The saturated photovoltage of a p-n junction

This paper explores the relationship between the energy-gap voltage of a p-n junction and the saturation value of the open-circuit photovoltage produced by high-intensity illumination. It is shown that high excess-carrier concentrations in the quasi-neutral regions are accompanied by significant open-circuit drops in the quasi-Fermi voltages of both carriers in these regions. When these drops are accounted for, the open-circuit photovoltage is found to be less than the split between the quasi-Fermi voltages in the space-charge layer (which split is approximately equal to the energy-gap voltage) by an amount which depends on the ratio of the mobilities of the two carriers. This approximate theory reconciles the apparent inconsistencies in previously reported measurements of the saturated photovoltages of silicon and gallium-arsenide p-n junctions.