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 (T-lum) and switching efficiency (Delta T-sol). The substrate/VO2/TiO2 double-layered structure showed the largest improvement of 21.2% in T-lum (from 40.3% to 61.5%). T-lum, could be further improved to the maximum of 84.8% by combining film thickness optimization and antireflection layer deposition. Delta T-sol, (usually below 10% for single VO2 films) could be improved by adjusting the position of antireflection peaks (the highest Delta T-sol, was 15.1%). A sample with balanced T-lum and Delta T-sol showed T-lum of about 58% (20 degrees C) and 54% (90 degrees C), and Delta T-sol of 10.9%. This work is an important technical breakthrough toward the practical application of VO2-based smart windows. (C) 2011 Elsevier B.V. All rights reserved.