Large‐Scale Multifunctional Carbon Nanotube Thin Film as Effective Mid‐Infrared Radiation Modulator with Long‐Term Stability

Abstract Mid‐infrared tunable materials have attracted increasing attention for thermal radiation management in various applications ranging from infrared camouflage to radiative thermoregulation. Functional films based on graphene and carbon nanotubes by electrical gating are promising candidates because of their ultrawide spectral range from visible to terahertz and structural flexibility. However, challenges in practical applications remain, such as short cycle life, rapid performance degradation, and difficulties in the synthesis of large‐scale electrochromic films. In this paper, a scalable strategy to produce large‐scale mid‐infrared electrochromic films with long‐term stability is demonstrated, in which a sandwich‐structured thin film based on multiwalled carbon nanotubes (MWCNTs) is fabricated via a universal roll‐to‐roll process. By ionic liquid gating, the electrochromic films exhibit tunable thermal emissivity from ≈0.15–0.7 and excellent stability with 96% modulation retention over 3500 cycles. This mid‐infrared electromodulation behavior is mainly ascribed to the change in free carrier concentration of few‐walled carbon nanotubes in MWCNT films via a reversible ion‐induced doping process. The electrochromic films are found to enable effective radiative thermal regulation, dependent on tunable thermal emissivity. Moreover, applications in infrared displays for secret communication and infrared camouflage for varied environmental backgrounds are also demonstrated with 10 × 10 multipixel arrays.