Abstract
White polymer light-emitting diodes (WPLEDs) have gained great attention over the last few decades due to their promising applications in full color flat-panel displays, backlighting sources for liquid-crystal displays, and next-generation solid-state lighting sources. In comparison with white organic light-emitting diodes (WOLEDs), WPLEDs fabricated by solution-process have advantages of low-cost manufacture in large-area displays and potential for the use of flexible substrate. In previous literatures, environment-sensitive metals (such as Ba/Ag、Mg：Ag/Ag 、Ca/Ag、Ba/Al、Ca/Al、CsF/Al) were commonly used as cathodes. While they facilitated electron injection, they might undergo degradation by reaction with oxgen and moisture at the interfaces. Also, metal ions formed at the metal-organic interface tended to migrate into the emitting layer (EML) to affect the stability of devices. In this study, we substitute polyfluorene grafted with 18-crown-6 ether (PFCn6) chelating to K+ for environment-sentive metals, due to the presence of electron-injection layer (EIL) of water/methanol-soluble PFCn6 chelating to K+, allowing the use of environment-stable Al as the cathode only. The advantage is that the device is stable to air, and we don't need package in vacuum environment, therefore, saving costs for fabrication. In this thesis, this contents are divided into two parts giving in chapters 4, 5. In chapter 4, we test many anode modifications in order to increase hole-injection in PFCn6-based devices. Among these modifications, using Chlorinated Indium Tin Oxide(Cl-ITO) is the best solution. Moreover, we demonstrate that the novel device configuration of Cl-ITO/PEDOT is reported for the first time, and we confirm that the raise of work function of PEDOT is induced by Cl-ITO. Also, Cl-ITO/PEDOT has interfacial dipole effect, which can increase hole-injection. The brightness and lumunous efficiency of PSBF-based devices are up to 35812 cd/m2 and 4.08 cd/A, respectively. As for EL spectra of PSBF, the emission at 500~525 nm becomes stronger with gradually increased voltage is observed. We owe this phenomenon to the excimer formation by electric field induction and polar side-chain motion in PSBF. Generally speaking, the whole color is blue-greenish. In chapter 5, we test many dopant systems in order to find appropriate dye for high performance WPLED. Among these systems, fluorescent orange small molecule Rubrene is the best choice for blending with PSBF. By device combination of Cl-ITO/PEDOT and PFCn6：K+=1：3/Al, the brightness and lumunous efficiency of PSBF-Rubrene-blended devices are up to 61523 cd/m2 and 10.3 cd/A, respectively. In comparison with the record in WPLED literature (~56000 cd/m2), the brightness is much better. By device combination of Cl-ITO/PEDOT and CsF/Al, the brightness and lumunous efficiency PSBF-Rubrene-blended devices are up to 87615 cd/m2 and 11.1 cd/A, respectively. Surprisingly, the brightness is predominately superior to the record in WPLED literature (~56000 cd/m2), and it can compete with the record in phosphorescent WOLED literature by multilayer and vacuum evaporation (~83000 cd/m2). The resulting high white brightness (~87615 cd/m2), to the best of our knowledge, is the highest in WPLED so far.