Flexible composite film utilizing VO2 self-adaptive photothermal and infrared radiative cooling for continuous energy harvesting

Self-adaptive photothermal (PT) and radiative cooling (RC) based on insulation-metal phase transition vanadium dioxide (VO 2 ) are among the most promising continuous energy harvesting technologies recently. However, previous work relies on rigid substrates that cannot fit complex or non-planar surfaces. Here, we propose a flexible composite film by bonding a VO 2 thin film and a polyimide (PI) substrate with polymethyl methacrylate (PMMA), which achieves efficient spectrally self-adaptive broadband absorption/emission and can convert between the daytime PT mode and nighttime RC mode. Because of the inherent absorption of VO 2 and the intricate interplay within multi-layer structure, the solar absorptance of the film could to up to 0.886 in the PT mode with the incorporation of an Al 2 O 3 anti-reflection layer. On the other hand, due to the phase change properties of VO 2 , this film exhibits a broadband infrared emissivity modulation from 0.32 to 0.82 and reaches a maximum RC power of approximately 244.59 W/m 2 in the RC mode at night. Moreover, the film maintains the infrared spectrum switching capability and high emissivity in RC mode even after 10 4 bending cycles. Our work shows potential to broaden the applications of VO 2 smart coatings, including tunable selective emitters, thermal management of spacecraft and smart skins.