As-Grown InGaAsN Subcells for Multijunction Solar Cells by Molecular Beam Epitaxy

In this article, we investigate the molecular beam epitaxy growth of unannealed 1.12 eV InGaAsN solar cells. The impact of the growth temperature, the As/III ratio and the bismuth used as a surfactant are reported. An in-situ curvature measurement setup enables to monitor and ensures a constant N incorporation during the InGaAsN growth. Ex-situ characterization results suggest that a high As/III ratio ensures good optoelectronic properties and that the growth temperature has a strong influence on the residual doping of the dilute nitride layer. Under AM0 > 870 nm and without antireflection coatings, our best InGaAsN solar cells exhibit J_sc and V_oc values of 7.94 mA/cm² and 0.375 V, respectively. Considering no internal reflection and no grid shading, generation up to 12 mA/cm² in a multijunction solar cell can be expected, which is the highest value ever reported for As-grown InGaAsN cells to our knowledge.