A new world record for thin-film solar cell efficiency – 20.4%
(Nanowerk News) In a remarkable feat, scientists at Empa, the Swiss Federal Laboratories for Materials Science and Technology, have developed thin film solar cells on flexible polymer foils with a new record efficiency of 20.4% for converting sunlight into electricity. 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. Now a team at Empa’s Laboratory for Thin Film and Photovoltaics, led by Ayodhya N. Tiwari, has made (yet another) leap ahead. They achieved a record 20.4% energy conversion efficiency for thin film CIGS solar cells on flexible polymer substrates, a massive improvement over the previous record of 18.7% achieved by the same team in May 2011. Tiwari’s team has been investigating and developing various thin film solar cell technologies for some time. Over the years the laboratory has boosted the photovoltaic conversion efficiency of flexible CIGS solar cells time and again, from 12.8% in 1999 – the group’s first world record – to 14.1% in 2005, 17.6% in 2010 and 18.7% in 2011.Closing the efficiency gap to silicon wafer cellsThe 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. What’s more, 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. “We have now – finally – managed to close the “efficiency gap” to solar cells based on polycrystalline silicon wafers or CIGS thin film cells on glass”, says Tiwari.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. “The series of record efficiencies for flexible CIGS solar cells developed at Empa demonstrates that thin film solar cells can match the excellent performance of polycrystalline silicon cells. Now it is time for the next step, the scale-up of the technology to cover large areas in a cost-efficient roll-to-roll manufacturing process with an industrial partner”, says Gian-Luca Bona the Director of Empa. For this purpose, Empa is collaborating with Flisom, a start-up company involved in industrialization of flexible CIGS solar cells.
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Wireless electric-car charging tech to be tested in London
Wireless electric-vehicle charging technology is to be tested in London. Chip developer Qualcomm says plug-in charging is too “cumbersome” and its tech could lead to batteries being topped up while cars are being driven. Trials involving an adapted version of Formula 1 car designer Delta Motorsport’s E4 coupe electric car will take place before the end of the year. Further tests involving vehicles made by the French manufacturer Renault will follow in 2013. Smaller batteries
Inductive charging – which involves using an electromagnetic field to transfer energy between two objects – is less power-efficient than alternatives such as charging posts or battery-swapping stations, but Qualcomm says the difference is only “marginal. “The adoption of WECV [wireless electric vehicle charging] technology will lead to a shift in charging behaviour,” said Qualcomm. “Drivers will charge their electric vehicle little and often and potentially use dynamic charging to complement local stationary charging, removing range anxiety. This means that batteries could be smaller with the resulting reduction in electric vehicle cost and weight. The firm added that its technology – dubbed Qualcomm Halo – could be used to keep vehicles’ battery charges at between 40-80%, thereby maximising the life expectancy of the equipment. For the moment, it will only work when a vehicle is stationary.
Delta said it had become involved to help it learn more about the innovation. The firm said it expected it to take a day’s worth of mechanical modifications to add the new kit to its test vehicles “It’s very straightforward to add the technology,” said Delta’s technical director Nick Carpenter. “We add a vehicle mounted pad which is connected to a Qualcomm controlled unit which in turn is connected directly to the battery. “We also make amendments to our vehicle’s touch screen interface to tell the driver when they are aligned with another pad on the ground to start the process, and if the car is charging.” The trial – which is scheduled to start around November – will see charging pads placed at Qualcomm’s west London office, in the east of the city close to the Silicon Roundabout tech hub, and at the premises of the minicab company Addison Lee. The private hire firm also intends to fit the equipment to some of its Citroen-built vehicles.
Race to market
Qualcomm is not alone in seeking to develop a plug-free solution. BMW, Daimler, Volkswagen and others are already involved in a rival induction charging trial in Germany. In addition, car makers Rolls-Royce and Delphi have shown off concept vehicles fitted with wireless energy transfer systems. Qualcomm suggests that road lanes could eventually be fitted with its wireless technology Paul Newton, an analyst at IHS Automotive, noted the Oxford-based start-up Liberty Electric Cars also had plans to explore the idea in the UK. But he questioned whether Qualcomm’s full ambitions would come to fruition. “Induction charging is a known technology and is already offered for devices like mobile phones – it’s not new as such,” Mr Newton said. “The principle is valid and is likely to prove popular when people park their cars. But the idea of rolling it out to vehicles on the move seems quite fanciful because of the cost of fitting the equipment to all the roads.”
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