The chemical potential of light in fluorescent solar collectors

The energetic aspect, discussed by the means of the chemical potential, involved into the absorption and radiation processes occurring in the operation of fluorescent solar collectors is of interest in this publication. The chemical potential of the fluorescent light incident on the solar cell is characterized by studying the fluorescence spectrum emitted by a special type of fluorescent collector, where absorption and fluorescence take place in a liquid medium, in effect a liquid fluorescent collector. It is shown that photon reabsorption (known also as photon recycling) gradually brings the emitted photon flux into thermal equilibrium with the collector. The fluorescence photon distribution is then characterized by a specific temperature, obtained from the Kennard-Stepanov law, and a chemical potential given by the generalized Planck's law. We find that the chemical potential of the fluorescent light incident on the solar cell is nearly equal to the thermodynamical limits imposed by a detailed balance argument. This equality indicates that nonradiative losses do not affect the chemical potential of the light escaping from the collector, a major benefit in comparison to simple semiconductor based solar cells where nonradiative losses significantly affect the open circuit voltage.