The development of conductive pastes began in the 1950s. In 1954, British scholar C.F. Powell first reported the method of preparing conductive pastes by suspending silver particles in organic solvents, laying the technical foundation. Subsequently, in the 1960s and 1970s, with the rise of thick film hybrid integrated circuits, precious metal conductive pastes such as silver paste and gold paste gradually achieved initial industrialization and were mainly used in the aerospace and military industries; Taking photovoltaic silver paste raw materials as an example, silver powder accounts for over 90% of the cost, and the purchase price of silver powder is greatly affected by market silver prices, with significant fluctuations Since 2020, driven by high silver prices and the demand for cost reduction, silver coated copper paste has been introduced and applied in HJT battery production lines. Breakthroughs have been made in pure copper paste and electroplated copper technology, and mass production has been launched. The silver content has been significantly reduced, and the silver free process has significantly accelerated.

At present, the three mainstream technological directions for replacing conductive silver paste are: silver coated copper paste, electroplated copper process, and pure copper/aluminum paste. They aim to solve the problem of high silver prices and have entered the industrialization stage in fields such as photovoltaics and LED packaging.

The core differences between these three technological routes are as follows:
1. Silver in Copper Technology Silver in Copper is currently the most mature and rapidly industrializing copper replacement solution. Its core is the core-shell structure of copper core and silver shell, partially replacing silver with copper. By adjusting the doping ratio of silver and copper, the slurry cost can be effectively reduced while ensuring the photoelectric conversion efficiency, and the cost reduction can reach more than 30%. However, due to the easy oxidation of copper powder in high temperature environments, the application of this scheme has obvious limitations and is only suitable for low-temperature silver paste systems in crystalline silicon heterojunction (HJT) photovoltaic cells and stacked photovoltaic cells.

The emergence of silver coated copper powder is mainly aimed at significantly reducing costs while maintaining conductivity close to pure silver. SAT NANO technician Dana obtained the following comparative data based on experiments with conductive silver powder and conductive silver coated copper powder.

 Here is a comparison of the key performance parameters between the two:

2. Copper electroplating technology is based on the principle of electrolytic deposition, which can utilize the transparent conductive layer and edge guide structure pre-set on both sides of the photovoltaic cell to synchronously prepare metal electrodes on the front and back of the cell, without the need for high-temperature sintering and single-sided step-by-step processing. It has natural double-sided metal compatibility and can fully utilize the performance advantages of HJT battery double-sided power generation; At the same time, copper plated electrodes have significantly better conductivity and contact characteristics with transparent conductive oxide (TCO) layers than traditional silver grid lines. They are made of pure copper material and have a dense structure without voids, with a much lower electrical resistivity than low-temperature silver paste. This can effectively reduce electrode ohmic losses and series resistance, and are tightly combined with TCO transparent conductive films without contact holes, which can reduce contact resistance, improve electrode adhesion and carrier transport collection efficiency; In addition, copper plated electrodes can achieve ultrafine line widths of 15-20 μ m, with better aspect ratios and good plasticity. Compared with silver grid lines printed with 30-40 μ m, they can significantly reduce shading losses. Combined with low resistivity characteristics, they can effectively improve the generation and collection efficiency of photo generated carriers, and increase the conversion efficiency of heterojunction photovoltaic cells by 0.3% to 0.5%. At present, the copper electroplating process still faces certain difficulties in mass production. Compared with traditional screen printing, the electroplating copper process has a longer process and is prone to situations such as grid detachment and oxidation. Moreover, due to the complex process flow, the initial equipment investment cost is relatively high. On the other hand, the electroplating solution contains a large amount of harmful chemicals, which poses environmental compliance risks and to some extent restricts its large-scale promotion. Currently, the industrialization of copper electroplating technology still needs time.

3. Pure copper paste is the most ideal silver free cost reduction solution in the medium to long term, which can completely replace silver paste and has the greatest potential for cost reduction. However, its large-scale application still faces core technical challenges. Due to the active chemical properties and high specific surface energy of copper powder, it is prone to contact with air during preparation and battery production to form insulating oxide films, resulting in a decrease in the conductivity of the slurry. Therefore, the technological breakthrough in antioxidant treatment of copper powder has become the key to the industrial application of copper slurry. At present, pure copper paste products for low-temperature and high-temperature routes are still in the research and development testing stage.

SAT NANO is a best supplier of silver powder, silver coated copper powder in China, we can supply different partcile size, if you have any enquiry, please feel free to contact us at admin@satnano.com