Light soaking measurements of commercially available CIGS PV modules

CIGS devices are known to exhibit metastabilities and performance changes with continuous light exposure, or light soaking (see Ref. [1], and references therein). Such metastabilities have an impact on the measurement of CIGS PV module performance, since efficiency and other parameters change on a time scale of hours. For this work we used an indoor continuous solar simulator to expose three commercially available CIGS modules from three different manufacturers to a simulated diurnal light exposure cycle for 16 days. We observed an initial increase in efficiency on the order of ~3% to ~5% at the start of each illumination cycle in all three modules. We also observed a a deviation of approximately -0.17%/°C between the measured value and data sheet value of one module´s Pmax/efficiency temperature coefficient, indicating that this module have ~5% lower power output at normal operating temperatures that indicated by the datasheet. In a follow-on experiment, the time required for modules to relax in the dark to their low-efficiency states was investigated by varying the length of time spent in the dark. One module, with an overall power conversion efficiency (PCE) of ~9.3%, required between 2 and 3 hours in the dark to relax to its low efficiency state, while the other two modules, with PCEs of ~10.3%, require between 9 and 16 hours to relax to their low-efficiency states.