How angular confinement increases the efficiency of photovoltaic systems

Angular confinement is the process of restricting the angular range in which a solar cell emits radiation. To this process several effects are connected of which two shall be discussed here. The first is a light trapping effect; the effective path length of light inside a solar cell is increased. This effect results in an increased absorption and, consequently, an increased quantum efficiency. The second effect concerns the suppression of losses due to radiative recombination. This effect results in an increased efficiency limit which is equal to the Shockley Queisser limit for maximum concentration. Both effects always occur but are differently important for different solar cell systems. In this paper we discuss how angular selectivity can be achieved with photonic filters. We show how angularly selective filters can be used to increase the quantum efficiency of a solar cell and we discuss how the Shockley Queisser limit is influenced by angular confinement.