As nocturnal creatures, moths need to maximize how well they can see in the dark whilst remaining less visible to avoid predators. This ability to collect as much of the available light as possible and at the same time reflect as little as possible, has inspired Researchers at the Swiss Federal Laboratories for Materials Science and Technology (Empa) to design a new type of photoelectrochemical cell using relatively low cost materials.
Photosynthesis turns light energy into chemical energy by splitting water atoms into hydrogen and oxygen. In recent years much effort has gone into developing artificial photosynthesis, with many researchers trying varied methods to generate the cheap and clean energy, but the process has not yet been perfected.
Simple, unlovely rust – iron oxide – could potentially hold the key to realizing cheap, effective photoelectrochemical cells which mimic photosynthesis. Rust absorbs high energy frequencies of sunlight, but because it is a poor conductor only a very thin coating of can be used in the cell design, which in turn inhibits collection of sunlight. But when iron oxide is covered with a thin layer of tungsten oxide the two elements form a kind of double mirror bouncing light back and forth until all has been absorbed.
That's where the moth-inspired microstructure comes in. Empa researchers Florent Boudoire and Artur Braun took a sheet of glass sprayed with a suspension of plastic particles containing a drop of tungsten salt solution. This was then placed in an oven to burn away the plastic leaving only the tungsten, which is then sprayed with an iron salt solution and fired once more to create the double layered absorption sheet – or light-trapping "moth eye."
One goal of these experiments is a more clear understanding of how much tungsten oxide contributes to the photo current versus iron oxide. A perfect ratio will ensure the highest efficiency and research is ongoing to perfect the recipe for the perfect moth eye solar cell recipe.
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