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

• Published in: Progress in photovoltaics Vol. 31; no. 8; pp. 824 - 839
• Main Authors: Villa, Simona, Aninat, Rémi, Yilmaz, Pelin, Kingma, Aldo, Dziechciarz, Mikolaj, Berg, Joran, Bakker, Klaas, Theelen, Mirjam
• Format: Journal Article
• Language: English
• Published: Bognor Regis Wiley Subscription Services, Inc 01.08.2023
• Subjects: Acetic acid; Circuits; Copper indium gallium selenides; Coring; Degradation; Electric contacts; Electrical properties; Ethylene vinyl acetates; Galvanic corrosion; Hydroxides; Moisture effects; Molybdenum; Photovoltaic cells; Reliability analysis; Vinyl acetate; Zinc oxide
• ISSN: 1062-7995; 1099-159X
• DOI: 10.1002/pip.3689

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. A local analysis of both electrical and material properties on a degraded field‐deployed commercial CIGS module was performed, allowing to trace back the occurring degradation mechanisms. The water‐induced degradation mainly resulted in acetic acid formation, Mo oxidation and corrosion at the P3 scribes, and ZnO degradation, through the formation of a Zn‐ and Mo‐based hydroxide. This resulted in a deterioration of the electrical properties, especially in terms of Rs increase, Voc reduction and Jsc limitation.