Räumlich definierte Homo- und Blockcopolymer Nanokomposite

Nanocomposites have been in the field of research since 20 years. The addition of additives to polymers can manipulate their properties, they can be optimized and intensified even at low volumes. In addition completly new properties can be introduced. When nanocrystals are used as additives the system is reffered to as polymer nanocomposite. Especially this combination opens a large field of systems with very specific properties. Förster et al. established a system to create stable polymer nanocomposites. In a crafting-to process specific ligands are covalently bound to nanocrystals to create polymerbrushes. The polymerbrushes are completly missible in the polymer matrix, as soon as they are covered with the same polymer as the matrix. As an example the addition of Tinoxid-nanocrystals leads to an UV-stabilized polymer. The spherical polymerbrushes enable the selective embedding of the nanocyrstals into an polymer matrix multiphase. The selectiv embedding within the composite opens a completly new field of research. This field will be a focus of research in this thesis. As an modelsystem microphase-separated blockcopolymer are very usefull. Blockcopolymers show self-assembly and highly ordered domains. This behaviour can be used to incoporate the nanocrystals into one of the matrices or boundary layer. To achive this the nanocrystal will be covered with the specific matrix polymer. The phenomena of self-assembly can be found in a variety of systems, an example can be found in the formation of lipid bilayers. In this thesis the selectiv embedding of the nanocrystals in triblockcopolymer polystyrene-polyisopren-polystryene (PS-PI-PS), with different polystyrene units was used as a model system. The polymer shows hexagonal packed cylindrical microdomains. Within this work the domains were embedded with different nanocrystals. The nanocrystals vari in diameter and the used polymeric ligand. When nanocrystals are introduced in a high volume fraction a well ordered packing can be found. Within this thesis a key issue was to prove the existence of an size exclusion effect. It was recognized that a certain domain size was required for the nanocrystals to be embedded. This result must be considered for applications of the system. An interesting application of these composites is the production of hybrid solar cells. A major challenge in the development of a hybrid solar cell is the optimization of charge transport. By carefully controlling the position of the nanoparticles within the composites an ideal charge transport can be achieved. For this application the semiconductor nanoparticles can be coated with a conductive polymer. First experiments with poly-3-hexyl-thiophene coated semiconductor nanoparticles were prepared and evaluated in this work. Furthermore, the nanoparticles and poly-3-hexylthiophene were used to prepare a simple two-layer hybrid solar cell. It was prepared via a floating process developed by Retsch et al.. This method was optimized for semiconductor nanoparticles and poly-3-hexylthiophenes. With this floating technique highly ordered ultrathin layers of the respective components can be produced. The np-interface is very small in this simple setting, the efficiency is limited. Nevertheless the components used in the solar cell can be tested for their effectiveness by this simple three-dimensional layer structure. In this thesis three different approaches have been investigated. An improved charge transport can be achieved via the ligand exchange. A direct contact between the semiconductor nanoparticles and the electrically conductive polymer can take place. In the second part, the orientation of the nanoparticles within a triblock will be investigated, carried out using of a model system. The two-layer solar cell is studied as a simple model using the given components in their functionality. All polymer films prepared were analyzed by X-ray small angle scattering (SAXS) and transmission electron microscopy (TEM). The ligand exchange was observed by dynamic light scattering (DLS) and TEM measurements. The prepared films were investigated by atomic force microscopy measurements (AFM). First current-voltage characteristics for simple two-layer solar cells were recorded.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Bayreuth

Year

2015

Author dc:creator

• Barelmann-Kahlbohm, Denise

Contributors dc:contributor

• Förster, Stephan

Repository record source_url

https://epub.uni-bayreuth.de/id/eprint/2123/

OAI identifier oai:identifier

oai:epub.uni-bayreuth.de:2123