Charge Carrier Extraction Following Multiple Exciton Generation (MEG) in Semiconductor Nanocrystals
Final Report Abstract
Within the framework of the project we have achieved the following important results: The reproducible synthesis of ZnO and TiO2 Sol-Gels and PbS nanoparticles that match their conduction bands, the methodologies to prepare the substrates with a high surface density of PbS NPs on the oxidic substrates as well as an effective ligand exchange procedure for the PbS, the syntheses and preparation of both opal and inverse opal structures, the preparation of the devices (ISC’s prepared from ZnO NPs, TiO2 NPs as well as ZnO/Eosin Y and inverse opals) and the development of a reliable protocol for the deposition of PbS NPs on all of these substrates as well as ITO coated glass. A comprehensive understanding of the nature of the binding of six technologically important linker molecules (oxalic acid (OA), malonic acid (MA), thioacetic acid (TAA), thioglycolic acid (TGA), mercaptopropionic acid (MPA), and hexandithiol (HDT)) to the oxide surfaces was obtained and the mode of attachment of the PbS nanoparticles was established. A full electrochemical characterisation (CV and EIS) of the combined layers (ITO substrate, Oxide layer, linker and PbS) of all devices (ZnO, TiO2, ZnO/Eosin Y and inverse photonic crystal) was undertaken and a direct method was found by which the energy position of the conduction band of the PbS NPs may be determined (and through this the valance band). The EIS data obtained from all of the devices has been modelled and an understanding of the interactions of each component in the device as well as the device as a whole has been obtained. Also by comparison of the models, the differences present within the different architectures have been elucidated and the effects introduced through the alteration of the device design observed. A full opto-electrochemical characterisation of the devices has also been carried out using current transients, IPCE and intensity modulated photocurrent spectroscopy. The opto-electrochemical response of the device under different applied potentials (to determine the energy levels) and different excitation wavelengths (to distinguish the optically active layer and/or centre) was achieved and the influence of the linkers on the photocurrent response described.
Publications
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Study of the Attachment of Linker Molecules and Their Effects on the Charge Carrier Transfer at Lead Sulfide Nanoparticle Sensitized ZnO Substrates, J. Phys. Chem. C 2011 115(26) 13047
Krüger S., Hickey S.G., Tscharntke S., Eychmüller A.
