Like today’s food industry, technology is going organic.
Research recently published by Dr. Greg Scholes and Elisabetta Collini of the Department of Chemistry, the Institute for Optical Sciences, and the Centre for Quantum Information and Quantum Control at the University of Toronto is at the forefront of the organic revolution.
“In general, the theme of our lab is to understand how light interacts with materials at the nanoscale level and how these interactions can help develop future technology,” explains Scholes. Specifically, this new research involves the study and manipulation of unique molecules known as conjugated polymers.
Conjugated polymers are large organic molecules composed of small repeating units. Since the 1950s, it has been known that these conjugated polymers can interact with light to let the molecule emit a unit of light known as a photon. This type of technology is currently used in new models of super thin televisions that contain organic light-emitting diodes (OLEDs).
“In conjugated polymer systems once we apply a voltage, the plus and minus charges come together at some point in the plastic (polymer) and it is now in an excited state,” says Scholes. What happens after this excited state is the main focus of research involving these polymeric systems. “Once this excited state is achieved the energy can be transferred along the chain throughout the system or it can emit light as is the case for OLEDs,” he adds.
Instead of emitting light, the desired result with organic solar cells is energy transference along the polymer chains. These cells will eventually encounter an interface where the electrical energy is extracted. “Today’s solar cells contain a semiconductor, which releases energy carries after excitation,” says Scholes. “But with organic solar cells, energy transfer [and not carriers] is involved and we need to design it completely differently.”
Like all plastics, polymers contain impurities that can take the excited energy of the polymer, usually dissipating it as unwanted heat. “Since it is very difficult to remove these impurities, another approach is for the energy to travel between different types of materials,” says Scholes. However, a new problem arises out of this method: there is no control over the energy transfer—instead, it “hops” along randomly.
“To control this transfer, we used quantum effects,” explains Scholes. A team of scientists used a powerful short-pulsed laser to alter the conjugated polymers to a new state of coherence. This quantum coherence means it is simultaneously in two different states. In this case, the system is in its normal ground state as well as an excited state, due to the laser pulses.
“We put the system in a purely quantum mechanical state and asked the question: can it move?” says Scholes. “Normally it shouldn’t do anything at all, especially at room temperature where a complex system like this is easily destroyed.” However, the researchers found that “the system can be in this quantum superposition state and actually move—just like energy—even at room temperature.”
Scholes and Collini’s discovered that energy transfer between molecules isn’t random hopping, and that a quantum mechanical reasoning and logic are behind this energy movement. Their research shows that these complex coherent states can actually exist and move at room temperature, not just at sub-zero levels as previously thought.
This research will not only advance the area of solar cells, it could potentially develop the field of quantum computing. Specifically, data storage and processing would be much faster and more efficient than today’s conventional computers.
For now, polymer chemistry needs improvement in order to develop successful organic solar cells. One of the major drawbacks of organic solar cells is their efficiency, which is much lower than modern cells. Dr. Scholes is optimistic about the future. “The next step is to understand what makes one polymer a better semiconductor than another one and then design a plastic that has all these properties.”
Scholes believes that this new research will spark the possibility of better and cheaper future organic technologies. “This research resonates in many areas of quantum physics and we hope it will inspire research worldwide,” says Scholes.
