Size selective photoetching of CdSe quantum dot sensitizers on single-crystal TiO₂

Cadmium selenide quantum dots covalently attached to and photosensitizing single-crystal TiO2 surfaces are observed to corrode under illumination in aqueous electrolyte containing iodide as a regenerator. Comparison of photocurrent spectra before and after long-term monochromatic illumination indicated that the CdSe QD sensitizers photocorroded and decreased in size until their band gap energy exceeded the excitation energy. This wavelength-dependent photoelectrochemical etching mechanism can be used to tune the size distribution of surface adsorbed QDs and may account for the instability of QD sensitized solar cells that do not employ sulfide-based electrolytes.