Not only does the yield efficiency improve compared with a layer of the material on a substrate but it does so using ten thousand times less material.
The primary operation of the solar cell is conventional producing electricity but that electricity can then be used to split water into oxgen and hydrogen gas that can be separated and stored. Hydrogen gas that can be used as a clean fuel in the chemical industry or combusted in fuel cells - in cars for example - to drive engines.
The GaP nanowires measure 500nm by 90nm. The yield of hydrogen stands at 2.9 percent, a record for GaP cells, but some way behind 15 percent achieved by coupling silicon solar cells to a battery. However the possibility of integrating the tiny amounts of GaP into solar cells which generate storable fuel would get around one of the major drawbacks of solar cells, their intermittent nature at lower cost and using less macro-scale engineering.
Related links and articles:
Anthony Standing et al., Efficient water reduction with gallium phosphide nanowires, Nature Communications (17 July 2015) DOI: 10.1038/nscomms8824