Swiss team develops effective and low-cost solar water-splitting device; 14.2% solar-to-hydrogen efficiency
Using commercially available solar cells and none of the usual rare metals, researchers at the Swiss Center for Electronics and Microtechnology (CSEM) and École Polytechnique Fédérale de Lausanne (EPFL) have designed an intrinsically stable and scalable solar water splitting device that is fully based on earth-abundant materials, with a solar-to-hydrogen conversion efficiency of 14.2%.
The prototype system is made up of three interconnected, new-generation, crystalline silicon solar cells attached to an electrolysis system that does not rely on rare metals. The device has already been run for more than 100 hours straight under test conditions. The method, which surpasses previous efforts in terms of stability, performance, lifespan and cost efficiency, is published in the Journal of The Electrochemical Society.
crystalline Silicon (c-Si) solar cells show high solar-to-electricity efficiencies, and have demonstrated stabilities in excess of 25 years. Propelled by their attractive performance, they have continuously dominated the market since their inception, with a current worldwide market share greater than 85%. Their high production volumes have largely contributed to a price drop of 80% since 2008, currently reaching levels below $1 per watt peak.
… Recently, c-Si modules have been implemented in solar-hydrogen devices, demonstrating SHE [solar-to-hydrogen efficiency] of 9.7%. As the VOC of the presented c-Si cells is only ∼600 mV, four cells need to be connected in series to achieve stable water splitting performance. This results in lower operating currents and limited SHE efficiencies. Alternatively, c-Si-based heterojunction (SHJ) cells can reach VOC values in excess of 700 mV. These VOC values are the highest ones reported for silicon wafer-based technologies, and are predominantly obtained by an excellent interface passivation with a thin (∼5 nm) film of hydrogenated intrinsic amorphous silicon (a-Si:H) between the c-Si wafer and the oppositely doped emitter, forming the p-n junction. We demonstrate in this study that, thanks to their high VOC, three series-connected SHJ cells can already stably drive the water splitting reaction at unprecedented SHE.—Schüttauf et al.
A 12-14 m2 system installed in Switzerland would allow the generation and storage of enough hydrogen to power a fuel cell car over 10,000 km every year.—Christophe Ballif, co-author
In terms of performance, this is a world record for silicon solar cells and for hydrogen production without using rare metals.
The key here is making the most of existing components, and using a hybrid-type of crystalline-silicon solar cell based on heterojunction technology. The researchers’ sandwich structure—using layers of crystalline silicon and amorphous silicon—allows for higher voltages needed to power directly the microstructured Ni electrocatalysts. Nearly identical performance levels were also achieved using a customized state-of-the-art proton exchange membrane (PEM) electrolyzer.
The researchers used standard heterojunction cells to prove the concept; by using the best cells of that type, they would expect to achieve a performance above 16%.
The research is part of the nano-tera SHINE— project to develop an efficient and cost-effective hydrogen production system using sunlight and water.
Jan-Willem Schüttauf, Miguel A. Modestino, Enrico Chinello, David Lambelet, Antonio Delfino, Didier Dominé, Antonin Faes, Matthieu Despeisse, Julien Bailat, Demetri Psaltis, Christophe Moser, and Christophe Ballif (2016) “Solar-to-Hydrogen Production at 14.2% Efficiency with Silicon Photovoltaics and Earth-Abundant Electrocatalysts” J. Electrochem. Soc. 163(10): F1177-F1181 doi: 10.1149/2.0541610jes