07 September 2012

The most effective spinach-based biohybrid photocell

Spinach gave current

Grigory Kolpakov, "Newspaper.Ru"For the second time this year, scientists confirm the correctness of the sailor Papaya, a Disney hero who considered spinach the most useful product in the world.

But if recently Swedish biologists proved that spinach really increases muscle strength, now this herb has shown itself from a completely unexpected side. With its help, US chemists from Vanderbilt University have managed to create a photocell that turns light into electricity much more efficiently than existing "biohybrid" devices of a similar type.

In the latest issue of the journal Advanced Materials, researchers say that they managed to create a "biohybrid" solar cell by combining silicon and spinach protein involved in photosynthesis (LeBlanc et al., Enhanced Photocurrents of Photosystem I Films on p-Doped Silicon). The protein is called PS1 and it is really unique. It was opened more than forty years ago and immediately attracted attention by the fact that, even when isolated, it continues to turn sunlight into electrical energy, and does it with almost one hundred percent efficiency. Recall that even today the efficiency of the most advanced solar cells does not exceed 40 percent. An additional advantage of PS1-based solar cells was their cheapness: such expensive materials as platinum or indium would not be required for their manufacture.

Therefore, it was then, forty years ago, that the first attempts to use the PS1 protein to generate electricity began in many laboratories around the world. The problem turned out to be not an easy one, since the PS1 did not stand up to criticism as a photocell. Firstly, the electricity produced with its help was much inferior in power to commercial solar cells. Secondly, the protein disintegrated after a couple of weeks of work. However, a group from Vanderbilt University managed to partially cope with this second problem back in 2010 - then they managed to create a "spinach" solar battery capable of operating for up to nine months. According to David Kliffel, one of the main authors of the article in Advanced Materials, they never doubted what could be achieved with a much more impressive service life, you just have to follow nature. "Nature knows very well how to do this," he says. "In evergreens, such a protein lives for years, and we just have to figure out how to do it."

And finally there was a breakthrough – the Vanderbilt group managed to establish contact between PS1 and silicon to such an extent that it was already possible to talk about the commercial future of a new solar battery. "This combination produces a current almost a thousand times higher than what we were able to obtain by combining this protein with various metals.

It also creates a little more tension," explains Cliffell. In other words, the new "spinach" photocell made it possible to remove a current of 850 microamps from one square centimeter at a voltage of 0.3 volts.

The secret of success lies in additives that change the electrical properties of the silicon substrate. It turned out that PS1 prefers silicon, the surface of which is positively charged.

To create a solar battery from this combination, scientists isolated protein from spinach leaves, dissolved it in water and poured this solution over a silicon substrate. Then they placed it in a vacuum chamber, where the water evaporated, leaving a thin protein film on the silicon surface. By trial and error, it was found out that the optimal thickness of this film should be about a micron.

PS1 is found not only in spinach. This is a universal protein, and its spinach origin is to a certain extent accidental. Kliffel's group, for example, is already planning to experiment with PS1 isolated from the kudzu plant.

Portal "Eternal youth" http://vechnayamolodost.ru07.09.2012

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