Theoretical efficiency of intermediate band solar cells with overlapping absorption coefficients for various combinations of band gaps

The most commonly used criteria for evaluation of the suitability of different intermediate band materials for use in intermediate band solar cells are their band gaps. One often sees that such an evaluation is made based on theoretical efficiency limits with non-overlapping absorption coefficients. In this work the theoretical efficiency limits for various degrees of overlap are calculated for relevant combinations of band gaps. It is found that the optimal position of the intermediate band moves towards the middle of the band gap when the overlap increases. It is also shown that overlap between the absorption coefficients can increase the theoretical efficiency for some band gap combinations. This work aims to serve as a rough guide for determining whether a combination of band gaps is promising for use in intermediate band solar cells or not.