Development and Analysis of Tungsten Thin film Coating for Solar Absorption

Abstract

Tungsten thin film has the potential for application in the field of solar thermal multi-layer coating due to its high solar absorption, low thermal emittance, superior thermal stability and diffusion barrier characteristics. Magnetron sputtered tungsten thin films are ideally suited for absorber coating and IR reflectors in solar selective coatings for solar thermal application. Tungsten thin films were coated on glass and stainless steel substrate using DC magnetron sputtering process in argon atmosphere. The effect of power density on coating microstructure, mechanical and optical properties has been presented in this paper by varying DC power from 0.6kw to 2kw. Coating deposited with 0.6 kW at room temperature, had finer microstructure (<10nm) and lower surface roughness (Ra<2nm) compared to the coating deposited with 2 kW. X-ray analysis of these coatings revealed the confirmation of tungsten deposition. Influence of mechanical thickness and varying applied power were analysed using UV-Vis-NIR spectrophotometer, 410-Solar and ET-100 reflectometer for absorptance (α) and thermal emittance (ε) values. Deposition with high power density at 2kw shows that the reflection in IR region is more compared to that of deposition at 0.6kw, hence emittance is around 0.07 and 0.16 respectively. The simulation and experimental responses of 50nm to 600 nm thick tungsten thin films deposited at RT in the wavelength range of 250-1500 nm were similar. The optimized results were used to determine the suitable condition for IR reflective layer and solar absorption for solar thermal component.