Differential Spectral Responsivity of Solar Cells Measured with an LED Based Experimental Setup

We have developed an experimental setup for measuring differential spectral responsivities of solar cells under bias light conditions. Instead of the commonly used monochromator light source, our setup uses 30 high-brightness LEDs as a tunable quasi-monochromatic light source covering the wavelength range of 290 - 1300 nm. Halogen lamps are used to generate bifacial bias-lighting conditions resembling the spectrum of AM1.5G. The setup has been fully characterized for spectral irradiances and spatial uniformities of all light sources. Validation measurements carried out using a reference cell of 2×2 cm² area from Fraunhofer ISE demonstrated an agreement better than 2% over the wavelength range of 425 - 940 nm, with an expanded uncertainty of 2.6%. In the UV and IR regions, the discrepancies are higher but still within estimated uncertainties. The setup is being employed as a reference in an interlaboratory comparison of indoor solar cells based on emerging technologies. A reference cell, an Epishine organic indoor cell, and a Panasonic amorphous silicon indoor cell are distributed among participants and measured for various parameters including short circuit current. We tested a method for deriving the reference values for short circuit currents mathematically from the differential spectral responsivities of the cells. The preliminary results shown indicate that the developed setup is feasible for measurements and calibrations of indoor solar cells.