High‐Performance Electrochromic Smart Window for Energy‐Saving Applications Based on WO ₃ and Polycarbazole

ABSTRACT Electrochromic technology has garnered significant attention for smart windows due to its dynamic solar regulation capability. However, current implementations suffer from limitations such as low optical contrast, slow switching speed, and poor cycling stability. This study addresses these challenges by designing a bipolar electrochromic architecture combining thermally‐cured WO 3 and alkoxy‐functionalized polycarbazole derivatives (CTPAO1 and CTPAO3). The optimized ECD2 (based on WO 3 and CTPAO3) achieves a comprehensive contrast of 77.4% (200–2350 nm) with a peak modulation of 87.5% at 730 nm. The device exhibits outstanding cycling stability, retaining 95% of its optical contrast after 20 000 cycles. Notably, benefiting from efficient ion transport pathways, it also shows excellent switching kinetics with a coloration time of 1.0 s and a bleaching time of 0.7 s. Building energy efficiency simulations predict that smart windows incorporating ECD2 can achieve total annual energy savings ranging from 13.1% to 50.8% across five climate zones in China. The energy‐saving effect is particularly significant in Haikou, with an estimated annual saving of 56.5 kW h/m 2 . This work provides a feasible solution for high‐performance, energy‐efficient electrochromic smart windows.