Influence of spectral mismatch, cell reflection properties and IQE on the efficiency measurement

The determination of the electrical parameters and in particular the efficiency of solar cells should be done according to STC. However, hardly any solar simulator or flasher features a spectrum perfectly matched to STC’s ASTM G173 (AM 1.5g) spectrum. If the external quantum efficiency (EQE) of the calibration cell and the cell to be tested differ, any spectral mismatch of the applied spectrum compared to STC may not only lead to an erroneous measurement of current and cell efficiency but also to de-optimization of cell properties or misinterpretation of experimental results. As an example it is shown that the combination of spectral and EQE mismatch yield a different optimum of the (effective) layer thickness of the anti-reflection coating (ARC) resulting in a de-optimization according to STC. As a second example, the misinterpretation of benefits due to the implementation of selective emitter technology is discussed