Two New Organic Molecules For Organic Light-emitting Devices

Organic Light Emitting Diodes (OLEDs) are advantages in that they are self-luminous,high-brightness,wide viewing angle, high contrast,thinness,low power consumption,fast response time and flexiblility and are leading next-generation technologies for electronic displays and lighting.As the key components of OLEDs,the development of organic light-emitting materials limits the practical use of OLEDs to a great extent. In this sense,to study and explore highly efficient fluorescence materials, especially those strongly emissive in the solid state, would be of great importance in both theory and practice.This thesis is mainly focus on two types of organic molecules in OLEDs, on their thermal properties, photophysical properties, electrochemical properties were studied. Two types of organic materials through the preparation of organic electroluminescent devices studied were two types of properties of hole transport properties and electroluminescent properties. More details are now listed below,1. In the Introduction part, the basic concepts of OLEDs are described, including the device structure, work principle, important steps during the development history, characterization and related instruments, and reviewed the recent work focusing on materials of active layers, device physics and processing, novel device structure, and so on.2. The dendrimers exhibited glass-transition at 115°C for Tr-TPA3 and 140°C for Tr-TPA9, respectively. The Tg of the dendrimers enhanced with the increase of the generation because the multibranched molecules with higher generation tend to hinder translational, rotational, and vibrational motions of the molecule. In addition, the dendrimers shows excellent decomposition temperature by TGA measurement at 409°C for Tr-TPA3 and 426°C for Tr-TPA9, respectively. The surface topographies clearly revealed that the spin-coated films exhibited fairly smooth morphologies with no obvious crystallized aggregation or cracks which demonstrate that Tr-TPA3 and Tr-TPA9 are capable of forming amorphous films through solution processing. The fluorescence quantum yields of Tr-TPA3 and Tr-TPA9 in dilute chloroform solution are measured to be 100% and 84.7%, respectively. The dendrimers exhibited proper HOMO energy level for hole injection.3. To investigate the hole-transport ability of triphenylamine-based dendrimers, double-layer OLEDs with the configuration of ITO/dendrimers/Alq3 /LiF/Al were fabricated, where dendrimers as HTL and Alq3 as emitting layer and ETL. The Tr-TPA3-based device turns on at a voltage of 3 V, and the brightness of the device is 4265 cd m-2 at 10 V. The Tr-TPA9-based device turns on at a voltage of 2.5 V, and the brightness of the device reach 11058 cd m-2 at 10 V. We also evaluate the hole mobilities of the dendrimers by analyzing space-charge-limited current (SCLC), the hole mobilities of Tr-TPA3 and Tr-TPA9 are about 10-5 cm2/Vs and 10-4 cm2/Vs, respectively, which are comparable to those of well-known triphenylamine derivatives. Therefore, the triphenylamine-based dendrimers with truxene as cores can be good candidates for HTM in OLEDs.4. Furthermore, two fluorene-centered oligocarbazoles have been characterized. The UV-vis absorption spectra of these compounds were complex, with multiple overlapping broad bands arising from both a conjugated backbone and carbazoles linked at the C9 position of fluorene. These compounds show strong blue emission in solution and high glass-transition and decomposition temperatures. These results indicated that they were of high thermal stabilities, which was a critical issue for device stability and lifetime.5. The EL properties of these compounds were investigated in double-layer devices with the configuration of ITO/PEDOT/Sample/TPBi/LiF/Al. The L-Z-390-based devices exhibit blue EL emission at low voltage, but when the voltage increases, they exhibit white EL emission with broad spectra that almost over the range of the visible light. Such a white light is considered as a combination of blue light from excimers and orange light from electromers.