| Description |
The goal of the work presented in this dissertation was to find out how physical ordering of organic semiconductors affects spin-dependent electronic charge carrier transitions. Organic light emitting diodes in distinct morphological phases were created out of thin films of the ï°-conjugated polymer poly[9,9-dioctylfluorenyl-2,7-diyl] (polyfluorene), allowing diodes to be studied with the sole difference being the degree of polymeric order in the active layer of the device. The polyfluorene morphologies studied ranged from an amorphous (glassy) phase through mixed phases, to a highly ordered (beta) phase. The phase control was achieved through a dipping procedure where a glassy polyfluorene layer is immersed in a solvent mixture that structures the side chains of a monomer unit into an alternating planar ladder structure. Continuous-wave (cw) and pulsed (p) electrically detected magnetic resonance (EDMR) spectroscopies were used to probe charge carrier spin states within the polyfluorene layers. For cw EDMR, microwave frequencies between ~1 and 20 GHz were used, while all pEDMR measurements were conducted at X-band (~9.6 GHz). The experiments allowed for a comparison of how polymer morphology affects spin-dependent charge carrier transitions, coherent spin motion, spin relaxation times, the local nuclear (hyperfine) magnetic fields and spin-orbit effects. In addition to film morphology, temperature and device-bias dependencies of the spin-dependent charge carrier transitions were studied experimentally and a set of global fit and bootstrap error analysis techniques were adapted for EDMR spectroscopy. |
