High-quality VO2 thin films sputter-deposited on borosilicate glass substrates for modulating solar transmission and thermal emission

M1-phase VO2 exhibits a reversible phase transition between the insulating and metallic states at T = similar to 341 K, and VO2-based smart windows have been extensively studied. The smart window application requires the growth of high-quality VO2 films with a large resistivity change and small hysteresis width (Delta T) on glass substrates using a scalable deposition method such as sputtering. However, the polymorphic nature of VO2 makes it challenging to obtain high-quality VO2 films on ordinary window glasses (borosilicate and soda-lime glasses). Thus far, VO2 films sputtered on glass substrates have exhibited resistivity changes of 1.5-2 orders of magnitude and Delta T = 3-19 degrees C. In this study, we show that high-quality VO2 films with a resistivity change of 2.5-3.0 orders of magnitude and Delta T = 2 degrees C can be grown on borosilicate glass substrates via radio-frequency sputtering followed by thermal annealing. The simultaneous achievement of such a large resistivity change and small hysteresis width is highly encouraging not only for smart windows but also for other applications. With respect to the modulation of solar transmission and thermal emission with temperature, the performance levels of the produced VO2 films were 70-75 % of those expected from pure M1-phase VO2 films.