backsheet

Backsheet is the rear cover of a solar photovoltaic module. It is a polymer film assembly that provides electrical insulation, a moisture barrier, UV protection, and mechanical protection for the photovoltaic cells and encapsulant. It also can help manage heat by reflecting sunlight when white.

Construction and materials: Modern backsheets are multilayer polymer films. They commonly come in two configurations: two-layer and three-layer. A typical three-layer backsheet consists of an outer fluoropolymer weather layer for UV resistance, a middle core such as polyester (PET) or polyamide for dimensional stability and strength, and an inner layer that acts as a moisture barrier and adhesion to the encapsulant. Some designs include a white pigment to increase reflectivity and reduce operating temperature. Two-layer backsheets substitute the middle layer with another polymer arrangement.

Manufacturing and performance: Backsheets are laminated to the rear of the module during lamination, between the encapsulant and the backsheet. They are designed to withstand outdoor exposure, including damp-heat, UV, and thermal cycling, as defined by international standards. Typical thickness ranges from about 0.15 to 0.30 millimeters.

Reliability and end of life: Common failure modes include delamination, yellowing, cracking, or moisture ingress, which can compromise insulation and promote corrosion of the cells or contacts. Backsheets are part of PV module recycling streams; their multi-layer structure can complicate recycling, and recovery strategies vary by region.