Strong barrier effect on the conversion efficiency of solar cells with buried type-II quantum dots

Abstract

A model of a quantum dot (QD) buried solar cell is described. The cell takes advantage of the generation of an additional photocurrent by a two-photon excitation of electrons from the valence band into the conduction band via the confined (intermediate) state. Since the intermediate states are active recombination centres suppressing the open-circuit voltage and the conversion efficiency either by increasing the dark-current or by arresting the quasi-Fermi level of mobile carriers, a barrier layer promoting the separation of the quasi-Fermi levels is built in around the QDs. Conditions for the separation of the quasi-Fermi levels and the activation of the two-photon generation of mobile carriers were found. Under these conditions the photocurrent and the conversion efficiency of the Ge QD buried Si solar cell exposed to concentrated sunlight must be approximately 25% larger than that of conventional Si solar cells.