A proposal for Intermediate Band Solar Cells with optimized transition energy - InAs QD / AlGaAs

Abstract

The Intermediate Band Solar Cell (IBSC) is a new concept proposed to better match the solar spectrum by absorbing sub-bandgap energy photons. One approach to implement this idea is to form an intermediate band (IB) with the confined levels of quantum dots embedded in a semiconductor host matrix, the Quantum Dot IBSC (QD-IBSC). With this configuration, not only the ordinary transition between the valence band (VB) and the conduction band (CB) - Eg -but also the transition between VB and the IB - Em - and between the IB and the CB - El -can take place. Theoretical calculations using the detailed balance model show that the conversion efficiency of this photovoltaic device can overcome the best performance reported so far by tandem cells. According to this model, the highest efficiency (63%) is obtained with the following energy combination: Eg = 1.95 eV, Em = 1.25 eV and El = 0.7 eV. In this paper, we present theoretical and preliminary experimental studies based on our proposal of QD-IBSC. By energy level calculations we demonstrate that our material choice is more advantageous in order to approach the ideal combination of transition energies compared with the systems studied so far.