5.1 The spectral responsivity of a photovoltaic device is necessary for computing spectral mismatch parameter (see Test Method E973). Spectral mismatch is used in Test Method E948 to measure the performance of photovoltaic cells in simulated sunlight, in Test Methods E1036 to measure the performance of photovoltaic modules and arrays, in Test Method E1125 to calibrate photovoltaic primary reference cells using a tabular spectrum, and in Test Method E1362 to calibrate photovoltaic secondary reference cells. The spectral mismatch parameter can be computed using absolute or relative spectral responsivity data.

5.2 This test method measures the differential spectral responsivity of a photovoltaic device. The procedure requires the use of white-light bias to enable the user to evaluate the dependence of the differential spectral responsivity on the intensity of light reaching the device. When such dependence exists, the overall spectral responsivity should be equivalent to the differential spectral responsivity at a light bias level somewhere between zero and the intended operating conditions of the device. Depending on the linearity response of the DUT over the intensity range up to the intended operating conditions, it may not be necessary to set up a very high light bias level.

5.3 The spectral responsivity of a photovoltaic device is useful for understanding device performance and material characteristics.

5.4 The procedure described herein is appropriate for use in either research and development applications or in product quality control by manufacturers.

5.5 The reference photodetector's calibration must be traceable to SI units through a National Institute of Standards and Technology (NIST) spectral responsivity scale or other relevant radiometric scale.3 ^,4 The calibration mode of the photodetector (irradiance or power) will affect the procedures used and the kinds of measurements that can be performed.

5.6 This test method does not address issues of sample stability.

5.7 Using results obtained by this test method and additional measurements including reflectance versus wavelength, one can compute the internal quantum efficiency of a device. These measurements are beyond the scope of this test method.

5.8 This test method is intended for use with a single-junction photovoltaic cell. It can also be used to measure the spectral responsivity of a single junction within a series-connected, multiple-junction photovoltaic device if electrical contact can be made to the individual junction(s) of interest.

5.9 With additional procedures (see Test Methods E2236), one can determine the spectral responsivity of individual junctions within series-connected, multiple-junction, photovoltaic devices when electrical contact can only be made to the entire device's two terminals.

5.10 Using forward biasing techniques5, it is possible to extend the procedure in this test method to measure the spectral responsivity of individual series-connected cells within photovoltaic modules. These techniques are beyond the scope of this test method.