YOU鈥橰E lying on the beach listening to music, and the battery in your MP3 player is running low. Not to worry: you can simply plug it into your towel for some extra juice.
That scenario might not be far off thanks to inexpensive spray-on solar cells that can be applied to almost any surface, from plastic to fabrics.
Conventional solar cells are expensive to make. One type, for example, is made using a technique called vapour deposition, in which a photovoltaic material is laid down on a surface at very high temperatures, and often in a vacuum.
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With a view to bringing costs down, and colleagues at the University of Texas at Austin have developed a light-harvesting ink containing nanocrystals of copper indium diselenide. This can be sprayed onto a range of surfaces at room temperature using an airbrush. 鈥淚t鈥檚 essentially how you might paint your wall, except the pigment has a purpose,鈥� says Korgel.
鈥淪praying on a solar cell is essentially like painting a wall, except the pigment has a purpose鈥�
The military is particularly interested in using sprayable photovoltaic materials to create tents that can generate energy, he says. The technology also opens up the possibility of mass-producing rolls of plastic solar cells, and could have everyday applications when painted onto car roofs or sprayed onto bags or clothing.
Various groups have been working on flexible solar cells, among them a team led by Harry Atwater at the California Institute of Technology in Pasadena. He points out that photovoltaic liquids will only become commercially viable if they can convert at least 7 per cent of the energy in the light shone on them into electricity.
Korgel admits his team is not there yet. 鈥淥ur best efficiency in the lab is just over 3 per cent,鈥� he says. To try to squeeze out more electricity, they are now working to eliminate irregularities in the sprayed nanocrystal layers.
The team has also come up with a partial workaround, namely to stack the spray-on cells on top of each other. This can increase the efficiency to about 4.5 per cent (Energy and Environmental Science, ).
