Precise Calibration of Solar Cells

For novel devices like the polymer solar cells described in this chapter, measurement procedures are not nearly so well-established as for inorganic devices, ft was reported earlier that all kinds of ill-defined efficiencies can be found in the literature [87]. This makes a meaningful comparison of efficiency values extremely difficult or even impossible, when they are measured at different institutes and using different measuring techniques. This section describes a procedure for obtaining better defined polychromatic efficiencies. 

The efficiency of a solar cell is strongly dependent on conditions such as cell temperature, and incident light intensity and spectral content. Standard reporting conditions (SRC) have therefore been defined so that the performance of a solar cell can be quantified in a reproducible way. The standard reporting conditions are specified as  

The most direct way to carry out the measurements is in places where the measured solar spectrum is found to be nearly identical to the standard AM1.5G spectrum. By measuring the temperature dependence and irradi-ance dependence of the I/V curve parameters, cell properties may be adjusted to the SRC. Since in most places around the world these SRC conditions cannot be met, characterisation laboratories have been set up with suitable apparatus and procedures to do accurate indoor efficiency measurements under SRC according to international standard norms (ASTM, IEC). This involves 

The match between a simulator spectrum E s(A) and the reference AM 1.5G spectrum r(A) is never perfect, even for the best solar simulators. Furthermore, a spectral mismatch is introduced because the spectral responses St (A) of the device under test and Sr.(A) of the reference cell are not identical. In order to correct for this, a spectral mismatch factor M can be computed from 

For each test cell, the spectral response St has to be measured relative to the known spectral response SR of the reference cell. The relative spectral irradiance E of the simulator should be measured in regular intervals on a regular basis. The mismatch factor can be calculated by taking the values of the reference cell and spectrum from the tables. 

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