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

An all-solution process was developed to prepare VO2-based double-layered films containing SiO2 and TiO2 antireflection layers. These double-layered films were optimized to improve luminous transmittance (Tlum) and switching efficiency (ΔTsol). The substrate/VO2/TiO2 double-layered structure showed the largest improvement of 21.2% in Tlum (from 40.3% to 61.5%). Tlum could be further improved to the maximum of 84.8% by combining film thickness optimization and antireflection layer deposition. ΔTsol (usually below 10% for single VO2 films) could be improved by adjusting the position of antireflection peaks (the highest ΔTsol was 15.1%). A sample with balanced Tlum and ΔTsol showed Tlum of about 58% (20 °C) and 54% (90 °C), and ΔTsol of 10.9%. This work is an important technical breakthrough toward the practical application of VO2-based smart windows.