Electroplating Copper: The Mainstream Process for Upgrading Photovoltaic Cells and Removing Silver
Subsequently, the long-term development of the photovoltaic industry has become increasingly important as it has become "de silver". As the ultimate solution, electroplating copper needs to step onto the historical stage simultaneously.
N-type battery approaching
Desilverization is imminent
The new N-type battery technology is already on the way.
According to CPIA data, the average mass production conversion efficiency of single crystal PERC batteries in 2021 exceeded 23%, which is very close to its efficiency limit of 24.5%. At the same time, the cost reduction rate is slowing down, and new battery technologies are rapidly developing. CPIA predicts that the conversion efficiency of TOPCon, HJT, and IBC batteries will exceed 25% by 2025, and the actual efficiency will improve or be faster, further widening the gap with PERC batteries.
According to the "Roadmap for the Development of China's Photovoltaic Industry" (2021 Edition), it is expected that the total proportion of TOPCon and HJT battery processes is expected to exceed half by 2030, becoming the main process route in the field of battery cells. N-type batteries are replacing P-type batteries as the next generation mainstream technology.
The resulting "de silver" approach to cost reduction has shown a trend of acceleration.
The "silver removal" has always been a necessary path for the long-term development of the photovoltaic industry, and TOPCon and HJT are both double-sided batteries. The upper and lower electrodes of the battery require the use of silver paste, and the amount of silver paste used is still increased compared to P-type PERC. Colleague, the low-temperature silver slurry used in HJT batteries has a higher silver content than high-temperature silver slurry to ensure conductivity, resulting in a higher consumption of silver slurry.
In addition, low-temperature silver slurry mainly relies on imports from Japan, and the price is significantly higher than high-temperature silver slurry. Due to the special battery design structure, the amount of silver paste used in IBC batteries will also increase. According to CPIA data, the cost of silver paste accounts for 59% of the non silicon cost of HJT batteries; In 2021, the consumption of silver paste on both sides of HJT and TOPCon batteries was 93.6 and 48.7 mg/piece higher than that of PERC batteries, respectively.
The cost of a single watt of HJT battery is about ten cents higher than that of TOPCon, and the cost of a single watt of HJT battery is eight cents higher than that of TOPCon battery, especially for the silver paste part. Silver slurry accounts for about 20% of the cost of HJT batteries and about 40% of non silicon costs. Silver slurry is a crucial and significant part of HJT battery cost reduction, and electroplating copper is the ultimate route of "de silver".
Significant revenue generated by electroplating copper appearance detection system
Electroplating is a commonly used traditional process in the fields of circuit board manufacturing, MEMS manufacturing, IC manufacturing, and other fields. It is usually used to make metal interconnection structures and achieve electrical connections between components and layers of multi-layer wiring circuits. The electroplating technology has a low process temperature and can be used not only for the production of traditional battery electrodes, but also for the production of heterojunction batteries, N-type double-sided batteries, PERC batteries, and IBC battery electrodes.
Copper electroplating refers to the electrode preparation process of depositing metallic copper on a chemically deposited copper layer through electrolysis, drawing on the maturity of the graphical electroplating copper circuit process in printed circuit board PCB production
Copper electroplating refers to the electrode preparation process of depositing metallic copper on a chemically deposited copper layer through electrolysis. Drawing on the maturity of the graphical electroplating copper circuit process in printed circuit board PCB production, HJT batteries develop a set of batteries and a set of electroplating copper electrode grid lines, achieving the goal of reducing silver slurry consumption through electroplating copper grid lines.
According to institutional calculations, HJT batteries are electroplated with copper electrodes to achieve silver removal, and it is expected to reduce the metallization cost to 0.06-0.09 yuan/W in the future.
The HJT copper electroplating process includes four major steps: seed layer deposition, graphitization, electroplating, and post-processing. There are different technological routes competing within each link.
(1) Deposited seed layer: Due to the poor adhesion of copper on the transparent conductive layer (TCO), it is easy to cause electrode detachment. Therefore, it is generally necessary to introduce a seed layer on the TCO before copper plating to improve the electrode adhesion performance.
(2) Graphical: Use photosensitive materials to cover the HJT battery, and through selective illumination, modify the photosensitive materials at locations that do not require copper plating. The photosensitive materials at locations that require copper plating remain unchanged, and the unchanged modified materials are removed during the development step, generating conductivity during electroplating, while copper deposition does not occur at other locations.
(3) Electroplating: Immersed in a copper sulfate solution of electroplating equipment, electrified for electrolysis, copper ions (Cu2+) are reduced, and copper is deposited on the surface of the battery that needs to be plated, forming a copper electrode.
(4) Post processing: Wash off the remaining photosensitive ink, etch off the remaining seed layer, and electroplate tin to resist copper oxidation.
At present, the exploration of copper electroplating technology has been going on for a considerable period of time, and the equipment link has gradually matured. The focus is on how to reduce costs and make the technology cost-effective, with the main focus on two parts: graphics and electroplating.
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