ASTM E1125-16

5.1 The electrical output of a photovoltaic device is dependent on the spectral content of the illumination source, its intensity, and the device temperature. To make standardized, accurate measurements of the performance of photovoltaic devices under a variety of light sources when the intensity is measured with a calibrated reference cell, it is necessary to account for the error in the short-circuit current that occurs if the relative quantum efficiency of the reference cell is not identical to the quantum efficiency of the device to be tested. A similar error occurs if the spectral irradiance distribution of the test light source is not identical to the desired reference spectral irradiance distribution. These errors are accounted for by the spectral mismatch parameter (described in Test Method E973), which is a quantitative measure of the error in the short-circuit current measurement. It is the intent of this test method to provide a recognized procedure for calibrating, characterizing, and reporting the calibration data for primary photovoltaic reference cells using a tabular reference spectrum.

5.2 The calibration of a reference cell is specific to a particular spectral irradiance distribution. It is the responsibility of the user to specify the applicable irradiance distribution, for example Tables G173. This test method allows calibration with respect to any tabular spectrum.

5.3 A reference cell should be recalibrated at yearly intervals, or every six months if the cell is in continuous use outdoors.

5.4 Recommended physical characteristics of reference cells can be found in Specification E1040.

5.5 High-quality silicon primary reference cells are expected to be stable devices by nature, and as such can be considered control samples. Thus, the calibration value data points (see 9.3) can be monitored with control chart techniques according to Practice E2554, and the test result uncertainty estimated. The control charts can also be extended with data points from previous calibrations to detect changes to the reference cell or the calibration procedures.

1.1 This test method is intended for calibration and characterization of primary terrestrial photovoltaic reference cells to a desired reference spectral irradiance distribution, such as Tables G173. The recommended physical requirements for these reference cells are described in Specification E1040. Reference cells are principally used in the determination of the electrical performance of photovoltaic devices.

1.2 Primary photovoltaic reference cells are calibrated in natural sunlight using the relative quantum efficiency of the cell, the relative spectral distribution of the sunlight, and a tabulated reference spectral irradiance distribution. Selection of the reference spectral irradiance distribution is left to the user.

1.3 This test method requires the use of a pyrheliometer that is calibrated according to Test Method E816, which requires the use of a pyrheliometer that is traceable to the World Radiometric Reference (WRR). Therefore, reference cells calibrated according to this test method are traceable to the WRR.

1.4 This test method is used to calibrate primary reference cells; Test Method E1362 may be used to calibrate secondary and non-primary reference cells (these terms are defined in Terminology E772).

1.5 This test method applies only to the calibration of a photovoltaic cell that shows a linear dependence of its short-circuit current on irradiance over its intended range of use, as defined in Test Method E1143.

1.6 This test method applies only to the calibration of a reference cell fabricated with a single photovoltaic junction.

1.7 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.