Plasmonics for Improved Thin-Film Photovoltaic Cells and Enhanced Light Extraction from Organic Light-Emitting Diodes

Surface plasmon resonance of metal nanoparticles has attracted much attention by creating unique interactions between light and nanoparticles. This special phenomenon can be utilized in optoelectronics applications such as photovoltaics and light emitting diodes, to improve their efficiency. This thesis focuses on the influence of gold and silver nanoparticles on the photoconductivity of amorphous silicon, the efficacy of organic solar cells, and light extraction from organic light-emitting diodes.;Enhancement of photovoltaics by integrating cells with gold nanorods is of potential interest to reduce the usage of semiconductor material. Gold nanorods with the ability to control surface plasmon resonance were synthesized and their thermal stability was increased by silica-coating to enable them to withstand standard semiconductor processing. Silica-coated gold nanorods maintain rod-like shape to over 600 °C and they can increase the photoconductivity of thin film amorphous silicon by much more than a factor of 2 across the entire visible spectrum. The enhancement mechanism studies show that absorption enhancement due to strong near-field light concentration is the primary effect rather than pathlength increases due to light scattering.;Bulk heterojunction polymeric solar cells have an extremely thin active layer with thickness of 100 ~ 200 nm and can take advantage of plasmonic effects on absorption to improve their efficiencies. Gold nanorods were introduced into model solar cells consisting of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM). No obvious improvements in short circuit currents were observed when particles were embedded in the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) anode layer. When blending silica-coated gold nanorods into the active layer, no significant improvements were obtained but the silica shell prevented metal nanorods from quenching excitons and trapping charge carriers so that future improvements using this materials design may yet be possible.;The external quantum efficiency of organic light-emitting diodes (OLEDs) is limited to ~ 20 % because of the refractive index mismatch between multiple layers in the devices. Large silver nanoparticles were synthesized and exhibited strong light scattering through the visible spectrum. These were incorporated into a layer between the indium tin oxide (ITO) anode and the glass substrate to improve light extraction from OLEDs. SiO2, TiO2 and mixed sol-gel films were developed to planarize silver nanoparticles. In spite of our hypothesis that strong scattering by large silver particles could be used to improve light extraction from OLEDs, our best results were to observe ~ 15 % decreases in light output even when the refractive index of the planarization layer was well matched to that of the ITO anode.