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Title: Defining Threshold Values of Encapsulant and Backsheet Adhesion for PV Module Reliability: Preprint

Abstract

The width-tapered cantilever beam method is used to quantify the debond energy (adhesion) of encapsulant and backsheet structures of 27 modules collected from the field. The collected population of modules contains both those that have remained in-tact and those with instances of either or both encapsulant and backsheet delamination. From this survey, initial threshold values (an adhesion value above which a module should remain intact throughout its lifetime) for encapsulant and backsheet interfaces are proposed. For encapsulants this value is about 60 J/m2 and for backsheets about 20 J/m2. It is expected that these values will continue to be refined and evolve as the width-tapered cantilever beam method becomes adopted by the PV industry, and that they may aid in the future improvement of accelerated lifetime tests and the development of new, low-cost materials.

Authors:
 [1];  [1];  [1];  [2];  [2]
  1. National Renewable Energy Laboratory (NREL), Golden, CO (United States)
  2. Stanford University
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Solar Energy Technologies Office (EE-4S)
OSTI Identifier:
1378265
Report Number(s):
NREL/CP-5J00-67767
Journal ID: ISSN 2156--3381
DOE Contract Number:
AC36-08GO28308
Resource Type:
Conference
Resource Relation:
Journal Volume: 7; Journal Issue: 6; Conference: Presented at the 2017 IEEE 44th Photovoltaic Specialists Conference (PVSC), 25-30 June 2017, Washington, DC
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; PV module reliability; encapsulant; backsheet; adhesion

Citation Formats

Bosco, Nicholas S, Kurtz, Sarah, Eafanti, Joshua, Tracy, Jared, and Dauskardt, Reinhold. Defining Threshold Values of Encapsulant and Backsheet Adhesion for PV Module Reliability: Preprint. United States: N. p., 2017. Web. doi:10.1109/JPHOTOV.2017.2746682.
Bosco, Nicholas S, Kurtz, Sarah, Eafanti, Joshua, Tracy, Jared, & Dauskardt, Reinhold. Defining Threshold Values of Encapsulant and Backsheet Adhesion for PV Module Reliability: Preprint. United States. doi:10.1109/JPHOTOV.2017.2746682.
Bosco, Nicholas S, Kurtz, Sarah, Eafanti, Joshua, Tracy, Jared, and Dauskardt, Reinhold. 2017. "Defining Threshold Values of Encapsulant and Backsheet Adhesion for PV Module Reliability: Preprint". United States. doi:10.1109/JPHOTOV.2017.2746682. https://www.osti.gov/servlets/purl/1378265.
@article{osti_1378265,
title = {Defining Threshold Values of Encapsulant and Backsheet Adhesion for PV Module Reliability: Preprint},
author = {Bosco, Nicholas S and Kurtz, Sarah and Eafanti, Joshua and Tracy, Jared and Dauskardt, Reinhold},
abstractNote = {The width-tapered cantilever beam method is used to quantify the debond energy (adhesion) of encapsulant and backsheet structures of 27 modules collected from the field. The collected population of modules contains both those that have remained in-tact and those with instances of either or both encapsulant and backsheet delamination. From this survey, initial threshold values (an adhesion value above which a module should remain intact throughout its lifetime) for encapsulant and backsheet interfaces are proposed. For encapsulants this value is about 60 J/m2 and for backsheets about 20 J/m2. It is expected that these values will continue to be refined and evolve as the width-tapered cantilever beam method becomes adopted by the PV industry, and that they may aid in the future improvement of accelerated lifetime tests and the development of new, low-cost materials.},
doi = {10.1109/JPHOTOV.2017.2746682},
journal = {},
number = 6,
volume = 7,
place = {United States},
year = 2017,
month = 8
}

Conference:
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  • The width-tapered cantilever beam method is used to quantify the debond energy (adhesion) of encapsulant and backsheet structures of 32 modules collected from the field. The collected population of modules contains both those that have remained intact and those with instances of either or both encapsulant and backsheet delamination. From this survey, initial threshold values (an adhesion value above which a module should remain intact throughout its lifetime) for encapsulant and backsheet interfaces are proposed. For encapsulants this value is ~ 160J/m 2 and for backsheets ~ 10J/m 2. Here, it is expected that these values will continue to bemore » refined and evolve as the width-tapered cantilever beam method gets adopted by the PV industry, and that they may aid in the future improvement of accelerated lifetime tests and the development of new, low-cost materials.« less
  • Presented at the 2001 NCPV Program Review Meeting: Measurements of backsheet moisture permeation and encapsulant-substrate adhesion. At the March 2001 NCPV workshop on ''Moisture Ingress and High-Voltage Isolation'', industry participants identified several properties associated with PV module durability that are critical for commercial success. These include interface conductivity, adhesion of encapsulants to substrate materials as a function of in-service exposure conditions, and moisture permeation through backsheet materials as a function of temperature. Electrical data is discussed in a companion paper; adhesion and water vapor transmission rate (WVTR) measurements are presented herein.
  • Among the infrequently measured but essential properties for thin-film (T-F) module reliability are the interlayer adhesion and cohesion within a layer. These can be cell contact layers to glass, contact layers to the semiconductor, encapsulant to cell, glass, or backsheet, etc. We use an Instron mechanical testing unit to measure peel strengths at 90{sup o} or 180{sup o} and, in some cases, a scratch and tape pull test to evaluate inter-cell layer adhesion strengths. We present peel strength data for test specimens laminated from the three T-F technologies, before and after damp heat, and in one instance at elevated temperatures.more » On laminated T-F cell samples, failure can occur uniformly at any one of the many interfaces, or non-uniformly across the peel area at more than one interface. Some peel strengths are << 1 N/mm. This is far below the normal Instron mechanical testing unit Instron mechanical testing unit; glass interface values of >10 N/mm. We measure a wide range of adhesion strengths and suggest that adhesion measured under higher temperature and relative humidity conditions is more relevant for module reliability.« less
  • Delamination of encapsulant materials from PV cell surfaces often appears to originate at regions with metallization. Using a fracture mechanics based metrology, the adhesion of EVA encapsulant to screen printed silver metallization was evaluated. At room temperature, the fracture energy, Gc [J/m2], of the EVA/silver interface (952 J/m2) was ~70% lower than that of the EVA/AR coating (>2900 J/m2) and ~60% lower than that of the EVA to the surface of cell (2265 J/m2). After only 300 hours of damp heat aging, the adhesion energy of the silver interface dropped to and plateaued at ~50-60 J/m2, while that of themore » EVA/AR coating and EVA/cell remained mostly unchanged. Elemental surface analysis showed that the EVA separates from the silver in a purely adhesive manner, indicating that bonds at the interface were likely displaced in the presence of humidity and elevated temperature, and may explain the propensity for delamination to occur at metallized surfaces in the field.« less
  • Engineering robust adhesion of the junction-box (j-box) is a hurdle typically encountered by photovoltaic (PV) module manufacturers during product development. There are historical incidences of adverse effects (e.g., fires) caused when the j-box/adhesive/module system has failed in the field. The addition of a weight to the j-box during the 'damp heat' IEC qualification test is proposed to verify the basic robustness of its adhesion system. The details of the proposed test will be described, in addition to the preliminary results obtained using representative materials and components. The described discovery experiments examine moisture-cured silicone, foam tape, and hot-melt adhesives used inmore » conjunction with PET or glass module 'substrates.' To be able to interpret the results, a set of material-level characterizations was performed, including thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. PV j-boxes were adhered to a substrate, loaded with a prescribed weight, and then placed inside an environmental chamber (at 85C, 85% relative humidity). Some systems did not remain attached through the discovery experiments. Observed failure modes include delamination (at the j-box/adhesive or adhesive/substrate interface) and phase change/creep. The results are discussed in the context of the application requirements, in addition to the plan for the formal experiment supporting the proposed modification to the qualification test.« less