Cheap Solar Using Plastic Electronics?

In order to make solar power cost-effective without governmental subsidies, we need to dramatically reduce the manufacturing costs of solar cells. (I discussed solar costs in a previous blog.) A lot of research is underway to do just that. One area of solar research focuses on finding a low-cost alternative to indium tin oxide (ITO), which is an expensive conducting material currently used in standard solar cells. ITO is a rare by-product of mining that is also used in flat-screen televisions, mobile phones, and other devices with display screens. As the demand for these popular devices increases rapidly, the price and availability of ITO for solar cells has become a real problem.

A team of chemical engineers think they’ve found the solution — plastic electronics. This collaboration of chemical engineers from Princeton University, University of Texas, and University of California Santa Barbara reported their latest results in the Proceedings of the National Academy of Sciences on March 30, 2010. Their research focuses on conductive polymers (plastics).

Conductive polymers have been around for a long time, but their ability to conduct electricity degraded when manufactured into devices. Basically the manufacturing process caused their structures to be trapped in a rigid form and that prevented electrical current to travel through them, thus severely limiting device performance.

The multi-institutional collaboration has overcome this problem, by treating the conductive polymers with dichloroacetic acid (DCA) after they are processed into the desired form. This “postdeposition solvent annealing” with DCA dramatically rearranges the structure of the polymer, resulting in a smooth film with high conductivity. As a result, they are able to make polymers that are translucent, malleable and highly conductive. These materials could have wide reaching applications as electrodes in transistors, anodes in solar cells, and light-emitting-diodes.

One amazing thing about this research is the simplicity of production. This collaboration made a transistor (a very basic device used to amplify and switch electronic signals) by printing the polymer onto a surface, using a method similar to that used by a standard ink-jet printer. In the future, they hope to distribute the conductive polymers in cartridges like printer ink.

What does this mean for solar power? An important thing for solar is that these conductive polymers are translucent. Although they are less transparent than ITO (e.g., transmissivity of 73% v.s. 84% respectively), they are dramatically cheaper. So the newly developed conductive polymers are still a promising low-cost alternative as anodes for solar cells. Hopefully this research will translate into cheap, commercially available solar cells soon.

Researchers have developed a new way to manufacture electronic devices made of plastic, employing a process that allows the materials to be formed into useful shapes while maintaining their ability to conduct electricity. In the transistor pictured above, the plastic is molded into interdigitated electrodes (orange), allowing current flow to and from the active channel (green). Courtesy of Loo Research Group.

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