Insights into the moisture-induced degradation mechanisms on field-deployed CIGS modules

Moisture ingress is known to be one of the most frequent and detrimental causes of photovoltaic (PV) modules degradation. In an original approach, the present work applies the full analytic capability of lab-scale equipment to characterize a commercial Cu(In,Ga)(Se,S)(2) (CIGS) module that degraded in the field due to moisture ingress. By extracting (coring) and unpackaging samples from different areas of the module, we are able to track the propagation of the degradation mechanisms with respect to both material and electrical properties. The three following locations in the device were found to be affected by the water ingress: first, the encapsulant, ethylene-vinyl acetate (EVA), resulting in delamination and acetic acid formation; second, the molybdenum (Mo) back contact, which oxidizes and corrodes entirely at the P3 scribes; lastly, the ZnO front contact, through the formation of Zn-based hydroxides and its further reaction with the Mo migrating from the degraded scribes. The main impact on the electrical properties is an increase in series resistance and a decrease in both open-circuit voltage and short-circuit current. In the last degradation stage, that is, the most degraded area of the module, a complete performance loss is observed. The results of this work further our understanding of the physics and chemistry involved in the moisture-induced degradation in CIGS modules. In particular, the study highlights the interactions between the various degradation products and associated degradation mechanisms. These results also illustrate the broader potential of the coring and unpackaging method for reliability studies of full-sized, field-degraded commercial PV modules.