Sandia/NIST reference cell calibration procedure

The Photovoltaic Device Measurement Laboratory (PDML) at Sandia in collaboration with the National Institute of Standards and Technology (NIST) has developed an indoor calibration procedure that improves the accuracy and reduces the time and cost of calibrating photovoltaic reference cells. The calibration procedure involves exposing the reference cell to an accurately known spectral irradiance provided by a 1000 W quartz-tungsten-halogen (FEL) lamp, measuring the cell´s short-circuit current and temperature, measuring the cell´s spectral response, and then applying a spectral mismatch correction to obtain the calibration constant for any desired reference spectrum. A comparative uncertainty analysis using wavelength-dependent measurement errors indicates that calibrations obtained using this new procedure have total uncertainties less than ±1%, less than standard ASTM outdoor calibration procedures. In addition, the new procedure has been validated for two years through intercomparisons with NREL, NASA-Lewis, the Fraunhofer Institute (FhG-ISE), and recalibrations at NIST