New Solar Cell Harvests Hydrogen From Water
15% efficiency would actually be pretty good considering by some calculations photosynthesis efficiency is around 5 to 20%.
Here is one calculation showing ~6.6% photosynthesis efficiency
It takes into account things like canopy shading, which wouldn't necessarily apply to this, but here's the link:
I tried to find a peer reviewed one, but can't find one right now(I'm at work, break almost over... :( )