Combination of angular selective photonic structure and concentrating solar cell system

One possibility to achieve higher efficiencies in solar cell systems is to integrate angularly selective photonic filters in order to decrease radiative losses. Thermodynamically, the use of an angularly selective filter and a concentrator are equivalent. In both cases the efficiency of solar cells is increased by a manipulation of the ratio of the solid angles from which light is received and into which light is emitted. This ratio enters the equation to calculate entropic losses connected to étendue: The larger this ratio gets, the lower the entropic losses will be and the higher is the potential efficiency of the solar cell system. The difference between concentration and angular confinement is the angle which is affected. In concentrating systems the angle of incidence is increased, whereas in angularly confined systems the angle of emission is decreased. Maximum efficiency is reached, if both angles are equal. Of course the angle of emission cannot get smaller than the angle of incidence. To achieve the highest efficiencies, both systems can be combined. For this reason a solar cell system that combines concentration and angular confinement is investigated and discussed. For a GaAs solar cell system, as it is assumed for the calculations, the Shockley-Queisser efficiencylimit with a perfect angular confinement is 41.71%, whereas in a system without any confinement the limit is 32.5%. Starting with this system, modified Bragg and quasi-Rugate filters are considered to approximate a realistic efficiency enhancement using real filters in a concentrator solar cell system