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Industrial Selective PLAting for Solar Heterojunction

Periodic Reporting for period 1 - iSPLASH (Industrial Selective PLAting for Solar Heterojunction)

Reporting period: 2022-10-01 to 2023-09-30

The rapid growth of the PV market is not an option, but a necessary step to mitigate climate change, but such growth can lead to new challenges in terms of material consumption. Currently, silver is the most critical metal, posing price, environmental impact, and supply risks as PV production expands. In 2022, PV will consume approximately 12.7% of annual silver production. Many studies have shown that the current estimated silver consumption is too high to enable sustainable terawatt-scale production. Furthermore, the cradle-to-gate impact of solar cell metallization shows that the use of silver impacts more than 14 kg CO2-eq per W of solar cell produced. The PV community is working to address this silver issue by replacing it with more abundant metals such as copper, but there are still processing and reliability challenges to overcome before mass production.
Currently, conductive copper paste is not used on an industrial scale. The main problem of conductive copper paste, even though it is screen printable like silver paste, is that it has high resistance, high oxidation, and is relatively expensive, costing almost 50% of HJT silver paste, and offers lower efficiency, about 2%, compared to silver paste. According to the leading suppliers of equipment for silver paste metallization of solar cells, it seems that even if the throughput can be improved by a factor of two with conductive copper paste, no company wants to go to the industrial level because of the cost as well as the decrease in efficiency of the solar cell. One alternative that paste manufacturers are considering is silver-coated copper nanoparticles. Such paste applied to HJT's solar cell technology is under evaluation but will reduce the silver content by no more than 75% compared to HJT's current silver paste, which contains 93% silver. Copper plating is considered the most credible technology to replace silver paste.
The 2013 International Technology Roadmap for Photovoltaics (ITRPV) predicted that plating would overtake silver paste screen printing technology. Plating was mainly focused on copper, but the possibility of silver deposition was also considered. The prediction failed completely due to technical reasons. The main problems were the adhesion of the plating techniques and the fact that the plating speed is slow (deposition rate is one micron per minute) while silver paste screen printing is a very fast process (tens of microns in seconds). As a result, the plating equipment is huge and has to manage huge amounts of chemicals (e.g. 1500 liters for 200MW throughput). In addition, it is a must to protect the solar cell with a protective film to overcome ghost plating where the deposited metal is not wanted, which makes the copper metallization plating much more complex and increases the price at the level of the silver paste.
The main issues to be solved for a full acceptance of copper with respect to silver paste are the reliability, the adhesion problem and the reduction of the complexity of the copper deposition, making it similar or even, if possible, simpler than the technique used for metallization with silver paste: stencil printing and curing.
The activities carried out and the main technical achievements during the first year of the iSPLASH project are as follows:
- Development of the new copper plating technology for HJT solar cells, which is expected to increase the efficiency and reduce the production cost of these cells.
- Collaboration agreements with leading solar energy research institutions
- Designed and manufactured initial prototypes of the plating equipment and systems required for the new technology. Successfully tested these prototypes for functionality and feasibility
- Conducted extensive research into the selection of materials used in the copper plating process, with a focus on finding environmentally friendly and cost-effective alternatives to silver.
- Scientific achievements include preliminary tests demonstrating an increase in the efficiency of HJT solar cells using the new plating technology.
- The project has made significant progress in identifying cost-saving measures and optimizing the production process, with the goal of reducing metallization production costs by more than 90%.
- The project team has initiated outreach to solar industry manufacturers to gather input and feedback on the project's progress.
- The project has begun the process of patenting the new technology to protect intellectual property rights and ensure that it remains a competitive advantage for the EU.
The major technological breakthrough introduced by the iSPLASH project is the ability to control the flow of chemical solution at high speeds (m/s) and confine it to perform localized metallization without the need to apply any type of protective coating or mask. In addition, the solution is recirculated in a closed loop, as are all vapors, making the process "totally safe" for operators. The technology is based on the Dynamic Liquid Drop/Meniscus (DLD/DLM) system. By specifying the geometric dimensions of the nozzles that control the DLD, we are able to define exactly where and how large the DLM should be and deposit materials at a deposition rate nearly 100 times faster than the current state-of-the-art deposition technique, reducing the amount of solution by a factor of 10 compared to all other chemical techniques. The deposition of the material is highly selective and does not require protection of the substrate. The iSPLASH project will create a paradigm shift in HJT cell metallization. Our technology will be the only process technology on the market that can cost-effectively take advantage of the low price of copper and enable reliable and precise fine-line deposition of copper on HJT cells, eliminating the use of silver. iSPLASH technology will reduce metallization costs and carbon emissions by more than 90%.
iSPLASH metallization route compared to silver metallization and other state-of-the-art copper route