Enhanced photo-conversion efficiency of CdSe–ZnS core–shell quantum dots with Au nanoparticles on TiO2 electrodes

This study demonstrates that configurations that include gold nanoparticles (Au NPs) as the primary layer attached to a TiO2 electrode with quantum dots (QDs) as the secondary layer have superior photoelectrochemical properties. We found that all Au-QD nanoparticle hybrid systems reveal enhanced photocurrent generation as compared to only a QD-nanoparticle interface. The enhanced J(sc) is attributed to sensitization that results indirectly from quantum dots becoming attached to Au NPs by intramolecular charge transfers. As a result of the improved performance, the overall energy conversion efficiency was increased by 100% as compared to that of a reference cell without Au NPs at 100 mW cm(-2). When (CdSe)ZnS is prepared from Au-coated TiO2, incident photon-to-current efficiency values approaching 20% can be achieved by (CdSe)ZnS devices. In the electrochemical impedance spectroscopy results, the intermediate frequency region of the Au-QD cells was more significantly reduced compared to that in bare QD cells due to the enhanced charge separation that occurs in the Au-QD structure. Mott-Schottky (C-2-phi) analysis shows that the lowest acceptor and donor densities having a positive effect on the efficiency could be found in (CdSe)ZnS-Au/TiO2 cells. Therefore, (CdSe)ZnS-Au/TiO2 has a very thin depletion layer that is restricted to the surface of Au/TiO2. Consequently, this system can be employed to enhance the effective efficiency in the design of the QD-sensitized solar cells.