Combined photo- and electroreflectance of multijunction solar cells enabled by subcell electric coupling

Abstract

Electric coupling between subcells of a monolithically grown multijunction solar cell in short circuit allows their simultaneous and independent characterization by means of photo- and electro-reflectance. The photovoltage generated by selective absorption of the pump beam in a given subcell during photoreflectance measurements results in reverse biasing the complementary subunits at the modulation frequency set on the pump illumination. Such voltage bias modulation then acts as external perturbation on the complementary subcells. The spectral separation of different subcell absorption ranges permits the probe beam to record in a single spectrum the response of the complete device as a combination of photo- and electro-reflectance, thereby providing access for the diagnosis of subcells on an individual basis. This form of modulation spectroscopy is demonstrated on a GaInP/GaAs tandem solar cell.