Fermi degeneracy and its effects on the open-circuit voltage of silicon solar cells

Abstract

A theoretical explanation of the high open-circuit voltage (Voc) in n+-p silicon solar cells despite the heavy doping effects (such as Auger recombination and rigid band-gap narrowing) is given. It is shown that, contrary to recent expectations, when the surface impurity concentration is Ns ≥2×1020 cm−3 the open-circuit voltage is approximately the same as that for surface passivated cells with Ns ≤2×1019 cm−3. Furthermore, in the case of high values of Ns the open-circuit voltage becomes almost independent of the surface recombination velocity. Our model shows that these facts are due to the Fermi degeneracy and the internal electric field. Therefore, high concentrations of activated donors should be looked forward to for obtaining high-efficiency n+-p solar cells.