Fermi degeneracy and quantum collection efficiency in heavily doped silicon solar cells

The importance of Fermi degeneracy of carriers on the collection efficiency of heavily doped silicon solar cells is shown by means of a simple analytical model. In the calculations, the effects of space-dependent parameters such as mobility, lifetime, and bandgap narrowing and the effect due to Fermi-Dirac statistics for donor concentrations higher than 1×10²⁰ cm^-3 are included. It is shown that for passivated thin emitters, the collection efficiency is high and almost independent of the surface dopant concentration. However, for thick emitters (X_j>2 μm) it is convenient to have small surface-impurity concentrations in order to achieve high collection efficiencies. For nonpassivated solar cells, the collection efficiency should be higher when the surface dopant concentration is high, in conjunction with a small emitter thickness. All of the above confirm that both thin and thick emitter solar cells that attain high conversion efficiencies can be made with an appropriate design