Effects of Fermi degeneracy on the open circuit voltage of silicon solar cells

A theoretical explanation is given for the high open-circuit voltage which n⁺-p silicon solar cells have despite bandgap shrinkage and surface recombination effects. It is shown that a high open-circuit voltage can be obtained when the surface donor concentration (N_s) is larger than 10²⁰ cm^-3, and that it becomes almost independent of the surface recombination rate when N_s is even higher. The proposed model shows that all of these phenomena are caused by the electron Fermi degeneracy and the electric field in the emitter of solar cells. Therefore, high surface donor concentrations should cause better efficiencies for silicon solar cells when other parameters such as base resistivity and junction depth have been optimized.