Short-circuit current enhancement in Bragg stack multi-quantum-well solar cells for multi-junction space cell applications

GaInP/GaAs tandem cells are limited by the current generated in the bottom GaAs junction. Strain-balanced multi-quantum well (MQW) solar cells offer a way of achieving a lower band gap for the lower junction, whilst retaining the lattice parameter of GaAs, and avoiding non-radiative recombination through dislocations. Further, the addition of a distributed Bragg reflector (DBR) allows the possibility of light not absorbed by the wells being reflected back into the structure, whilst allowing sub-well band-gap light through to a third Ge junction. Experimental results are presented from MQW cells grown with and without DBRs. These show a higher internal quantum efficiency in the 880 nm–1 μm region without detriment to the bulk response, when compared to MQW cells without DBRs.