Multi-junction solar cell design using strain balanced dilute nitride quantum wells

For over a decade various schemes, involving the use of bulk-like 1.0-1.2 eV Ga(In)NAs subcells, have been contemplated to further enhance the efficiency of existing triple and quadruple junction solar cells[1] which are mainly limited by the poor carrier properties of bulk dilute nitrides [2]. Previously [3] we had considered an alternate path toward the realization of 1.1eV solar cells where dilute nitride quantum wells with thicknesses much smaller than the minority carrier diffusion length are utilized in the GaAs solar cell. In this work we have modified this design by taking into account the strain effects via strain balancing with GaAsSb, and also the effect of the electric field on the QW energy and absorption characteristics. The results for triple junction solar cells encompassing these MQW in the GaAs sub-cells (~ 1.1 eV) under 500 suns at AM1.5 show possibilities for reaching photoconversion efficiencies in excess of 45%, while reaching upto 40% under AM1.5 for the quadruple junction configuration (GaInP, GaAs, GaAsN/GaAsSb, Ge).