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New World Record in Photovoltaic Efficiency Australian Researchers Achieve 34.5% PV Efficiency! R esearchers at the University of New South Wales Australian Centre for Advanced Photovoltaics have pushed sunlight-to-electricity conversion efficiency of solar cells to 34.5% – establishing a new world record for unfocussed sunlight and nudging closer to the theoretical limits for such a device. The record was set by Senior Research Fellow Dr Mark Keevers and ACAP Director, Professor Martin Green. They used a 28cm2 four-junction mini-module – embedded in a prism – that extracts the maximum energy from sunlight. It does this by splitting the incoming rays into four bands, using a hybrid four-junction receiver to extract even more electricity from each beam of sunlight. The new UNSW result, confirmed by the U.S. National Renewable Energy Laboratory, is almost 44% better than the previous record of 24% efficiency, held by Alta Devices of the USA. That record was created over a larger surface area of 800cm2. by Ross Tester The four-junction mini module is embedded in a prism to split the incoming sunlight into four colour bands, which allow maximum efficiency in conversion to electricity. “This encouraging result shows that there are still advances to come in photovoltaics research to make solar cells even more efficient,” said Dr Keevers. “Extracting more energy from every beam of sunlight is critical to reducing the cost of electricity generated by solar cells as it lowers the investment needed, and delivers payback faster.” The result was obtained by the same UNSW team that set a world record in 2014, achieving an electricity conversion rate of over 40% by using mirrors to concentrate the light – a technique known as CPV (concentrator photovoltaics) – and then similarly splitting out various wavelengths. The new result, however, was achieved using normal sunlight with no concentrators. “What’s remarkable is that this level of efficiency had not been expected for many years,” said Professor Green, a pioneer who has led the field for much of his 40 years at UNSW. “A recent study by Germany’s Agora Energiewende think tank set an aggressive target of 35% efficiency by 2050 Dr Mark Keevers (left) and Professor Martin Green were responsible for the breakthrough and new world record, breaking the old mark by 45%. 84  Silicon Chip siliconchip.com.au for a module that uses unconcentrated sunlight, such as the standard ones on family homes.” “So things are moving faster in solar cell efficiency than many experts expected, and that’s good news for solar energy,” he added. “But we must maintain the pace of photovoltaic research in Australia to ensure that we not only build on such tremendous results but continue to bring benefits back to Australia.” Australia’s research in photovoltaics has already generated flow-on benefits of more than $8 billion to the country. Gains in efficiency alone, made possible by UNSW’s PERC cells, are forecast to save $750 million in domestic electricity generation in the next decade. PERC cells were invented at UNSW and are now becoming the commercial standard globally. The triple-junction cell targets discrete bands of the incoming sunlight, using a combination of three layers: indium-gallium-phosphide; indium-gallium-arsenide and germanium. As sunlight passes through each layer, energy is extracted by each junction at its most efficient wavelength, while the unused part of the light passes through to the next layer, and so on. Some of the infrared band of incoming Different photovoltaic compounds have a maximum efficiency at sunlight, unused by the triple-junction cell, different wavelengths – hence splitting sunlight into various bands using is filtered out and bounced onto the silicon a prism achieves a much better result than current cells, which use white cell, thereby extracting a large proportion of light. Note that three of the four bands are in the infrared. the energy from each beam of sunlight hitting the mini-module. create cheaper multi-junction cells. The 34.5% result with the 28cm2 mini-module is already However, the spectrum-splitting approach is perfect for a world record, but scaling it up to a larger 800cm2 – thereby solar towers, like those being developed by Australia’s Rayleaping beyond Alta Devices’ 24% – is well within reach. Gen Resources, which use mirrors to concentrate sunlight “There’ll be some marginal loss from interconnection which is then converted directly into electricity. in the scale-up, but we are so far ahead that it’s entirely The research is supported by $1.4 million grant funding feasible,” Dr Keevers said. The theoretical limit for such a from the Australian Renewable Energy Agency (ARENA), four-junction device is thought to be 53%, which puts the whose CEO Ivor Frischknecht said the achievement demonUNSW result two-thirds of the way there. strated the importance of supporting early stage renewable Multi-junction solar cells of this type are unlikely to energy technologies. find their way onto the rooftops of homes and offices soon, “Australia already punches above its weight in solar R&D as they require more effort to manufacture and therefore and is recognised as a world leader in solar innovation,” cost more than standard crystalline silicon cells with a Frischknecht said. “These early stage foundations are insingle junction. But the UNSW team is working on new creasingly making it possible for Australia to return solar techniques to reduce the manufacturing complexity, and dividends here at home and in export markets – and there’s no reason to believe the same results can’t be achieved with this record-breaking technology.” He noted that the UNSW team is working with another ARENA-supported company, RayGen, to explore how the advanced receiver could be rolled out at concentrated solar PV power plants. “With the right support, Australia’s world leading R&D is well placed to translate into efficiency wins for households through the ongoing roll out of rooftop solar and utility-scale solar projects such as those being advanced by ARENA through its current $100 million large-scale solar round, ” he added. “Over the longer term, these innovative technologies are also likely to take up less space on our rooftops and in our fields.” Other research partners working with UNSW include Professor Green said that there is a long way to go from the Trina Solar, a PV module manufacturer and the U.S. Naworking modules to commercial production – “perhaps as tional Renewable Energy Laboratory. much as ten years” – but this is an enormous breakthrough. 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