With an efficiency of 20.1 percent, scientists at the Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg, Germany (Centre for Solar Energy and Hydrogen Research, ZSW) have set a new world record for thin-film solar cells. The record-breaking solar cell, made of copper, indium, gallium and selenium - or CIGS for short - was produced in the ZSW research laboratory in Stuttgart. This breakthrough in materials development should significantly improve the cost-effectiveness of CIGS thin-film photovoltaics over the medium term. With this success the Baden-Württemberg researchers have brought a world record to Germany: The US research institute NREL has held this record for 16 years.
"This record is for thin-film technology in general and not just CIGS solar cells," says Dr. Michael Powalla, Member of the Board and Head of the Photovoltaics Division at ZSW. "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. A major factor in achieving this top position was the close cooperation between basic research at the university, applied research at the ZSW, and production development at our industrial partner Würth Solar."
The area of the world record cell is 0.5 square centimetres. The solar cell 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. It has a total thickness of only four thousandths of a millimetre. The electrical and optical properties must be exactly matched when manufacturing the cell - a process that is extremely difficult to master. The Fraunhofer ISE in Freiburg, Germany has confirmed the new results.
Higher efficiencies improve the electrical power output and thus the financial returns delivered by photovoltaic systems. "Further up-scaling for industrial application is the next development step," says Michael Powalla. However, it would take a while before the increased efficiency of CIGS solar cells can be commercially utilised.
Solar cells convert sunlight into electricity. They are a key technology for providing a climate-friendly energy source. Compared to standard crystalline silicon solar cells, thin-film photovoltaic cells save materials and costs since their active layers are only a few micrometers thick. The market share of thin-film photovoltaics has increased from 7 to around 17 percent over recent years. There are three basic variants of thin-film solar technology (amorphous silicon, cadmium telluride, and CIGS), with CIGS thin-film technology offering the highest efficiency.
Commercially available CIGS modules currently range from 10 to 12 percent efficiency. A complete module always has a lower total efficiency than a single solar cell. The new efficiency record shows the great potential of CIGS technology for lower-cost, efficient photovoltaic systems. Michael Powalla assumes that efficiency levels of up to 15 percent can also be achieved in commercial modules within the next few years.
The ZSW is an international leader in the development of CIGS thin-film modules. Together with the company Würth Solar, the institute has advanced this technology to enable industrial production. In 2006, Würth Solar launched the world's first mass production of CIGS solar modules in Schwäbisch Hall, Germany. It now achieves a capacity of 30 megawatts per year. The ZSW is the research and development partner of Würth Solar.
The ZSW is one of the most renowned German research institutes in the fields of photovoltaics, energy systems analysis, renewable fuels, battery technology, and fuel cells. Around 170 scientists, engineers, and technicians are currently employed at its three facilities in Stuttgart, Ulm, and Widderstall. They generate an annual turnover of 22 million euros.