In recent years, with the continuous expansion of photovoltaic demand and the rapid increase of photovoltaic installed capacity, the consumption of silver paste has increased, which in turn has driven up the price of silver. The original silver-clad copper technology may increase the cost.
In order to achieve large-scale expansion, cost reduction and efficiency increase are the key to its industrialization, and the cost of silver paste accounts for up to 11% of the total cost of HJT battery.
De-silverization has a long way to go for the photovoltaic industry
At present, there are two main ways to reduce the cost of silver paste: one is to save silver paste consumption by optimizing the grid line pattern, such as busbar-free technology. The other is to reduce the silver content of paste and find alternatives to precious metals, such as silver copper cladding technology is to reduce the amount of silver by covering the surface of copper powder particles with silver.
If we want to achieve the ultimate “silver removal” and completely solve the problem of HJT using silver, electroplating copper is undoubtedly the worth-considering choice among all the means of reducing silver today.
This is mainly because electroplated copper reduces the shading area due to the thinner grid lines, which further improves the conversion efficiency and reduces the unit cost. Nowadays, compared with the silver-clad copper route, the competitive advantage of electroplating copper technology is increasingly revealed, and the industrialization process is accelerating, which has become an important means to curb the price rise of silver paste.
Also read: Direct Plating Copper(DPC) Process
What is the process of copper plating?
Photovoltaic copper electroplating technology is an electrode preparation process that uses the maturity patterned copper plating circuit process in the production of printed circuit boards (PCB). It deposits metal copper by electrolytic method on the electroless copper layer.
The main process includes four major links of seed layer deposition, patterning, electroplating and post-processing. Different technical routes emerge in each link, resulting in many electroplating copper process solutions.
(1) Seed layer deposition: Due to the poor adhesion of copper on the transparent conductive layer (TCO), it is easy to cause the electrode to fall off. Therefore, it is generally necessary to introduce a seed layer on the TCO before copper plating to improve the adhesion of the electrode. The equipment mainly uses PVD.
The main technical differences lie in whether to prepare the seed layer, prepare the entire surface/partial seed layer, and the selection of metal for the seed layer.
(2) Graphical: Cover the HJT battery with a photosensitive material, and through selective illumination, the photosensitive material will undergo a modification reaction where copper plating is not required.
The photosensitive material at the position where copper plating is required remains unchanged, and the unchanged modified material will be removed in the development step. Conduction occurs during electroplating, while copper deposition does not occur in other positions.
The main technical difference lies in the use of mask-type photolithography/LDI laser direct writing/laser slotting in the exposure and development process.
（3）Electroplating: Soak in the copper sulfate solution of the electroplating equipment, electrify for electrolysis, copper ions (Cu2+) are reduced, deposit copper on the surface of the battery that needs copper plating, and form copper electrodes. The main technical differences lie in horizontal plating/vertical plating/optical plating induction plating.
(4) Post-processing: wash off the remaining photosensitive ink, etch off the remaining seed layer, and electroplate tin to resist copper oxidation.
Advantages of electroplated copper
Copper electroplating technology can not only improve conversion efficiency through lower resistance and higher grid lines, but also can completely replace high-priced silver to achieve cost reduction, all of which cater to the development direction of future battery metallization processes.
Looking at several mainstream battery technologies: P-type batteries use silver on one side, the consumption of silver paste is less, and the cost reduction space brought by electroplating copper is extremely limited, so there is no need to use electroplating copper technology.
The complex process of XBC battery itself requires multiple masking and etching, and there is no need to consider shading loss. Electroplating copper technology will only further increase its complexity.
Under the high temperature process of TOPCon battery, copper is easy to oxidize and fail. At the same time, TOPCon electrodes are directly in contact with silicon wafers, lacking a film barrier, copper is easy to diffuse into silicon, and reliability is reduced. TOPCon’s own equipment and process costs are low, and cost reduction is of little significance.
In contrast, HJT batteries are quite different, and are more compatible with electroplating copper technology.
First of all, the low-temperature process of HJT battery coincides with the electroplating copper process; secondly, the electrodes of HJT battery and the film are in contact with each other, which can prevent copper from polluting the inside of the silicon wafer.
Also read: How to solve the semiconductor wafer failure?
In addition, HJT uses silver on both sides and the consumption of low-temperature silver paste is greater and the price is higher, resulting in the most urgent demand for cost reduction of HJT silver paste. According to calculations, the electroplating copper technology has the most obvious effect in reducing the non-silicon cost of HJT, and the non-silicon cost reduction rate is as high as 21%.
