As a core component of photovoltaic modules, the photovoltaic diode's encapsulation structure must balance photoelectric conversion efficiency and long-term environmental adaptability, with a particular focus on breakthroughs in resistance to ultraviolet (UV) aging. UV radiation can cause molecular chain breakage, yellowing, and decreased light transmittance in encapsulation materials, leading to diode performance degradation. Therefore, encapsulation design needs to collaboratively improve UV resistance through material selection, structural optimization, and process control.
Encapsulation materials are fundamental to UV aging resistance. Traditional EVA films are prone to photo-oxidation under long-term UV exposure, generating carbonyl and other chromophores, resulting in yellowing and reduced light transmittance. Modern photovoltaic diode encapsulation uses UV-resistant EVA films, which, by introducing benzotriazole UV absorbers, effectively block UV rays in the 280-400nm wavelength range, converting them into harmless heat energy. Meanwhile, polyolefin (POE) films, due to their saturated carbon chain structure, naturally possess excellent UV resistance and offer an order of magnitude higher water vapor barrier than EVA, making them the preferred encapsulation material for high-end photovoltaic modules. Furthermore, the choice of glass cover is equally crucial. High-transmittance, low-iron tempered glass, by optimizing the iron content, shortens the UV cutoff wavelength to below 320nm. Combined with an anti-reflective coating, it can reduce UV penetration while maintaining light transmittance.
Multi-layer composite encapsulation structures achieve UV gradient shielding through functional layering. Taking a typical structure of "glass + anti-UV film + diode chip + backplane" as an example, the upper anti-UV film acts as the first line of defense, absorbing most short-wave UV rays; the middle diode chip, by optimizing the PN junction depth, reduces carrier recombination caused by direct UV irradiation; the lower backplane uses fluoropolymer materials, such as polyvinylidene fluoride (PVDF), whose high C-F bond energy resists residual UV corrosion and prevents secondary aging caused by moisture penetration. This layered design allows different materials to leverage their respective advantages, forming a synergistic protective effect.
Edge sealing technology is key to preventing lateral UV intrusion. Traditional components use silicone sealant at the edges, but long-term UV exposure can cause the silicone to become brittle and crack. The new packaging utilizes laser welding technology to fuse the glass, adhesive film, and backplane together to form seamless edges, completely eliminating UV penetration channels. Furthermore, some high-end products also apply a titanium dioxide nano-coating to the edge areas, utilizing its photocatalytic properties to decompose residual UV rays, further enhancing protective redundancy.
Surface treatment technology blocks direct UV radiation through physical barriers. The titanium dioxide anti-UV coating prepared by the sol-gel method forms a dense oxide film on the glass surface, with a refractive index matching the glass. This reduces UV intensity through reflection and scattering without affecting light transmittance. Fluoropolymer coatings form a stable protective layer on the material surface through chemical bonding, effectively inhibiting UV-induced free radical reactions and extending material lifespan.
Structural optimization design reduces the UV exposure area geometrically. For example, using a circular or hexagonal chip layout instead of the traditional rectangular design reduces the UV accumulation effect at the edges; optimizing the shape and spacing of the solder strips reduces the reflection and focusing of UV rays by the metal electrodes, preventing localized overheating and accelerated material aging. These seemingly minor design details significantly improve overall UV resistance.
In the process control stage, precise parameter management ensures encapsulation quality. During lamination, temperature, pressure, and time parameters must be strictly matched to material properties to avoid performance degradation due to insufficient or excessive cross-linking. For example, the cross-linking degree of the UV-resistant EVA film needs to be controlled between 75% and 85% to ensure a balance between its elastic modulus and UV resistance. Simultaneously, the production environment must employ a UV filtration system to prevent premature material aging during encapsulation.
Improving the UV resistance of photovoltaic diodes requires a comprehensive approach across the entire chain of materials, structure, and processes. Through the application of UV-resistant materials, multi-layer composite structure design, edge sealing reinforcement, surface treatment technology, structural optimization, and precise process control, a comprehensive protection system can be constructed from the surface to the depths, and from local to overall protection. This significantly extends the lifespan of photovoltaic diodes in harsh outdoor environments, providing a solid guarantee for the long-term stable operation of photovoltaic modules.
