61.3% at 900 nm, fast switching speeds (3.3 s for coloration and 1.7 s for bleaching), and high coloration efficiency (up to 296.2 cm² C^-1). Furthermore, it demonstrates good cyclic stability, maintaining 90% of its initial contrast after 1000 cycles. These results highlight the potential of thermally crosslinked conjugated polymers as highly stable and efficient electrochromic materials, making them promising candidates for practical electrochromic applications.