Photosynthetic molecule plus semiconductor make efficient biophotovoltaics

Knoxville, TN--Barry Bruce and colleagues at the University of Tennessee, Knoxville have created photovoltaic cells containing a nanostructured semiconductor on which a photosynthetic pigment/protein (photosystem-I, or PS-I) has self-assembled.¹ The device has an open-circuit voltage of 0.5 V, an electrical power density of 81 µW/cm² and a photocurrent density of 362 µA/cm² -- a current density more than 10,000 times higher than any previous biophotovoltaic device based on PS-I.

The researchers collaborated with others from the Massachusetts Institute of Technology (Cambridge, MA) and Ecole Polytechnique Federale (Lausanne, Switzerland). “As opposed to conventional photovoltaic solar power systems, we are using renewable biological materials rather than toxic chemicals to generate energy," says Bruce. "Likewise, our system will require less time, land, water and input of fossil fuels to produce energy than most biofuels.”

PS-I bioengineered for the purpose

The PS-I is extracted from blue-green algae, then bioengineered to specifically interact with nanostructured conductive zinc oxide so that, when illuminated, the process of photosynthesis produces electricity. The approach is simple enough that it can be replicated in most labs, allowing others around the world to work toward further optimization.

The mechanism is orders of magnitude more efficient than earlier work done by Bruce for producing bioelectricity thanks to the interfacing of PS-I with the large surface provided by the nanostructured conductive zinc oxide; however it still needs to improve manifold to become useful. Still, the researchers are optimistic and expect rapid progress.

Andreas Mershin, a research scientist at MIT, conceptualized and created the nanoscale wires and platform. He credits his design to observing the way needles on pine trees are placed to maximize exposure to sunlight.

Mohammad Khaja Nazeeruddin in the lab of Michael Graetzel, a professor at the Ecole Polytechnique Federale in Lausanne, Switzerland, did the complex testing needed to determine that the new mechanism actually performed as expected. Graetzel is a pioneer in energy and electron transfer reactions and their application in solar energy conversion.

Michael Vaughn, once an undergraduate in Bruce’s lab and now a National Science Foundation predoctoral fellow at Arizona State University, also collaborated on the paper.

Bruce’s work is funded by the Emerging Frontiers Program at the National Science Foundation.

REFERENCE:

1. Andreas Mershin et al., Nature: Scientific Reports, accepted 05 Jan. 2012, published 02 Feb. 2012; doi:10.1038/srep00234