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PROCIS
 Big boost for thin-film solar cells
Long-term European research has advanced thin-film photovoltaic cells to the point where they may now compete with silicon-based varieties. Most recently, the Procis project supported the technology development for the mass production of indium-based thin-film cells of 120 ´60 cm. Mass production methods will lower the price and further open the market for the use of solar cells in buildings as an alternative source of electricity.
 | | A CIS photovoltaic system on a school in Marbach, Germany. |
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As governments continue to push for more renewable energy, the use of solar cells is increasing rapidly. The market is growing by 20-30% each year. But although sales are increasing, solar-powered buildings are still rarely seen.
Reluctance to incorporate solar panels into new buildings is due to two factors – cost and functionality. Solar cells are still extremely expensive. They are competitive on small, low-power devices such calculators or other consumer products, and are also well suited to powering equipment in remote areas. But to power a whole building you need to cover a significant proportion of the exterior with panels. An average home, for instance, needs about 20-40 m2 of photovoltaic modules, costing €15-20 000 at today’s prices. The costs for a large office block, which uses far more energy that any home, are prohibitive.
Competitive cells
There are two main types of photovoltaic cell. Single-crystal silicon-based cells are the most common. Silicon is perfect for microelectronic applications. Although the cost of silicon wafer technology has fallen dramatically, these cells are still relatively expensive to produce.
Thin-film cells are made by sequentially depositing layers of material, including semiconductors, on to an inert substrate – usually glass. “Because these cells can be manufactured over a large surface area and you can make the electrical series interconnects between the depositions steps, they should be much cheaper than silicon,” says Hans-Werner Schock, the Procis coordinator. “The problem is that the technology to make them is not yet well developed, and the economic benefits of thin-film production rely on high production volumes. Scaling-up requires a lot of capital investment, and someone to take the risk.”
Procis is the latest in a long line of EU-funded projects that have brought thin-film photovoltaics to the point of commercial success. Back in 1982, the EURO-CIS project demonstrated the thin-film principle with a cell that was 15% efficient. Further projects increased the surface area of the cell from a 10X10 cm module to one of 30X30 cm.
Large-scale success
Procis partner Würth Solar, a small company that manufactures photovoltaic cells, is producing the world’s largest Cu(In, Ga)Se2 (CIGS) thin-film modules in a pilot operation. They measure an impressive 120X60 cm and are produced with high throughput and a much lower unit cost.
Research by the Centre for Solar Energy and Hydrogen Research Stuttgart (ZSW) and the CNRS Laboratoire d’Electrochimie et de Chimie Analytique (ECA) in Paris led to the development of an alternative deposition method for one of the thin-film materials. Instead of using chemicals, the innovative technique, which has a patent pending, takes place in the gas phase. This process also permits the deposition of much thinner layers.
Several of the project partners also combined their expertise to eliminate the very small amount of cadmium from the cells’ junction electrodes.
“These three main developments all help to decrease costs and improve the efficiency of in-line production,” says Schock. “First, the thinner layers use less material and reduce process time. In the lab prototype we reduced by a factor of four the amount of indium, which is a rare and expensive metal, and eliminated the heavy metal cadmium altogether.” This will have a big impact on the cost and sustainability of the technology. And it makes the cell far more efficient too.
Building opportunities
Producing breakthrough discoveries in a laboratory is a good start, but transferring and incorporating them into industrial processes is rarely straightforward. Nevertheless, Procis is successfully transferring the technology through the industrial project partner. Indeed, the main goal of the project is to implement the laboratory results as a pilot thin-film production line. Würth Solar is incorporating the new production methods into its pilot thin-film production and has successfully manufactured the 120X60 cm module. The company has now acquired the patent rights and is considering the commercial future of thin-film solar cells.
Electricité de France, meanwhile, has focused on the testing and characterisation of the new cell’s performance with a view to its full certification prior to release on the market.
“The potential for thin-film cell technology is huge,” says Schock. “The project is now at the crucial stage where a decision on large-scale investment is in process. We have reached the point where large-area thin-film modules can compete in the market. This is extremely promising for the photovoltaic industry in Europe, since it will make solar cells much more attractive to constructors. I believe we will see solar technology integrated into many more buildings in the future. Not only will Procis help the European photovoltaics industry. It will also boost the manufacturers of the equipment needed for thin-film production and help this niche sector to remain competitive.”
Before long, shiny, power-saving panels will almost certainly appear on a roof near – or even above – you.
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Production of large area CIS modules (PROCIS) Reference
ENK5-CT-2000-00331 Programme
FP5: Energy, Environment and Sustainable Development Partners
Institut für Physikalische Elektronik, Universität Stuttgart (IPE), Germany
Zentrum fuer Sonnenenergie und Wasserstoff-Forschung (ZSW), Germany
Würth Solar, Germany
Ångstroem Solar Center, Uppsala University, Sweden
Laboratoire d’Electrochimie et de Chimie Analytique (ECA-CNRS), France
Swiss Federal Institute of Technology (ETHZ), Switzerland
Electricité de France, France
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