Theoretical, experimental, device fabrication, and degradation studies of materials for optoelectronic devices.

摘要

The work presented in this thesis has two distinct objectives. The first objective is to design, synthesize, and study new materials for OLEDs and OPV cells and in the process make more efficient devices. The second objective is to study the extrinsic degradation mechanism of OLED and find a way to stop or slow down the degradation, so in the future more air stable devices can be produced.; Development of high triplet energy materials is important for both OLEDs and OPV cells. In OLEDs these materials can be effectively used either as hosts or as hole blocking materials and in OPV cells the materials can be used as exciton blocking layers (Buffer layers). The second chapter of this thesis describes the design, synthesis, and characterization studies of new phthalimide based high triplet energy materials for OLEDs and OPV cells. The chapter gives a detailed narrative of the electrochemical, photophysical, and density functional theory analysis (Ground and excited states) of all the materials.; The third chapter deals with thermochemistry, thin-film photophysics, and OLED fabrication studies of the phthalimide materials. The chapter delves into the OLED fabrication studies and investigates the behaviors of the devices fabricated with the phthalimides as hosts and as hole blocking layers (HBL) with red and green dopants. Very efficient green and red devices were obtained with the phthalimide HBL compared to the conventional BCP hole blocking layer.; Theoretical studies of platinum based broadband emitter, (dmappy)Pt(acac) are described in chapter four. In room temperature fluid solution, the (dmappy)Pt(acac) has been shown to emit in two different wavelengths, which shifts from blue to red depending on solvent polarity. Rotation of the dimethyl amino moiety on the phenyl ring causes the molecule to emit in different wavelengths. In the planar geometry, increased conjugation between the p orbital of the nitrogen atom and the pi orbitals of the phenyl ring causes the triplet energy of the system to decrease. When the dimethyl amino group rotates perpendicular to the plane of the molecule, the geometry of the dimethyl amino moiety becomes trigonal-by-pyramidal giving rise to two structural isomers: One with the nitrogen lone pairs facing up and the other with the lone pairs facing down. As a consequence, the conjugation between the p-pi orbitals decreases and the emission shifts to higher energy. In chapter four we investigate the spectroscopic behavior of this molecule by comparing the photophysical data with DFT and TDDFT calculations.; Theoretical investigation of (5NO2ppy)Pt(acac) is covered in chapter five. This molecules is important for both OLEDs and OPV cells. At 77K glass in 2me-THF and at room temperature in hexanes and polystyrene matrix emission from this molecule is observed around 550nm. In acetonitrile, toluene, and 2me-THF at 298 K no emission is observed. We believe that the emission of (5NO2ppy)Pt(acac) is controlled by the rotating NO 2 group on the pyridine ring. Rotation of the NO2 group to the plane or perpendicular to the plane of the molecule may alter the emission properties of the molecule. Chapter five uses theoretical methods (DFT and TDDFT) to investigate the spectroscopic properties of (5NO2ppy)Pt(acac).; In open air degradation of OLEDs proceeds through the formation and growth of nonemissive regions called dark spots. Since the dark spots form on the cathodes and grow by reacting with the water and oxygen molecules that tunnels through the cathode to the ETL, an effective way of stopping the formation and growth of dark spots would be by overcoating the cathode with hydrophobic materials and replacing the ETL with materials that can act as desiccants. Chapter six investigates the role of electron transporting layers (ETLs) and various overcoating materials on the degradation OLEDs.