M.Sc Thesis


M.Sc StudentZhahi Shahar
SubjectOptoelectronic Properties of Conjugated Polymer Layered
Nanocomposites
DepartmentDepartment of Materials Science and Engineering
Supervisor Full Professors Frey Gitti
Full Thesis textFull thesis text - English Version


Abstract

Conjugated organic species are promising active light-emitting components for luminescence devices and displays due to their high luminescence efficiency and low fabrication cost. However, environmental instability and intermolecular interactions lead to luminescence degradation and color impurity. Confinement in a layered inorganic matrix was shown to locally isolate the organic guests, effectively improving durability and providing color tunability. However, encapsulation using the traditional exfoliation-restack process yields low guest uptake, limiting the utilization of the nano-composites in opto-electronic applications. Here, a new methodology for organic guest incorporation into the inorganic layered host SnS2 is suggested and studied. This host is a member of the layered transition metal dichalcogenides, characterized by strong covalent bonds within the inorganic sheets and weak Van Der Waals force between sheets. As a result, the inter-sheet spaces can be significantly increased without decomposing the molecular structure. Hence, it is possible to achieve incorporation of guest organic species into the interlayer galleries while maintaining the layered structure of SnS2 and the associated semiconducting nature.

In the traditional incorporation method, the layered material is delaminated into single sheets and allowed to restack in presence of the organic guest. The statistical nature of this process limits the composite yield to such extent that it cannot be used for device fabrication. In the approach suggested in this study, organic molecules bearing polar groups react with Lithium-intercalated SnS2 and are electro-statically driven into the inorganic galleries. This approach was first tested for the encapsulation of small organic species bearing amine groups which are in their liquid phase at room temperature. It was found that the new approach lead to high organic species uptake in SnS2. The successful yield-increase, with respect to the exfoliation-restack method, lead to examination of this approach feasibility for the encapsulation of high-volume amine-bearing solute organic species. X-ray powder diffraction patterns indicate full incorporation of solvents and liquid organic spices, while bulky solute species such as dendrimers, conjugated small molecules and conjugated polymers are encapsulated less efficiently. Finally, the new method was used to incorporate organic light emitting species between the inorganic sheets of SnS2. Photoluminescence spectra of composites that include the light-emitting guests, small conjugated molecule or extended polymers, show shifts of the main emission peak and new vibronic transitions, compared to the corresponding pristine materials, indicating successful isolation of the organic guests between the inorganic sheets.