| Organic light-emitting diodes (OLEDs) are considered to be the candidate for the next generation flat panel displays and light source. Polymer electroluminescent devices based polymer materials can be achieved by solution-processing, such as spin-coating, inkjet printing, screen printing and so on. It has natural advantages and has been attention widely. Even so, efficiency and spectra stability of polymer light-emitting diodes need to be further improved. In the dissertation, we performed the researches on the polymer light-emitting diodes based on polyfluorene (PFO) and multilayer OLEDs using alcohol-soluble electron transport materials. The main results are as follows:1. We studied on some ways to induce the formation of β-phase. PFO shows different phase properties in different solvents with the reason of its rich phase structures. According to previous reports, β-phase PFO has the characteristics of high efficiency and EL stability. The films of β-phase were realized using1,2-dichloroethane as solvent and tested photophysical properties in this thesis. Through the study on the photophysical properties,β-phase PFO using1,2-dichloroethane as solvent can obtain longer molecular conjugation P-phase structure. Furthermore, device with β-phase exhibits stable deep blue emission.β-phase poly(9,9-dioctylfluorene)(PFO) was realized by dipping amorphous films in1,2-dichloroethane (DCM) for several seconds. The absorption and photoluminescence spectra indicates the formation of β-phase in the films. The stable pure-blue polymer light-emitting devices were fabricated based on the films of β-phase PFO. The efficiency of the device based on chloroform (toluene) with β-phase is increased to2.52cd/A (3.64cd/A), which is3.3times (2.8) higher than that of the devices with amorphous phase. Moreover, the device with β-phase emission shows higher color purity than that of amorphous-phase device.2. Researches have performed on the spectra stabilities of PLED with thermal annealing PFO films which based on different solvents. We did thermal annealing treatment to the series of PFO films base on1,2-dichloroethane, toluene and chloroform under different conditions, and found that the performance of PLED devices with the treated films showed different properties. With temperature increased, the spectral stability got better while the PFO films soaked by chloroform. It was found that performance of device performance showed more stable when the films were annealed at120℃for60minutes. 3. We used hydrophilic monodisperse conjugated starburst macromolecule TrOH as electron transport/injection layer (ETL) for solution-processed organic light emitting diodes (OLEDs). Multilayer OLEDs with device configuration of ITO/PEDOT:PSS/emissive layer/TrOH/Al have been facilely constructed by solution processing due to the orthogonal solubility of the ETL and the active layer. For comparison, devices with Al, Ca/Al cathodes and a conjugated polymer grafted with the same polar pendant groups (PFN-OH) as ETL with Al as cathode have also been fabricated. The device based on TrOH/Al cathode showed superior Current efficiency (CE) of3.01cd/A to those using Al cathode (0.08cd/A), Ca/Al cathode (1.32cd/A) and PFN-OH/Al (2.00cd/A). In order to understand the role of hydrophilic TrOH as ETL on improving the device performance, open-circuit voltage (Voc) of the devices, the water contact angles, and atomic force microscopy (AFM) were used to investigate the surface properties before and after deposition of ETL. The results confirmed that the electron injection barrier from the Al electrode could be effectively decreased by inserting hydrophilic TrOH as ETL. |
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