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Ultrafast lasers used to create a ‘perfect’ solar energy absorber
Researchers at the University of Rochester have used ultrafast laser processing to develop metal surfaces capable of absorbing solar energy at exceptional efficiency. In Light: Science & Applications they
described how they have used powerful femtosecond laser pulses to etch metal surfaces with nanoscale structures that selectively absorb light at the solar wavelengths, while not absorbing other wavelengths. While the researchers had previously
succeeded in creating black hydrophobic surfaces using ultrafast lasers that were also highly absorptive of solar energy, some of this energy was lost at wavelengths beyond the solar spectrum. Now, they have created a new selective absorber that is highly efficient at absorbing sunlight, while also being able to reduce the heat dissipated at other wavelengths. According to the researchers, this makes the surface the first ‘perfect metallic solar absorber’. The researchers used a ti:sapphire laser
from Coherent. A maximum pulse energy of 7mJ, a maximum average power of 7W and a 1kHz repetition rate was used. After experimenting with aluminium,
copper, steel and tungsten, the researchers found the latter – already commonly used as a thermal solar absorber – had the highest solar absorption efficiency when treated with the new nanoscale structures. Using a thermal electric generator, they demonstrated that solar energy harnessing efficiency was 130 per cent higher with the treated tungsten, compared to untreated tungsten. ‘This will be useful for any thermal solar
energy absorber or harvesting device, particularly in places with abundant sunlight,’ said Professor Chunlei Guo, who led the team. The research was funded by the Bill and Melinda Gates Foundation, the US Army Research Office and the US National Science Foundation.
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Ultrafast lasers can be used to etch metal surfaces with exceptional solar energy absorption efficiency
Lasers augment production of organic photovoltaic cells Organic photovoltaic (OPV) cell production is also set to see advancement thanks to both short- and ultrashort-pulsed lasers. The lasers will be used in the ‘EffiLayers’ project, launched in September, to increase the efficiency of roll-to-roll processes, which can be used to manufacture the cells on an industrial scale. OPV cells, while less efficient than
traditional silicon-based solar cells, are flexible and transparent, enabling them to be functionally and decoratively integrated, for example into building facades. Manufacturing them using industrial-scale roll-to-roll processes removes the need for energy- intensive and costly process steps, required in classical silicon photovoltaic production. In the new approach, the functional layers
of the cells are applied on top of each other via wet-chemical solutions by means of heated slot-die coating. The 10 to 250nm- thick layers are then processed using multiple
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laser sources wielding both short and ultrashort pulses. A femtosecond laser is used to separate the individual layers, so that individual cells can be connected in series. Laser scribing is performed using 11 partial beams, which selectively separate the composite layers so that, at the end, 12 serially connected subcells can be produced on a single film. The OPV cells are later sealed by laser encapsulation with a barrier film to protect from environmental factors.
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