Characterizing Photovoltaic Backsheet Adhesion Degradation Using the Wedge and Single Cantilever Beam Tests, Part II: Accelerated Tests

Scott Julien, Michael Kempe, Joshua Eafanti, Joshua Morse, Yu Wang, Andrew Fairbrother, Sophie Napoli, Adam Hauser, Liang Ji, Gregory O'Brien, Xiaohong Gu, Roger French, Laura Bruckman, Kai-tak Wan, Kenneth Boyce

Research output: Contribution to journalArticlepeer-review

15 Scopus Citations


Photovoltaic (PV) backsheets provide critical moisture, mechanical, and electrical insulation to the backside of PV modules, but their continued functionality depends upon their ability to remain well adhered over years of harsh environmental exposure. A study of adhesive strength was conducted on several PV backsheet types exposed to indoor accelerated weathering. Two adhesion tests – the wedge test and single cantilever beam test – were used to measure adhesion energy in four backsheets: two with fluoropolymer-based outer (airside) layers – polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF) – and two with non-fluoropolymer-based outer layers–polyamide (PA) and polyethylene terephthalate (PET). The effects of changes in temperature, ultraviolet (UV) irradiance, relative humidity, and a periodic water spray were studied. The PET-, PVF- and PVDF-based backsheets all showed instances of debonding in an adhesive layer, which is commonly reported. For the PA-, PET-, and PVDF-based backsheets, adhesion energy dropped fairly rapidly with exposure, reaching very low levels by 4000 h. The PVF-based backsheet was relatively robust to weathering. Pull-off of an outer chalking layer in the PA- and PET-based backsheets suggested a sensitivity to UV. Adhesion in these two backsheets was also highly sensitive to changes in moisture level. Changes in UV irradiance and temperature did not show a statistically significant effect on adhesion loss for the exposure levels used. The present work is part of a two-part adhesion study on both field-weathered and indoor-exposed backsheets, and forms a basis for understanding adhesion degradation across a variety of backsheet types and degradation factors.

Original languageAmerican English
Article numberArticle No. 110524
Number of pages10
JournalSolar Energy Materials and Solar Cells
StatePublished - 1 Jul 2020

Bibliographical note

Publisher Copyright:
© 2020 Elsevier B.V.

NREL Publication Number

  • NREL/JA-5K00-77161


  • Accelerated weathering
  • Adhesion
  • Backsheet
  • Degradation
  • Delamination
  • Photovoltaic


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