Solar cell material repairs itself

17 Jun 2002

Self healing properties have been discovered in a semiconducting material that could be used in solar cells.

Solar modules based on the semiconducting material, copper indium gallium diselenide, are resistant to damage by the sun's radiation and stable in long term outdoor tests.

The stability of copper indium gallium diselenide is surprising because the material has a complex structure that might be easily disrupted. However, researchers from the Weizmann Institute and Tel Aviv University in Israel, France's CNRS and Stuttgart University Germany believe that the complexity of the structure might be the reason for its long life span in harsh conditions.

The researchers have found that the copper atoms in a related material, copper indium diselenide, are only weakly bound in the structure, making them mobile. When the material has been damaged by radiation, the copper atoms, and the holes that they vacate, move to other parts of the material and repair the damage. The atoms do this in order to return the energy distribution in the material to equilibrium.

Damage by radiation is a major concern with materials currently used for solar cells, particularly on satellites. For a commercially viable technology, stability is thought to be as important as the efficiency of the material in converting solar energy into electricity.

The migration of the copper atoms in crystals of copper indium diselenide was observed using high energy X-rays at the European Synchrotron Research Facility in Grenoble, France. Radioactive tracer experiments have also provided evidence of this behaviour.

The team has calculated that the time scale of the repair is in the range of about 6 hours to 14 days. This time is short enough to be useful as solar modules are expected to last for several years.

David Cahen, of the Weizmann Institute, commented that a similar mechanism has been observed before in the fabrication of radiation detectors by drifting lithium into silicon.

The research is due to be published in the journal Advanced Materials.