All-in-One Complementary Electrochromism for Ultra-Stable Broadband Smart Windows

We report a broadband, high-contrast electrochromic system based on two newly designed triphenylamine (TPA) derivatives, NMTPDA and MMTPDA, bearing electron-withdrawing and electron-donating substituents. These substituents modulate the HOMO-LUMO energy levels and stabilize oxidized radical cations, enabling efficient charge transfer and spectral tuning. Together with ethyl viologen, the materials were integrated into a monolithic liquid-phase electrolyte to construct a complementary anodic-cathodic electrochromic device. This "all-in-one" architecture minimizes interfacial resistance and supports multistep redox transitions, enabling broadband visible-to-NIR modulation. The devices exhibit up to 93.8% optical contrast, fast switching times, and excellent cycling stability (0.77% degradation after 14,000 cycles). Stabilized ion-pairing (CIP/SIP) structures contribute to long-term durability. Infrared imaging and DeST-based energy simulations demonstrate that smart windows employing these devices achieve up to 3.8 °C cooling and annual energy savings of 13.76 kWh m^-2. These benefits stem from synergistic optical filtering and thermal shielding. This work offers an integrated strategy spanning molecular design, device engineering, and building energy modeling for next-generation smart windows.