Backbone‐Integrated UV‐Absorbing ECPs: Synergistic UV Shielding and High‐Efficiency Electrochromism for Ultra‐Stable Outdoor ECDs

Electrochromic polymers (ECPs) face significant challenges related to ultraviolet (UV)‐induced degradation in outdoor applications. To address this issue, a molecular engineering strategy is presented that covalently integrates the classical UV absorber 2‐(2H‐benzotriazol‐2‐yl)phenol (BTA) into the conjugated backbone of a thiophene‐based ECP. The resulting optimized polymer, PEBTAF, enables dual functionality: efficient UV‐to‐thermal energy conversion and enhanced electrochromic performance. PEBTAF exhibits rapid switching time (2.79 s), high coloration efficiency (732.06 cm 2 /C), and excellent cycling stability (>10,158 cycles). Crucially, under intense UV irradiation (365 nm, 35 min), PEBTAF retains 85% of its optical contrast—more than double that of conventional electrochromic polymers. Femtosecond transient absorption spectroscopy reveals that incorporating BTA extends the excited‐state lifetime, facilitates charge transport, and enhances photothermal conversion, while simultaneously suppressing UV‐induced radical formation. This work overcomes the long‐standing trade‐off between environmental durability and electrochromic functionality, offering a promising pathway toward long‐lasting smart windows and adaptive camouflage technologies.