Improving the thermochromic performance of VO2 films by embedding Cu-Al nanoparticles as heterogeneous nucleation cores in the VO2/VO2 bilayer structure

VO₂-based films show great potential applications in thermochromic smart windows. However, enhancing luminous transmittance (T_lum) while maintaining high solar modulation ability (ΔT_sol) remains a formidable challenge. Here, we present a novel VO₂/Cu-Al nanoparticles (NPs)/VO₂ composite film structure, seamlessly integrating Cu-Al bimetallic NPs within VO₂ films by pulsed laser deposition on alkali-free glass substrates. The content of Cu-Al NPs in the composite films is controlled by the pulse number (N_p) applied to the Cu-Al alloy target. X-ray diffraction results indicate that the crystallinity of VO₂ films is significantly enhanced by the incorporation of an appropriate amount of Cu-Al NPs. The SEM characterization results revealed that the particle size of VO₂ composite films initially increases to approximately 131 nm and subsequently decreases to around 120 nm as N_p increases, with a concurrent transition in particle shape from quasi-circular to elongated. The T_lum and ΔT_sol of the resulting composite films were dramatically improved to 71.6 % and 9.5 %, respectively, when N_p was 300. These enhanced thermochromic properties are attributed to the localized surface plasmon resonance (LSPR) of the VO₂ particles. This research opens up a promising avenue for the convenient production of customized high-quality VO₂ films tailored for smart window applications.