Sensitization of ZnO single crystal electrodes with CdSe quantum dots

CdSe quantum dots (QDs) were attached to single crystal ZnO(0001) and ZnO(1100) substrates using capping groups, 4-mercaptobenzoic acid, 2-mercaptoacetic acid, 3-mercaptopropionic acid, 8-mercaptooctanoic acid, and 11-mercaptoundecanoic acid, as bifunctional linker molecules. The spectral response and photosensitization yields of the adsorbed QDs were studied with photocurrent spectroscopy. Atomic force microscopy (AFM) was used to verify the surface structure of the ZnO crystals and to examine the coverage and arrangement of the QDs on the single crystal surface. The inner-sphere aqueous redox couple Sx(2-)/S(2-), often used as a regenerator for chalcogenide-based QDs, as well as outer-sphere redox couples such as ferrocene, were able to regenerate the photoexcited CdSe QDs and suppress their photocorrosion. Differences in the binding of the QDs to different ZnO crystal faces are also reported.