Impact of realistic energy levels on the efficiency of intermediate Band Solar Cells: Impact of carrier loss

Intermediate Band Solar Cells (IBSCs) were proposed [1] as a variation of a compound III–V semiconductor pn junction solar cell [2] with a proposed efficiency of 63% with concentration of light [3]-making them the highest efficiency pn junction solar cell possible. A schematic energy band profile of a p-i-n junction IBSC is given in Fig. 1. There are several possible approaches to create the Intermediate Band (IB): high density quantum dots, of a smaller band gap material can be introduced into a larger bandgap semiconductor or high density impurity states can also be introduced into the semiconductor host material to create an IB. A detailed balance approach is used to calculate the efficiency for a specific energy band gap with an IB positioned at the ideal position within the bandgap as shown in Fig. 2. This approach produces the high efficiency of 63% for a bandgap of 1.95 eV with the IB positioned 0.71 eV above the Valence Band (VB) or below the Conduction Band (CB). Experimentally efficiencies of < 20% have been observed for such devices employing QD-based IBs.