As the outermost layer protecting photovoltaic (PV) modules, the backsheet is directly exposed to harsh environmental conditions and cyclic mechanical stress. Key performance parameters—such as adhesion, UV resistance, and mechanical strength—are critical factors that determine the overall service life of the module.

PV Module Backsheets

PV Module Backsheets

The Role of the Backsheet

The solar backsheet is located on the outermost layer of the module’s backside, maintaining direct contact with the external environment. Its performance is a decisive factor in both the functionality and longevity of the PV module. In outdoor environments, the backsheet protects solar cells from moisture ingress and acts as an oxygen barrier to prevent oxidation. Consequently, a high-quality backsheet must possess excellent high/low-temperature resistance, superior electrical insulation, aging resistance, and corrosion resistance. Furthermore, the backsheet serves to reflect sunlight to enhance conversion efficiency and provides high infrared emissivity to help reduce the module’s operating temperature.

 

The Role of the Backsheet

 

Common Failure Modes

Low-quality backsheets that have not undergone rigorous laboratory testing and outdoor validation inevitably lead to increased module failure rates. Cracked or failed backsheets severely compromise the performance and safety of the module, potentially causing electrical failures, safety hazards, and ground faults.

Common Failure Modes

Common Failure Modes

Impact and Consequences of Backsheet Failure

(1) Insufficient Interlayer Peel Strength / Delamination

  • Potential Causes: Inadequate corona treatment of the inner layer; instability in the coating process; insufficient adhesive strength of the interlayer glue; or failure to meet curing conditions during manufacturing.

  • Consequences: This issue reduces the sealing and water resistance of the module, significantly compromising its electrical insulation and safety performance.

Insufficient Interlayer Peel Strength

Insufficient Interlayer Peel Strength

(2) Backsheet Yellowing

  • Potential Causes: Under intense UV exposure, UV light penetrates the EVA layer, degrading the polyurethane adhesive layer and forming chromophoric groups (C=C conjugated double bonds). Once the adhesive layer degrades, UV light strikes the PET layer directly, causing molecular chain scission, powdering, and reduced mechanical properties.

  • Consequences: This leads to insulation failure and, in severe cases, cracking of the backsheet.

Backsheet Yellowing

Backsheet Yellowing

(3) Backsheet Lamination Failure (Layer Separation)

  • Potential Causes: Hydrolysis of the adhesive or incomplete curing of the glue.

  • Consequences: This significantly affects the sealing and moisture-proofing of the module, drastically reducing its electrical insulation safety and overall service life.

Backsheet Lamination Failure

Backsheet Lamination Failure

(4) Backsheet Cracking

  • Potential Causes: Use of substandard backsheet materials; poor weatherability of the inner PET layer.

  • Consequences: This leads to a decline in the sealing and water-repellent performance of the module, severely impacting its safety and electrical insulation reliability.

Backsheet Cracking

Backsheet Cracking

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