OPTICAL AND ELECTRICAL PROPERTIES OF ORGANIC SEMICONDUCTORS: EXPERIMENT AND SIMULATION\ud

This dissertation focuses on the charge transport of organic semiconductors, particularly in the presence of traps and defects. Rather than attempting to ultimately pure materials, intentional mixtures were made and studied. The materials were characterized by electrochemistry, UV/Vis spectroscopy and computational studies using density functional theory (DFT) and time dependent DFT (TDDFT). \ud In experiment, the phthalocyanine films were prepared from solution. We explored how to improve the coatings of organic semiconductors on different substrates. Moreover, the effect of how intentionally introduced traps or barriers change the charge transport was studied using the spin-coated octabutoxy phthalocyanine and naphthalocyanine mixed films. It was found that the introduced barriers decreased the mobility. And a negative differential resistance was observed in the saturated region of the Field-effect-transistor (FET) measurements in the mixed films.\ud In simulation, density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations were performed to predict optical and electrical parameters of the semiconducting materials. In the calculations of phthalocyanine molecules with different metal or ligand substitutions, it was found that the electrical and optical properties of the phthalocyanine semiconductors could be tuned more with different organic ligands than by modifying the metal centers. For the mixed valence (MV) bipyridine bridged triarylamine systems, the simulation perfectly predicted the absorption of the spectra and the blue-shift of the spectra with different solvents reported by our collaborator in experiments. \u