This part of IEC 62788 defines test methods and datasheet reporting requirements for safety and performance-related properties (mechanical, electrical, thermal, optical, chemical) of non-rigid polymeric materials intended for use in terrestrial photovoltaic modules as polymeric front- and backsheets.

The test methods in this document define how to characterize front- and backsheet materials and their components in a manner representative of how they will be used in the module, which eventually includes combination with other matched components such as encapsulants or adhesives. It is impractical to conduct all characterization and endurance tests for the front- or backsheet component on the module level. Instead, testing is performed directly on these components or on dedicated test coupons prepared under comparable processing conditions (i.e. lamination) as for PV modules.

Results of testing described in this document are called by IEC 62788‑2‑1 for safety qualification of polymeric front- and backsheets on component level and support the safety and performance-related tests defined on the PV module level as defined in the series IEC 61730 (for safety) and IEC 61215 (for performance). This document also defines test methods for assessing inherent material characteristics of polymeric front- and backsheets or their components, which can be required in datasheet reporting or can be useful in the context of product development or design of PV modules.

Backsheets provide the electrical insulation at the backside of a photovoltaic (PV) module under the environmental stress factors and use conditions encountered during the intended lifetime of the module. Frontsheets have the same function at the sun-facing side of the module. Both can be made from glass or polymeric material.

Polymeric front- and backsheets are typically compositions of layered materials, such as films, adhesives or coatings, in which at least one material layer delivers the relied-upon insulation (RUI) for electrical safety. Other layers can provide extended protection of the RUI against the environmental factors or adhesive functionality. As an integral part of the PV module, the front- or backsheet provides their durable electrical insulating function in the presence of the other components of the PV module, such as solar cells, electrical circuits and connectors, encapsulant, sealing material, and junction boxes. These elements can introduce additional stresses on the front- or backsheet (e.g. by chemical interactions or introducing thermal load or mechanical stress) or alter environmental stresses (e.g. filtering of ultraviolet radiation reaching the sun-facing side of the backsheet).

Material characterization in this document is performed on unaged samples (after a thermal pre-exposure) or after accelerated ageing including thermo-oxidative ageing (thermal endurance and failsafe tests), hydrolytic ageing (damp heat), photolytic ageing (UV weathering), abrasion, and sequential UV ageing plus thermal cycling.

Rigid polymeric sheet materials (also providing mechanical support) can require further consideration, which is outside the scope of this document.