With PV solar cell manufacturing advances a cornerstone of the 26th European Photovoltaic Solar Energy Conference and Exhibition (EU PVSEC) in Hamburg, Germany this week as a number of materials providers are showcasing new products intended to push cell efficiencies higher and manufacturing cost lower. Front-side metallization paste materials in particular are a hotbed of development due to the rising cost of silver. However, competition in the sector would seem to be heating-up and a legal spat has erupted just days before EU PVSEC.
In a US federal court filing, Friday September 3, DuPont has alleged that Heraeus has infringed DuPont U.S. Patent No. 7,767,254 B2, ‘by manufacturing solar cells and inducing its customers to manufacture solar cells, using Heraeus H94XX series and H92XX series front-side silver pastes.’
“As a market-driven science company, DuPont invests significant resources and millions of dollars in research to develop innovative products for our customers,” said David B. Miller, president, DuPont Electronics & Communications. “Our intellectual property enables us to continue investing in innovative technologies for the photovoltaic industry, and to ensure that our customers receive the performance expected from DuPont products. We will continue to take appropriate actions to protect our patent estate against infringement.”
More than likely due to the time difference, Heraeus has yet to respond to the patent infringement claims.
EU PVSEC: pedal to the metal
Echoing the need to reduce solar cell manufacturing costs, Targray pre-announced EU PVSEC week that it would be showcasing Heraeus-based front and back-side silver paste for crystalline solar cells, as well as its new Giga Solar back surface aluminum paste for mono and multicrystalline silicon solar cells at the show.
“With over 900 companies and solar organisations expected to attend PVSEC, this continues to be a key venue for Targray,” stated, Dan Murray, Vice-President Solar Division, Targray Technology International. “In today’s tough economy, it’s crucial for manufacturers to reduce costs while maintaining efficiency and performance. Using the right materials is critical to that equation. Our participation at PVSEC will enable us to demonstrate how our differentiated materials can make all the difference in lowering their costs per watt.”
The front and back-side silver paste were said to have been optimized for varying emitter depths and concentrations, while the new ‘Giga Solar’ back surface aluminum paste was claimed to provide a uniform, high quality back surface field (BSF) and was designed for excellent efficiency, low bowing and high material compatibility.
A wide process window and improved adhesion strength had led to increased Voc and reduced cell breakage.
Ferro Electronic Materials is also highlighting at EU PVSEC this year, a newly optimized paste system to enhance performance of p-type Metal WrapThrough (MWT) cells and aluminum pastes for back-surface passivated cells.
The paste system includes a next-generation rear silver plug hole paste, high efficiency front silver contact pastes, and a back contact aluminum paste.
“New solar cell architectures require novel new materials to achieve their potential electrical efficiencies,” commented Dr. Aziz Shaikh, Ferro director of photovoltaic R&D. “We have focused a significant portion of our development efforts to supporting next generation technologies, and these innovative new materials are designed to address their specific needs.”
According to Ferro, its NS 3166 MWT rear silver plug hole paste increases cell efficiency by providing improved conductivity and contact with the front silver paste, and forms a solid plug upon firing.
Better shunt resistance of what the company claimed was novel glass chemistry also makes it suitable for use as the p-contact paste, with strong adhesion to the silicon wafer and robust soldering behaviour.
The focus of the new range of pastes is to take advantage of significant efficiency gains with MWT technology.
DuPont Microcircuit Materials had already introduced several new ‘Solamet’ branded metallization pastes with the kudos of collaborating with Canadian Solar and its ELPS cell technology that had resulted in 19.5% conversion efficiency for its monocrystalline cells using Metal Wrap Through (MWT) technology.
Zhang Lingjun, technical vice president of Canadian Solar had noted at the launch of the paste at Intersolar Europe in June, 2011: “When compared with N-type cell structures, the manufacturing process for ELPS technology is easy to ramp-up and is cost-effective.”
Ferro, like others has been busy with a string of new paste offerings, including the launch of 5 silver-based materials at EU PVSEC, which are low-temperature based that are claimed to improve electrical conductivity and printability.
The materials firm also recently introduced ‘cost-saving’ AL 5130 and AL 5131 rear aluminum pastes that is claimed to reduced reduce paste consumption by up to 20%.
Ferro has also collaborated with Applied Materials to introduce NS 3132 BP bottom layer and NS 3133 TP top layer pastes optimized for higher electrical efficiency and improved paste savings in double printing applications using Applied Baccini systems
Indeed, DuPont Microcircuit Materials (MCM) has also introduced a low temperature processing Solamet PV414 paste but this time designed for rotary screen printing intended to support high speed roll to roll processing of thin and flexible solar cells and modules. According to MCM Flexcell had recently qualified the material for production.
Heraeus is another materials specialist placing increasing emphasis on pasted that produce high efficiency with low consumption and silver content. At EU PVSEC this year, Heraeus will showcase its SOL 9410/9411 product offering.
Heraeus noted in its pre-show announcement that SOL 9410/9411 was designed to help achieve improved aspect ratio of width to height for finer conducting paths.
In separate news released before EU PVSEC, Fraunhofer ISE touted life after silver paste and further cost reductions and improved cell effciiencies. ISE said it was showcasing a galvanic process that primarily uses copper.
ISE said it had demonstrated 21.4 % efficiency cells (2×2 cm²) with long-term-stable copper metallization and was working on migrating the results to industry standard wafer sizes.
Researchers noted that due to the significant cost difference between silver and copper, just changing the material and keeping the efficiency the same, it was possible to reduce the production costs by about 8 euro cent/WP, or by up to 10%.