Abstract
The intermediate band (IB) concept is regarded as a way of exceeding the Shockley–Queisser efficiency limit through a more efficient use of the solar spectrum. Quantum dots (QDs) have been proposed to achieve a practical implementation of this concept. So far, only few QD material systems, such as In(Ga)As/GaAs and related compounds, have been tested experimentally giving rise to two important conclusions: on the one hand, the verification of the concept fundamentals and on the other hand, the need to seek new QD candidate materials in order to produce high efficiency devices. As regards the latter, in this paper we present an analytical model to assess the potential of QD IB solar cells (IBSCs) consisting of the following steps: (1) calculation of the heterojunction band alignment taking material strain into account, (2) calculation of the QD confined energy levels constituting the IB, and (3) calculation of the efficiency limits in the detailed balance realm and optimization of the QD systems in terms of QD size and material composition. The search criteria are reviewed and three QD systems (InAs/AlxGa1−xAs, InAs1−yNy/AlAsxSb1−x, and InAs1−zNz/Alx[GayIn1−y]1−xP) are identified together with their optimum QD sizes. Efficiencies of over 60% are calculated at maximum light concentration.
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