Issues in the physical measurement of the intermediate band effect

The intermediate band (IB) solar cell offers a route to higher efficiency solar cells by inserting a band into the band gap of large band gap material. Theoretically, the open circuit voltage of the IB solar cell is close to that of the high band gap regions, and the current is increased through the addition of the intermediate band. However, experimental results have shown a decrease in the open circuit voltage, and a small increase in the short circuit current. We explain the decrease in Voc, as well as the small increase in Jsc though a thermodynamic and physical model. These models show that both these results are consistent with the absence of multiple quasi-Fermi levels. Because of the importance of realizing multiple quasi-Fermi levels, the definitive proof of this effect is critical in demonstrating the viability of the intermediate band, but show that demonstrated indicators of an intermediate band may be caused by other physical mechanisms. Instead, a key indicator of a quasi-Fermi level separation not explained by non-idealities are the features associated with the intermediate band quasi-Fermi level crossing the intermediate band energy level, demonstrated by shifting peak energies.