New efficiency record: This small device is able to convert 14 percent
of the incoming solar energy into hydrogen. Credit: M. May
(September 15, 2015) An international team has now succeeded in considerably increasing the efficiency for direct solar water splitting. They are using a tandem solar cell whose surfaces have been selectively modified. The new record value is 14 % and thus considerably above the previous record of 12.4 % held by the National Renewable Energy Laboratory (NREL) in the USA, broken now for the first time in 17 years. Researchers from the Institute for Solar Fuels at the Helmholtz-Zentrum Berlin, TU Ilmenau, the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg and the California Institute of Technology (Caltech) participated in the collaboration. The results have been published in Nature Communications.
The tandem cell is covered with a catalyst for hydrogen formation.
Credit: M. May
Solar energy is abundantly available globally, but unfortunately not constantly and not everywhere. One especially interesting solution for storing this energy is artificial photosynthesis. This is what every leaf can do, namely converting sunlight to “chemical energy”. That can take place with artificial systems based on semiconductors as well. These use the electrical power that sunlight creates in individual semiconductor components to split water into oxygen and hydrogen. Hydrogen possesses very high energy density, can be employed in many ways and could replace fossil fuels. In addition, no carbon dioxide harmful to the climate is released from hydrogen during combustion, instead only water. Until now, manufacturing of solar hydrogen at the industrial level has failed due to the costs, however. This is because the efficiency of artificial photosynthesis, i.e. the energy content of the hydrogen compared to that of sunlight, has simply been too low to produce hydrogen from the sun economically.