| Semiconducting polymers are promising materials for optoelectronic devices such as light-emitting diodes (LEDs) for displays, xerographic photoreceptors for imaging and printing, and photovoltaic cells for energy conversion. Photophysics, electroluminescence, and photoconductivity of a wide range of semiconducting polymer systems, including homopolymers, copolymers, binary polymer blends, and polymer/polymer heterojunctions, have been investigated in this thesis. Optoelectronic devices such as LEDs, photodetectors, and photoreceptors have been designed, fabricated, and evaluated to understand the structural and physical factors that govern the performances of semiconducting polymers devices and to provide feedback and guidelines for the design, synthesis, and development of new materials and for device engineering.; Optical absorption, photoluminescence excitation, emission, and fluorescence decay dynamics measurements were performed on conjugated polyquinolines, oligoquinolines, and block copolymers to investigate the effects of macromolecular structures on chromophore aggregation and the effects of mesostructures of supramolecular assemblies on the photophysics of conjugated polymers. Macromolecular J-aggregates have been observed in concentrated solutions and solid films of conjugated polymers. The emission of conjugated polymers originates from aggregates or excimers depending on the chromophore aggregation of supramolecular assemblies.; Electronic, photophysical, and electroluminescent properties of a series of n-type polyquinolines with varying molecular structures were investigated to explore structure-property relationships of semiconducting polymers. The emission colors and electroluminescence efficiencies strongly depend on molecular and supramolecular structures of the polymers. Enhanced electroluminescence was observed in binary blends of conjugated polyquinolines, originating from the exciton confinement effect, which leads to improved electron-hole recombination probability and exciton stability. Semiconducting polymer/polymer heterojunction LEDs exhibited voltage-tunable colors and enhanced electroluminescence efficiency and brightness. The color-tunable LEDs may find applications in full-color displays. The semiconducting polymer heterojunctions also provide ways to investigate polymer/polymer interfaces and charge injection, transport, and recombination in semiconducting polymers.; Bilayer photoreceptors and photodetectors from conjugated polymers, which showed comparable or superior performances to current organic or inorganic devices were designed, fabricated and evaluated. Nanoscale size effects on charge photogeneration in bilayer photoreceptors were observed, indicating the extrinsic nature of charge photogeneration in bilayer photoreceptors and the small exciton diffusion lengths in conjugated polymers. |
