Impact ionization effects on the efficiency of the intermediate band solar cells

The thermodynamic limit of the maximum energy conversion efficiency of an intermediate band solar cell has been calculated taking into account the effect of impact ionization. We developed the calculations of impact ionization effect on the efficiency of the single-gap solar cells to intermediate band quantum dot solar cells by introducing the parameter probability (P  ) that a charge carrier will impact ionize. The parameter θθ gives a criterion for the solar cell material selection to increase the probability and effectivity of the impact ionization by considering the effect of carriers effective masses on the energy conversion efficiency. A thermodynamic efficiency of about 81.2% is obtained, which is higher than the maximal efficiency of 63.2% for an intermediate band solar cell without Auger or impact ionization mechanism. The optimum bandgap and sub-bandgap is shifted towards the Silicon bandgap. Therefore, impact ionization effect is more applicable for sub-bandgap and bandgap energies below about 1 eV and for photons with appropriate kinetic energies.

We considered the probability and advantage of the impact ionization effect as an up-converting phenomena in the intermediate band solar cells.Figure optionsDownload as PowerPoint slideHighlights
► We developed the efficiency calculation of a single gap solar cell to an IBSC.
► We considered the impact ionization effect on the efficiency of IBSCs.
► We considered the effect of probability that a charge carrier will impact ionization.
► We considered the effective mass effects on the efficiency of IBSC.
► We conclude that the lower values of bandgap are appropriate for higher efficiencies.