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EETE MAR 2017

NEWS & TECHNOLOGY ENERGY HARVESTING Low-temp printed perovskite solar cell tops 20% efficiency By Nick Flaherty Researchers at the University of Toronto have developed a technique for low-temperature printing of perovskite solar cells with high efficiency. Dr Hairen Tan and his team have cleared a critical manufacturing hurdle in the development of perovskite solar cells with a new printing process. “Economies of scale have greatly reduced the cost of silicon manufacturing,” said Professor Ted Sargent, an expert in emerging solar technologies and the Canada Research Chair in Nanotechnology. “Perovskite solar cells can enable us to use techniques already established in the printing industry to produce solar cells at very low cost. Potentially, perovskites and silicon cells can be married to improve efficiency further, but only with advances in low temperature processes.” In order to generate electricity, electrons excited by solar energy must be extracted from the crystals so they can flow through a circuit. That extraction happens in a special layer called the electron selective layer (ESL) and this has been holding back development. “The most effective materials for making ESLs start as a powder and have to be baked at high temperatures, above 500 °C,” said Tan. “You can’t put that on top of a sheet of flexible plastic or on a fully fabricated silicon cell - it will just melt.” Tan and his colleagues developed a new chemical reaction than enables them to grow an ESL made of nanoparticles in solution, directly on top of the electrode. While heat is still required, the process always stays below 150°C. The new nanoparticles are coated with a layer of chlorine atoms, which helps them bind to the perovskite layer on top for efficient extraction of electrons. This has produced a conversion efficiency of 20.1%. “This is the best ever reported for low-temperature processing techniques,” said Tan. He adds that perovskite solar cells using the older, high-temperature method are only marginally better at 22.1 per cent, and even the best silicon solar cells can only reach 26.3 per cent. Another advantage is stability. Many perovskite solar cells experience a severe drop in performance after only a few hours, but Tan’s cells retained more than 90 per cent of their efficiency even after 500 hours of use. “I think our new technique paves the way toward solving this problem,” said Tan. This opens up possibilities for applications of perovskite solar cells, from smartphone covers that provide charging capabilities to solar-active tinted windows that offset building energy use. “With our low-temperature process, we could coat our perovskite cells directly on top of silicon without damaging the underlying material,” said Tan. “If a hybrid perovskite-silicon cell can push the efficiency up to 30 per cent or higher, it makes solar power a much better economic proposition.” Europe invests in Estonian ultracapacitor pioneer By Peter Clarke Skeleton Technologies OU (Tallinn, Estonia), a developer of graphene-based ultracapacitors, has received €15 million (about $16 million) in equity funding from the European Investment Bank (EIB). The funds are described variously as a loan and as “quasi-equity” funding. The EIB loan is guaranteed under the European Fund for Strategic Investments (EFSI) and brings the amount raise by Skeleton to €41.7 million (about $44 million) since the company was founded in 2009. Whether a repayable loan or equity funding the money will be used to finance R&D for the further development of its products and systems and pursue global markets. Skeleton already includes the European Space Agency and German automotive manufacturers among its customers. Ultracapacitors are capable of rapid charging and discharging in a matter of seconds and are able to provide over 1 million charge/discharge cycles that offer benefits in industries where reliable, instant power is a necessity. Batteries, conventionally used in automobiles, provide slower charging and slower energy release. Skeleton aims to reach an energy density target of 20 Wh/kg by 2020 and claims its ultracapacitors deliver twice the energy density and four times the power density of competitor offerings. The company plans to invest in manufacturing to increase its competitive advantage on a component level. In particular, Skeleton plans to open an electrode manufacturing facility in Dresden, Germany. This will create employment locally, in line with the objectives of the Investment Plan for Europe “Given Skeleton’s cutting-edge technology and the eco-friendliness of its products, it’s only logical that EIB supports such European innovators,” said Jan Vapaavuori, vice president of the EIB “We want to see innovative companies scale-up and flourish here in Europe, That’s why I am delighted that Skeleton can benefit from the support of the EFSI as it takes its exciting next steps,” said Andrus Ansip, European Commission vice president. 16 Electronic Engineering Times Europe March 2017 www.electronics-eetimes.com


EETE MAR 2017
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