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Quality control route to efficiency gains

With its fully integrated production line for CIGS thin-film solar modules and developments in the use of X-ray fluorescence for maximum precision inspections, Manz AG is helping achieve record-breaking power conversion efficiencies for thin film PV

With the potential for higher conversion efficiency over traditional thin-film technologies, interest in the development of copper indium gallium selenide (CIGS) thin-film PV development is growing. Plus, as German engineering firm Manz AG says: “CIGS technology is currently considered the technology with the largest cost-cutting potential among the competing thin-film technology such as amorphous silicon or cadmium telluride.”


At September’s EU PVSEC 2011 trade show in Hamburg, the company presented a CIGS based thin film module – where a sunlight-absorbing CIGS layer is vapour-deposited on the substrate – with an aperture efficiency of 15.1 per cent, “something never before achieved”, according to the firm. “This level of efficiency refers to the photosensitive area of a module, and corresponds to a module efficiency of 14 per cent.”


That’s a world record and is, notes the company, the result of a one-year partnership with the Centre for Solar Energy and Hydrogen Research Baden-Wurttemberg (ZSW) based in Stuttgart, and module manufacturer Würth Solar from Schwäbisch Hall. The three are working together as part of the Photovoltaics Innovation Alliance, aiming to “rapidly increase efficiency while simultaneously reducing investment and manufacturing costs”.


The project has a total budget of EUR 12.5m. Manz will receive EUR 3.8m subsidies over the next four years from Germany’s Federal Ministry for the Environment for its work on the project.


Manz and Würth have a know-how licensing and cooperation agreement for constructing manufacturing facilities for CIGS PV modules modeled after the CISfab plant in Schwäbisch Hall.


“A cooperation of this kind between a manufacturer of solar modules and a technology provider for production systems has never been seen so far in the photovoltaics industry,” notes Würth.


In a laboratory setting, CIGS cells have already reached an efficiency of over 20 per cent today, as demonstrated by the world record cell from Manz’s partner ZSW, which has an efficiency of 20.3 per cent (under lab conditions).


“The challenge now is to significantly close the gap between the laboratory values and the levels of efficiency achieved in mass production,” says Dieter Manz, founder and CEO of Manz AG.


With its CIGSfab, the company is currently the only supplier of a fully integrated production line for CIGS thin-film solar modules “that can be operated profitably today”, it claims. The CIGS solar module presented at PVSEC, which has an original production size of 600 × 1,200 mm, offers an output of more than 100 watts and was mass-produced at Würth Solar’s factory in Schwäbisch Hall.


“Since worldwide module manufacturers are currently facing a considerable decline in prices, the only manufacturers who will survive financially are those who position themselves as cost leaders and can offer products with the best possible efficiency,” says Manz. “Our CIGSfab perfectly meets these two demands and, in addition, is also based on the thin-film technology with the most potential.”


The company’s “Total Fab Solution” concept offers equipment for mechanically scribing CIS and CIGS layer systems as well as equipment for laser scribing and laser edge isolation for all established thin-film systems (aSi, aSi/μcSi, CI(G)S, and CdTe), and laser cutting equipment for cutting glass substrates. Wet chemical etching equipment to clean or pre-etch the TCO layer rounds out Manz’s range of products.


X-ray precision

A key development by the company for its thin-film products is its new IQ-XRF system for inline quality control, which uses X-ray fluorescence for maximum precision.


“X-ray fluorescence is one of the most practical methods of inspecting the composition and homogeneity of a layer of metal,” says Dr. Thomas Umschlag, Head of Sales in Manz’s thin-film solar division. “Since the efficiency of a thin-film module is largely dependent on these two characteristics, accurate quality control is extremely important for module manufacturers in order to ensure that they actually deliver products with the promised level of efficiency.”


An additional benefit for customers is that production costs can be optimized by conducting rigorous quality inspections after critical processing steps, since doing so allows defective substrates to be rejected early in the process instead of after they pass through the entire production line, the company suggests.


The fully automated XRF system, suitable for mass-production applications, is available for a variety of different substrate sizes. It has already been integrated into the first customers’ production lines and, since then, has been used continuously, while Manz also offers a modified version of the XRF system as a free-standing/independent unit.


The metrological core of the system is an ELBRUS.COMPACT.DUO measuring head from IFG GmbH. This makes both highly accurate and extremely fast measurements possible.


In order to measure different areas of the substrate, the measuring head can be moved extremely precisely along one axis. “By moving the substrate perpendicular to the head, it can access and take a measurement at every point of the substrate,” says Manz. “The measuring head can be positioned above the area to be inspected with an accuracy of less than one millimeter and is also self-calibrating.”


The results of the measurements are displayed on Manz’s human-machine interface, the Aico View Display, in order to optimize the coating system’s parameters. Modern interfaces allow the unit to be directly connected to the coating system as well as connecting it to an overarching MES system.


“Cell and module manufacturers can achieve efficiency advantages primarily by increasing module efficiency, reducing material consumption, or through the systematic optimization of individual process steps,” stresses the company.


“In order to achieve this Manz offers affordable automation systems, innovative laser technology, and high-performance inspection equipment.”