In this study, we investigate the interpretation of the Stokes shift (SS) by employing the optoelectronic reciprocity relation (ORR), which provides a fundamental link between optical absorption and emission processes. We first revisit the van Roosbroeck-Shockley relation and the generalized Planck's law, both of which have been widely used in conventional analyses of the SS. While these relations are valid when the quasi-Fermi level splitting (QFLS) is spatially uniform within the optically active region, it becomes difficult to accurately reproduce photoluminescence spectra from absorption measurements in the presence of parasitic optical absorption that is not accompanied by QFLS. Such parasitic absorption can originate from free-carrier absorption, absorption in nonactive layers such as transparent electrodes and antireflection coatings, as well as absorption via defect-related states. To overcome this limitation, we apply ORR to a quantum-structured superlattice solar cell exhibiting a sharp excitonic absorption peak. External quantum efficiency (EQE) spectra are measured and subsequently used to calculate electroluminescence (EL) spectra via ORR. A direct comparison between the calculated and measured EL spectra, together with the measured EQE, demonstrates that the experimentally observed SS is quantitatively reproduced within the ORR framework, with the reconstructed EL peak coinciding at 943 nm (within the 1 nm spectral resolution) and with close agreement in spectral line shape. This result demonstrates at the device level that the observed SS is consistent with the detailed-balance relation between optical absorption and carrier recombination. The analysis further shows that ORR provides a practical framework for evaluating the SS in the active region while reducing the influence of parasitic absorption processes that do not contribute to collected carriers.

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• Electroluminescence
• Luminescence
• Optoelectronics
• Photocurrent
• Photovoltaic effect