Bifacial solar cells in STC measurement

New cell concepts need to be evaluated for their potential in competition with standard solar cell technologies. At Fraunhofer ISE CalLab PV Cells measurement methods are developed which shall allow including newer cell technologies in this competition. This work investigates the influence of bifaciality on high precision measurements under standard test conditions on bare solar cells. A certain degree of bifaciality is an intrinsic property of most back contact solar cell concepts due to the gaps in the back metallisation. We measured the reflectivity for a range of chuck surfaces and the optical transmission of bifacial cells from actual cell technologies. With the measured rear spectral response then the extent of the additional current contribution is calculated for the different chuck surfaces both, spectrally resolved and integral. This is the basis for an optimisation of cell mounting systems suitable to ensure comparable measurement results. The results clarify the contribution from bifaciality to the measurement uncertainty and help to define standard conditions.