Alternate Monolayers of CdSe Nanocrystals and Perylene Tetracarboxylate: Quantum Dot Hypersensitization for Dye-Sensitized Solar Cells

Mono- and multilayers from CdSe nanocrystal dispersion and perylene tetracarboxylate solution are reported for the first time. The layers were investigated by UV-visible spectroscopy, cyclic voltammetry, photoconductivity, and photoelectrochemical techniques. The n-type organic semiconductor gives enhanced photoconductivity to the CdSe-NC multilayer structure. The photoactive perylene monolayer acts also as hypersensitizer of CdSe-NC structures. The perylene-modified CdSe-NC monolayer on indium tin oxide (ITO) electrode in a three-electrode photoelectrochemical cell upon illumination in the presence of oxygen generates an intense steady photocurrent as high as 10-20 times that expected from the individual contributions of perylene and CdSe-NCs. The hypersensitization mechanism is discussed on the basis of the energy level diagram of the components.