New functional polymers for sensors, smart materials and solar cells

摘要

Organic polymers can be used as the active component of sensors, smart materials, chemical-delivery systems and the active layer of solar cells. The rational design and modification of the chemical structure of polymers has enabled control over their properties and morphology, leading to the advancement of nanotechnology. A deeper understanding of structure-property relationships, as described in this thesis, affords control over the nanostructure of devices made from these macromolecular materials, which is crucial to the optimization of their performance. In Chapter 1, a new sensor for ionizing radiation based on composites of electron beam lithography resists, poly (olefin sulfone)s (POSs), and multiwalled carbon nanotubes is presented. The polymeric active component is radiation labile and its degradation after a sensing event leads to morphological and electrical changes in the composite at the nanoscale. As a result, a signal can be detected. Systematic sensitivity improvements can be accomplished by rational modifications of the chemical structure of the polymer side-chains. Orthogonal postpolymerization modifications performed using "click" chemistry, incorporate functional groups capable of increasing either the homogeneity of the composite, or its opacity towards radiation. In Chapter 2, a smart hybrid polymer composed of a POS and a silicone linked by "click" chemistry is described. By tuning the chemical structure of these two components and varying their ratio, composites with different mechanical properties and hardness can be achieved. This elastomeric smart material exhibits switchable mechanical properties: exposure to mild bases triggers disassembly into its monomers and individual constituents. In Chapter 3, the design, synthesis and properties of new polymer surfactant additives for photovoltaic devices is shown. The AB alternating regioregular polythiophene copolymer additives are obtained via a combinatorial approach, and contain functional groups in every other repeat unit. In Chapter 4 incorporation of small amounts of these polymer additives (0.25 weight %) is shown to result in large increases of up to 30% in the power conversion efficiency of organic solar cells consisting primarily of the benchmark system of poly (3-hexylthiophene) and Phenyl-C6 1-butyric acid methyl ester (PCBM) as the active layer. This effect is mainly due to the presence of dipoles at the interface of the bulk heterojunction introduced by the additives, which prevent charge recombination and lead to increases in the photocurrent collected across the polymer-fullerene interface. In Chapter 5, the synthesis of liquid crystalline polymer brushes is described, and their supramolecular and self-assembly properties are studied. The solid-state ordering and alignment properties of these highly substituted polymers can be affected by chemically tuning their mesogenic oligomeric side-chains, the length of the polymer backbone and the degree of crosslinking. The morphologies obtained with these macromolecules are interesting from the point of view of future photovoltaic applications.