Analysis of design parameters for wavelength selective holographic solar concentrators

This paper presents a detailed discussion on optimization of design parameters of thick phase holographic lenses to achieve wavelength selective concentrating system. Such lenses perform the dual function of dispersion and focusing and thus can be used for filtering out the unwanted portion of the solar spectrum. The present investigation reveal that design parameters such as refractive index modulation (n1), depth of the film(d) and fringe spacing(∧) can be optimized to fabricate holo-concentrators exhibiting maximum efficiency over desired wavelength range to match with a solar cell of given band gap. It has been shown that we can achieve broad band filter for n1 = 0.095, ∧ = 0.8696 ¼m and d = 4¼m having appreciable diffraction efficiency over the wavelength range of about 0.6 ¼m to 1.5 ¼m. Also, for n1 = 0.09, ∧ = 0.8696 ¼m and d = 12¼m we may achieve narrow filter that allows mainly wavelengths of around 0.7 to 0.9 ¼m to diffract through it with high diffraction efficiency.