Mild Solution-Based Processing of Zn(OH)_2 Nano-Arrays on Thermochromic VO_2 Films: Improved Optical and Hydrophobic Properties

摘要

Nano-structured honeycomb-like Zn(OH)_2 arrays, which consisted of vertically standing Zn(OH)_2 walls, were deposited onto thermochromic VO_2 films using a mild solution process. The thermochromic VO_2 film, which was in a chemically unstable state against pH and temperature under ambient atmosphere, survived almost entirely during the Zn(OH)_2 deposition process. Further analyses revealed that the Zn(OH)_2 nano-arrays reduced the mismatch in the refractive indices at the air-VO_2 film interface as a broadband antireflection coating, which effectively improved the optical performance of the VO_2 films (luminous reflection was improved from 25.8% to 16.1%; luminous transmittance was improved from 32.3% to 37.2%; and solar switching ability was improved from 13.0% to 15.6%). The Zn(OH)_2 nano-arrays simultaneously demonstrated enhanced hydrophobic properties (the water contact angles increased from 46.5° to 144.3°) because of their high surface roughness/porosity. These features advance the application of VO_2 in self-cleaning smart windows.