Optical Constants of Vanadium Dioxide Films and Design of a Solar Energy Control Window

Abstract

We determined the optical constants of a vanadium dioxide (VO2) thermochromic film deposited on glass substrate by ellipsometry in wavelength range from 380 nm to 1700 nm. The optical constants were employed to design the optimal stacked thin film structure for smart windows which control the solar radiation and heat transmission from the viewpoint of high luminous transmission.

Bifunctional Template-Induced VO2@SiO2 Dual-Shelled Hollow Nanosphere-Based Coatings for Smart Windows

“…Unfortunately, it was difficult to measure the optical constants of bare VO 2 coating by ellipsometry probably because of the sever aggregation of disorder-arrayed nanoparticles. 45 Comparing with the bare VO 2 (RI ≈ 2.5 at 600 nm) reported by previous literatures, 28,46 the RI of VO 2 @SiO 2 DSHNs coatings obtained in the current work show dramatic reduction, and reached 1.63 at the wavelength of 630 nm, which is closer to the ideal one, imbuing the coating with a better AR effect. Furthermore, we fitted the transmittance spectra at low temperature by finite-different time-domain (FDTD) using the measured optical constants (Figure 4b).…”

Photothermal Characterization of Thermochromic Materials for Tunable Thermal Devices

“…(a) First, we calculated the average optical constants of vanadium dioxide, far from the SMT, in both the semiconductor state (at 30 • C), and in the metallic state (at 90 • C) by the simultaneous fit of the transmittance (T r ) and the front and rear reflectances (R f , and R r ), assuming that the silicon refractive index is n Si = 3.43, Although this method is rather inaccurate to retrieve the refractive index for nanolayers, with respect to ellipsometry, the best fit values found for the semiconductor phase (n S + ik S = 2.7 + i0.04), and for the metallic phase (n M + ik M = 2.9 + i4.8) are in agreement with the wide range of values reported in the literature for (2 µm to 3 µm) [19][20][21][22][23][24][25][26] depending on the different fabrication process (for rf sputtering Tazawa et al [24] found n M + ik M = 2.8 + i4.4). It is worth noting that our values were retrieved without using any effective medium approximation to simulate the surface roughness or [22,27].…”

VO2-based double-layered films for smart windows: Optical design, all-solution preparation and improved properties

“…DT lum is caused by the different RIs of VO 2 films at 20 and 90 1C, which influences the value and the position of reflectance minima. Simply, the RI of VO 2 films at 20 1C is a little higher than that at 90 1C [31]. The reflectance minima at 20 1C appears at a longer wavelength than that at 90 1C according to the simplified model mentioned above, resulting in the DT lum difference at 20 and 90 1C.…”

“…For these simulations, the optical constants of gas-phase VO 2 and a quartz glass substrate were derived from Refs. [31,32]. Different film structures were simulated and compared with experiment results.…”

“…For this purpose, a simplified model was evaluated using low-temperature RI of gas-phase reaction VO 2 thin films at 560 nm. Optical constants of gas-phase reaction VO 2 [31] were used to verify this simplified model. Specially, VO 2 spectral reflectance was simulated using a fixed RI of 3.14 at 560 nm and wavelength-dependent optical constants for a VO 2 film obtained from the gas-phase reaction.…”