Self-assembled layers of Bi 2 S 3 nanoparticles have been used to sensitize nanocrystalline titanium dioxide, replacing the ruthenium dye used in conventional dye-sensitized solar cells. We report band-edge tuning of the bismuth sulfide quantum dot particles by adsorption of sulfide ions. In the absence of sulfide ions, only smaller Bi 2 S 3 particles with a large band gap inject electrons into the TiO 2 . Progressive addition of sulfide ions shifts the conduction band of the Bi 2 S 3 upward, so that larger nanoparticles begin to inject and the long wavelength component of the photocurrent response increases. The observation suggests that band-edge tuning may form a useful part of strategies designed to exploit semiconductor quantum dots as sensitizers.

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