Research On OLED Performance Enhancement Via Localized Surface Plasmon Resonance

Organic light-emitting devices(OLEDs)have drawn wide attention in the field of lighting and display due to their superior advantages of light-weight,large-area,simple process,excellent low-temperature characteristics and low cost.It has become the third-generation display device.It has great potential in the field of flat panel display and solid-state lighting(SSL).Up to present,the internal quantum efficiency(IQE)of OLEDs has been significantly improved through adopting phosphorescence or thermally activated delayed fluorescence or thermally activated delayed fluorescence(TADF)emitters because they can harvest nearly 100% excitons.However,a disadvantage of these materials is that the long excited state lifetimes involved cause inevitable exciton quenching effects,such as the exciton-exciton annihilation and the exciton-polaron annihilation,leading to low external quantum efficiency(EQE)and high roll-off in efficiency.It is well known that the exciton quenching are close related to the exciton-density,and the exciton-density strongly depends on the exciton lifetime It is thus important to fine modulate the excited state lifetimes and extend the spontaneous emission rates for enhancing the phosphorescence and TADF.Besides,blue Ph OLEDs generally show inferior performance relative to the green and red ones,it is also highly desirable to develop an effective strategy to enhance the performance of blue phosphorescence which is actually of particular importance for the development of high-performance full-color flat-panel displays and solid-state lighting sources.In this thesis,vacuum-evaporated Ag-island nanostructures were incorporated into ETL and HIL.Their effects on the performance of non-doped blue Ph OLEDs using an ultrathin phosphorescent dye as EML were investigated systematically.By changing the thickness and deposition rate of Ag layer,the surface morphologies and resonance absorption spectra of the Ag-island nanostructures can be fine modulated.The device performance is significantly dependent on the structure and position of Ag layer.The experimental results indicate that 0.5 nm Ag layer deposited at a rate of 0.06 ?/s presents excellent spectral overlap between the resonance absorption spectra of Ag-island layer and the emission spectra of EML that impacts the electrical properties.Compared to the reference device without Ag-island layer,the current efficiency of the optimized device was enhanced by 54% and 28% when 0.5 nm Ag-island layer was incorporated into ETL and HTL with 20 nm away from EML respectively.The performance enhancement is attributed to the synergistic effects for the improved electron transport properties induced by the Ag-island layer and the effective couplings between excitons and localized surface plasmons(LSPs).