By growing layers of zinc oxide and titanium dioxide on a semiconductor surface, researchers from the École polytechnique fédérale de Lausanne (EPFL) have managed to create solar cells that can ultimately extract hydrogen from water under the direct action of sunlight, just like leaves do their natural photosynthesis.
Previous attempts had existed before, but the semiconductors used in the reaction (such as cuprous oxide) have proved to be unstable in the presence of water and sunlight at the same time.
Adriana Paracchino and Elijah Thimsen, helped by Michael Grätzel, the man who invented organic solar cells (and who got a Millennium Technology Prize for that), have this time covered the cuprous oxide with a one-atom-thick film of zinc oxide and titanium dioxide through a method called “atomic layer deposition” (ALD).
The ALD technique they used can control the deposition so well that the film only has one atom in thickness. Thus, the cuprous oxide preserves all of its hydrogen-producing efficiency and is still protected by the film. Technologies that can scale up the technique to industrial usage are being researched.