Abstract

The efficiency of hybrid photothermal/photovoltaic (PT/PV) energy conversion can be increased by separating the solar spectrum into portions matched to the PT and PV processes. Thin-film multilayer filters can implement this concept; five such filters consisting of all-dielectric or metal-dielectric layers have been designed. Three of the five are based on conventional symmetric period, induced transmission, and metal-dielectric filter designs; they transmit the most effective wavelengths, 0.68–0.95 μm, for PV conversion based on silicon cells, and reflect the remainder to absorbers in a PT loop. The other two designs, a simple high reflectance filter and an optical minus filter, perform the inverse function, reflecting the optimum PV photons and transmitting the balance. The transmission profile of each design has been computed, considering dispersion, absorption, and angle of incidence effects. These profiles are compared and evaluated with respect to the desired spectral performance. The most successful candidate design is an optical minus filter consisting of films of TiO₂, ZrO₂, and SiO₂. Results show very sharp selection of the targeted PV spectral region and low ripple in the transmission region outside the bandstop. The main drawback to this design is its sensitivity to high incident angles; half of the bandstop moves out of the prime PV band at a 30° angle.

© 1985 Optical Society of America