Small titanium barrier halts big problem in fuel-producing solar cells
The new design coats molecular components and drastically improves stability under difficult and oxidizing conditions.
What if we could turn sunlight and water into fuel? That is the idea behind certain types of solar cells. Known as dye-sensed photoelectrochemical cells, these devices use the energy contained in sunlight to divide the water into hydrogen and oxygen. The hydrogen itself can be used as fuel, or it can be used to make other types of fuels. The problem? The conditions necessary to divide the water tend to damage the solar cell. Now researchers have designed a more stable dye-sensitized photoelectrochemical cell.
This study presents a new design for a solar cell that separates water, more stable and more efficient. In designing the design, the team made discoveries about a fundamental part of the cell. Specifically, they have a better view of what happens when the material that collects electrons from sunlight finds the material that divides the water to produce fuel. Follow-up work based on this and other studies could open the door to efficient and stable devices that produce fuel from sunlight.
Green leafy plants readily convert sunlight into dense fuels into energy. Conventional solar cells do not. Why not? A key reaction, dividing water into oxygen and hydrogen, only occurs under adverse conditions that damage the materials of the cell. Specifically, the division of water occurs under strongly oxidizing conditions (the same type of conditions that cause iron rust). The researchers designed a dye-sensitized solar cell that can withstand these difficult conditions. It displays good current density and is more stable than its predecessors. In the new project, the team coated the molecular components of the solid state cell with a thin layer of titanium dioxide (2 nanometers). At the outset, the coating made the performance of the cell somewhat difficult. To compensate for the loss of performance, the team separated the dye from the solid solution interface. This change allows the use of dyes that absorb more light (working in the visible range). In addition, it allows scientists to optimize pH to divide water more efficiently. This research is an important step forward in the division of water powered by solar energy. The project builds on the science developed within the Department of Energy's solar photochemistry program and Energy's frontier research centers over the past two decades.
The Department of Energy, Office of Science, Basic Energy Sciences, Chemical Sciences, Geosciences and Biosciences and the China Scholarship Council funded this research.
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P. Xu, T. Huang, J. Huang, Y. Yan and T.E. Mallouk, "Oxidation of photoelectrochemical water sensitized by dye through a buried junction". Annals of the National Academy of Sciences of the USA 115, 6496 (2018). [DOI: 10.1073/pnas.1804728115]