Tunnel-Junction-Limited Multijunction Solar Cell Performance Over Concentration

• Published in: IEEE journal of selected topics in quantum electronics 2013-09, Vol.19 (5), p.1-8
• Main Authors: Walker, A. W., Theriault, O., Wilkins, M. M., Wheeldon, J. F., Hinzer, K.
• Format: Article
• Language: English
• Subjects: Aluminum gallium arsenides; Computer simulation; concentrated photovoltaics; Current density; Doping; Electron traps; Gallium arsenide; Gallium arsenides; Junctions; modeling and simulation; multijunction solar cells; Photovoltaic cells; Solar cells; Sun; Tunnel junctions; Tunneling
• ISSN: 1077-260X; 1558-4542
• DOI: 10.1109/JSTQE.2013.2258140

The simulation of tunnel junctions is performed by using nonlocal band-to-band and trap assisted tunneling models that are capable of reproducing the experimental current-voltage characteristics of p ++ AlGaAs/ n ++ AlGaAs and p ++ AlGaAs/ n ++ GaAs based devices. These simulated characteristics are then implemented within a lattice matched InGaP/(In)GaAs/Ge multijunction solar cell (MJSC) to assess the performance as a function of tunnel junction layer doping in the regime where the TJ limits the performance of the MJSC. At 500 suns, a 4.6% absolute drop in simulated efficiency is observed for an AlGaAs/GaAs bottom TJ corresponding to a degenerately p-doped layer of 2.5 × 10 19 cm -3 compared to a TJ with a doping of 4×10 20 cm -3 . A minimum p ++ doping level of 3.3 × 10 19 cm -3 is required in order to avoid bottom TJ limitation up to 1000 suns concentration for an n ++ doping of 2 × 10 19 cm -3 based on the calibrated models. Furthermore, the effects of the peak and valley current densities are shown to have a strong influence on the efficiency over concentration within the TJ limiting regime.