Title: Cohesive and adhesive degradation in PET-based photovoltaic backsheets subjected to ultraviolet accelerated weathering

Abstract

Delamination between layers in photovoltaic (PV) backsheets is often reported in the literature, causing voids that can collect moisture, diminish module backside heat dissipation, and reduce the backsheet’s effectiveness as a physical barrier. While backsheets with weathering-resistant fluoropolymer outer layers have traditionally been used in modules, more recent backsheets using non-fluoropolymer outer layers, such as polyethylene terephthalate (PET), have been developed. These backsheets have shown signs of premature degradation, and their adhesion degradation, in particular, has not been widely studied. In the present work, the single cantilever beam (SCB) adhesion test was used to quantify the adhesion energy in two commercially available PET-based backsheets. To study the effect of minor changes in formulation, the backsheets were obtained from same manufacturer and product line but during different years. To study the effect of environmental variables on adhesion degradation, the backsheets were subjected to artificial weathering at controlled temperature, humidity, and ultraviolet (UV) radiation in an indoor weathering chamber, and the adhesion energy was quantified at several intervals of exposure time. Layering structure, composition, and adhesion failure mode were compared between the backsheets, using Raman and infrared spectroscopy and thermogravimetric analysis. The results show a large difference in initial (unexposed) adhesion energymore » between the backsheets, despite very similar structures and compositions. Following exposure, adhesion energy dropped significantly, primarily due to thermo-hydrolytic degradation of the polyurethane (PU)-based adhesive layers. Significant UV-induced adhesion degradation of the PET outer layer surface was also observed. The study represents an important step in understanding adhesion degradation in PET-based backsheets, suggesting ways in which adhesion integrity – and, correspondingly, module service life – can be improved.« less

Authors:

Julien, Scott E.  ^[1];

• Search DOE PAGES for author "Julien, Scott E."
• Search DOE PAGES for ORCID "0000-0003-3881-1215"

Kim, Jae Hyun ^[2]; Lyu, Yadong ^[2]; Miller, David C.  ^[3];

• Search DOE PAGES for author "Miller, David C."
• Search DOE PAGES for ORCID "0000-0002-4698-5277"

Gu, Xiaohong ^[2]; Wan, Kai-tak ^[1]

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+ Show Author Affiliations

1. Northeastern Univ., Boston, MA (United States)
2. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)
3. National Renewable Energy Lab. (NREL), Golden, CO (United States)

Publication Date:

Tue Jun 22 00:00:00 EDT 2021

Research Org.:

National Renewable Energy Lab. (NREL), Golden, CO (United States)

Sponsoring Org.:

USDOE Office of Energy Efficiency and Renewable Energy (EERE)

OSTI Identifier:

1806558

Report Number(s):

NREL/JA-5K00-80456
Journal ID: ISSN 0038-092X; MainId:42659;UUID:5688056a-27c8-4e8a-a87e-23bec86d95cd;MainAdminID:25756

Grant/Contract Number:  

AC36-08GO28308

Resource Type:

Accepted Manuscript

Journal Name:

Solar Energy

Additional Journal Information:

Journal Volume: 224; Journal ID: ISSN 0038-092X

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

14 SOLAR ENERGY; accelerated weathering; adhesion; backsheet; delamination; photovoltaic