  Extraction of charge carriers from a hot carrier solar cell using energy
selective contacts, and the impact on limiting power conversion efficiency is
analyzed. It is shown that assuming isentropic conversion of carrier heat into
voltage implies zero power output at all operating points. Under conditions of
power output, lower voltages than in the isentropic case are obtained due to
the irreversible entropy increase associated with carrier flow. This lowers the
limiting power conversion efficiency of a hot carrier solar cell.
