IU lab looks to revamp solar cells

Based in Simon Hall, the Li Group led by Dr. Liang-Shi Li is currently working on a project to develop an efficient, low-cost solar cell using a carbon-based molecule, or organic molecule.

Solar cells convert the sun’s energy into electricity — and the lab’s work might hold the key to their future.

Current methods of generating solar cells include the use of silicon, ruthenium or cadmium telluride as a base. Each of these solutions is effective, but all have their disadvantages.

Silicon is very popular and effective, but it is expensive, making solar cells economically inaccessible to large populations.

Using ruthenium as a base for a processed solution is much cheaper but less efficient than silicon, and ruthenium is a relatively rare element.

Finally, cadmium telluride offers an alternative solution, but cadmium is toxic and tellurite is rare. Thus, while these ideas might be useful now, in the development of solar cells, they do not stand as viable options for long-term solutions.

With this in mind, the Li lab set out in 2006 to develop a solar cell material that is cheaper and better for the long term so as to promote more widespread use of renewable resources. The material? Graphene, a single layer of graphite that is found in most pencils.

More specifically, graphene is as a single atomic layer of benzene rings, hexagonal rings of bonded carbon atoms in a crystal lattice formation.

“Graphene is very interesting because if you change the number of benzene rings bound together in the layer, you see different physical properties,” Li said.

For example, a solution of just one benzene is colorless, but two benzene rings bound together are yellow in solution. Put a bunch of them together into a five-by-five square, and you’ve got a black substance, which can absorb all colors of light.

Exploiting this property allows the group to develop cells that can absorb different colors of light depending on the size of their graphene sheets.

Graduate students in the lab are working on learning more about the unique properties of graphene in its different forms.

One graduate student, Xiao Cui, has been with the lab since its beginning and is working on organic synthesis of graphene molecules. Organic synthesis is a branch of chemical synthesis that is concerned with the construction of organic compounds via organic reactions.

Irma Hamilton, a second-year graduate student in the lab, works on characterizing the molecules synthesized by her colleagues.

“It’s very interesting, because you expect one thing, and then it will behave completely differently,” Irma said of her work.

The group has already succeeded in making a solar cell using their materials in the lab with about 2 percent efficiency.

Now, they are working on ways to make that cell more efficient while also trying to find better ways of making the carbon soluble.

“We think that eventually this will go to application, but it will take time,” Li said. “A solar cell is a very complicated thing. There are so many components that have to work together.”