S. H. Lim, et al., Progress in Photovoltaics: Research and Applications, (2011).
The effects of luminescence coupling on the external quantum efficiency (EQE) measurement of an InGaP/InGaAs/Ge triple junction solar cell were investigated. A small signal model was used to study the interaction of the subcells during EQE measurement. It was found that an optical–electrical feedback mechanism results in EQE measurement artifacts. Measurements of luminescence from the InGaP p–n junction are also performed to quantitatively determine the strength of the luminescence coupling

J.-J. Li, et al., IEEE J. of Photovoltaics 1, 225-230 (2011).
The combined effects of shunt and luminescence coupling on the measurement artifacts of external quantum efficiency (EQE) are modeled and analyzed for the top, middle and bottom subcells of multi-junction solar cells. The measurement artifacts of a Ge bottom cell caused by the combined effects are explained with the models.

J.-J. Li, et al., IEEE J. of Photovoltaics 3, 769 – 775 (2013).
A pulsed voltage bias (PVB) method is demonstrated to eliminate artifacts in external quantum efficiency (EQE) measurements of multijunction solar cells that are caused by the shunt effect or the combined effects of shunt and luminescence coupling. This method uses a PVB superimposed on the dc voltage and light biases in conventional EQE measurements. The PVB method is compared with the recently reported pulsed light bias (PLB) method and unity rule. It is found that the PVB method has a similar accuracy as the PLB method, while the unity rule shows a larger discrepancy between the measurement results and the true EQE under certain conditions.

.-J. Li and Y.-H. Zhang, IEEE J. of Photovoltaics 3, 364-369 (2013).
A method using a pulsed light bias synchronized to the probing monochromatic light and superimposed on the conventional dc light and voltage biases is proposed to eliminate the artifacts in external quantum efficiency (EQE) measurements for multijunction solar cells. It is demonstrated experimentally that this method effectively eliminates the EQE measurement artifacts caused by the shunt effect, the luminescence coupling effect, or their combination.

                              
EQE in the Ge wavelength range measured using the conventional method (black squares) and the PLB method (red dots) for the Ge subcell in a triple-junction solar cell with strong shunt effect and negligible luminescence coupling effect.