Hydrogen production by light comes closer
The team around Jan-Philipp Becker from the Jülich Research Centre has devised a multijunction solar cell that can produce hydrogen, following the principle of artificial photosynthesis. The solar cell has an overall energy efficiency of 9.5 percent – a record efficiency for this type of solar cell. Hitherto, this efficiency amounted to just 7.8 percent. Plus, it can be manufactured rather cheap.
Compared to solar power, hydrogen has a strong advantage: It can be stored. Thus, the energy is available even in times when the sun doesn’t shine. A common approach to produce hydrogen directly from sunlight is photosynthesis. Much like a leaf in the nature, the solar cells transform solar energy directly into hydrogen by splitting water into oxygen and hydrogen. This approach however is still far from practical and economical use. Here the Jülich silicon multijunction stacked solar cell steps in. Optimised for artificial photosynthesis, the device has a much better efficiency than available ones. “The challenge is to achieve a photo voltage high enough to make it work”, says Jan-Philipp Becker from the Institute of Energy and Climate Research of the Forschungszentrum Jülich. “In practice, about 1.6 volts are needed to maintain the water splitting reaction. With available crystalline silicon solar cells which generate voltages of significantly less than 1 volt, this cannot be done.”
Becker’s team has developed solar modules made of three or four stacked cells which in turn contain multiple layers. “This multi-layer approach makes it possible to utilise the sunlight more efficiently across a broad spectrum of wavelengths”, explains fellow researcher Félix Urbain. “At the same time, the voltage is increased up to 2.8 volts. This offers enough elbow room to utilise relatively cheap materials like nickel as catalysers instead of expensive platinum catalysers”.
Unlike crystalline solar cells, the silicon thin film cells are not made from a silicon wafer. Instead, they are deposited under vacuum on a glass or plastics substrate, utilising several various techniques. The thin film technology has the advantage that it takes significantly less material than the classical wafer technology”, explains Friedhelm Finger, head of the Materials and Solar Cells Department at the Institute of Energy and Climate Research. “In addition, the semiconductor materials can be applied over large areas at relatively low cost.”
Without utilising special high-performance semiconducting materials – which in turn are expensive to process –, silicon thin film solar cells achieved only an efficiency of maximum 7.8 percent. The new array from Jülich marks a major step towards industrialisation in that the researchers could increase the efficiency to 9.5 percent. “Our tests show that silicon thin film solar modules can be used efficiently to produce hydrogen”, says institute manager Uwe Rau. “Overall efficiencies above 10 percent seem to be feasible”.
The next step will be scaling the solar cells to larger areas, the researchers said.
These results have been published originally here: https://pubs.rsc.org/en/content/articlehtml/2015/ee/c5ee02393a
More information: https://www.fz-juelich.de/iek/iek-5/DE/Home/home_node.html
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