InGaAs/GaAsP quantum-well superlattice solar cell for better carrier collection and higher efficiency

InGaAs/GaAsP quantum wells (QWs) have been inserted into a GaAs p-i-n cell aiming at a better current matching of an InGaP/GaAs/Ge tandem solar cell: photon absorption at a longer wavelength range than the GaAs bandedge was attempted while keeping pseudo-lattice-matching to GaAs for the QW structure as a whole. The efficient extraction of photo-generated carriers from the InGaAs wells to an external circuit was vital for minimizing the drop in open-circuit voltage, which necessitated extremely-thin (~3 nm) GaAsP barriers and tunnelling-assisted carrier transport. Such a superlattice structure was grown by metal-organic vapour-phase epitaxy (MOVPE) and evidenced a promising gain in current output. Under sunlight concentration (~100 suns), the open-circuit voltage of the GaAs p-i-n cell was almost unchanged upon the insertion of the superlattice and the superlattice just resulted in the gain in current output.