7 May 2010


ZSW sets thin-film PV cell efficiency record of 20.1%

Scientists at the Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg, Germany (Centre for Solar Energy and Hydrogen Research, ZSW) have achieved record efficiency for thin-film solar cells of 20.1%. This surpasses the previous record, which has been held for the last 16 years by the US Department of Energy’s National Renewable Energy Laboratory (NREL) – most recently 19.9%, achieved in March 2008.

The copper indium gallium di-selenide (CIGS) solar cell was produced in ZSW’s research laboratory in Stuttgart. The development could significantly improve the cost-effectiveness of CIGS thin-film photovoltaics in the medium term, the institute reckons.

"This record is for thin-film technology in general and not just CIGS solar cells," says Dr Michael Powalla, ZSW board member & head of the Photovoltaics Division. "It is the result of continuous systematic research which has been supported for years by the Federal Ministry of the Environment, Nature Conservation and Nuclear Safety, the Baden-Württemberg Ministry of Economics and the European Community,” he adds. A major factor in the achievement is the close cooperation between basic research at university, applied research at ZSW, and production development at our industrial partner Würth Solar.”

The solar cell has an area of 0.5cm2 and was produced in a CIGS laboratory coating plant using a modified co-evaporation process, which in principle can be scaled up to a commercial production process. The solar cell consists of the semiconducting CIGS layer and contact layers, and has a total thickness of 4 microns. The electrical and optical properties must be exactly matched when manufacturing the cell, which is difficult to master. The new results have been confirmed by Fraunhofer Institute for Solar Energy Systems ISE in Freiburg, Germany.

Higher efficiencies improve the electrical power output and thus the financial returns of photovoltaic systems. "Further up-scaling for industrial application is the next development step," says Powalla. However, it would take a while before the increased efficiency of CIGS solar cells can be commercially utilized, he adds.

Compared to standard crystalline silicon solar cells, thin-film photovoltaic cells save materials and costs, since their active layers are just a few microns thick. The market share of thin-film photovoltaics has hence risen from 7% to about 17% in recent years.

Of the three basic variants of thin-film solar technology (amorphous silicon, cadmium telluride, and CIGS), CIGS offers the highest efficiency. Commercially available CIGS modules currently range from 10% to 12% (a complete module always has a lower total efficiency than a single solar cell). Nevertheless, the new efficiency record shows the great potential of CIGS technology for lower-cost, efficient photovoltaic systems, says ZSW. Powalla assumes that efficiency levels of up to 15% can also be achieved in commercial modules within the next few years.

While ZSW develops CIGS thin-film modules, as the R&D partner of the firm Würth Solar it has advanced the technology to enable industrial production. In 2006, Würth launched what is claimed to be the world’s first mass production of CIGS solar modules (in Schwäbisch Hall, Germany) and it now has a capacity of 30MW per year.

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