Microstructure changes during failure of PVDF‐based photovoltaic backsheets

Abstract

The backsheet layer of a solar module provides a safety and environmental barrier to the high voltages running through the photovoltaic (PV) cells and electrical contacts within the core of the module. However, in the past decade, backsheet cracking has become one of the most observed failure modes in PV module field surveys. In this work, the degradation of polyvinylidene fluoride (PVDF)-based backsheets is explored. Backsheet samples are either exposed to accelerated laboratory aging (UV light, heat, and moisture) or collected from the field. Fourier transform infrared and Raman spectroscopy, fragmentation testing, atomic force and scanning electron microscopy, and small-angle neutron scattering are combined to develop an understanding of how chemistry and microstructure evolve during aging. Chemical degradation, surface pitting, polymer phase changes, and anisotropic polymer domains are all observed in aged backsheet samples. The results provide insight into the degradation mechanisms that lead to cracking and field failure of PVDF-based backsheets. The comparison of aged PVDF-based backsheets helps to lay the groundwork for limiting polymer-based failure modes in PV modules.

Comprehensive review on performance, reliability, and roadmap of c‐Si PV modules in desert climates: A proposal for improved testing standard

“…[176][177][178] Unfortunately, the influence of the blend composition on these phenomena causing backsheet cracking is not fully understood yet. 177,179 Additionally, certain backsheet types have shown tendencies for insulation failures after some years of field exposure. 125,180 Until these effects are fully known and can be mitigated, backsheets made from these materials should be avoided in desert climates.…”

“…Also, polymers with metastable morphology like PVDF/polymethyl methacrylate (PMMA)/TiO 2 blends are potentially problematic, as the high temperature can induce a change in the crystalline phase, leading to shrinkage, embrittlement, and cracking 176–178 . Unfortunately, the influence of the blend composition on these phenomena causing backsheet cracking is not fully understood yet 177,179 . Additionally, certain backsheet types have shown tendencies for insulation failures after some years of field exposure 125,180 .…”

Effects of UV radiation on natural and synthetic materials

“…Importantly, yellowing is an indicator of degradation in progress of the backsheet, which can lead to more severe degradation. Advanced stages of degradation lead to delamination, embrittlement, or cracking resulting in the backsheet no longer providing electrical insulation [154,[169][170][171]. Cross-sections of weathered-adhered laminate sandwich constructions of a PV module (glass/encapsulate/ backsheet), using spatially resolved fluorescence imaging, for instance, show disproportionately high UV radiation damage to the adhesive layers [170].…”

Analysis of fracture damage mechanical properties of particle reinforced polymer composite film based on micro-macro finite element method

“…Shu et al [13] have proposed an adaptive finite element method for simulating the tangential fretting wear of PVDF piezoelectric thin films based on threedimensional (3D) sphere-on-flat contact model. Moffitt et al [14] have analyzed the chemistry and microstructure evolve of PVDF based back sheets during aging, including chemical degradation, surface pitting, polymer phase changes and anisotropic polymer domains. Kim et al [15] have compressively studied the mechanical properties of acrylonitrile butadiene styrene, polyethylene (PE) and PVDF under different temperature (−100 ∼ 25 • C) and strain rate (10 −4 ∼ 10 −2 s −1 ).…”