A small-bundle single-wall carbon nanotube electrothermal film for smart windows

• • Small-bundle SWCNT films (average bundle diameter 7.1 nm) achieve 26 Ω/□ sheet resistance at 82% transmittance, outperforming large-bundle counterparts by enabling higher areal nanotube density and more efficient conductive paths at equivalent optical transparency; this directly addresses the transparency–conductivity trade-off that limits ITO and metal nanowire alternatives. • • The film reaches a stable 102 °C at only 20 V applied voltage, demonstrating low-power electrothermal operation suitable for integration into flexible smart windows and other thermal management systems where energy efficiency and precise temperature control are critical. • • Integration with a PW/PDMS thermochromic layer yields a flexible smart window with a reversible visible transmittance range of 0.17% to 78% and exceptional cycling stability, enabling dynamic transparency control for energy-saving architectural and automotive glazing applications. • • The FCCVD-synthesized small-bundle SWCNT film overcomes the brittleness and high cost of ITO and the oxidation and roughness issues of metal nanowires, offering a scalable, flexible, and stable transparent heater platform for next-generation curved and wearable electronics.