Interlaboratory comparison of short-circuit current versus irradiance linearity measurements of photovoltaic devices

•Proportionality approach more suitable than linear regression for ISC linearity.•ISC linearity measurements of reference cells to full-size modules are compared.•Results show good agreement between all partners, with few exceptions at low light.•Uncertainty should be with the limit of ±2% linearity required by the IEC standard.•Uncertainty correlations on the uncertainty budget need to be considered.