How spinach helps produce electricity

Don’t eat your spinach. Put it on your solar panel instead.

OK, that’s not actually advisable. However, it is true that the latest attempt to put photosynthesis to work to produce electricity finds researchers at Vanderbilt University reporting big gains with a new concept that uses a protein found in spinach in combination with carefully formatted silicon.

It’s hard to say when or even if such “biohybrid” technology will ever amount to much in the real world – the power output obtained at Vanderbilt is a record, but it’s still pretty small – but there’s no denying its lure to scientists.

The research at Vanderbilt uses a specific protein involved in photosynthesis called photosystem 1, which was discovered 40 years ago and apparently quickly seduced solar researchers with its ability to convert sunlight into electrical energy with nearly 100 percent efficiency, according to Vanderbilt.

That the stuff is cheap and plentiful – it can be extracted from the rapidly growing kudzu vine, not just 99-cents-a-bunch spinach – compared to common microelectronic materials only increased the lure, according to Vanderbilt.

Vanderbilt had had some limited success earlier playing with PS1 to produce power, but it wasn’t until it found a way to make its device work more like a plant that it found a breakthrough. It did this by “p-doping” the silicon wafer before applying the PS1 from spinach. This is a doctoring of the silicon with impurities that turns it from an insulator into a conductor by creating “holes” in the silicon lattice.

This p-doped silicon helped allow electrons to flow through the circuit in a common direction, instead of producing both positive and negative currents that could cancel each other out and leave a very small net current, as had been the case. “This isn’t as good as protein alignment (seen in actual leaves), but it is much better than what we had before,” researcher Kane Jennings said in a Vanderbilt press release.

The result was nearly a milliamp (850 microamps) of current per square centimeter at 0.3 volts, Vanderbilt reported – two and one-half times the old biohybrid cell record. In real terms, that might mean “a two-foot panel could put out at least 100 milliamps at one volt – enough to power a number of different types of small electrical devices.”

That’s a big panel to power small devices, but the researchers think they can do better.

“If we can continue on our current trajectory of increasing voltage and current levels, we could reach the range of mature solar conversion technologies in three years,” said research collaborator David Cliffel.

* Pete Danko, EarthTechling