Results of an interlaboratory comparison of adapted reference solar cells among nine metrological institutes

This paper presents the results of an interlaboratory comparison of four adapted reference solar cells, carried out among nine metrological institutes, including eight European and one non-European laboratory. Two high-pass filtered, and two low-pass filtered silicon reference cells were measured for short-circuit current at standard test conditions (STC) as stated in IEC-TS-61836, and as optional parameters, for open-circuit voltage, maximum power produced, and differential spectral responsivity. Each laboratory applied its own measurement procedure, and a comparison of these results was carried out to investigate the consistency of the measurements relative to a reference value. The Physikalisch-Technische Bundesanstalt in Germany served as the reference laboratory, performing initial, intermediate, and final measurements. The results were in quite good agreement. For short-circuit current measured at STC, 84% of the 44 reported values showed agreement within their expanded uncertainties, presenting |E_n| values smaller than 1. The discrepancies of the outliers with |E_n|'1 were in the range of -2.2% to 3.5% with E _n ranging between -2.1 to 3.3. For open-circuit voltage, 15 out of 20 measurements presented |E_n| values smaller than 1. For maximum power point similarly, 12 out of 20 measurements were in agreement. This is the first interlaboratory comparison on adapted reference cells that are important for calibrating advanced photovoltaic devices. This comparison shows how adapted reference cells perform across different calibration practices and things that should be considered in standardisation. The study revealed problems linked to temperature control, metastability of high-pass cells affecting their fill factors, and measurement techniques that are discussed.