Analysis and solution of quality problems in photovoltaic module lamination

　 From a structural perspective, photovoltaic modules can be divided into single glass and double glass, with the main difference being the

materials used on the back. The back of the single glass uses a backing plate, while the back of the double glass uses glass, as shown in the

following figure:

    1. Quality issues with photovoltaic modules

    At present, the mainstream processing technology for photovoltaic modules is composed of laminated materials such as EVA, backsheet,

glass, and solar cells. From welding to finished product testing and packaging, each process affects and constrains each other. The quality of the

modules affects the user's outdoor service life. In actual production, the main problems with module quality include: hidden cracks and

fragments of solar cells, bubbles, empty glue, deformation of module appearance, and burning of junction boxes.

    Analyze the bubbles and component edge delamination that occur during the production process, and provide reference for improving the

lamination process and raw materials to address the issues of bubbles and component edge delamination.

    2. The influence of bubbles

    The use of crystalline silicon photovoltaic modules on the national standard ground requires the modules to be broken, cracked, or

detached from the surface; The formation of continuous bubbles or delamination channels between the edges of components and any part

of the circuit is considered a serious appearance defect. When the component is used outdoors, due to the influence of light and the normal

operation of the component, the bubbles will show a trend of expansion. Over time, the EVA at the bubble position will delaminate from the

glass and backplate, and water vapor will enter the component. The performance and power of the component will be seriously affected,

ultimately leading to the component being scrapped.

    3. Analysis of the causes of bubble formation and solutions

    3.1 Bubble at the edge of the busbar

              3.1.1 There is a height difference between the busbars, which hinders gas flow. In addition, the evacuation time is short, and the edges of

the components begin to crosslink during the lamination process, resulting in the inability to smoothly extract the gas generated during the

lamination process; Solution: Adjust the process of the busbar and increase the isolation thickness.

     When the laminating temperature set by the laminating machine is high or the laminating time is too long, the heating rate of the busbar is

fast during the laminating process, and the EVA at the busbar position is pre crosslinked. When the crosslinking degree of the component

reaches the standard, the crosslinking degree at the busbar position has passed crosslinking. Solution: Adjust the laminating process parameters

appropriately.

    3.2 Bubbles at the root of the welding strip

    3.2.1 There are gaps at the bending points of the welding strips, and there is a height difference between the welding strips. During the

lamination process, EVA becomes soft and has fluidity. The flowing EVA fills the gaps in the components, and the height difference between the

welding strips is greater than the amount of adhesive flowing from EVA, causing EVA to be unable to fill the gaps between the welding strips.

Solution: Increase the amount of adhesive between the solder strips.

    3.2.2 During the lamination process, the lamination time is short, and the gas generated during the curing stage of EVA cannot be extracted,

resulting in gas residue inside the component. Solution: Adjust the laminating process parameters appropriately and increase the exhaust time

for curing.

    3.3 Bubbles between battery cells

    3.3.1 If EVA is stored for too long and the humidity and temperature of the storage environment do not meet the specified storage

requirements, the crosslinking agent and auxiliary crosslinking agent in EVA will evaporate, making it impossible for EVA to undergo normal

crosslinking chemical reactions during the curing stage, resulting in EVA failure and irregular bubbles inside the components. Solution: The

unpacked EVA should be used within 12 hours. Unused and unopened EVA should be placed in an environment with a temperature below 25 ℃

and humidity below 70%.

    3.3.2 EVA processing technology is divided into casting method and rolling method. During the processing technology, local thickness

unevenness occurs, and EVA is cured in advance in areas where the thickness is thin during the curing stage. Due to the long curing time, the

crosslinking agent in EVA reacts sufficiently, and the evacuation time and EVA reaction rate cannot match, resulting in the inability to eliminate

the gas generated by the crosslinking agent, thus encapsulating the gas inside the component. Solution: Adjust the process parameters and

adjust the laminating time appropriately.

    3.4 Bubbles on battery cells

    3.4.1 Bubbles on both sides of the interconnect strip, due to the fact that the interconnect strip was soaked in solder flux and did not wait for

all the solder flux to dry before soldering, resulted in residual solder flux on the battery cell, causing bubbles in the component. Solution: After

soaking the flux, the interconnecting strips should be fully evaporated, and the soldering work should be carried out after the interconnecting

strips are completely dried.

    The bubbles on both sides of the interconnection strip form a droplet shape due to the fast heating rate of the interconnection strip. During

the EVA curing stage, the EVA on both sides of the interconnection strip solidifies prematurely, causing the gas released from the VA in the EVA

to be unable to be discharged. Solution: Adjust the temperature during the curing stage to ensure that the reaction rate and curing time of the

crosslinking agent in EVA are suitable.

    3.5 Large area bubbles in components

    3.5.1 Equipment malfunctions during the evacuation phase, during which EVA undergoes pre curing due to heating. Ethylene and vinyl acetate

react preliminarily with the crosslinking agent in EVA, releasing a large amount of gas that cannot be discharged through the evacuation phase.

Solution: Perform a second lamination of the components; And carry out maintenance at levels one, two, and three on the equipment, inspect

the main systems of the equipment daily, and ensure that the equipment is put into use normally.

    3.5.2 The EVA reaction speed is too fast and the evacuation time is insufficient, which cannot timely discharge the gas generated inside the

component. Solution: Adjust the lamination parameters and adjust the evacuation time to adapt to the EVA reaction speed.

    3.6 Bubbles in repaired components

    3.6.1 The appearance of bubbles in the unrepaired area is due to the complete reaction of the crosslinking agent in EVA during the initial

lamination process, which prevents further crosslinking reaction during the subsequent lamination process, resulting in over crosslinking

between EVA and glass. Solution: Strictly control the crosslinking degree during the first lamination, maintaining it at around 80%. When the

components are laminated again, a small amount of crosslinking agent in EVA can react again.

    4. Component edge layering

    There are two types of edge layering for components, one is that the edges form an arc shape, and the other is that the edges form a

sawtooth shape.

    4.1 Arc shaped edges: Due to the stress between the backing plate and the glass, low adhesion after lamination can lead to edge delamination,

and the size of delamination will become even worse with increasing placement time. After curing, the edge of the component will form

arc-shaped elongated bubbles (slight bubbles can be repaired). Solution: Increasing the temperature and prolonging the pressurization time can

improve the adhesion.

    4.2 The edge is serrated due to the fact that EVA, which is in a molten state at high temperatures after lamination, undergoes slight shrinkage

due to stress between the backing plate and glass. Air can easily penetrate between the backing plate and glass, forming recoil bubbles (which

cannot be repaired). Solution: Lowering the temperature and reducing the pressurization time can reduce the generation of bubbles, and the

relationship between edge stratification and edge bubbles and time and temperature is inversely proportional; The components to be laminated

should be cooled to room temperature before proceeding to the next process.

    The problem of bubble and edge delamination is caused by multiple factors. Considering the process, raw materials, production environment,

and other issues, we analyze each type of bubble and edge delamination in different areas and shapes, identify the causes, and comprehensively

consider the problem of bubble and edge delamination. The causes of bubble and edge delamination are diverse, and the solutions to solve

them are not fixed. Through practical exploration and theoretical assistance, we can solve this problem.

    3.6.2 The appearance of bubbles in the repair area is due to the gap between the EVA cutting size and the original size. The pre cured EVA

cannot fill the gap between them, resulting in the appearance of bubbles. Solution: Adjust the repair process to make the cut EVA 1-2mm larger

than the repair area, ensuring sufficient adhesive to fill the gaps between them.