A photoelectrochmical cell assembled with quantum dots—nanometer-sized semiconductor particles—catalytically achieved quantum efficiency for hydrogen gas production exceeding 100 percent.

The device developed by the U.S. researchers absorbs one visible solar photon and produces two or more electrons through a process known as multiple exciton generation (MEG), which are further utilized to reduce water to generate hydrogen gas. New Jersey Institute of Technology (NJIT), U.S. National Renewable Energy Laboratory, the Colorado School of Mines and San Diego State University collaborated in the study.

Scientists worldwide are engaged in efforts to achieve quantum efficiency as close as possible to 100 percent for solar hydrogen production. The U.S. team exceeded this goal by directly documenting a peak external quantum efficiency of 114 percent, and proving that their photoelectrochemical cell design is much more efficient than a quantum dot solar cell with respect to quantum yield.

Lead sulfide quantum dots replace semiconductor materials such as silicon and copper indium gallium arsenide. The advantage is that such a photoelectrochemical device can, potentially, convert a greater portion of the solar spectrum into useful energy.

Says lead researcher and author Yong Yan, an assistant professor at NJIT, “These results do present the possibility of generating more energy more efficiently with such a solar-capture device in the future. This could also lead to a fundamental change in the entire process of producing hydrogen fuel. We can now obtain hydrogen fuel from water by using electricity supplied by conventional power plants that consume fossil fuels. But by building on the basic step of achieving such high quantum efficiency for solar hydrogen generation, we could make the process of producing a ‘green’ fuel much greener as well.”