Angular confinement and concentration in photovoltaic converters

For a solar cell in the radiative limit there is an imbalance between the angular spreading of incident and emitted radiation. This imbalance is one reason for the generation of entropy in a solar cell and shall be called optical entropy. The generation of entropy reduces the maximum efficiency of a solar cell. In case of a silicon solar cell, the maximum efficiency is reduced from 42% to 31% because of the generation of optical entropy. Various techniques exist to influence the different entropic factors. The angular spreading of incident light is changed by concentration, e.g. with lenses, while the angular spreading of emitted radiation is changed by angular confinement, e.g. with angularly selective filters. In this work we show the relationship between these techniques, how they influence the solar cell efficiency limit and how angular confinement and concentration can be combined to minimize the aforementioned losses.