Impeded photo-oxidation of conducting polymer films using metal nanoshells
Hale, Gregory David
Halas, Naomi J.
Doctor of Philosophy thesis
Interest in the use of conducting polymers as the active layer in electroluminescent devices has grown steadily over the last decade, and the commercialization of such devices is imminent. The stumbling block to the widespread adoption of conducting polymer based devices is their short lifetime due to the rapid photo-oxidation of the films under ambient conditions. Improved processing and encapsulation techniques have been studied extensively in an effort to reduce photo-oxidation of these devices, with limited success. The pathway for photo-oxidation in conducting polymer films involves energy transfer from the polymer triplet exciton to triplet (ground state) oxygen in the film. The oxygen is excited to a highly reactive singlet state, which reacts with the conducting polymer backbone, resulting in the formation of luminescence-quenching defects. Since the triplet exciton drives this process, controlling the triplet exciton dynamics will slow the photo-oxidation process. To control the triplet exciton dynamics in conducting polymer films, small concentrations of metal nanoshells are added. Metal nanoshells are composite particles consisting of a nanometer-scale dielectric core coated with a thin metal shell. The plasmon resonance of the metal nanoshells depends on the ratio of their core radius to shell thickness, and can be tuned to a wavelength from the visible to near-IR. By incorporating metal nanoshells specifically designed to interact with the triplet excitons in two commercially important conducting polymers, P3OT and MEH-PPV, the rate of photo-oxidation can be slowed and the density of luminescence-quenching traps reduced by a factor of twenty relative to an undoped polymer film. The photo-oxidation process is efficiently impeded at extremely small nanoshell concentrations (<0.1% volume fraction).
Engineering, Electronics and Electrical; Physics, Condensed Matter; Engineering, Materials Science