Light Helps Design Polymer Circuits

Photovoltaic materials could be made thinner, more efficient, and more stable thanks to a discovery from scientists in London.

The researchers at Imperial College London discovered a new way to position polymer solar cellnanoparticles in plastics. The method uses a combination of heat, and low-intensity visible and UV light to arrange the nanoparticles in patterns, reports Energy Harvesting Journal. The researchers believe that in the future the development will provide a low-cost tool to build thin-film circuits on 3-D printers.

The development may be particularly helpful for fullerene-polymer solar cells. These cells have many applications, including low-power wireless sensor networks that can monitor ocean temperatures and the stress inside a car engine. Engineers and designers like them because they are lightweight, inexpensive to make, flexible and can be manipulated at the molecular level. But they are notorious for being inefficient and unstable.

The researchers wanted to see how light plays a role in the stabilization of these films. So, conducting neutron reflectometry experiments at the Institut Laue-Langevin, an internationally-financed scientific facility in Grenoble, France, the researchers “shaved” layers off the films to see what happens to fullerene and the polymers separately on an atomic scale.

Energy Harvesting Journal explains more about the experiments:

Whilst previous theories suggested that thin film stabilization was linked to the formation of an expelled fullerene nanoparticle layer at the substrate interface, neutron reflectometry experiments showed that the fullerenes remain evenly distributed throughout the layer. Instead, the team revealed that the stabilization of the films was caused by a form of photo-crosslinking of the fullerenes. The process imparts greater structural integrity to films, which means that ultrathin films, (down to 10000 times smaller than a human hair) readily become stable with trace amounts of fullerene.

The finding would allow for thinner plastic devices, which means there would be shorter distances that signals would have to travel to electrodes. This structural development would lead to increased efficiencies and longer lifetimes.

Light sensitivity also means that circuit patterns can be written onto the films. The research team used a photomask to control the distribution of light and added heat. Both made the fullerenes self-assemble into well-defined patterns that then could be into circuits with 3-D printers.

“Using just light, we can ask specific parts of the film to segregate or connect, stabilize and function for photovoltaic purposes,” says Dr. Joao Cabral of Imperial College London. “After this, it is not difficult to create on-demand, self-assembling complex patterns on these films by the simple addition of heat. If replicated for more complex compositions, this would represent a major advance in their commercial application in electronics as well as in energy harvesting of low power sources.”

Source: “A new low cost tool for 3D circuit printing?,” Energy Harvesting Journal, 4/23/13
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