Study of the Attachment of Linker Molecules and Their Effects on the Charge Carrier Transfer at Lead Sulfide Nanoparticle Sensitized ZnO Substrates

Abstract

In order to attach nanoparticles to substrates using solution based assembly methodologies, one invariably relies on linking molecules whose importance is not solely as the binding component between the semiconductor substrate and the nanocrystal but also as an important in-series component in any charge carrier transfer (CCT) processes occurring in the circuit. The role of these linker components and their exact influence on CCT is presently ambiguous. In the present work a substrate consisting of ITO/ZnO/linking molecule (linker) onto which PbS nanocrystals (NCs) have been covalently bound is characterized. In this study a great deal of emphasis has been placed on the role of the linker, and it is shown that the linker is a major key to the understanding of the CCT processes and has an important influence by not only transferring or blocking the electron and hole intermediates in such systems but also making its own inherent and often substantial contribution to the optoelectronic response. To gain a greater understanding concerning the complex roles played by the linker, a number of different molecules with different functional groups and different alkyl chain lengths were used to connect the NCs to the ZnO layer, with the attachment of the linkers and NCs to the ZnO substrate being verified by spectroscopic methods and the optical and optoelectronic response being studied. In addition the results presented allow the possibility to propose a model for how the linker and NCs interact spatially and electrochemically with the ZnO layer.