| Organic light-emitting diode(OLED)possesses many prominent advantages,such as self-emission,pro-environment,high brightness,wide viewing angle,low power consumption,ultra-thin,fast response and flexible display.OLED has already been developed as a hot-point technology in the field of display and lighting,and gradually realized commercial popularization.In recent years,with the development of new materials,device structures and preparation processes,the significant progresses of scientific research and technology application have been made in OLED.However,the device efficiency,stability,yield rate and cost are still the main problems in OLED.It is necessary to continue to design and optimize the structure of the device on the basis of basic research,and to study the influence of the internal carriers and triplet excitons regulation on the device performance.Specific content is as follows:1.The development process and industry status of organic light-emitting diode were b.riefly introduced.The relevant theory on carrier injection,transportation and the dynamics of exciton in the device physics was summarized and reviewed.Finally,the research significance and content framework of this paper were expounded.2.It was found that the single layer F4TCNQ and LiF can form good quasi-ohmic contact with the anode ITO and the cathode Al,respectively,based on the current-voltage characteristics of the single carrier devices with different buffer layers.The effect of thickness on the mobility of typical transport materials TAPC,NPB and TPBi was studied by SCLC method.The experimental results showed that the electron mobility of TPBi was almost independent of thickness and was about 3×10-cm2/Vs,while the hole mobility of TAPC and NPB augmented obviously with the increase of thickness,which remained around 6×10-3 cm2/Vs and 4×10-4 cm2/Vs.The change rule of the mobility parameter was analyzed.Based on the disordered model,the energetic disorder ? and positional disorder E under different thicknesses of TAPC and NPB were deduced.The reason why the mobility changes with thickness was,in essence,revealed.3.The mobility of MADN doped with BuBD-1 was studied by SCLC method.It was found that the mixed system exhibited good bipolar charge transporting characteristics when the doping concentration was 3%.Fixed BPhen as the electron transport layer,the maximum external quantum efficiency of the blue fluorescent OLED reached 6.58%through regulating the hole transport layer.Fixed TAPC as the hole transport layer,the device's maximum external quantum efficiency increased to 8.15%through using the electron transport material AnTPy to improve the carrier balance.Based on the trade-off optimization material design concept,CNPI-p3Py possessed high electron mobility(1.05×10-3 cm2/Vs)and high triplet energy level(2.53 eV).The blue fluorescent OLED,based on CNPI-p3Py,achieved a maximum external quantum efficiency of 9.11%at a high current density of 101.6 mA/cm2.The microsecond delayed emission of the device was observed in the transient electroluminescence test,demonstrating that the TTA effect contributes to the high efficiency of the device.4.By testing transporting characteristics and spectral properties of the host material mNBICz,it was found that mNBICz possessed bipolar charge transporting property and could realize efficient energy transfer to blue phosphorescent guest FIrpic.The blue phosphorescent OLED,based on mNBICz,achieves a maximum external quantum efficiency of 25.6%,a maximum current efficiency of 53.2 cd/A and a maximum power efficiency of 50.6 lm/W,which are almost twice as much as the efficiency of the mCP-based device.The systematical impedance test was performed on mCP and mNBICz-based monolayer device by impedance analyzer,and the carrier dynamics process and its equivalent circuit parameters in different devices were analyzed.5.Unilateral homogeneous green phosphorescent OLED consisting of electron-type material pPBIPO showed high device performance,its maximum current efficiency,power efficiency and external quantum efficiency reached 96.1 cd/A,103.8 lm/W and 26.7%,respectively.Through single carrier devices experiment,it was found that pPBIPO and phosphorescent guest Ir(ppy)3 formed a unique carrier dual transporting channel due to the complementary matching of energy level and transporting property.Then,the self-created Gaussian multi-peak fitting method is used to accurately quantify the exciton distribution.It was found that the concentration of the guest were able to availably regulate the exciton recombination zone of the system,so as to optimize the carriers' balance in the homogeneous device and verify it by the concentration gradient device.Finally,we had successfully fabricated an entirely homogeneous phosphorescent device with low efficiency roll-off,which greatly simplifies the device preparation process.6.By introducing green dye Ir(ppy)3,the double guest yellow phosphorescent OLED obtained the maximum current efficiency of 53.6 cd/A,which increased by 25%higher than that of the single doped conventional device.The mobility,photoluminescence spectra and lifetime of the double-doped mixed system were tested.It was found that Ir(ppy)3 could effectively collect the excitons of the host material and transfer its energy to the PO-01 for lighting,and realize the cascade energy transfer process then increase the exciton utilization,whether intra-zone doping or inter-zone mixing.Based on the regulation of intra-zone triplet exciton transfer,the yellow phosphorescent OLED achieved the maximum power efficiency of 71.5 lm/W and the maximum external quantum efficiency of 22.3%,moreover,the efficiency roll-off proportion at 1421 cd/m2 was only 3.1%.By optimizing the inter-zone triplet exciton transfer device,it was found that when the thickness of exciton collection layer was 3 nm,the yellow OLED could obtained relatively pure yellow light spectrum and high efficiency with low roll-off at the same time. |
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