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2009 130µm Sol9117 ”Our newly introduced front-side metallization pastes, the SOL9610 Series, allow manufacturing of highly efficient crystalline solar cells. These are optimized for high throughput processing and low costs. Since 2009, we have been able to use these innovative formulas to reduce the finger line width from 130 to less than 50 micrometers.” Dr. Arno Stassen, Staff Technologist in the Photovoltaics Business Unit 2013 >50µm SOL9610A Carsten Mohr, Head of the Photovoltaics Business Unit Europe, explains the basic formulation of silver metallization pastes as follows, “The pastes consist of silver powder, organic vehicles, additives, and glass. Knowledge and competence with all these raw materials are available within the group, and this decisively influenced the development process. The silver paste ensures a more efficient contact inside the solar cell between the wafer and the conductor carrying the electricity.” The solar paste business has developed out of the business in conductive pastes for electronic switching devices, which has existed for over 40 years. Since 2008, the business unit has become a market leader. Globally, around a third of the employees work in development and applications technology. “We are always developing new formulations, in order to improve the contacting in the solar cells, and hence their efficiency. The main requirement of our customers is to use cheaper materials and lower consumption of silver to reduce the costs per watt of solar power,” says Carsten Mohr. Physicists, semiconductor technicians and glass-ceramic experts work in international teams, from the development of new formulations to the printing of new solar cell types, as in Singapore. The objective during the printing process is to produce the narrowest, highest silver finger lines with the most uniform profiles possible. This means that less of the area of the solar cell is covered by finger lines, meaning more sunlight can be collected. “The market never sleeps, and continuously improving silicon solar cells require appropriate silver pastes. The pressure to innovate is very high, the half-life of new pastes is low, and every customer and every solar cell has different requirements,” explains Dr. Arno Stassen, Staff Technologist of the Photovoltaics Business Unit, who works at the Singapore location. One major requirement is whether the pastes can be used to achieve an exceptional “aspect ratio”, i.e. an optimized width-to-height ratio for the fine finger lines. Each innovative cell design requires different pastes Technology and materials are the key to success in increasing the efficiency of silicon solar cells. One recent technology, for example, is the MWT-PERC concept, with efficiency ratings of over 20 percent. For this combined solar cell concept (MWT and PERC technology), Heraeus developed an MWT paste for producing contacts through vias (holes), in a joint research project with the Fraunhofer Silver finger lines on solar cells are always getting narrower. International development teams optimize metallization pastes The photovoltaic industry has been able to record high growth over recent years. At the same time, the market has undergone profound structural and regional change. Virtually all German solar companies have been forced to file for insolvency since 2011, due to the enormous cost pressure, and the vast majority of solar cells are now produced in Asia. For Heraeus, this means being where the customers are producing. The Photovoltaics Business Unit is represented internationally by full service sites (development, production, technical service) in Hanau (Germany), Singapore and the USA. Shanghai and Taiwan are additional production sites, each with their own technical service. Since the acquisition of the paste business of the Ferro Corporation in February 2013, the business unit has also been offering its customers technical service in Japan. 12 technology report Issue 4 | 2013 technology report Ausgabe 4 | 2013 Photo: Bert Bostelmann/photon-pictures.com
Functional principle of a silicon-based solar cell In the intermediate layer between positively (p-type) and negatively (n-type) doped silicon, solar radiation load generates an electrical charge. The charge is transferred sunlight by means of metal contacts on the surfaces: current • The front-side grid is made of silver paste • The contacts on the back-side are made both of silver paste and photons aluminum paste n-doped silicon pn-junction p-doped silicon electron flow “hole” flow ENERGY & ENVIRONMENT More information: • www.pvsilverpaste.com (web address of the Photovoltaics Business Unit) • www.heraeus-photovoltaics.com (here the Heraeus Group provides information on all services supplied to the photovoltaic industry) Institute for Solar Energy Systems ISE. By using this paste in combination with a front paste, Heraeus was decisively involved in achieving this success. The MWT-PERC solar cell is a crystalline solar cell. MWT stands for “Metal Wrap Through”, and means that the busbars for the front contacts on the cell are located on the rear. In contrast to conventional cell types, this reduces shading on the front, allowing more light to be absorbed by the cell. Efficiency is increased with absolutely no additional material cost. PERC stands for “Passivated Emitter and Rear Cell”. The rear of the cell is designed such that incoming light is reflected back to the wafer. This makes it possible to produce additional energy. Heraeus products for the photovoltaic industry Mechanical and plant engineering: • Infrared emitters for sintering processes • Quartz glass holders for wafers Consumable materials: • Sputter targets for thin-film cells • Ruthen solutions for organic cells • Silver metallization pastes for solar cell Responses to increasing cost pressure Why is silver used for the metallization of solar cells? Silver is extremely conductive, especially resistant to corrosion, solders well, and remains stable in the long term. This is important, because solar cells have a service life of up to 30 years, and sometimes even longer. These advantages come at a high price, however, making silver metallization paste a significant cost factor for solar cell manufacturers. In order to counteract the cost factor of silver, it is necessary to minimize its impact in the production of photovoltaic cells. Such potential cost savings can be accomplished in new solar cell designs, and optimization of the screen printing process, as well as in utilizing new printing methods such as dispensing and extrusion. Since 2010, silver consumption has been reduced from 0.3 to 0.2 grams per cell. Experts believe that it should be possible to reduce this further, to less than 0.05 grams of silver per cell by 2020. “Given the current state of knowledge, it is inconceivable that the precious metal silver could be replaced, since no other material fulfills the requirement for ‘cost in relation to performance’ in a comparable manner. Silver is also excellent due to high process stability,” explains Dr. Arno Stassen with conviction. The complete replacement of silver, e.g. with copper, does not seem possible in the foreseeable future. Nevertheless, technology report Issue 4 | 2013 researchers around the world are searching for alternative materials. The photovoltaic experts at Heraeus have their finger on the pulse of the photovoltaic industry also in this field of research, and are involved in various projects working on methods for substituting silver. Dr. Jörg Wetterau Do you have any further questions? Carsten Mohr Manager Photovoltaics Business Unit Europe Heraeus Precious Metals GmbH & Co. KG Heraeusstr. 12-14, 63450 Hanau Phone: +49(0)6181.35-3730 Email: carsten.mohr@heraeus.com www.pvsilverpaste.com Photo: Bert Bostelmann/photon-pictures.com 13
Page 1 and 2: technology report Heraeus Technolog
Page 3 and 4: Contents technology report Heraeus
Page 5 and 6: Materials Dr. Richard Walter von He
Page 7 and 8: Large Hadron Collider The “LHC Be
Page 9 and 10: Schematic drawing of a fiber laser
Page 11: ENERGY & ENVIRONMENT Silver for mak
Page 15 and 16: A long tradition of platinum sensor
Page 17 and 18: safer cavities. These cavities, or
Page 19 and 20: UVC UVB UVA UV light 200-280 nm 280
Page 21 and 22: Exceptional properties and applicat
Page 23 and 24: “Wherever medical implants are us
Page 25 and 26: than 160 years ago in Hanau of inno
Page 27 and 28: Biomaterials and MEDICAL products H
Page 29 and 30: 2010 Danyang/CN 2012 Singapore/SG D
Page 31 and 32: Research & Development Materials ne
Page 33 and 34: Research & Development SEM microgra
Page 35 and 36: Modern wind turbines are up to 130
Page 37 and 38: Microorganisms brought in from fore
Page 39 and 40: Exhaust catalytic converters The ca
Page 41 and 42: Research & Development Dr. Ekaterin
Page 43 and 44: Product innovation - 2nd place: Ant
Page 45 and 46: The timeline shows the respective f
Page 47 and 48: Research & Development Heraeus offe
Page 49 and 50: The Company Heraeus, the precious m

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