MIT Researchers Use Army of Subjugated Viruses to Build Solar Cells ANS

an interesting idea. 
Find it here:  http://www.dailytech.com/MIT+Researchers+Use+Army+of+Subjugated+Viruses+to+Build+Solar+Cells/article21468.htm  
--Kim

Science

  MIT Researchers Use Army of Subjugated Viruses to Build Solar Cells

Jason Mick (Blog) - April 26, 2011 10:35 AM

The M13 virus reproduces in bacteria and is used broadly in nanomanufacturing for its ability to load biominerals and to express a variety of useful proteins.  (Source: Ki Tae Nam/MIT)

MIT trained the viruses to grab hold of carbon nanotubes and secrete a layer of light energy harvesting titanium dioxide.  (Source: MIT)

The process could improve the efficiency of commercial dye-sensitized solar cells by a third or more, with a single low-cost step.  (Source: GigaOM)

Go my microscopic minions, go and power my empire!

It sounds like a mad scientist's dream come true.  Researchers at the Massachusetts Institute of Technology (MIT) have ensorcelled viruses with the wonders of modern genetic engineering and set them forth in building power capturing solar cells.

I. Research Down the Tubes -- in a Good Way

All solar cells at a fundamental level rely on some sort of energy harvesting layer.  For most cells today this layer is either a thin film or layers of elements deposited on a silicon substrate.

Outside of solar cells, in the realm of nanomedicine and materials engineering, carbon nanotubes are a hot item.  These nanoscopic tubes, composed of hexagonal units of bonded carbon, are super strong  -- and in some cases -- highly conductive.

Many researchers have considered tossing the tubes in solar cells, but early results were not promising.

Undeterred the MIT team set out to find why.  What they determined was that past efforts had failed as they deposited a mix of certain types of tubes that acted as conductors and certain types of tubes that acted as semiconductors.  Worse, the tubes clumped together, further impairing the efficiency.

In order to create the desired target -- a conductive nanotube layer -- the MIT team opted for a novel approach, enlisting the help of viral henchmen. Graduate students Xiangnan Dang and Hyunjung Yi, along with Energy Professor Angela Belcher [profile], found that a specific genetically engineered virus -- known as M13 -- improved the tube conductivity by reducing clumping and the number of semiconducting tubes.

Since they were already going the unconventional route, the team decided to test the newly created material layer on a special type of cell, based on titanium dioxide.  These TiO2 cells don't use a silicon substrate and are known commercially as "dye-sensitized" solar cells.  Their advantages include that they can be less expensive to produce and are lighter than silicon substrate designs.

Adding the nanotube layer improved the efficiency from 8 percent to 10.6 percent -- an increase of about a third.  And that huge boost comes despite the fact that the virus/nanotube mix only takes up 0.1 percent of the finished cell's weight.  Professor Belcher summarizes, "A little biology goes a long way."

II. How it Works

The virus is at the heart of the gains.  It offers two key effects.  The first is that it excretes proteins that literally "grab" the nanotubes.  Each virus secretes around 300 of these proteins, enough to hold 5 to 10 nanotubes in place.  Typically nanotube assembly requires high temperatures.  But thanks to the viruses, the nanotube mix is water-soluble and can be produced using an inexpensive room temperature, water-based process.

But that's not all.  The viruses contain a genetic "switch" which is flipped when the PH (acidity given by free hydrogen ions) changes.  At a certain PH the viruses begin to secrete titanium dioxide -- the material that is involved, along with dye/pigment, in producing electrons in the cell.

The nanotubes act as tiny wires.  Typically larger, less efficient physical wires would have to be attached to collect electrons at the bottom of the TiO2 layer.  But thanks to the marvelous viruses, the cell itself is interspersed with tiny wires, closing the distance and reducing efficiency losses.

III. From Viruses to Greenbacks -- Commercialization is Imminent

The team believes that approach which yielded this new material will be broadly applicable to other types of novel solar cells, as well -- like quantum dot or organic cell designs.  The viruses would likely be tailored to excrete novel compounds that would assist in the collection process for these cell types.

The M13 viruses reproduce by infecting bacteria.  They can be quickly and inexpensively mass produced using modern lab technology.

Prashant Kamat, a professor of chemistry and biochemistry at Notre Dame University and expert in the field of solar cells, gave high praise to the work, calling it "impressive".  He was surprised not only that MIT was able to overcome the long standing roadblock to building nanotube-based cells, but also that they did it in such novel fashion.

In MIT's press release he says that the team should be able to rapidly commercialize their discovery, stating, "Dye-sensitized solar cells have already been commercialized in Japan, Korea and Taiwan. [Given the efficiency gains] the industry is likely to adopt [the team's] processes."

Professor Belcher agrees pointing out that adding the new material essentially only adds one inexpensive step to the manufacturing process.  She expects the new process to enter the industry quickly.

The new work was published [ abstract] in the prestigious Nature Nanotechnology and was funded by the Italian company Eni (ADR:E), through the MIT Energy Initiative�s Solar Futures Program. 

Other participating members of the team included Chemical Engineering Professor Michael Strano [profile]; and four other graduate students and postdoctoral researchers.


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