THE CARNOT FACTOR IN SOLAR-CELL THEORY

In a two-level system the open circuit voltage or difference between the electro-chemical potentials at the contacts, is related to the energy gap E g by a Carnot factor; V=(1−T s /T p )E g . Here, T s and T p are the absolute temperatures of the ambient (surroundings) and of the incident black-body radiation (“pump”), respectively. A simple two-step statistical thermodynamic argument is given here which makes this result plausible. Its standing in a more general context is also discussed.