Investigation On The Electroluminescence Performance Of QLED Devices Enhanced By Gold Nanoparticles And Wrinkle Structure

Quantum Dot has a broad application prospect in lighting and display due to its advantages of high quantum yield,long fluorescence life,wide absorption spectrum and narrow luminescence spectrum.Since the introduction of Cd Se quantum dots into light emitting diodes(QLED)for the first time in 1994,QLED devices have achieved great progress through materials synthesis and device structure optimization.The core of the application of QLED device is to realize the high external quantum efficiency(EQE)of the device under comprehensive conditions.However,due to the limitation of carrier injection imbalance and interface defects which caused an increase in the non-radiation recombination rate in the QLED devices,the fluorescence intensity of the quantum dot film thereby is weakened,and the internal quantum efficiency of device is degraded.The external quantum efficiency of QLED is the product of the internal quantum efficiency and the light extraction efficiency.Among them,the light extraction efficiency is mainly affected by the modes of surface plasma,waveguide and substrate of QLED devices,which resulting the higher light loss and lower light extraction efficiency of traditional QLED electroluminescent devices.Furthermore,how to simultaneously improve the internal quantum efficiency and the light extraction efficiency of the device,and ultimately improve the external quantum efficiency of the device,is the focus of this paper.In this paper,local plasma resonance(LSPR)effect between gold nanoparticles(Au NPs)and quantum dot films is firstly used to enhance the internal quantum efficiency of the device.Furthermore,the photon limited in the waveguide mode is extracted by the micro-nano structure to enhance the light extraction efficiency..Finally,through the improvement of the internal quantum efficiency and the light extraction efficiency of the device,the higher external quantum efficiency is obtained,and the better comprehensive performance of the QLED light-emitting device is realized.Specifically,the research work of this thesis can be summarized as follows:(1)Au NPs & PEDOT:PSS composite system improves device performanceThe Au NPs & PEDOT:PSS composite system was used as hole injection layer(HIL)and built into QLED device.The device optimization and luminescence performance were realized by fine regulation of Au NPs particle size and system content.When the Au NPs particle size was 20 nm and the system content was 5%(volume ratio),the QLED device obtained the highest photoelectric performance.Compared with non-Au NPs devices,the introduction of Au NPs makes the brightness of devices increase from 190300 cd/m~2 to 216400 cd/m~2,with an increase of up to 12%.Furthermore,the external quantum efficiency increased from 16% to 21.28%,with an increase of 24.81%.The device performance improvement was attributed to the coupling of Au NPs resonance absorption peak(522 nm)and QDs PL peak(526 nm).Au NPs and QDs enhanced the radiation recombination rate of excitons through the local surface plasmons resonance,promoted the photoluminescence of QDs films,and obtained higher luminous efficiency of devices.(2)TFB/Au NPs/TFB laminated structure improves device performanceBased on the laminated structure of TFB/Au NPs/TFB,the distance between Au NPs and quantum dot film was adjusted to achieve the regulation of the resonance coupling strength between Au NPs and quantum dot,and the enhancement and promotion mechanism of LSPR on the luminescence of QLED devices was studied.Compared with non-Au NPs devices,the introduction of Au NPs increased the maximum brightness of devices from 156300 cd/m~2 to 183900 cd/m~2,with an increase rate of 17.8%.The external quantum efficiency increased from 16.08% to 22.76%,achieving a 29.34% improvement under the condition of higher external quantum efficiency.When the distance between the quantum dot and Au NPs is too close,excitons are prone to non-radiative recombination in the metal,resulting in fluorescence quenching.Accordingly,when the distance between QDs and Au NPs is appropriate,Au NPs has a strong coupling effect with the quantum dot film,which helps to improve the radiation recombination rate of excitons and enhance the photoluminescence performance of QDs film.Furthermore,by analyzing the J-V characteristic curve of single carrier(hole)device,it is observed that Au NPs reduces the leakage current of device and increases the working current of QLED.(3)The wrinkle structure improves the luminous performance of QLED devicesThe PDMS template of wrinkle structure was prepared by reactive ion beam etching(RIE)technology,and the PDMS folding template with balanced parameters was obtained by adjusting the etching time.Then,the PEDOT:PSS substrate of patterned wrinkle structure was obtained by Nano-imprinting technology and constructed into QLED device.Experimental results show that,compared with control devices,without changing the peak potential of electroluminescence spectrum,the photoelectricity performance of the mapped QLED device is improved,the brightness is increased from 128300 cd/m~2 to 153500 cd/m~2,with an increase of 16.41%,and the external quantum efficiency is improved by 30%.According to the FDTD simulation and the optical mechanism,the device efficiency is improved because the wrinkle structure can realize the coupling output of light between heterogeneous layers.