Theory of solar cells incorporating impurity gradients

This paper discusses the theory of solar cells incorporating impurity gradients as a potential means of improving the efficiency. Both abrupt changes in doping as at high-low junctions and gradual changes resulting in drift fields have been considered. The advantages of high-low junctions have been demonstrated both theoretically and experimentally for silicon cells where the minority carrier diffusion length is larger than the cell thickness. Predicted advantages of other drift fields have not been clearly demonstrated. It appears that the advantages of drift fields throughout the device in enhanced carrier collection efficiency are largely offset by reduced open circuit voltages and/or reduced curve factors.