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Abstract
To achieve high efficiency, the intermediate band (IB) solar cell must generate photocurrent from sub-bandgap photons at a voltage higher than that of a single contributing sub-bandgap photon. To achieve the latter, it is necessary that the IB levels be properly isolated from the valence and conduction bands. We prove that this is not the case for IB cells formed with the confined levels of InAs quantum dots (QDs) in GaAs grown so far due to the strong density of internal thermal photons at the transition energies involved. To counteract this, the QD must be smaller.
Highlights
To achieve high efflciency, the intermedíate band (IB) solar cell must genérate photocurrent from sub-bandgap photons at a voltage higher than that of a single contributing sub-bandgap photon
It is known that this structure is not optimal in that the bandgaps are too small; it has permitted the study of the concept and the proof of its basic principies.8'9 One of the shortcomings of present cells is thought to be the strong IB-CB thermal contact that prevents the CB quasi Fermi Level (QFL) from being above the IB QFLs, so preventing the appearance of a voltage above the valence band (VB)-IB sub-bandgap
This paper proves that, at room temperature, a strong thermal contact is produced by radiative interaction and that this interaction is enough to prevent substantial splitting of the QFLs in this material system
Summary
It is necessary that the IB levéis be properly isolated from the valence and conduction bands We prove that this is not the case for IB cells formed with the conflned levéis of InAs quantum dots (QDs) in GaAs grown so far due to the strong density of internal thermal photons at the transition energies involved. Each state is fllled by the electrons pumped from the valence band (VB) by high energy external photons with máximum current rates /yin, Jvm, ha\ (modulated by the presence of empty sites in the IB levéis) and is emptied by the net thermal generation (the opposite of the net thermal recombination in Eq (3)) towards other BS and VBS. This condition should be fulfllled near short circuit; in any case it represents an upper limit of the electrón flow transferred to the IB levéis
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