PVB (Polyvinyl Butyral) film: composition and application
PVB is the abbreviation of Polyvinyl butyral film which is a resin that is used as a back sheet material in solar modules.
The backsheet of a solar module consists of multiple layers of barrier films and adhesives. The backsheet construction is instrumental in protecting the solar cells from different environmental conditions like moisture, UV exposure and other performance threats while also improving solar module efficiency by aiding the reduction of partial discharge. To accomplish this, the solar panel material should be of a robust construction, usually a three-layer laminate, and it should possess high dielectric properties. Most backsheets consist of combinations of films chosen for their different properties. Examples of standard films include: PET or EVA, Tedlar and Kynar. Combinations can be TPT (Tedlar/PET/Tedlar), KPK (Kynar/PET/Kynar) or PPE (PET/PET/EVA) among other combinations.
What is PVB ?
Polyvinyl butyral is a resin which is typically used in different applications which require strong binding properties, transparency, adhesion to different surfaces, flexibility and toughness. PVB is prepared from the reaction of polyvinyl alcohol with butyraldehyde. The main application for PVB is laminated safety glass used for car windshields and solar backsheets. Market names for PVB– films include Saflex, Butacite and EVERLAM.
PVB use in solar panels
PVB became popular in manufacturing of thin film solar PV modules. The PV circuit is formed on a glass sheet using thin film deposition and patterning techniques. Two layers, which are a PVB layer and a second layer of glass (called back glass) are then placed directly on the circuit. This lamination encapsulates the circuit and protects it from the environmental conditions. PVB backsheet provides a range of properties as it has good impact properties and is considered a cheaper alternative to tedlar based backsheets. The optical properties of PVB are better than that of EVA, also the adhesion of PVB to photovoltaic cell is better than EVA.
Alternatives to PVB
PVB layers need to be combined with a low WVTR layer due to its higher water uptake and high sensitivity to hydrolysis. EVA is still the most popular encapsulant material for pv modules. (Tedlar/Polyester/Eva Film) backsheets among other combinations. Other famous alternatives are Tedlar and Kynar based backsheets.