Doubling the Excitons From a Photon of Light

Columbia University scientists have designed organic molecules capable of generating two excitons per photon of light. The process is called singlet fission. Of importance is the excitons can live for much longer than those generated from their inorganic counterparts, which leads to an amplification of electricity generated per photon that is absorbed by a solar cell.

The Columbia researchers is a development of a way to harness more power from singlet fission to increase the efficiency of solar cells, providing a tool to help push forward the development of next-generation devices.

In a study published this month in Nature Chemistry, the team details the design of organic molecules that are capable of generating two excitons per photon of light, the process called singlet fission where the excitons are produced rapidly and can live for much longer than those generated from their inorganic counterparts.

Luis Campos, an associate professor of chemistry and one of three principal investigators on the study said, “We have developed a new design rule for singlet fission materials. This has led us to develop the most efficient and technologically useful intramolecular singlet fission materials to date. These improvements will open the door for more efficient solar cells.”

All modern solar panels operate by the same process – one photon of light generates one exciton, Campos explained. The exciton can then be converted into electric current. However, there are some molecules that can be implemented in solar cells that have the ability to generate two excitons from a single photon, a process called singlet fission.

These solar cells form the basis for next-generation devices, which are still at infancy. One of the biggest challenges of working with such molecules, though, is that the two excitons “live” for very short periods of time (tens of nanoseconds), making it difficult to harvest them as a form of electricity.

In the current study, funded in part by the Office of Naval Research, Campos and colleagues designed organic molecules that can quickly generate two excitons that live much longer than the current state-of-the-art systems. It is an advancement that can not only be used in next-generation solar energy production, but also in photocatalytic processes in chemistry, sensors, and imaging, Campos explained, as these excitons can be used to initiate chemical reactions, which can then be used by industry to make drugs, plastics, and many other types of consumer chemicals.

Campos explained, “Intramolecular singlet fission has been demonstrated by our group and others, but the resulting excitons were either generated very slowly, or they wouldn’t last very long. This work is the first to show that singlet fission can rapidly generate two excitons that can live for a very long time. 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.”

The team’s design strategy should also prove useful in separate areas of scientific study and have many other yet-unimaginable applications, he added.

Campos’ study co-authors are: Samuel Sanders and Andrew Pun, of Columbia University; Matthew Y. Sfeir, of City University of New York; and Amir Asadpoordarvish, of the University of New South Wales.

This is likely an important milestone in light based energy harvesting. However there is some risk in the reporting. Singlet fission is not a nuclear reaction producing radiation. With how reporting is going on nowadays and folks jump to self serving conclusions with falsified “facts” we might think using words like fission could be misused. There is no nuclear reaction in photon to exciton splitting.

Nor is there a claim of energy being added. More adroitly, the press release is saying “light amplified signals” which might be semi accurate but fairly descriptive without a scary inference. What is not said is the excitons offer a solar collector two cracks at generating a current ready electron. Further development will show us just how much energy gain there might be. And your humble writer hopes the energy harvested soars and makes light harvesting much more attractive for an energy source.

The certainly is this group has done worthy useful and impressive work with congratulations in order for their success.