Validated method for repeatable power measurement of CIGS modules exhibiting light-induced metastabilities
We report on the validation of a stabilization procedure designed to minimize variations in repeated power measurements at standard test conditions caused by transient light-induced metastabilities in copper indium gallium diselenide (CIGS) modules. Such metastable effects frustrate the repeatable and accurate measurement of a module's performance in the electrical state to which it stabilizes under normal operation outdoors. The procedure studied here is based on a light exposure followed by forward electrical bias as the module cools to the measurement temperature. The procedure was tested in a lab-to-lab intercomparison involving five different labs. Results show that the procedure is effective in yielding repeatable measurements and that the variations due to metastabilities are of roughly the same magnitude as those associated with variations in illumination conditions between different flash simulators. We also find that temperature-corrected measurements made immediately upon completion of the light exposure are less repeatable than those made after the module has cooled to 25 degrees C under bias.