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Thin film solar cells on flexible polymer foils with new record efficiency for converting sunlight into electricity

Thin film solar cells on flexible polymer foils with new record efficiency for converting sunlight into electricity

28-Feb-13

Thin film solar cells on flexible polymer foils with a new record efficiency of 20.4% for converting sunlight into electricity have been developed by scientists at Empa, the Swiss Federal Laboratories for Materials Science and Technology. The cells are based on CIGS semiconducting material (copper indium gallium (di)selenide) known for its potential to provide cost-effective solar electricity. The technology is currently awaiting scale-up for industrial applications. To make solar electricity affordable on a large scale, scientists and engineers the world over have long been trying to develop a low-cost solar cell, which is both highly efficient and easy to manufacture with high throughput. A team at Empa's Laboratory for Thin Film and Photovoltaics, led by Ayodhya N. Tiwari, has achieved this massive improvement over its previous record of 18.7% achieved by in May 2011. Empa's new record efficiency for flexible solar cells now even exceeds the record value of 20.3% for CIGS solar cells on glass substrates - and equals the highest efficiencies for polycrystalline silicon wafer-based solar cells. The latest in the series of records has been achieved, thanks to innovative ideas and excellent team work in the lab, especially by PhD students Adrian Chirila and Fabian Pianezzi. The team has succeeded in modifying the properties of the CIGS layer, grown at low temperatures, which absorbs light and contributes to the photo-current in solar cells. The cell efficiency value was independently certified by the Fraunhofer Institute for Solar Energy Systems (ISE) in Freiburg, Germany. With this, the team has managed to close the "efficiency gap" to solar cells based on polycrystalline silicon wafers or CIGS thin film cells on glass. Thin film, lightweight and flexible high-performance solar modules are attractive for numerous applications such as solar farms, roofs and facades of buildings, automobiles and portable electronics and can be produced using continuous roll-to-roll manufacturing processes that offer further cost reductions compared to standard silicon technologies. In other words, they have the potential to enable low-cost solar electricity in the near future. To scale-up the technology to cover large areas in a cost-efficient roll-to-roll manufacturing process with an industrial partner, is collaborating with Flisom, a start-up company involved in industrialization of flexible CIGS solar cells. The research work has been supported over the years by the Swiss National Science Foundation (SNSF), the Commission for Technology and Innovation (CTI), the Swiss Federal Office of Energy (SFOE) and the EU Framework Programmes.

A new world efficiency record has been set for thin film silicon solar cells by EPFL's Institute of Micro-engineering, reaching an impressive 10.7%. The new single-junction microcrystalline silicon solar cell had it's record independently verified by the Fraunhofer Institute for Solar Energy Systems. EPFL's Institute of Microengineering has reached a remarkable 10.7% efficiency single-junction microcrystalline silicon solar cell, clearly surpassing the previous world record of 10.1% held by the Japanese company Kaneka Corporation since 1998. Such significant efficiency was achieved in addition with less than 2 micrometers of photovoltaic active material. "Deep understanding has been gained these last years in material quality, efficient light-trapping and cell design, which in combination with careful process optimization led to this remarkable world-record efficiency" says Simon Hänni, PhD student at IMT Neuchâtel. Importantly, the employed processes can be up-scaled to the module level. While standard wafer-based crystalline silicon PV technology implements absorber layers with a thickness of about 180 micrometers for module conversion efficiency of 15 to 20%, 10.7% efficiency was reached here with only 1.8 micrometers of silicon material, i.e. 100 times less material than for conventional technologies, and with cell fabrication temperature never exceeding 200°C. Thin-film silicon technology indeed offers the advantages of saving up on raw material and offering low energy payback time, thus allowing module production prices as low as 35 €/m2, reaching the price level of standard roof tiles.

 
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