Finding the Flow of Energy in Organic Photovoltaic Batteries
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Japanese Researchers at the University of Tsukuba have found that the best batteries may in fact come from living matter. Plants harness the sun's power through the chemical process of photosynthesis, so why can't we power our batteries on the same principle?
Unless you're an electrical engineer, or someone who has had the unfortunate opportunity of being forced into an upper-division chemistry course, you may never have given much thought into how the batteries that power your every electronic need work, or even where they come from. Well, in terms of science, they're fairly simple technological necessities. Founded on acid-base reactions with metal conductors that either give or receive electrons as they are dissolved or deposited, batteries create electricity on the fundamental concept: electricity is the flow of electrons. But, as you may have already seen in recent years, batteries are expensive to make. Li-ion batteries, for example, use expensive lithium as their reagent; others use copper or even platinum. But with dwindling natural resources like semi-precious metals, the days of affordable voltaic cells is nearly over.
Looking to nature for some solar-driven inspiration, a group of researchers at the University of Tsukuba, Japan, recently submitted their method for finding energy cells in nature in the journal Applied Physics Letters. Organic photovoltaic cells (organic solar-powered batteries) have recently shown tremendous promise as cost-effective alternative to traditional batteries. However, with a much different form of energy conversion than the simple acid-base reactions that can be refined down to perfect concentrations, the efficacy and true power of organic photovoltaic cells is much less understood.
Combining two forms of light-induced spectroscopy, to analyze light excitation and the electrochemical reactions for absorption that followed, the researchers led by professor Yutaka Moritomo are able to determine the absolute value of the charge formation efficiency; something not previously quantifiable.
"By qualitative analysis of the spectral change, we can deduce how many charges are produced by one [single] photon; it's 'charge formation efficiency'" Moritomo says. "But our work shows that the charge formation process of an organic photovoltaic device is purely quantum mechanical, and any theoretical model should explain the high charge formation efficiency at low temperatures."
Thought to have only formed optimal levels of charge formation at high temperatures, also known as thermal activation, the spectroscopy methods used by the research team show that previous models were not correctly structured. A large step forward in the formation of sustainable energy for tomorrow, Mortitomo's discovery that charge formation efficiency can remain high even at extremely low temperatures (80K, aka -315oF) far below freezing will allow researchers to continue to develop far more efficient organic solar batteries by better means of identifying organic cells.
Now that Moritomo can easily identify these cells, he says that the next step in the progression of his research will focus on determining the mechanism that forms the charges he was able to quantify.
Moritomo says "Now that we have a method to determine the key physical parameter (charge formation efficiency) we're exploring the interrelation between it and the nanoscale structure of the organic photovoltaic device to clarify the mechanism of the charge formation."
