06 February 2012
If MIT researcher Andreas Mershin is right, cheap solar panels made from plants will be a reality in a few years.
Basis for the biosolar breakthrough is earlier research work by Shuguang Zhang, a principal research scientist and associate director at MIT’s Center for Biomedical Engineering. Zhang had extracted photosystem-I (PS-I), a key component of photosynthesis, from plants, stabilized it chemically and formed a layer on a glass substrate that could produce an electric current when exposed to light. However, this earlier setup required expensive chemicals and lab equipment, and the solar cell only produced a very weak current.
Mershin, a research scientist at the MIT Center for Bits and Atoms, now simplified this process to the point where even the most rudimentary lab can replicate it. Though 10,000 more efficient than before, the new system still only converts 0.1% of sunlight’s energy to electricity. Mershin’s vision, however, is to “crowdsource” further improvements, eventually making the process more stable, efficient and ultimately useful in the field.
To achieve the 10,000-fold efficiency improvement over Zhang’s system, which was designed as a thin flat layer, Mershin had to find a way to expose much more of the PS-I complex per surface area of the device to the sun. His inspiration: pine trees in a forest that have small branches all the way down the length of the trunk to capture any sunlight that trickled down from above. He decided to create a microscopic forest on a chip, PS-I-coating his “trees” top to bottom.
After years of work, Mershin was able to create a tiny forest of zinc oxide (ZnO) nanowires as well as a sponge-like titanium dioxide (TiO2) nanostructure coated with the light-collecting material derived from bacteria – his electric nanoforest. When illuminated by sunlight, the metal oxide interface excites PS-I to produce an electron, which then jumps into the zinc oxide semiconductor, producing an electric current.
According to Mershin, any green plant material can be used as the raw material, from grass clippings to otherwise worthless agricultural waste. His team has proposed using inexpensive membranes to concentrate the PS-I molecules. The system is engineered to self-assemble and no special laboratory conditions are needed, which means MIT’s cheap, simple system using renewable biological materials could someday bring low-tech electricity to remote, off-grid villages in the Third World. The only ingredient to be purchased would be chemicals to stabilize the PS-I molecules. The chemicals would be mixed with the plant material and painted on a roof, for instance, to start producing “green” power.
Barry D. Bruce, professor of biochemistry, cellular and molecular biology, at the University of Tennessee, Knoxville and Michael Graetzel, a pioneer in energy and electron transfer reactions and their application in solar energy conversion, from the Ecole Polytechnique Federale in Lausanne, Switzerland, collaborated with MIT on the project.
The new paper Self-assembled photosystem-I biophotovoltaics on nanostructured TiO2 and ZnO by Shuguang Zhang, Andreas Mershin et al. appears in this week’s Scientific Reports.
Photo: M. Scott Brauer