5.1 It is the intent of these test methods to provide a recognized procedure for calibrating, characterizing, and reporting the calibration data for non-primary photovoltaic reference cells that are used during photovoltaic device performance measurements.

5.2 The electrical output of photovoltaic devices is dependent on the spectral content of the source illumination and its intensity. To make accurate measurements of the performance of photovoltaic devices under a variety of light sources, it is necessary to account for the error in the short-circuit current that occurs if the relative spectral response of the reference cell is not identical to the spectral response of the device under test. 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 quantified with the spectral mismatch parameter M (Test Method E973).

5.2.1 Test Method E973 requires four quantities for spectral mismatch calculations:

5.2.1.1 The quantum efficiency of the reference cell to be calibrated (see 7.1.1),

5.2.1.2 The quantum efficiency of the calibration source device (required as part of its calibration),

Note 1: See 10.10 of Test Method E1021 for the identity that converts spectral responsivity to quantum efficiency.

5.2.1.3 The spectral irradiance of the light source (measured with the spectral irradiance measurement equipment), and,

5.2.1.4 The reference spectral irradiance distribution to which the calibration source device was calibrated (see G173).

5.2.2 Temperature Corrections—Test Method E973 provides means for temperature corrections to short-circuit current using the partial derivative of quantum efficiency with respect to temperature.

5.3 A non-primary reference cell is calibrated in accordance with these test methods is with respect to the same reference spectral irradiance distribution as that of the calibration source device. Primary reference cells may be calibrated by use of Test Method E1125.

Note 2: No ASTM standards for calibration of primary reference cells to the extraterrestrial spectral irradiance distribution presently exist.

5.4 A non-primary reference cell should be recalibrated yearly, or every six months if the cell is in continuous use outdoors.

5.5 Recommended physical characteristics of reference cells are provided in Specification E1040.

5.6 Because silicon solar cells made on p-type substrates are susceptible to a loss of I_sc upon initial exposure to light, it is required that newly manufactured reference cells be light soaked, see 4.8.

5.7 The choice of natural sunlight versus solar simulation for the test light source involves tradeoffs between the advantages and disadvantages of either source. Natural sunlight provides excellent spatial uniformity over the test plane but the total and spectral irradiances vary with the apparent motion of the sun and changes of atmospheric conditions such as clouds. Calibrations in a solar simulator can be done at any time and provide a stable spectral irradiance. Disadvantages of solar simulators include spatial non-uniformity and short-time variations in total irradiance. The procedures in these test methods have been designed to overcome these disadvantages.

1.1 These test methods cover calibration and characterization of non-primary terrestrial photovoltaic reference cells to a desired reference spectral irradiance distribution. 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 a photovoltaic device.

1.2 Non-primary reference cells are calibrated indoors using simulated sunlight or outdoors in natural sunlight by reference to a previously calibrated reference cell, which is referred to as the calibration source device.

1.2.1 The non-primary calibration will be with respect to the same reference spectral irradiance distribution as that of the calibration source device.

1.2.2 The calibration source device may be a primary reference cell calibrated in accordance with Test Method E1125, or a non-primary reference cell calibrated in accordance with these test methods.

1.2.3 For the special case in which the calibration source device is a primary reference cell, the resulting non-primary reference cell is also referred to as a secondary reference cell.

1.3 Non-primary reference cells calibrated according to these test methods will have the same radiometric traceability as that of the calibration source device. Therefore, if the calibration source device is traceable to the World Radiometric Reference (WRR, see Test Method E816), the resulting secondary reference cell will also be traceable to the WRR.

1.4 These test methods apply only to the calibration of a photovoltaic cell that demonstrates a linear short-circuit current versus irradiance characteristic over its intended range of use, as defined in Test Method E1143.

1.5 These test methods apply only to the calibration of a photovoltaic cell that has been fabricated using a single photovoltaic junction.

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

1.7 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.8 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.