Developments in Brief : Solar Power Cell Reaches a Record 15% Level of Efficiency in Experiment

An experimental type of solar power cell has reached record efficiency levels, and one version continued to provide power at night, scientists reported last week. Although the experimental cells still are less efficient than photovoltaic cells, they may compete commercially in the future.

The experimental cells use solids and a liquid solution to generate power, while existing commercial photovoltaic cells use only solids.

The experimental photoelectrochemical cells generate power when light strikes a solid called a semiconductor that touches the liquid. The semiconductor then draws electrons out of the solution, and the electron flow--which is electrical current--runs through a circuit to do its work before returning to the solution.

The experiments involving photoelectrochemical cells appear in the current issue of the British journal Nature.

In one report, Stanford University scientists describe a photoelectrochemical cell that converted 15% of the solar energy falling on the semiconductor into useful electrical power. The highest efficiency reported previously for such a cell was 14%, said Nathan Lewis of the Stanford team. In comparison, state-of-the-art photovoltaic cells reach 21%, he said.

Although the increase in efficiency appears small, the work is important because it shows a direction for further research, said Mark Wrighton, a chemistry professor at the Massachusetts Institute of Technology.

The other Nature paper describes a cell that stores part of the energy it produces, then draws on the stored power to maintain its electrical output after sunlight disappears.

Researchers from the Weizmann Institute of Science in Rehovot, Israel, reported that the cell delivered a steady current over two days and nights.