LED and Solar Lights

Inexpensive solar cells, vastly improved medical imaging techniques and lighter and more flexible television screens are among the potential applications envisioned for organic electronics. Yes, that means that soon you could have a solar powered TV or even a solar x-ray machine at the local hospital. (Hopefuly your bill will go down with their power costs). Recent experiments conducted by Greg Scholes and Elisabetta Collini of University of Toronto’s Department of Chemistry may bring these within closer by provding more information on the way molecules absorb and move energy. These findings were published inl journal Science on January 16.

The U of T team looked specifically at conjugated polymers which are believed to be one of the most promising candidates for building efficient organic solar cells.

What exactly is a conjugated polymer anyway?

I know, it is not exactly a household name and most of us need the introduction. Conjugated polymers are very long organic molecules that possess properties like those of semiconductors and so can be used to make transistors and LEDs. When these conductive polymers absorb light, the energy moves along and among the polymer chains before it is converted to electrical charges.

“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,” explains Collini. “Our experiment suggests it is possible to achieve control using quantum effects, even
under relatively normal conditions.”

“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,” explains Scholes. “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,” he says.

This discovery opens the way to designing organic solar cells or sensors that capture light and transfer its energy much more effectively. It also has significant implications for quantum computing because it suggests that quantum information may survive significantly longer than previously believed.

These experiments consist of the use of ultrashort laser pulses to put the conjugated polymer into a quantum-mechanical state, whereby it is simultaneously 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 they can, to a limited extent.

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