Claudia Villarreal1,Christopher Espinoza-Araya1,Jose Daniel Zelada-Ramírez1,Dariana Aguilar1,Alexandra Tames1,Jesse Bergkamp2,Ernesto Montero-Zeledón1,Venkatesan Renugopalakrishnan3,4,Barry Bruce5
Instituto Tecnológico de Costa Rica1,California State University2,Harvard Medical School3,Northeastern University4,University of Tennessee at Knoxville5
Claudia Villarreal1,Christopher Espinoza-Araya1,Jose Daniel Zelada-Ramírez1,Dariana Aguilar1,Alexandra Tames1,Jesse Bergkamp2,Ernesto Montero-Zeledón1,Venkatesan Renugopalakrishnan3,4,Barry Bruce5
Instituto Tecnológico de Costa Rica1,California State University2,Harvard Medical School3,Northeastern University4,University of Tennessee at Knoxville5
The bio-sensitized solar cell is the architecture with the highest power conversion efficiencies (PCE) amongst photovoltaic devices that integrate natural photosynthetic proteins (1-2%). In these devices, a nanostructured wide-bandgap semiconducting electrode is coated with the protein and used as the photoanode in an electrochemical cell. Our team studies two different biosensitizers that stand out as some of the best performing natural light absorbers in bio-photovoltaic devices: <b>bacteriorhodopsin</b> (bR), a light-driven proton pump from archaebacteria, and <b>photosystem I </b>(PSI), a chlorophyll-protein complex from cyanobacteria and green plants that catalyzes photoactivated unidirectional electron transfer in oxygenic photosynthesis. Two factors that currently limit the <b>charge transfer efficiency</b> from the protein to the TiO<sub>2</sub> are the reduced contact area between the two materials and the non-specific orientation of the protein with respect to TiO<sub>2</sub>. The proteins here studied are significantly larger than traditional synthetic dyes, which hinders their penetration into the pores of the TiO<sub>2</sub> nanoparticle layer during impregnation. The use of <b>TiO<sub>2</sub> nanorods doped with CNTs</b> is proposed to provide larger contact area where the protein can inject the photoelectrons into the semiconductor. In nature, electron transfer occurs in very specific electrical pathways that have evolved over millions of years, while simple dropcasting of a protein onto the electrode results in random orientations that may or may not connect these natural electrical wires with the electrode surface. Alternative techniques to promote an organized interface with <b>preferential orientation of the proteins</b> on the TiO<sub>2</sub> are here explored, so that the electron injection is directional according to the natural function of the biomolecule in the organism.<i> In situ </i>crystallization and structural modifications of the protein are proposed to drive a preferential orientation on the electrode. The effect of these variables in photovoltaic performance of devices is determined. The devices here proposed consist on the biosensitized TiO<sub>2 </sub>photoanode and a PEDOT/CNT counterelectrode. A gel electrolyte is used to connect the two electrodes, containing the hydroquinone/benzoquinone pair or aqueous-soluble bipyridine cobalt(II/III) complexes as direct redox mediators for bR and PSI, respectively. These work intends to deepen the understading of electron transfer in a bio-hybrid interface for photogeneration of bioelectricity.