Multi-junction thermophotovoltaic converters based on dilute nitride superlattices lattice matched to InP

Recently we have shown that by adjusting the thickness of individual sublayers and the nitrogen composition, strain balanced GaAs1-xNx/InAs1-yNy superlattices can be designed to be both lattice matched to InP and have effective bangaps in the desirable 0.4-0.65 eV range. The effect of insertion of such superlattice-like alloy within the intrinsic region of a 0.74 eV InGaAs p-i-n diode was also evaluated and it was shown that such a single junction device exhibits a photovoltaic response comparable to its lattice-mismatched 0.55 eV-InGaAs counterpart. In this work we have extended the approach to multi-junctions devices. Here two or more subcells with different effective bandgaps for the superlattice region are monolithically series connected. Maximum power output and performance of double, triple and quadruple junction TPV cells are evaluated as a function of the superlattice/cell design for a relatively low temperature black body emitters (1350K). The study stresses the potential of the proposed approach for a significant enhancement of TPV converter performance.