Band-band impact ionization and solar cell efficiency

Abstract
The effect of impact ionization has been taken into account in the calculation of the maximum solar cell efficiency in the thermodynamic limit. A red shift of the optimum band gap is observed with respect to the Shockley–Queisser result. A maximum solar cell efficiency of 60.3% at Eg=0.8 eV is predicted, which compares with 43.9% at Eg=1.1 eV for the usual case. In order to obtain a significant increase in η, an impact ionization probability of at least a few percent is required. A most pronounced effect is observed for bandgap energies below about 1 eV.

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