Regulating surface morphology and thermochromic properties of VO2 films by Cu-Ag bimetallic nanoparticles

For decades, the synchronous improvements of solar modulation ability (ΔTsol) and luminous transmittance (Tlum) has always been a challenge for VO2-based smart windows. In this research, Cu-Ag bimetallic nanoparticles (Cu-Ag NPs) were embedded into VO2/VO2 bilayer films by pulsed laser deposition. The effects of Cu-Ag NPs on crystal quality, surface morphology and optical properties of VO2 film were investigated. The results showed that the intensity of localized surface plasmon resonance (LSPR) effect could be adjusted by changing the number of laser pulses during Cu-Ag NPs deposition process. SEM and EDS characterization further suggested that Cu-Ag NPs preferred to nucleate at the "concave" formed by several VO2 grains. Compared with VO2/VO2 bilayer film (ΔTsol = 8.1%, Tlum = 40.0%), VO2/Cu-Ag NPs/VO2 composite film showed excellent energy saving performance, the ΔTsol and Tlum were further improved to 10.6% and 55.7%, respectively. In addition, the finite-difference time-domain simulations revealed that the improvements of thermochromic properties could be attributed to the LSPR effect induced by the unevenly distributed VO2 nanoparticles. The results in this work confirmed that the existence of the irregular Cu-Ag NPs could both improve the crystallinity and regulate the grain shape of VO2 films, which is an effective way to enhance the performance of VO2 smart windows.