Design constraints of n-p InGaAsN dilute nitride sub-cells for 3- and 4- junction solar cell applications under concentrated illumination

Solar cells with an n-p structure consisting of an InGaAsN dilute nitride emitter with n-type background doping and a p-type doped InGaAsN base are numerically simulated on GaAs and Ge substrates. The InGaAsN material parameters are chosen based on of structures reported in the literature. The short-circuit current of cells on GaAs substrates is 11% greater than similar designs on Ge substrates due to an increased photon path length. The current density to optical intensity ratio of 0.135 A/W, required to match the operating current density of an InGaP/InGaAs/InGaAsN 3-junction solar cell, is readily obtained for devices on GaAs substrates, but the required current density is not attainable when a Ge substrate is used. The InGaAsN sub-cell demonstrates enhanced performance for increasing levels of concentration up to 1000 suns. Open-circuit voltage increases near logarithmically with concentration, and the ratio of maximum-power point current to short-circuit current is constant at 82% between 10 and 1000 suns.