Unified model of fundamental limitations on the performance of silicon solar cells

Previous attempts to explain the substantial discrepancy between observed and predicted efficiencies in silicon solar cells are shown to have treated inadequately two important features of typical devices: 1) In the diffused region the electric-field distribution is much wider than generally believed and the field values away from the junction are generally higher; 2) Auger processes in heavily doped regions have a more pervasive impact than has been recognized. By incorporating a suitable modification of the junction model and a consistent treatment of Auger effects into the analysis, a unified model is developed for the principal limitations on the performance of Si solar cells. This model accounts for limits to I
sc
and V
oc
arising in either the front or base region. The present analysis reinterprets the "violet-cell" observations of the effect of the diffusion profile and presents an alternative to the bandgap-narrowing model of the heavy-doping effect on V
oc
. A new method is developed for evaluating the junction saturation current in heavily doped regions of such solar cells and transistor emitters.