Understanding interfacial chemistry of positive bias high-voltage degradation in photovoltaic modules

Sinha, Archana; Moffitt, Stephanie L.; Hurst, Katherine; Kempe, Michael; Han, Katherine; Shen, Yu-Chen; Miller, David C.; Hacke, Peter; Schelhas, Laura T.

doi:10.1016/j.solmat.2021.110959

Understanding interfacial chemistry of positive bias high-voltage degradation in photovoltaic modules

Journal Article · Sun Jan 24 00:00:00 EST 2021 · Solar Energy Materials and Solar Cells

DOI:https://doi.org/10.1016/j.solmat.2021.110959· OSTI ID:1770895

^[1]; Moffitt, Stephanie L. ^[1]; ^[2]; Kempe, Michael ^[2]; Han, Katherine ^[3]; Shen, Yu-Chen ^[3]; ^[2]; Hacke, Peter ^[2]; ^[1]

SLAC National Accelerator Lab., Menlo Park, CA (United States)
National Renewable Energy Lab. (NREL), Golden, CO (United States)
SunPower Corporation, San Jose, CA (United States)

Photovoltaic module degradation from a high system voltage is a prevalent degradation mode in the field, where the enabling degradation mechanisms are inherently dependent on the voltage bias polarity of the installed system. In this study, the effects of positive bias on module performance are confirmed and the underlying chemical degradation processes are more thoroughly investigated to reveal different degradation pathways from those previously reported in negative bias studies. When cells are under +1000 V stress, crystalline silicon mini-modules with poly(ethylene-co-vinyl acetate) (EVA) encapsulant demonstrated a significant photocurrent loss due to EVA discoloration and delamination from increased chemical reactivity at the front-side EVA/cell metallization interface. Brown discoloration of the EVA encapsulant near the cell gridlines is linked to an electrochemical reaction at the Ag gridlines under hot and humid conditions (85 °C, 85% relative humidity). Chemical compositional analysis using X-ray photoelectron spectroscopy (XPS) confirmed that the discoloration is attributed to the formation of silver sulfide (Ag₂S) and/or silver oxide (Ag₂O) species at the EVA/Ag gridline interface. The subsequent migration of Ag ions from the cell gridlines into the bulk of the EVA was evident from XPS depth profiling and optical microscopy. However, the Ag signal was not detected at the EVA/glass interface, inferring limited ionic transport through the nominally 0.45 mm thick encapsulant. For the samples studied herein, the sulfur is believed by the process of elimination to come from the ambient air, diffusing into the module through the permeable polymer backsheet.

View Accepted Manuscript (DOE)

Research Organization:: National Renewable Energy Laboratory (NREL), Golden, CO (United States); SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)

Sponsoring Organization:: National Science Foundation (NSF); USDOE; USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Solar Energy Technologies Office; USDOE Office of Science (SC), Basic Energy Sciences (BES)

Grant/Contract Number:: AC02-76SF00515; AC36-08GO28308

OSTI ID:: 1770895

Alternate ID(s):: OSTI ID: 1808865
OSTI ID: 1809668

Report Number(s):: NREL/JA--5K00-78496; MainId:32413; UUID:1413b6f4-09af-43f5-8337-df796cfe7610; MainAdminID:19924

Journal Information:: Solar Energy Materials and Solar Cells, Journal Name: Solar Energy Materials and Solar Cells Vol. 223; ISSN 0927-0248

Publisher:: ElsevierCopyright Statement

Country of Publication:: United States

Language:: English

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