Preparation of Multilayered CdSe Quantum Dot Sensitizers by Electrostatic Layer-by-Layer Assembly and a Series of Post-Posttreatments TiO2 Solar Cells

摘要

A multilayer of CdSe quantum dots (QDs) was prepared onnthe mesoporous surface of a nanoparticulate TiO2 film by a layer-by-layern(LBL) assembly using the electrostatic interaction of the oppositely chargednQD surface for application as a sensitizer in QD-sensitized TiO2 solar cells.nTo maximize the absorption of incident light and the generation of excitonsnby CdSe QDs within a fixed thickness of TiO2 film, the experimentalnconditions of QD deposition were optimized by controlling thenconcentration of salt added into the QD-dissolved solutions and repeatingnthe LBL deposition a few times. A proper concentration of salt was found tonbe critical in providing a deep penetration of QDs into the mesopore, thusnleading to a dense and uniform distribution throughout the whole TiO2nmatrix while anchoring the oppositely charged QDs alternately in ancontrollable way. A series of post-treatments with (1) CdCl2, (2) thermalnannealing, and (3) ZnS-coating was found to be very critical in improving the overall photovoltaic properties, presumablynthrough a better connection between QDs, effective passivation of QD’s surface, and a high impedance of recombination, whichnwere proved by transmission electron microscopy (TEM) and electrochemical impedance spectroscopy (EIS) experiments. Withna proper post-treatment of multilayered QDs as a sensitizer, the overall power conversion efficiency in the CdSe QD-sensitizednTiO2 solar cells could reach 1.9% under standard illumination condition of simulated AM 1.5G (100 mW/cm2).