Carrier dynamics in quantum-dot multijunction solar cells under concentration

The key performance metrics of quantum-dot (QD)- lattice-matched multijunction solar cells (MJSCs) composed of InGaP/(In)GaAs/Ge with InAs/GaAs QDs are explored under high-concentration illumination with a focus on the carrier dynamics in the QD layers of the middle subcell. An effective medium approach is used to describe generation and recombination in the QD system, including carrier escape and capture from the weakly confining quantum well and the QD states. At a concentration of 1000 suns, simulations indicate that the specific QD MJSC studied outperforms a standard MJSC by 1.1% in relative efficiency operating at 25 °C. However, this gain in efficiency is highly dependent on the confinement potentials of the wetting layer, as well as the resulting current mismatch between the top and middle subcells when carrier escape rates from within the wetting layer confinements are reduced.