How to turn leaves into solar panels
03.02.12 - Photovoltaic panels made from plant material could become a cheap, easy alternative to traditional solar cells.
An entirely novel approach to photovoltaics has been developed in joint collaboration between MIT and EPFL. By taking the very protein in plants that allows for photosythesis and engineering it to produce electrical current, MIT researcher Andreas Mershin has opened the door for potentially cheap and easy to reproduce solar energy. The work appears this week in the open-access journal Scientific Reports and is an extension of a project begun eight years ago by Shuguang Zhang from MIT’s Center for Biomedical Engineering and EPFL professor Michael Graetzel.
In his original work, Zhang was able to enlist a complex of molecules known as photosystem-I (PS-I), the tiny structures within plant cells that carry out photosynthesis. Zhang and colleagues derived the PS-I from plants, stabilized it chemically and formed a layer on a glass substrate that could — like a conventional photovoltaic cell — produce an electric current when exposed to light. The next step was to find ways to amplify this current.
In Michael Graetzel’s lab, Mershin was able to adapt a photovoltaic substrate that is significantly more responsive to sunlight. The substrate is similar to the one used in dye-sensetized solar cells (DSSC) for which the lab is well-known, but the substance—PS-I—is radically different from the dye normally used. The challenge engendered by such a modification has brought about its own improvements in DSSC, notably the development of a mechanism that shuttles electrons more efficiently between poles, like in a battery.
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. The nanowires not only served as a supporting structure for the material, but also as wires to carry the flow of electrons generated by the molecules down to the supporting layer of material, from which it could be connected to a circuit. “It’s like an electric nanoforest,” he says.
Mershin says the process has been simplified to the point that virtually any lab could replicate it — including college or even high school science labs — allowing researchers around the world to start exploring the process and making further improvements. The new system’s efficiency is 10,000 times greater than in the previous version — although in converting just 0.1 percent of sunlight’s energy to electricity. Ultimately, once the efficiency reaches 1 or 2 percent, he says, that will be good enough to be useful, because the ingredients are so cheap and the processing so simple.
The research was funded in part by an unrestricted grant from Intel Corp., and also included researchers at the University of Tennessee.