Spectral response measurements of multi-junction solar cells with a grating monochromator and a Fourier-spectrometer

During the past few years a great variety of multi-junction solar cells has been developed with the aim of a further increase in efficiency beyond the limits of single junction devices. To characterise this development adequately, new measurement techniques for spectral response and I-V characteristics must be investigated. For spectral response measurements, new set-ups should be developed to deal with the problems arising from the various kinds of multi-junction devices. In this paper, two set-ups for spectral response measurement are described, which are based on standard calibration equipment with the addition of coloured bias illumination and voltage biasing. The difficulties in spectral response measurements are discussed in the case of two-junction (tandem) cells and some examples are given showing the errors arising from the direct transfer of the measurement technique from single to multi-junction devices. In addition methods to measure the correct spectral response of two-te rminal and four-terminal tandem cells are explained.