Optimization of angularly selective photonic filters for concentrator photovoltaic

To achieve higher efficiencies in solar cells one possibility is to integrate angular selective filters, with the aim of decreasing losses caused by radiative recombination. In fact, thermodynamically, angular selectivity is equivalent to concentration. In both cases the Shockley-Queisser-Limit of solar cells is overcome by manipulating the ratio of incoming and outgoing radiation represented by the angles of incidence and emission. In concentrating systems the angle of incidence is increased, whereas in systems with an angular confinement the angle of emission can be decreased. Another possibility to achieve highest efficiencies is to combine both, concentration and angular confinement. Starting with a given concentrating system, photonic angularly selective filters such as thin film stacks are investigated and optimized for the use in this system. We present results of wave optical simulations of these filters and show some of their characteristics. The goal of this study is, however, not only to optimize optical filters but also to consider the whole system. One approach is to use results from optical simulations as input values for detailed balance simulations of the solar cell. So, the main advantage is, that in fact not the optical characteristics are optimized separately, but rather the whole system is taken into account, which allows predictions of theoretical efficiency enhancement.