Low Solar Absorptance, High Emittance Performance Thermochromic VO2-Based Smart Radiator Device

Thermochromic vanadium dioxide (VO2)-based smart radiator devices (SRDs) display emittance variation with changes in temperature, making them very promising for energy-efficient thermal control of spacecrafts in general, and nanosatellites in particular. However, the high solar absorptance of the VO2-based SRDs remains too high for their intended application. Based on an approach combining optical simulation and experimental work, I demonstrate that an additional top stack layer alternating between high and low refractive indices made of a-Si(25 nm)/SiO2(67 nm) reduces the solar absorptance of a VO2-based SRD by 35% (from 0.43 to 0.28) while keeping the emittance performance of the SRD within the requirements for the intended application (low-temperature emittance epsilon(L) = 0.35, high-temperature emittance epsilon(H) = 0.81 and emittance tuneability with temperature delta epsilon = 0.46). I also discuss factors to consider while designing additional top stack layers alternating between high and low refractive indices to further decrease the SRD's solar absorptance without affecting its emittance performance.