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Increasing the Efficiency of Ideal Solar Cells by Photon Induced Transitions
at Intermediate Levels

Antonio Luque and Antonio Martı´
Instituto de Energı´a Solar, Universidad Politécnica de Madrid, 28040 Madrid, Spain
(Received 7 February 1997)

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Recent attempts have been made to increase the efficiency of solar cells by introducing an impurity
level in the semiconductor band gap. We present an analysis of such a structure under ideal conditions.
We prove that its efficiency can exceed not only the Shockley and Queisser efficiency for ideal
solar cells but also that for ideal two-terminal tandem cells which use two semiconductors, as well
as that predicted for ideal cells with quantum efficiency above one but less than two.