Evaluation of a Selection of Intermediate Band Materials Based on Their Absorption Coefficients

The intermediate band materials BSSi₂₁₄, Cu₄CrGa₃S₈, Cu₄TiGa₃S₈, Mg₂In₃VS₈, S₃₂Zn₃₁Cr, and Te₃₂Zn₃₁Cr, as well as a certain configuration of InAs quantum dots in GaAs, are evaluated as candidates to implement highly efficient intermediate band solar cells. The evaluation implies calculating theoretical efficiencies by combining an existing mathematical model and the absorption coefficients for the investigated materials. The model takes into account the energy dependence and spectral overlaps of the absorption coefficients related to transitions between various pairs of electronic bands. The presented results represent theoretical efficiencies for flat-plate solar cells, without light-trapping schemes, based on absorption coefficients publicly available in scientific journals. Only BSSi₂₁₄ and InAs quantum dots in GaAs turn out to have theoretical efficiencies close to or above the detailed balance efficiency limit for single-bandgap cells. It appears unlikely that cells made of the other materials will be able to show efficiencies higher than single-bandgap cells either due to unfortunate absorption coefficients or due to bandgap combinations that are too far from the optimal. The results highlight the fact that materials have to be selected with great care when attempting to make IBSC prototypes with higher efficiency than conventional solar cells.