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Solar cell backsheet performance and detection method
- May 16, 2018 -

The back sheet of the solar battery is located on the outermost layer of the back of the module and protects the solar module from water vapor in the outdoor environment. Generally, it has a three-layer structure. The outer protective layer has good resistance to environmental erosion (prevents water vapor attack, UV resistance, etc.), the middle layer is PET polyester film has good insulation properties and strength, the inner layer film PEVA or PE and EVA film have good adhesion Performance.


First, thickness


For different materials, the thickness of the finished product is also not the same, in order to achieve a certain degree of insulation performance, in general, the thickness of PET is 250μm, the thickness of PVDF film is 25μm, the thickness of PEVA film is 70μm, the thickness of two layers of adhesive are About 10μm. Therefore, the thickness of the solar back plate KPK is 320±10 μm, and the thickness of the KPE is 365±10 μm.


Detection method: Thickness gauge is used to measure the material thickness.


Second, tensile strength, elongation at break, peel strength, etc.


1, tensile strength (divided into MD, TD):


The maximum load at the time of back-sheet specimen breakage is different for different backings of different thickness and different materials.


2, elongation at break (divided into MD, TD):


The maximum elongation at break of the back-sheet specimen has different elongation at break for different thicknesses and different materials.


3. Initial interlayer peel strength (MD, TD and first and second sides):


The bond strength between the layers of the backsheet was tested and the most common criterion was ≥ 4 N/cm (1 N/cm = 1000 Pa).


4. Peel strength after boiled (MD, TD and first and second sides):


After the backplane was placed in a boiling water bath for 24 hours, the bond strength between the layers of the backboard was tested. The most common standard was ≥4 N/cm (1 N/cm=1000 Pa). No boiled, yellowed after boiling. , folds, delamination and other undesirable phenomena.


5. Peel strength after backing and EVA film lamination:


Test the bonding strength of the backplane and EVA film after lamination. This test is to simulate the production status of the module. There is a certain gap between the bond strengths of different backplanes and different EVA films, but the general standard is ≥40N. /cm.


Detection method: Take a piece of tempered glass with a length of about 300mm and a width of 150mm. Laminate the same size of backplate and EVA in turn on the tempered glass and laminate them in a laminator. After lamination and curing, it was left to cool at room temperature for more than 4 hours, and the cured part was cut into 1*300 mm strips. Take several of them, manually separate the backplane from EVA by about 20mm, fix the sample on a tensile tester, peel 180° at a speed of 100mm/min, peel each time by 100mm, record the data, and test the results to the data. Median value.


The above-mentioned tensile strength, elongation at break, and peel strength were all measured by a tensile tester.


Third, dimensional stability (heat shrinkage)


The MD and TD directions were measured, and the backsheet was baked at 150°C for half an hour to test its shrinkage in the length and width directions. The more common standard is less than or equal to 1.5%.


Fourth, water vapor transmission rate


Detection methods: There are three kinds of detection methods, namely cup method, electrolysis method, infrared method, and photovoltaic industry electrolysis method is more common.


Electrolysis method for water vapor transmission rate detection: the pre-treated sample is fixed in the middle of the test chamber and the test chamber is divided into upper and lower chambers. The gas with relatively stable humidity flows in the upper chamber of the membrane, and the dry gas flows in the lower chamber of the membrane. Water molecules diffuse through the sample to the other side of the drying gas, and are carried by the flowing gas to the sensor. The water vapor concentration measured by the sensor is analyzed to calculate the moisture vapor transmission.


Fifth, light transmittance


According to GB2410-80 "transparency of transparent plastics and haze test method", is the standard method for the determination of transmittance of EVA film. The test instrument selected in this standard is an integrating sphere haze meter. Other test instruments that can achieve the same result can also be used.