Enhanced The Performance Of Blue QLED Devices Via The Gold Plasmonic Resonance

Quantum Dot Light-emitting Diode(QLED)has great potential for applications in display and lighting fields due to its high color saturation,high luminance,adjustable luminescence spectrum,and low manufacturing cost.Through material synthesis and device structure optimization,the performance of QLED devices has been greatly improved,and the external quantum efficiency(EQE)of red,green and blue QLED has reached 30.9%,28.7%and 21.9%,respectively.However,due to the larger band gap of blue quantum dots,the energy required for exciton compounding increases accordingly,resulting in a lower radiation compounding rate.In addition,the inherent short wavelength of blue quantum dots makes the Rayleigh scattering phenomenon more severe,which increases the optical loss.Therefore,in terms of efficiency and stability,blue QLED still suffer from low EQE and short lifetime compared to red and green QLED.Currently,the use of Surface Plasmon(SP)effect to enhance the coupling between local surface plasmon resonance and excitons is considered as one of the most attractive methods to improve the efficiency of optoelectronic devices.The surface plasmon effect is a significant enhancement of the localized photoelectric field caused by the collective oscillation of free electrons at the interface between a metal and a dielectric material.Localized Surface Plasmon Resonance(LSPR)can absorb photons at specific wavelengths and generate an enhanced optical electric field in the space of a few to several tens of nanometers.In QLED devices,metal nanostructures are coupled with excitons in quantum dots through LSPR localized surface plasmon resonance electromagnetic fields,thus enabling energy transfer and increasing the radiation compounding rate,which in turn improves QLED device performance.Based on this,this thesis constructs quasi-periodic folded gold nanostructures by introducing gold nanoparticles(AuNPs)inside the device to enhance the radiation compounding rate of excitons using its surface plasmon resonance effect to further enhance the quantum efficiency inside the device,while the internal micro-nano structure can also enhance the optical extraction of waveguide modes and further improve the optical output coupling efficiency to enhance the performance of blue light QLED devices.Specifically,the main work of this thesis is summarized in the following two sections:(1)Preparation of gold nanoparticles with plasmon resonance efficiency and their application in blue QLED devicesGold nanoparticles were prepared by seed synthesis and introduced into the poly(3,4-ethylenedioxythiophene):polystyrene sulfonate(PEDOT:PSS)hole injection layer to construct blue light QLED devices.The device performance was optimized by precisely tuning the AuNPs particle size,concentration and PVK hole transport layer thickness.The experimental results show that the best performance of the QLED devices is achieved with the AuNPs particle size of 4 nm,the doping ratio of0.3:1,and the spin-coating speed of PVK film of 3500 rpm.Compared with the standard device,the introduction of AuNPs effectively improves the device luminance and external quantum efficiency from13350 cd/m~2 and 9.68%to 16410 cd/m~2 and 12.49%,respectively,an improvement of 30%and 23%.Meanwhile,the current efficiency is improved from 6.46 cd/A to 8.22 cd/A and the power efficiency is improved from 4.05 lm/W to 5.16 lm/W.Further analysis by photoluminescence(PL)and time-resolved photoluminescence(TR-PL)spectroscopy,hole-only device(HOD)testing,and time-domain difference finite simulation(FDTD)reveals that the performance improvement is mainly due to due to the increased exciton radiation complexation rate caused by the local surface plasmon resonance effect between AuNPs and QDs and the increased hole injection of AuNPs in the PEDOT:PSS layer.(2)Constructing gold plasma nanostructures to enhance blue QLED performance using nanoimprinting technologyFirstly,gold nano-islands with plasmon resonance effect were constructed by vapor deposition and thermal annealing to improve the performance of blue QLED devices by matching the blue quantum dot emission peaks.The results show that the islanded gold nanostructures have the problem of increasing leakage current,which affects the device performance by increasing the device start-up voltage.To address these problems,we prepared quasi-periodic folded structure PDMS soft templates by RIE etching,and then constructed PEDOT:PSS substrates patterned with gold-doped nanoparticles using nanoimprinting technology.The etching power and PVK hole transport layer thickness were precisely tuned to optimize the device performance of the plasmonic gold nanostructures.The best performance of the constructed blue QLED devices was achieved when the etching power was 70 W and the spin coating speed of PVK film was 4000 rpm.Compared with the standard device,the luminance and exo-quantum efficiency were improved from 14480 cd/m~2 and 10.62%to 16490 cd/m~2 and 15.89%,respectively,an increase of 14%and49%.Meanwhile,the current efficiency and power efficiency reached 6.52 cd/A and 10.49 lm/W,respectively,an improvement of 43%and 47%.The performance enhancement was verified by PL,TR-PL,and HOD test analysis and FDTD simulation theory,and the reason for the performance enhancement is the synergistic effect of the surface plasmon resonance effect and the internal micro-nano structure on the waveguide mode light extraction.