Newer coated PET backsheets reduced fluorine content to below 1%, compared to more than 12 wt% in older designs
The study identifies a gradual industry shift toward thinner fluoropolymer layers, coated PET backsheets, and glass-glass module designs
Although fluoropolymer use has declined in recent years, older fluorinated backsheets will continue entering recycling streams for decades due to the long operating lifetime of PV modules
The rapid growth of PV is bringing more attention to what happens to modules at the end of their life. Global installed solar capacity reached around 2.2 TW in 2024, and deployments have continued to expand since. As more and more modules are retired over time, recycling is becoming an increasingly important part of the PV value chain.
Given their material composition, there is increasing focus on backsheets. While they make up only a small part of a module, backsheets are important for insulation and protecting the module from environmental exposure. Fluoropolymers such as PVF and PVDF have long been used in backsheets because of their strong resistance to weathering and long-term degradation. However, these materials can complicate recycling, as thermal treatment may release hydrofluoric acid (HF), necessitating dedicated gas-handling systems.
Researchers from TU Wien and OFI conducted a study, investigating backsheet designs used between 1988 and 2024 and tracking shifts in fluorine content as the industry moved toward different material structures.
The researchers analyzed 23 backsheet samples taken from end-of-life modules. The work focused on identifying layer composition, measuring thickness, and estimating fluorine content across different structures. Older PVF/PET/PVF backsheets from the late 1980s showed fluorine content as high as 12.3 wt% at the backsheet level. At the layer level, PVF materials contained around 30 wt% fluorine, while PVDF layers contained roughly 42 wt%. In some THV-based structures, fluorine content was even higher, exceeding 70 wt%.
The study shows a gradual reduction in the use of fluorine over time. Manufacturers started using thinner fluoropolymer layers and replaced inner fluorinated layers with polyethylene and other non-fluorinated materials. This reduced the total fluorine content in many backsheet designs to ~2.8%-4.7%.
A bigger change came with the adoption of coated PET backsheets. Instead of using thick multilayer laminates, these designs rely on thin protective coatings over a PET base layer. In many of these newer structures, the fluorine content dropped below 1%, typically ranging between 0.04% and 0.8%.
The market has gradually shifted toward simpler backsheet structures. Coated PET backsheets gained share over the last decade, while glass-glass module designs further reduced the need for polymeric backsheets altogether. According to the study, fluoropolymer use increased through the 2010s before beginning to decline as coated PET and glass-glass designs gained share.
This transition is also reflected in TaiyangNews Backsheets & Encapsulation Market Survey 2025. Between 2023 and 2024, the share of PVDF-based backsheets declined from 15% to 7%, while Tedlar-based structures dropped from 6% to 3%. At the same time, non-fluoropolymer backsheets increased from 24% to 30%, alongside continued growth in double-sided coated backsheets.
Even as newer low-fluorine designs gain share, older fluoropolymer-based modules will continue to enter the waste stream for decades. Given the long operating lifetimes of PV systems, many high-fluorine backsheets installed in earlier years are only now reaching the end of their life. This leaves recyclers managing a mix of legacy fluorinated materials and newer low-fluorine structures.
The study also points to an important trade-off: fluoropolymer-based backsheets have shown strong durability under long-term field exposure, while certain fluorine-free alternatives have raised questions around long-term reliability. As material designs evolve, recyclability and long-term performance need to be addressed together.
Full findings are available in the paper titled Evolution of the fluorine content in photovoltaic module backsheets, published on ScienceDirect.
