All-Solution-Processed Mid-Infrared Electrochromics (ASPIRE) for Thermoregulation with Arbitrary Curvatures

Mid-infrared (mid-IR) electrochromism is a promising technology that enables new ways to control radiative heat, which is particularly crucial for applications such as building thermoregulation efficiency, industrial process efficiency, spacecraft thermal engineering, and personal heat management. However, most mid-IR electrochromic devices are fabricated on planar substrates with fixed surface topography. When these planar devices are applied to three-dimensional and arbitrarily curved objects, they cannot fully conform to the objects’ surfaces, leaving an air gap and, thus, substantial thermal contact resistance that significantly compromises the efficacy of radiative thermoregulation. To address this long-standing issue, in this study, we developed a fabrication methodology that enables all-solution-processed electrochromic devices on the surface of arbitrarily curved 3D objects, effectively transforming the object surface into an electrically variable emittance layer. The key components are poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as the active layer and charge storage layer, separated by the heterogeneous mixed ionic-electronic conductor consisting of HNO3-doped carbon nanotubes (CNTs) and crosslinked polyacrylamide (PAM)/lithium chloride (LiCl), all of which conform to the object surface layer-by-layer. The mid-IR electrochromic device exhibits an apparent temperature difference of 6.1 ℃ by adjusting emissivity on the planar substrate and 1.8 ℃ on the curved substrates. Our work demonstrates a promising approach and platform to achieve outward-facing flexible electrochromic cells with broad scientific and technological impacts on light and heat management.