Built‐In Electric Field‐Assisted Polyaniline for Boosting Dual‐Band Electrochromic Smart Windows with Multicolor Displays and Four‐Mode Conversion

Abstract Dual‐band electrochromic smart windows (DESWs) can selectively adjust the transmittance of visible (VIS) and near‐infrared (NIR) light, significantly reducing building energy consumption. However, current DESWs face challenges in achieving multi‐color control and fully independent modulation of VIS and NIR light. Herein, a DESW with multi‐color display capabilities and four distinct operational modes is presented, achieved by utilizing polyaniline (PANI) in combination with a built‐in electric field. The electric field, formed at the interface between Au and PANI, enhances the transport speed of ions and electrons during the electrochromic (EC) process, facilitating electronic transitions between polarons, bipolarons, and quinonoid units. This improvement significantly enhances the EC performance of the Au/PANI Schottky junction films compared to pure PANI films. The enhanced performance not only expands the control modes from three to four, but also provides faster response times (τ _c /τ _b = 1.1/5.4 s at 1600 nm, τ _c /τ _b = 0.9/1.3 s at 633 nm) and superior cycle stability. Additionally, a large‐scale (5 × 5 cm ² ) device is demonstrated, effectively controlling both temperature and light flux. The incorporation of the built‐in electric field accelerates electron and ion transfer, providing a promising strategy for developing high‐performance DESW applications in energy‐efficient buildings.