First Iron-Based, Light-Emitting Molecules Have Potential for Low-Cost Solar Cells, Displays

Scientists at Lund University in Sweden have successfully manipulated the electronic properties of iron-based molecules so that they better resemble the ruthenium-based substances typically used in metal-based dye molecules that form the basis for applica

Researchers in Sweden have advanced the effort to develop more environmentally friendly materials for solar cells and displays with the development of the first iron-based molecule that can emit light. 

Scientists at Lund University in Sweden have successfully manipulated the electronic properties of iron-based molecules so that they better resemble the ruthenium-based substances typically used in metal-based dye molecules that form the basis for applications such as solar cells and displays.

Chemists have been developing these dye molecules for more than 50 years and have sought to use common metals like iron, but to date no one, until now, has been able to develop an iron-based dye molecule that can emit light, said researcher Kenneth Wärnmark, professor of chemistry at the Faculty of Science at Lund University.

 

Iron-Based, Light-Emitting Molecules
The chemical model for the first iron-based molecule that can emit light, invented by researchers in Sweden with potential to develop more environmentally friendly materials for solar cells and displays. (Lund University)

 

“We want to replace expensive, toxic, and scarce metal such as ruthenium and [other] metals currently used in solar energy conversion technologies, with iron—which is inexpensive, non-toxic, and above all part-abundant,” he told Design News. “The latter is especially important since there is simply not enough of insect ruthenium—used in solar energy-conversion technologies. Thus, for a global energy solution based on solar energy, there are not enough of the required metals.”

For example, there are only 5,000 tons of ruthenium available on earth, with 12 new tons being excavated per year for solar and its other various applications, Wärnmark said.

What he and his team have done is not only to achieve an iron-based dye molecule that can capture light, but also emit light of a different color—a feat that is much more difficult, he added.

Researchers published a paper about their work in the journal Nature, describing an iron complex with an unprecedented life span in its light-absorbing and luminescent state: 100 picoseconds, which is less than a billionth of a second.
While this does not seem like a long time, “in the world of chemistry, this is enough time for the molecules to emit light,” explained Villy Sundström, another chemistry professor at Lund.

Researchers achieved their milestone by a well-studied and careful chemical procedure that gradually increased the electron density of the iron, Wärnmark explained.

“We have over some time developed different generation of iron carbene in which we have step by step increased the electron density at the iron center by adding more and more carbene ligands--in this way destabilizing deactivating pathways for the excited state electrons to go to a metal-centered state,” he said. “This has also been done by increasing the electron-donating properties of the carbene itself and also increasing the octahedral geometry of the iron-carbene complexes.”

The resulting light-emitting iron represents a key step forward for using iron as a luminescent material in lighting and displays, as well as for light absorbers in solar cells and photocatalysts for producing solar fuel, researchers said.

The team—which also included researchers from the Ångström Laboratory in Uppsala and from Copenhagen—plans to continue their work to optimize the molecule for its various potential applications, Wärnmark said.

Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 15 years. She currently resides in a village on the southwest coast of Portugal.

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