A Study of Degradation Mechanisms in PVDF-Based Photovoltaic Backsheets

Sona Ulicna, Michael Owen-Bellini, Stephanie Moffitt, Archana Sinha, Jared Tracy, Kaushik Roy-Choudhury, David Miller, Peter Hacke, Laura Schelhas

Research output: Contribution to journalArticlepeer-review

12 Scopus Citations

Abstract

Commercial backsheets based on polyvinylidene fluoride (PVDF) can experience premature field failures in the form of outer layer cracking. This work seeks to provide a better understanding of the changes in material properties that lead to crack formation and find appropriate accelerated tests to replicate them. The PVDF-based backsheet outer layer can have a different structure and composition, and is often blended with a poly(methyl methacrylate) (PMMA) polymer. We observed depletion of PMMA upon aging with sequential (MAST) and combined (C-AST) accelerated stress testing. In field-aged samples from Arizona and India, where PVDF crystallizes in its predominant α-phase, the degree of crystallinity greatly increased. MAST and C-AST protocols were, to some extent, able to replicate the increase in crystallinity seen in PVDF after ~ 7 years in the field, but no single-stress test condition (UV, damp heat, thermal cycling) resulted in significant changes in the material properties. The MAST regimen used here was too extreme to produce realistic degradation, but the test was useful in discovering weaknesses of the particular PVDF-based outer layer structure studied. No excessive β-phase formation was observed after aging with any test condition; however, the presence of β-phase was identified locally by Fourier transform infrared spectroscopy (FTIR). We conclude that both MAST and C-AST are relevant tests for screening outdoor failure mechanisms in PVDF backsheets, as they were successful in producing material degradation that led to cracking.

Original languageAmerican English
Article number14399
Number of pages11
JournalScientific Reports
Volume12
Issue number1
DOIs
StatePublished - Dec 2022

Bibliographical note

Publisher Copyright:
© 2022, The Author(s).

NREL Publication Number

  • NREL/JA-5900-83763

Keywords

  • accelerated stress testing
  • durability
  • DuraMAT
  • material characterization
  • photovoltaic backsheets
  • polymers
  • PVDF

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