Detailed balance efficiency of a three level system with thermionic transitions

A three energy level model used in previous detailed balance analyses has been modified to allow the transition of carriers across one of the internal band gaps to be completely non-radiative. The transitions across all three of the band gaps in the model are typically taken to be radiative, however, in this work the transitions across the smaller internal band gap are taken to be thermionic in nature. Calculations using the modified model were performed for GaAs based devices under one sun illumination. The results show an efficiency improvement for the three energy level system over the homojunction limit for low values of the smaller internal band gap. The efficiency improvement is shown to increase as the thermionic rates are increased artificially. The implications of these results in terms of devices such as Quantum Well Solar Cells are discussed.