Greg Scholes and Elisabetta Collini of University of Toronto´s Department of Chemistry are investigating how light initiates physical processes at the molecular level and how humans might take better advantage of that fact by looking specifically at conjugated polymers that are believed to be one of the most promising candidates for building efficient organic solar cells.

Conjugated polymers are very long organic molecules that possess properties like those of semiconductors. That’s the organic path to make transistors, LEDs and photovoltaic cells. When these conductive polymers absorb light, the energy moves along and among the polymer chains before it is converted to electrical charges.

Collini explains, “One of the biggest obstacles to organic solar cells is that it is difficult to control what happens after light is absorbed: whether the desired property is transmitting energy, storing information or emitting light. Our experiment suggests it is possible to achieve control using quantum effects, even under relatively normal conditions.”

Scholes explained the research results, “We found that the ultrafast movement of energy through and between molecules happens by a quantum-mechanical mechanism rather than through random hopping, even at room temperature. This is extraordinary and will greatly influence future work in the field because everyone thought that these kinds of quantum effects could only operate in complex systems at very low temperatures.”

The Scholes Collini experiment used ultrashort laser pulses to put the conjugated polymer into a quantum-mechanical state, where it is simultaneously both in the ground (normal) state and a state where light has been absorbed. This is called a superposition state or quantum coherence. Then they used a sophisticated method involving more ultrashort laser pulses to observe whether this quantum state can migrate along or between polymer chains.

“It turns out that it (the energy) only moves along polymer chains,” Scholes said. “The chemical framework that makes up the chain is a crucial ingredient for enabling quantum coherent energy transfer. In the absence of the chemical framework, energy is funneled by chance, rather than design. This means that a chemical property — structure — can be used to steer the ultrafast migration of energy using quantum coherence. The unique properties of conjugated polymers continue to surprise us.”

Conjugated polymers are an accelerating field with huge market potential. From solar cells and video screens where one adsorbs energy and the other emits, to controls such as transistors and other electronics where the energy is manipulated to do work on to sensors of high sensitivity the range of applications just expanding.

At the core of the research is the assertion that the discovery is based in a better understanding of how energy works at the quantum mechanical level. At a minimum the research shows a way to make observations more direct and the maximum is today sheer speculation. Two other things stand out. Efficiency can be enhanced in organic cells with the new tools to see what’s going on at such a deep level and that energy activity can now be seen suggests that quantum formed information may survive in such systems much longer than thought so far.

At the base level this research is fundamental. It offers no breakthrough products. But if others can replicate and expand on the ideas, new designs, new compounds of polymers and innovation should lead to much better products across much of the energy, electronics and computing markets just to start.

This is a hot field. The Canadians paper titled Coherent Intrachain Energy Migration in a Conjugated Polymer at Room Temperature,” made it into Science Magazine in the Reports section. In the very same issue Jean-Luc Brédas at the Georgia Institute of Technology’s School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics and Robert Silbey at the Massachusetts Institute of Technology’s Department of Chemistry have a piece in the Perspectives Section titled “Excitons Surf Along Conjugated Polymer Chains.”

It’s an exciting field. More work, more energy gathering, all much more efficient headed out to make new markets and change existing markets making one more part to an economic recovery.


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