Hierarchically Porous Polyaniline Film via Interfacial Self-Assembly for Ultrafast Dual-Band Electrochromic Smart Window

Abstract Dual-band electrochromic smart windows, capable of independently regulating visible and near-infrared solar radiation, offer an effective route toward reducing building/vehicle energy consumption. However, their practical implementation is often limited by slow switching kinetics, insufficient bistability, as well as challenges in fabricating polychromatic, uniform, and scalable electrochromic films with efficient ion and charge transport. Here, we report an interfacial self-assembly strategy to fabricate large-area polyaniline (PANI) thin films featuring a hierarchically porous architecture and thickness-dependent porosity gradient. The self-assembly process, driven by solvent exchange at the air–water interface and modulated by surfactant confinement, produces interconnected PANI nanoparticle networks with both in-plane hierarchical pores and out-of-plane structural gradation. This architecture facilitates electrolyte penetration and charge transport across the film thickness. As a result, the PANI films enable rapid and stable dual-band electrochromic modulation, exhibiting three distinct optical states (“bright”, “cool”, and “dark”) with independent control of visible and near-infrared transmittance. The assembled devices demonstrate fast response (coloration/bleaching times of 1.8/4 s at 633 nm and 1.2/3.6 s at 1200 nm), high coloration efficiency, and excellent optical bistability, together with effective indoor thermal regulation. These results establish interfacial self-assembly as a versatile approach for engineering functional polymer films for next-generation energy-efficient smart windows.