Two nanotech methods for engineering solar cell materials are showing " particular promise", US academics reported today.

Researchers at the University of California, Santa Cruz explained that one method uses thin films of metal oxide nanoparticles, such as titanium dioxide, "doped" with other elements such as nitrogen.

Another strategy employs quantum dots, or nano-sized crystals, that strongly absorb visible light.

Combining these approaches appears to yield better solar cell materials than using one method alone, according to Jin Zhang, professor of chemistry at the University of California, Santa Cruz.

Professor Zhang led a team of researchers from California, Mexico and China to created a thin film doped with nitrogen and sensitized with quantum dots.

When tested, the new nano-composite material performed better than predicted, as if the functioning of the whole material was greater than the sum of its two individual components.

"We have discovered a new strategy that could be very useful for enhancing the photo response and conversion efficiency of solar cells based on nanomaterials," said Professor Zhang.

"We initially thought that the best we might do is get results as good as the sum of the two, and maybe if we did not make this right, we would get something worse. But surprisingly, these materials were much better."

Professor Zhang's team prepared films with thicknesses of 150nm and 1,100nm with titanium dioxide particles that had an average size of 100nm.

They doped the titanium dioxide lattice with nitrogen atoms, and chemically linked quantum dots made of cadmium selenide for sensitisation to this thin film.

The group's findings were reported in the Journal of Physical Chemistry in a paper posted online on 4 January.