Enhanced photo-conversion efficiency of CdSe–ZnS core–shell quantum dots with Aunanoparticles on TiO2electrodes

Abstract

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–ϕ) 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.