Intermediate band solar cell with many bands: Ideal performance

When the intermediate band solar cell (IBSC) absorbs sunlight, electrons are excited not only between the valence and conduction bands of the semiconductor material constituting the cell, but also between these bands and one or more additional bands that lie within the normally forbidden band gap of the material. Therefore, this device has the potential to reach high conversion efficiencies by increasing the photogenerated current (due to these multiple step excitations) without reducing the open-circuit voltage. In this article, a general method of describing the operation of the IBSC with N bands is presented for the cases where both the valence and conduction bands are unrestricted and restricted in their width. It is found that for the restricted IBSC, all of the intermediate bandwidths must be zero to satisfy the applied constraints. The efficiency for the unrestricted IBSC device under maximally concentrated black-body radiation with an infinite number of bands is estimated to be 85.0%. Under an air mass (AM) of 1.5 global radiation, an efficiency of 53.5% for the five-band IBSC is found to be the upper limit. Finally, the IBSC is found to be robust to changes in the AM. (C) 2003 American Institute of Physics.