Exciting excitons

A research team from Columbia University has designed organic molecules that can produce excitons with a longer lifecycle than inorganic equivalents. The excitons have the potential to amplify the amount of electricity generated by the photons a solar cell absorbs.

Scientists at Columbia University in the U.S. claim to have created a new design rule for singlet fission materials that could lead to drastically improved efficiencies for solar cells and other PV devices.

In the study Ultra-fast intramolecular singlet fission to persistent multiexcitons by molecular design, published in Nature Chemistry, the researchers explained the materials consist of specially designed organic molecules said to be capable of generating two excitons per photon of light. That is made possible by singlet fission, a photophysical process in molecules and molecular aggregates whereby a singlet exciton generated by irradiation splits into two triplet excitons.

Two for the price of one

The revolutionary power of such duplication of excitons is particularly interesting for the solar industry. In conventional PV panels one photon of light can generate only one exciton. When two excitons are generated, however, they have much shorter lives than their single equivalents, limiting their ability to convert light into electricity.

The authors of the new research, however, claim their design rule for singlet fission materials has enabled them to create the most efficient and technologically useful intramolecular singlet fission materials to date.

“This work is the first to show that singlet fission can rapidly generate two excitons that can live for a very long time,” said research coordinator Luis Campos. “This opens the door to fundamentally study how these excitons behave as they sit on individual molecules and also to understand how they can be efficiently put to work in devices that benefit from light-amplified signals.”

According to another recent U.S. study, singlet fission has the potential to raise the theoretical efficiency of solar cells from 33% to 44%.

Singlet fission has already been used in several research projects to reduce thermalization losses in conventional solar cells.

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