What is photovoltaic film and what are its types?
1. What is Photovoltaic Film?
Photovoltaic film is a thin film material used for photovoltaic module encapsulation, primarily for module-level encapsulation of solar panels. It is positioned between the cell and the photovoltaic glass and backsheet, providing bonding, protection, light transmission, and insulation. The performance of photovoltaic film directly impacts the module's power generation efficiency, weather resistance, and service life. It is one of the core materials affecting photovoltaic module quality, accounting for 3%-4% of the module cost.
2. Types of Photovoltaic Film
EVA Film
EVA film is primarily composed of a copolymer of ethylene and vinyl acetate, with additives such as crosslinkers, thickeners, antioxidants, and light stabilizers. It exhibits excellent flexibility, impact resistance, elasticity, optical transparency, low-temperature flexural strength, adhesion, environmental stress cracking resistance, weather resistance, corrosion resistance, heat sealing, and electrical properties. EVA film can be further categorized into four types: high-transmittance, high-cutoff, white, and black. Single-glass modules typically utilize a combination of high-transmittance EVA and white EVA for encapsulation. This increases both light transmittance from the front and light reflectivity from the inner layers, thereby improving the module's photovoltaic conversion efficiency. Black single-glass modules typically utilize a combination of high-transmittance EVA, high-cutoff EVA, and a black backsheet, or high-transmittance EVA, black EVA, and a white backsheet for encapsulation. The high-cutoff EVA blocks UV rays from sunlight, reducing damage to the inner backsheet. Currently, transparent EVA film remains the most widely used film in the market, accounting for approximately 42.5% of the market share.
POE Film
POE film is made from POE resin with the addition of appropriate processing aids. POE is a random copolymer elastomer formed by the polymerization of ethylene and 1-octene. It features a low melting point, a narrow molecular weight distribution, and long chain branches. In the ethylene-octene copolymer system, octene units can be randomly attached to the ethylene backbone, resulting in excellent mechanical properties and light transmittance. POE film offers excellent water vapor barrier properties, with a water vapor transmission rate approximately one-eighth that of EVA. Its stable molecular chain structure and slow aging make it ideal for protecting solar cells from water vapor corrosion in high-temperature and high-humidity environments, enhancing the resistance of solar panels to potential-induced degradation (PID). It also exhibits excellent weather resistance, lacking hydrolyzable ester bonds in its molecular chain, which prevents the generation of acidic substances during aging. POE film is primarily used in double-glass N-type photovoltaic modules.
EPE film
EPE film is a multi-layer co-extruded EVA/POE/EVA film formed by co-extrusion of EVA and POE. POE film is prone to additive precipitation during lamination, resulting in film slippage during use and affecting product yield. EPE film addresses this issue. It combines the advantages of both EVA and POE, offering the water barrier and PID resistance of POE with the high adhesion of EVA. With the development of double-glass modules and N-type cells, the market share of EPE film has gradually increased, reaching 27.8% in 2023.
Other Films
In addition to the three common films mentioned above, there are also films used in specific scenarios. For example, PVB film (polyvinyl butyral) has gained a foothold in BIPV (building-integrated photovoltaic) modules due to its cross-linking resistance and recyclability. However, its light transmittance (89-90%) is lower than that of POE, and its water vapor barrier properties are poor, limiting its application range. Perovskite modules, due to their high sensitivity to moisture and oxygen, use TPO film or POE film as encapsulation materials. Furthermore, silicone film has seen an increase in market share in high-temperature regions, and butyl film is also being explored for heterojunction encapsulation.
Different types of photovoltaic films vary in performance, cost, and application scenarios. With the continuous development of the photovoltaic industry, the performance requirements for photovoltaic films are becoming increasingly stringent. Film companies are constantly innovating to develop products that better meet market demands.
As a professional EVA membrane manufacturer, Shengding (trademark name) has always been committed to the development and research of this industry. If you have any related questions, you are welcome to give us your suggestions!
