1. Molecular dynamics perspective:In high temperature and high humidity environments, the molecular motion inside the material is further intensified. For polymer materials, the increase in temperature and humidity significantly increases the thermal energy of their molecular chains, resulting in faster movement of molecular segments. The originally tight arrangement between molecular chains becomes looser, and the gaps increase. Taking EVA, the packaging material for photovoltaic modules, as an example, under high temperature and high humidity conditions, its molecular chains are more prone to large gaps. Water vapor molecules can not only pass through the gaps generated at high temperatures, but also more easily penetrate into the interior of the material through the accumulation and diffusion of water vapor in high humidity environments, thereby seriously reducing the barrier performance of the material. In addition, according to Fick's law, high temperature and humidity will significantly increase the diffusion coefficient of water vapor molecules in the material, making their diffusion speed faster and easier, further weakening the material's ability to block water vapor.

2. From the perspective of changes in the physical and chemical properties of materials:

physical change:Many materials undergo more significant physical changes in high temperature and high humidity environments. Under high temperature and high humidity conditions, the speed at which thermoplastic packaging materials transition from a harder glass state to a soft and highly elastic state accelerates. Additionally, due to the influence of humidity, the volume expansion of the material is greater, and the internal structure becomes looser. For example, the sealant in photovoltaic modules undergoes increased volume expansion under high temperature and humidity, which makes it easier for small gaps to appear at the sealing point. A large amount of water vapor and oxygen can easily enter the interior of the photovoltaic module through these gaps.

Chemical changes:High temperature and humidity can also cause more complex chemical changes in materials. In photovoltaic module materials, chemical bonds are more likely to break or recombine in this environment. For materials containing additives, the decomposition reaction of the additives under high temperature and humidity may accelerate, producing more small molecule substances. These small molecule substances not only form more channels inside the material, but also may react with water vapor, changing the chemical structure of the material and making it more easily penetrated by water vapor and oxygen. Materials containing carbon hydrogen (C-H) bonds exhibit accelerated oxidation reaction rates and more severe damage to their barrier properties in the presence of high temperature, high humidity, and oxygen.

Taking ethylene vinyl acetate copolymer (EVA) as an example, at room temperature, it has a certain barrier effect on water vapor and oxygen through the interaction of molecular chains, and has good flexibility and adhesion, which can effectively encapsulate battery cells with other component materials. When in a high temperature and high humidity environment, the barrier performance of EVA decreases more significantly. On the one hand, EVA, as a thermoplastic material, exhibits intense molecular chain movement under high temperature and high humidity, resulting in a further increase in the spacing between molecular chains; On the other hand, the decomposition reaction of vinyl acetate (VA) component in EVA is accelerated under high temperature and high humidity, resulting in an increase in small molecule substances. These factors work together to double the water vapor permeability of EVA compared to room temperature, which is extremely detrimental to the protection of components such as solar cells inside photovoltaic modules.

1. Testing method

➣ Water vapor permeability test

Infrared sensor method:Use infrared sensors to detect the concentration of water vapor passing through the material. In a high-temperature and high humidity testing environment, the material is placed between a sensor and a water vapor source. The sensor can measure the amount of water vapor passing through the material in real time and quickly calculate the water vapor transmission rate. If the W413 2.0 water vapor permeability tester developed and produced by Guangzhou Biaojian is used in conjunction with the GB-YBT photovoltaic sheet testing platform, the water vapor permeability performance of the material can be accurately measured under simulated high temperature and high humidity conditions.

▲ Y310 2.0 Oxygen Transmittance Tester+GB-YBT310 Photovoltaic Sheet Testing Platform

In the photovoltaic industry, different countries and regions have varying requirements for the water vapor transmission rate of backsheet materials. Sharp, Kyocera and other Japanese companies have strict requirements, which must be below 0.3 g/m ² · day; Similar products in Germany and Austria require a WVTR of 1.6 g/m ² · day, while domestic industry standards stipulate a WVTR of less than 2.5 g/m ² · day. There are corresponding qualified range standards for barrier performance indicators such as water vapor permeability and oxygen permeability. If the barrier performance test results of the material under high temperature and high humidity exceed these standard ranges, the material may not be suitable for use in photovoltaic modules, or its formula and production process may need to be further improved to ensure the reliability, durability, and safety of photovoltaic modules in actual high temperature and high humidity application environments.