Design trade-offs and rules for multiple energy level solar cells

Solar cell efficiency limit are receiving renewed examination due to the realisation that many types of solar cell structures can theoretically achieve similar efficiencies to those of multiple p-n homojunctions, without the need for a large number of different semiconductors. This paper shows that the proposed high efficiency device structures fit into one of three general classes and therefore only three ideal efficiency limit calculations are required. However, many of the suggested structures violate assumptions in the ideal efficiency limit calculations. Hence, these calculations should be modified to include additional transport, generation and recombination effects.