Optimal Band Gaps For Non-Ideal Intermediate Band Solar Cells

A detailed balance model for intermediate-band solar cells (IBSCs) has been adapted to include non-radiative recombination. We search for the band structure which would allow for a >30% efficient IBSC with minimum required material quality. With 1-sun AM1.5G illumination, a band gap E-g=2.4 eV with an intermediate band located at 0.6 E-g yields 30% efficiency with material quality well below the radiative limit. This optimum band gap is 0.1 eV larger than the 2.3 eV found from optimization in the radiative limit. We find that materials with E-g in the range of 2.2 to 3.0 eV offer the best opportunity to demonstrate efficient IBSCs. For lower quality material, larger band gaps compensate for loss of open-circuit voltage.