Electroluminescence Performance And Stability Of The Phosphorescent OLED Based On Novel Phosphorescent Materials

In recent years,phosphorescent ytterbium(?)complexes became favorable due to their short exciton lifetime,wide luminescent color range and high quantum efficiency in comparison with other metal complexed phosphorescent materials,which are under extensive investigations.In commercial applications of organic light emitting devices(OLEDs),both high efficiency and long device life are required in phosphorescent materials.However,highly efficient phosphorescent materials often resulted in poor OLED device stability,which is detrimental and slow down the commercialization of red,green and blue phosphorescent materials in OLED applications.In this work,novel phosphorescent materials have been developed,novel device structures are designed in order to balance the efficiency and stability of the device.That is,a concentration gradient doped double-emitting structure was fabricated to optimize device performance and study mechanism.These investigations include:1.For the novel material MG05,the photophysical properties of all materials involved in the device were studied by fluorescence spectrophotometer,ultraviolet-visible spectrophotometer and electrochemical workstation.2.In order to improve the efficiency and stability of the device,a dual-emitting layer structure based on the concentration gradient of phosphorescent material MG05 was prepared.The device has a lifetime of 47.66 h at T95(initial brightness of 7000 cd/m2 and brightness decay to 95%of initial brightness).Compared with the single-emitting layer,the low concentration of 10wt%and the high concentration of 20wt%of the uniformly doped device have a T95 lifetime increase of 100%and 276%,respectively,under the same efficiency.The device has a lifetime of 47.66 h at T95(initial brightness of 7000 cd/m2 and brightness decay to 95%of initial brightness).The T95 lifetime increased by 100%and 276%,respectively,at the same efficiency compared to a single-emitting layer with a low concentration of 10wt%and a high concentration of 20wt%uniformly doped devices.The improvement in efficiency and stability with a concentration-gradient doped structure is mainly due to the improvement of carrier balance.3.In order to further improve the carrier transport balance,the thickness of each functional layer of the phosphorescent material MG05 concentration gradient doped double-emitting device is optimized to obtain the optimal thickness of carrier transport balance in each layer.At a current density of 20 mA/cm2,the efficiency reaches 60.37 cd/A and the T95 reaches 28.83 h?The efficiency and T95 lifetime are increased by 23%and 33%,respectively,relative to the unoptimized reference device.The mechanism of influence of thickness adjustment on device performance is analyzed.It is proved that carrier balance not only improves device efficiency,but also improves device stability.4.Research on the AT series electron transport layer found that the AT414 material is more suitable as the electron transport layer of the dual light emitting layer structure.Finally,the E228 buffer layer was introduced,and although the efficiency was reduced to 52.56 cd/A,the device lifetime T95 was increased to 52 h.