Large-Area Polyaniline/Carbon Nanotube Composite Film for the Zn-Ion Electrochromic Window toward Energy-Sustainable Buildings

Abstract Polyaniline (PANI) holds promise as cathode material for energy-saving electrochromic windows due to its reversible optical modulation and intrinsic energy storage capability. However, the simultaneous realization of large-area electrode fabrication, high electrochromic performance, and superior energy storage remains a key challenge for PANI-based electrochromic windows. Herein, we report a scalable and facile approach to fabricate a PANI/carbon nanotube (CNT)/PANI composite film on transparent conductive glass through combination of chemical oxidation polymerization and spray coating. The introduction of a CNT interlayer, low-temperature polymerization of PANI, and dual-cathode design collectively endows the hybrid structure with enhanced electrical conductivity, accelerated ion diffusion, and increased active sites. The resulting Zn-ion electrochromic device delivers a high optical modulation of 82.3% at 650 nm, a low coloration transmittance of 5.4%, fast switching speeds (coloration/bleaching time: 5.8 s/4.6 s), and a neutral tint in the colored state. Notably, the device also exhibits attractive energy storage performance with a specific capacitance of 45.6 mF cm–2 and an energy density of 12.4 μWh cm–2. Under simulated solar irradiation, the electrochromic window achieves an optical power modulation of 67.3% and enables a temperature regulation of 6.6 °C by switching between transparent and colored states. As a proof of concept, a large-area prototype (10 × 10 cm2) demonstrating uniform color change and good adhesive stability is presented. This work provides a scalable and effective route toward high-performance, conducting polymer-based electrochromic windows for intelligent thermal management and on-site energy recovery, contributing to sustainable energy utilization and building energy efficiency.