Study On Electron Injection And Light Coupling Characteristic Of Inverted OLED

After a long period of in-depth research and development,organic light-emitting diode has begun to realize the transition from research stage to practical application stage,its application in the field of display and solid state lighting has been carried out.However,there are still many problems to realize the high performance of OLED.For example,luminous performance and stability can not be guaranteed because of imbalanced carrier injection and low external quantum efficiency,which seriously hinders the further development of OLED.In view of the above problems existing in OLED,inverted OLED was taken as the research object in this paper.Through the introduction of the new electron injection layer,the doping electron transport layer,the emitting interlayers and the light extraction scattering layer,the electron injection transfer and optical extraction of inverted bottom-emitting OLED has been improved,and the luminous efficiency of the OLED has also been improved.The main work is as follows:?1?The effect of different Al layer thickness in ITO/Al/LiF new composite cathode on the electron injection and luminescence performance of inverted OLED was studied.The research showed that the addition of Al layer can significantly improve the electron injection level of the device.Moreover,when the thickness of the Al layer was 3 nm,the device showed a lower driving voltage and higher current efficiency.The current efficiency of the device at 7 V reached 19.75 cd·A^-1,it was 1.24,1.17,and 17.03 times of that of the devices with 2 nm,4 nm and 5 nm Al layer respectively at the same voltage.The device performance also reached the correspond to the inverted device level.At the same time,the performance of the device also reached the level of the corresponding non-inverted device.?2?The effect of different doping ratios Bphen:Li₂CO₃ used as electron transport layer on the electron injection and transmission of inverted OLED was studied.The research showed that using Li₂CO₃ doped electron transport layer material Bphen can significantly improve the level of electron injection to the emitting layer,balance the composite of electron and hole,and improve the photoelectric performance of the inverted device.For single electronic devices without doped materials Li₂CO₃,doping Li₂CO₃ can increase the current density of the same drive voltage.By changing the doping ratio of Li₂CO₃ in the inverted whole device,it was found that the current efficiency of the device increases first and then decreases with the increase of doping proportion.When the doped volume concentration was 13%,the device obtained the maximum current efficiency of 23.99 cd·A^-1,which reached the level of the corresponding traditional non-inverted device.?3?The effect of using p-n junction as electron injection layer on electron injection and luminescence efficiency of inverted OLED was studied.The research indicated that using p-n junction structure including HATCN/Bphen:Li and HATCN/Bphen:Mg as the electron injection layer of inverted OLED can effectively inject electrons into the device because the p-n junction with reverse bias can produce carrier at the interface.The way was changed in which electrons were injected only through the heat electron emission and tunneling effect.The current efficiency of inverted devices with p-n junction electron injection layers exceeded that of the corresponding non-inverted device.In particular,the maximum current efficiency of the inverted OLED using Bphen:Li reached 24.8 cd·A^-1,which was 26%higher than that of the normal device.?4?The effect of different emitting interlayers on the carrier injection transfer and device performance of double-emitting layer inverted OLED was studied.The results showed that there were better performance in inverted OLEDs with BCP,Bphen and TCTA interlayers than the device with CBP interlayer.When the driving voltage was 9 V,the current efficiency of inverted OLEDs with TCTA,Bphen and BCP interlayers were 1.03,1.19 and 1.23 times of that of the CBP device,respectively.Moreover,the current efficiency of BCP device can be up to 24.15 cd·A^-1,which was obviously superior to traditional non-inverted device.In addition,with the increase of the driving voltage,all inverted OLED showed small change in color coordinate resulting from the method of co-doping and the effective restriction effect of the interlayer on the carriers in the emission layer.?5?The effects of different light extraction methods on luminescence efficiency of inverted OLED were studied.The research indicated that with the increase of the roughness of the glass substrate and spin coating SiO₂ particles on the surface of substrate,the light out-coupling increases because of scattering.Therefore,the brightness and current efficiency of the device improved,and the current efficiency of the devices using the rough glass and the spin coating scattering layer were 1.15 times and 1.39 times of that of the normal device respectively.