Simulations and experimental studies of thermochromic performances of multilayered VO2 nanocone array for energy-saving smart window applications

Abstract

In this work, VO2 parabolic nanocone array (PNA) was studied. Using the idealized geometry of truncated nanocone array (TNA), simulations demonstrated that VO2 TNA with the low and graded effective refractive index could greatly increase the luminous transmittance (Tlum) compared to VO2 film. Meanwhile, isolated VO2 nanocones with rutile phase could improve the solar modulation (ΔTsol) due to LSPR-enhanced absorption. Experimentally, the single-layered VO2 PNA, fabricated by annealing as-deposited V films with thicknesses of 6, 9 and 12 nm, exhibited ultrahigh Tlum, and multilayered VO2 PNAs were fabricated to improve ΔTsol with slight decrease in Tlum. For film thickness of 6 nm, ΔTsol of multilayered VO2 PNA could be improved from 4.9 % to 23.1 % by adding the layer number from one to eight, while Tlum decreased from 96.6 % to 75.8 %. For film thickness of 9 nm, three-layered VO2 PNA showed the optimum performances of ΔTsol = 16.5 % and Tlum = 78.2 %. By manipulating the size, porosity and layer number of VO2 PNA, thermochromic performances were tunable to achieve the requirements for smart window applications (ΔTsol > 10 % and Tlum > 60 %). In addition, multilayered VO2 PNA displayed the suitable pale-yellow color for actual applications. Thus, multilayered VO2 PNA could be a potential nanostructure for energy-saving smart window applications.