Synthesis And Characterization Of Phosphine Oxide Derivatives As Electron-Transport Small Molecule Material For Solution-Processed Electrophosphorescent Devices

Solution-processible OLEDs have recently received great attention due to the cost-efficient fabrication from solution and significant potential applications in flat-displays and flexible display. For achieving high device performance, multilayered device structures are always needed since the simple sandwich structure cannot meet relevant device physics considerations. Electron transport layer is used to balance the charge carriers. Unfortunately, owing to the similar solubility of the materials in common organic solvents, interfacial mixing problem alway exists while depositing the multilayered films via sequential solution processing, which is exceedingly harmful to the device performance. Orthogonal solvents have been developed to solve this obstacle. Therefore electron-transport small molecule material for solution-processed electrophosphorescent devices has been paid close attention.In this thesis, we designed and synthesized a series of novel solution-processing electron-transport (ET) materials with high triplet energy. The thermal property, film forming ability, electrochemical and photophysical properties of the materials have been studied in detail, and the highly efficient solution-processed multilayer phosphorescent OLEDs have also been fabirated. The main content of this dissertation is as follows:1. A novel alcohol-soluble electron-transport material was designed and synthesized. This material not only possesses high triplet energy and a low HOMO level but also exhibits excellent electron-transport properties and good film-forming ability. Efficient fully solution-processed multilayer white electrophosphorescent devices have been fabricated by using this alcohol-processable material as an orthogonal electron-transport layer. The device using PhPO as ET material showed a turn-on voltage of 5.8 V and gave a maximum LE of 32.6 cd/A with a corresponding EQE of 11.5%.2. A new series of alcohol-soluble electron-transport material TPBI-POE and TPBI-PO for solution processed green electrophosphorescent devices were designed and synthesized. It was demonstrated that the new electron-transport materials show high glass-transition temperatures and excellent film forming ability. Compared with TPBI, they have excellent solubility in general organic solvents. The star-shaped configuration can enhance the morphological and thermal stability of the materials, and effectively inhibit the aggregation effect between the molecules. Introducing P=O group on the N-phenyl ring would result in a significant change in the LUMO levels of the TPBI core, which would achieve an effective electron injection. Utilizing those new compounds as electron-transport layers, the multilayer solution-processed green phosphorescence OLEDs with Ir(mppy)3 as a dopant show a turn-on voltage of 4.3 V, and a maximum current efficiency of 37.3 cd/A.