Study on the feasibility of bacteriorhodopsin as bio-photosensitizer in excitonic solar cell: a first report.

Bacteriorhodopsin (bR) is a membrane protein found in the archae Halobacterium salinarum. Here, we studied wild type bR and especially the triple mutant bR, 3Glu [E9Q/E194Q/E204Q], in combination with wide gap semiconductor TiO2 for their suitability as efficient light harvester in solar cell. Our differential scanning calorimetry data show thermal robustness of bR wild type and 3Glu mutant, which make them good candidates as photosensitizer in solar cells. Molecular modeling indicates that binding of bR to the exposed oxygen atoms of anatase TiO2 is favorable for electron transfer and directed by local, small distance interactions. A solar cell, based on bR wild type and bR triple mutant immobilized on nanocrystalline TiO2 film was successfully constructed. The photocurrent density-photo voltage (J-V) characteristics of bio-sensitized solar cell (BSSC), based on the wild type bR and 3Glu mutant adsorbed on nanocrystalline TiO2 film electrode were measured. The results show that the 3Glu mutant displays better photoelectric performance compared to the wild type bR, giving a short-circuit photocurrent density (J(sc)) of 0.09 mA/cm2 and the open-circuit photovoltage (V(oc)) 0.35 V, under an illumination intensity of 40 mW/cm2.