Improved grating monochromator set-up for EQE measurements of multi-junction solar cells

Grating monochromator set-ups are widely in use for the measurement of the external quantum efficiency (EQE) of solar cells. This paper describes the grating monochromator setup for EQE measurements of multi-junction and concentrator cells at the calibration laboratory (ISE CalLab) at Fraunhofer ISE. The set-up has been updated with innovative features. This includes an optional LED based bias illumination system which is of particular interest for the measurement of multi-junction cells whose subcells show narrow or overlapping absorption bands. Additionally the set-up has been improved in order to allow for the reliable EQE measurement of concentrator cells with areas below 1 mm². Moreover, the set-up has been modified to measure the I-V-curve of the solar cell under bias light condition. In the case of multi-junction cells this allows to retrieve information about the shape of the I-V-curves of the individual subcells. Low temperature EQE measurements can be performed by replacing the measurement chuck through a cryostat.