Solar cells made through oil-and-water 'self-assembly'

[Joanne98]

Researchers have demonstrated a simple, cheap way to create self-assembling electronic devices using a property crucial to salad dressings.

It uses the fact that oil- and water-based liquids do not mix, forming devices from components that align along the boundary between the two.

The idea joins a raft of approaches toward self-assembly, but lends itself particularly well to small components.

The work is reported in Proceedings of the National Academy of Sciences.

Crucially, it could allow the large-scale assembly of high-quality electronic components on materials of just about any type, in contrast to "inkjet printed" electronics or some previous self-assembly techniques.

Specific gravity

Such efforts have until now exploited the effect of gravity, assembling devices through so-called "sedimentation".

In this approach, "blank" devices are etched with depressions to match precisely-shaped components. Simply dumped into a liquid, the components should settle down into the blank device like sand onto a riverbed, in just the right places.

"That's what we tried for at least two years and we were never able to assemble these components with high yield - gravity wasn't working," said Heiko Jacobs of the University of Minnesota, who led the research.

SELF-ASSEMBLY EXPLAINED

The oil/water mix contains a number of individual solar cell elements
Each is coated with a "water-loving" molecule on the bottom and a "water-hating" one on top
The elements align neatly at the oil/water boundary in a two-dimensional sheet
The "blank" solar cell has pre-cut places for the elements and is dipped through the boundary
As it is slowly drawn upwards, the elements pop into place
"Then we thought if we could concentrate them into a two-dimensional sheet and then have some kind of conveyor belt-like system we could assemble them with high yields and high speed," he told BBC News.

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http://news.bbc.co.uk/2/hi/science/nature/8452912.stm