Record for Solar Hydrogen Production

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The US Department of Energy’s National Renewable Energy Laboratory (NREL) has captured the record for highest efficiency in solar hydrogen production via a photoelectrochemical (PEC) water-splitting process. The new solar-tohydrogen efficiency record is 16.2 per cent, topping a reported 14 per cent efficiency in 2015 by a team made up of researchers from HelmholtzZentrum Berlin, TU Ilmenau, Fraunhofer ISE, and the California Institute of Technology. A paper in Nature Energy, titled ‘Direct Solar-to-hydrogen Conversion via Inverted Metamorphic Multijunction Semiconductor Architectures,’ outlines how the new record was achieved.

According to NREL, both the old and new PEC processes employ stacks of light-absorbing tandem semiconductors that are immersed in an acid/water solution (electrolyte) where the water-splitting reaction occurs to form hydrogen and oxygen gases. But unlike the original device made of gallium-indium-phosphide grown on top of gallium arsenide, the new PEC cell is grown upsidedown, from top to bottom, resulting in a so-called inverted metamorphic multijunction device. Another key distinguishing feature of the new advancement was depositing a very thin aluminum indium phosphide ‘window layer’ on top of the device, followed by a second thin layer of gallium indium phosphide, NREL said.