Solar cell powers water-to-hydrogen conversion

A class of materials that has quickly become the rising star of the solar cell world could enable production of hydrogen fuel using sunlight.

Michael Grätzel, a chemist at École Polytechnique Fédérale de Lausanne in Switzerland, and colleagues built a photovoltaic device using cheap and abundant materials called perovskites.

In the Sept. 26 Science, Grätzel’s group describes a device that uses sunlight to split water into oxygen and hydrogen gas with 12.3 percent efficiency. That figure puts the device above the 10 percent benchmark for useful solar-to-hydrogen conversion. Hydrogen holds promise as clean fuel to power cars or produce electricity.

Over the last five years, perovskites have been found to rival the efficiency and cost of silicon in converting sunlight to electricity. Grätzel’s team created its device using perovskite cells and a catalyst made from nickel, iron, oxygen and hydrogen.

Perovskite photovoltaics also generate higher voltages than silicon cells, making them better at powering the water-splitting reaction. A similar device developed by MIT chemist Daniel Nocera and colleagues (SN Online: 9/16/14) used three or four silicon solar cells in series to produce the necessary voltage; Grätzel’s used only two.

For now, perovskite cells aren’t as durable as the silicon-based solar cells, which were invented in the 1950s and have been in wide use since the 1970s. “Like any photovoltaic device, it will take years to really get all the data on outdoor and indoor stability,” Grätzel says.

Editor’s Note: This story was updated October 2, 2014 to clarify how long silicon-based solar cells have been in use.