BOCHUM, Germany, Aug. 22, 2014 — Semi-artificial leaves could function as photovoltaic systems, and with unprecedented performance. In leaves, the membrane protein complex photosystem I (PS I) absorbs light, and its energy is utilized for converting carbon dioxide into biomass. In a study, researchers from Ruhr University Bochum replaced a photovoltaic semiconductor with highly stable PS I from thermophilic cyanobacteria. The electron transfer achieved through this mechanism could exceed natural photosynthesis rates, the researchers claim. While leaves use the energy from sunlight to convert carbon dioxide into biomass, photovoltaic devices harness the light to produce electricity. Courtesy of Dr. Nicolas Plumeré/Ruhr University Bochum. Integration of this natural component into the artificial photovoltaics poses a challenge, however. The researchers said PS I displays both hydrophilic and hydrophobic domains that complicate its immobilization on electrodes. To overcome this, they developed complex electron-conducting materials, redox hydrogels, that possess stimuli-responsive properties. The hydrophobic/hydrophilic properties of the hydrogel can be controlled by a pH shift and were adjusted to the hydrophobic requirement of the photosystem. This purpose-built environment provided optimal conditions for PS I, according to the researchers, and overcame the kinetic limiting steps found in natural leaves. The new process yielded high photocurrents for semi-artificial biophotoelectrodes, while the electron transfer rate exceeded that found in nature by one order of magnitude, the researchers said. Such biophotovoltaics could be used to generate power for micro-sized medical devices, such as sensors that are implanted in contact lenses, the researchers said. The work was funded by the Cluster of Excellence RESOLV, the Deutsche Forschungsgemeinschaft, the Bundesministerium für Bildung und Forschung (within the Project Taschentuchlabor), and the COST Action TD1102 Phototech. The research was published in Chemistry — A European Journal (doi: 10.1002/chem.201402585). For more information, visit www.ruhr-uni-bochum.de.