This is a question relating to Photovoltaics. Specifically, I would please like to know what Luminescence Coupling is, and what effect it has on Artifact Formation during External Quantum Efficiency measurements?
Luminescence coupling in multi-junction devices corresponds to the recollection of a fraction of the radiative emission of cells of larger bandgaps by the cells with lower bandgaps. This phenomenon is non-negligeable only when the External Radiative Efficiency of the top cells are sufficiently important (as in high efficiency III-V multijunction devices for example). It can lead to an artefact in EQE measurements of tandems because, when the EQE of the bottom cell is measured, the top cell is biased and can thus emit a significant photon flux density that can be absorbed by the bottom cell and add to the photogenerated current.