Discussion on the selection of photovoltaic adhesive film from the perspective of reliability in outdoor application of components
Jul 17, 2024
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2024 will be an important year for the survival of the fittest in the photovoltaic industry, as fierce competition leads to the iteration of battery technology and the speed of industrial application far exceeding that of ten years ago.
However, no matter how the battery is iterated, whether to choose POE (polyolefin elastomer), EVA (ethylene vinyl acetate copolymer), or EPE for packaging of double glass components, single glass components, or flexible components, this is always an unavoidable and fiercely discussed topic.
The heat, oxygen, water, ultraviolet radiation, and biological activity in the environment are the main factors causing material failure. In outdoor applications of photovoltaic modules, besides excluding biological activity, the other four major environmental factors cannot be ignored. Therefore, the selection of materials should first consider the impact of these four factors on the materials.
This article compares the effects of EVA and POE on these four environmental factors, providing a new approach and method for selecting materials.
1. Heat
Both EVA and POE materials can withstand short-term high temperature exposure of about 150 ℃ after crosslinking, but if the temperature continues to increase, EVA will decompose and release a large amount of acetic acid above 200 ℃. The thermal decomposition temperature of POE requires at least 300 ℃.
2. Oxygen
EVA and POE are not easily oxidized at room temperature, but due to the presence of a small amount of free acetic acid monomer in EVA, they will be oxidized at high temperatures. However, POE is all chemically stable carbon hydrogen bonds, and the temperature at which it reacts with oxygen is much higher than EVA.
3. Water
From a molecular structure perspective, EVA contains ester groups, which are easily hydrolyzed. The carboxyl end groups produced by hydrolysis further promote the hydrolysis reaction, leading to rapid aging of the material. And POE has high chemical stability of all carbon hydrogen chains, which is not affected by hydrolysis. On the other hand, the water vapor transmission rate of EVA film at 38 ℃ and 90% RH is about 25g/m ^ 2 · 24h, while the water vapor transmission rate of POE film is 3g/m ^ 2 · 24h. That is to say, the water vapor transmission rate of POE is much lower than that of EVA film, which makes POE not only difficult to hydrolyze, but also has much higher water resistance than EVA, thus providing strong protection for other components inside the module.
4. Ultraviolet radiation
Similarly, POE is a fully carbon hydrogen chain structure with a high chemical bond energy, with C-H bond energy of 414 kJ/mol and C-C bond energy of 332 kJ/mol. It is not easily broken by UV radiation when exposed to the ground, while the C-O bond energy of the ester group in EVA is less than 330 kJ/mol, making it more susceptible to UV radiation and fracture.
In summary, in the use of packaging materials, POE is superior to EVA in terms of the four major elements of outdoor application reliability: heat, oxygen, water, and ultraviolet performance. In today's increasingly "high-efficiency" and "strict requirements" for batteries, POE is still the best choice to ensure long-term stable and continuous "output" of batteries.