Roll‐to‐Roll Processable EC/TC Hybrid Smart Windows Driven by a Bidirectional Dual‐Chromic Polymer Electrolyte

ABSTRACT Smart windows are a promising technology for reducing building energy consumption by dynamically regulating solar transmittance. The integration of thermochromic (TC) and electrochromic (EC) functionalities into a single device offers an effective strategy for realizing multifunctional smart windows and adaptive optical systems. Here, we report a dual chromic polymer electrolyte (DCPE) that simultaneously serves as an ionic conductor and a bidirectional thermochromic medium. Moreover, incorporation HPMC into the DCPE enhances thermal stability by limiting water loss, while optimizing the ion storage layer (ISL) improves electrochromic performance via increased ion storage and coloration efficiency (308.65 cm 2 C − 1 ). The EC/TC hybrid film demonstrates the highest durability, maintaining stable thermochromic cycling for over 200 cycles and electrochromic cycling for 10,000 cycles. Tunable solar modulation is achieved, with ΔT sol ranging from 15.18% under EC only operation to 43.09% under simultaneous EC and TC activation. Using roll‐to‐roll (R2R) coating, large‐area PEDOT:PSS and WO 3 films are fabricated with high uniformity, enabling EC/TC devices up to 750 × 600 mm that maintain fast switching (<90 s) and strong heat‐blocking performance (10–14°C temperature reduction, η thermal = 50–80%) under both IR‐simulated and outdoor conditions. This work establishes a practical strategy for large‐area, energy‐efficient smart‐window applications.