Electroluminescence-based quality characterization of quantum wells for solar cell applications

Material quality is a critical factor which determines the performance, particularly the open-circuit voltage, of multiple quantum well (MQW) solar cells. In this study, we report an electroluminescence-based characterization technique for evaluating luminescence efficiency and Shockley-Read-Hall recombination lifetime in MQW structures as a measure of the material quality. As a demonstration, various structures of InGaAs/GaAsP MQWs inserted in GaAs solar cells are investigated. The complete compensation of strain and the insertion of GaAs interlayers between heterointerfaces result in significant improvement of electroluminescence homogeneity, external luminescence efficiency, and lifetime, agreeing well with the tendency of the open-circuit voltage. We show that this characterization technique can detect even subtle degradations, which are not easily detectable by other typical techniques, such as in-situ reflection, X-ray diffraction, and spectral and transient photoluminescence, but still have a significant impact on the performance of solar cells.