Light soaking measurements of commercially available CIGS PV modules

Abstract

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.

Metastable changes to the temperature coefficients of thin-film photovoltaic modules

“…Previous work has investigated the possibility of light-induced changes to temperature coefficients, but no substantial effect was observed [7]. This highlights the importance of considering each product and CIGS formulation separately, because different devices can have different dominant physics, and thus, different performance changes due to illumination.…”

The performance of a combined solar photovoltaic (PV) and thermoelectric generator (TEG) system

“…The values given for CdTe are theoretical maximum values. The CIGS module data are from commercial modules, which seems to be accurate in testsDunn and Gostein [2012]. The values for c-Si are an average of values fromSkoplaki and Palyvos [2009].…”

Experimental Evidence of PID Effect on CIGS Photovoltaic Modules

“…Conversely, a small increase of the fill factor and of the short circuit current is observed during the first hours. This is due to the metastabilities of the PV modules in CIGS [35,36] and does not prevent the degradation of the modules because of the strong PID effect. Another important indication is that the positive bias does not influence much the performance of the modules, while the negative bias leads to an extensive degradation of their performance…”

“…Conversely, a small increase of the fill factor and of the short circuit current is observed during the first hours. This is due to the metastabilities of the PV modules in CIGS [35,36] and does not prevent the degradation of the modules because of the strong PID effect.…”