Researchers at Ruhr-Universitat Bochum have created a bio-based solar cell capable of generating a continuous electrical current of several nanowatts per sq cm. The new approach avoids damage to the tapped photosynthetic cells, an issue that has plagued previous attempts to harness nature's "power plant."
While the technology is still in its infancy, bio-based solar cells could offer several advantages over photovoltaic systems, namely greater efficiency and the fact that they are not dependent on silicon and expensive rare earth metals. On the downside, the systems developed thus far are not very durable and do not produce much power.
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Past attempts at harnessing the process of photosynthesis to generate electricity have concentrated on tapping in to only one of the two steps known as the Z-Scheme.
The Z-Scheme is the process of photoreduction where light energy is converted to chemical energy in two steps or photosystems. When a plant, algae or cyanobacteria absorb a light photon an electron within photosystem 2 (PS2) is excited and attains a higher energy level. This unstable electron is transferred via a series of redox reactions down the electron transport chain before entering photosystem 1 (PS1).
In a first, the team at RUB, led by Prof Wolfgang Schuhmann and Prof Matthias Rögner, has integrated both PS1 and PS2 into a photovoltaic cell. Rather than capturing electrons at either the PS1 or PS2 stage of photosynthesis, as has been the approach in previous bio-based cells, they have used the charge separation between the two photosystems to create an anode and diode, generating continuous electrical current through a redox hydrogel when exposed to light.
To achieve this, the team isolated the two photosystems in thermophilic cyanobacteria found in hot springs, which are attractive because the extreme environmental conditions they exist under makes their photosystems relatively stable. These photosystems were then embedded into redox hydrogels with different potentials developed by the team. The result is a system that generates electricity rather than converting carbon dioxide into oxygen and biomass.
This approach also seems to overcome problems experienced by other researchers at the University of Georgia (UGA) and Stanford University, where cells rapidly deteriorate rendering them useless within as little as a few hours.
“The system may be considered a blueprint for the development of semi-artificial and natural cell systems in which photosynthesis is used for the light-driven production of secondary energy carriers such as hydrogen,” says Prof Rögner.