NiCr-MgF2 spectrally selective solar absorber with ultra-high solar absorptance and low thermal emittance

摘要

NiCr-MgF2 spectrally selective solar absorber, which consists of the tandem films of Au, high-metal-volume-fraction (HMVF) NiCr-MgF2, low-metal-volume-fraction (LMVF) NiCr-MgF2 and MgF2, is designed and fabricated for ultra-high solar absorptance and low thermal emittance. The performance of Au/NiCr-MgF2 (HMVF)/NiCr-MgF2 (LMVF)/MgF2 is simulated using the effective medium theory and film matrix method, and the optimized NiCr-MgF2 spectrally selective solar absorber has a normal solar absorptance (alpha(sn)) of 0.981 and a normal thermal emittance (epsilon(n)) of 0.042 at 25 degrees C. The tandem films of Au/NiCr-MgF2 (HMVF)/NiCr-MgF2(LMVF)/MgF2 are fabricated by magnetron sputtering and measured by UV-VIS-IR spectrometer, and it has an ultra-high near normal solar absorptance of alpha(sn) = 0.976 and a low near normal thermal emittance of epsilon(n) = 0.045 at 25 degrees C, which approaches very closely to the simulated limit. Furthermore, NiCr-MgF2 spectrally selective solar absorber allows a wide incident angle (theta) with its angular solar absorptance a(s)(theta)>= 0.957 and angular thermal emittance epsilon(theta)<= 0.054 if theta <= 50 degrees. Such spectrally selective solar absorber is an outstanding candidate for solar thermal applications.