Visible Light Sensitization of TiO2 Nanotubes by Bacteriochlorophyll-C Dyes for Photoelectrochemical Solar Cells

Biomimetic sensitizers have evolved over millions of years to absorb and utilize sunlight and therefore are highly desirable to produce efficient, low cost, dye-sensitized photoelectrochemical solar cells. We report on the sensitization of TiO2, nanotubes by bacteriochlorophyll-c (BChl c) extracted from photosynthetic bacteria. BChl c is notable for its high conversion efficiency inside the bacteria, which makes it a promising candidate for a naturally derived sensitizer for TiO2. A photocurrent conversion efficiency of 0.1% was observed at 600-800 nm, corresponding to the absorption peak in BChl c; a photoanode efficiency of 0.23% was measured at around -0.1 V-SCE. Stability tests under simulated sunlight showed stable photocurrents over the course of 14 mm. Mechanisms that currently limit the efficiency include the formation of BChl c aggregates on TiO2, which may increase recombination, and possibly interface defects, which decrease charge injection to the nanotubes and trapping of photogenerated charges.