Study On The Influence Of CGU Structure Design For The Performance Of Tandem OLED

Organic Light Emitting Diodes（OLEDs）have become a promising technology for commercial display and lighting applications due to their self-emissiveness,high efficiency and flexible fabrication.However,OLEDs need to address the low efficiency and short lifetime of the devices at high luminance in practical applications.The use of a laminated structure with several EL units connected in series and connected by an intermediate connecting layer can effectively solve the problem of short carrier transmission distance due to low exciton mobility and lifetime in OLED devices,improving the efficiency and lifetime of OLED devices.Laminated devices,on the other hand,are still limited by the material of the connecting layer,the interface contact and the process,and have problems such as low power efficiency and large driving voltage.To solve these problems,we introduced photovoltaic heterojunctions into the connecting layer structure to facilitate internal charge transfer by absorbing some of the internal photons to generate charge and reduce the driving voltage of the stacked devices.This thesis is based on the study of the connecting unit that is a combination of a photovoltaic heterojunction and a buffer modification layer on either side of it,as follows:The paper introduces the current developments and problems encountered in tandem organic light-emitting device（TOLED）,describes the working mechanism and relevant physical theory of organic light-emitting devices;introduces the device process and performance parameters.Based on the C₆₀/Cu Pc optoelectronic heterojunction,Al and NPB:F4-TCNQ have been added as charge buffer layers.By improving the carrier balance within the device,the charge injection is greatly improved and the device performance is further enhanced.With this connecting unit,both yellow and red tandem OLEDs have been prepared,and the developed tandem devices have improved optical and electrical properties compared to yellow and red devices with a single light-emitting unit,with the maximum lumen brightness of the yellow tandem OLED reaching 1.82 times that of the single-layer yellow devices.The reasons for the insignificant performance improvement of the red devices were also analysed,and the results were obtained for the different performance of the Al/C₆₀/Cu Pc/NPB:F4-TCNQ structure on OLEDs with different light-emitting modes.Results show that the concentration of dopant material has a substantial effect on the operation of the charge generation layer in the stacked device for devices with different luminescence modes and luminescence efficiencies of different coloured luminescent materials.Using the carbon template method,hollow spherical Sn O₂nanoparticles were prepared and successfully applied to the connecting layer and the light-emitting unit of the stacked red-light device,and the stacked device with Sn O₂/C₆₀/Cu Pc/NPB:F4-TCNQ structure as the connecting layer and the light-emitting unit with NPB/Alq₃:Rubrene:DCJTB/Sn O₂/Alq₃were prepared respectively.devices.The results show that the application of Sn O₂nanoparticles in a laminated device with a photovoltaic heterojunction as the charge-generating layer enhances the carrier transport in the device and increases the monochromaticity of the OLED.In addition the ease of processing and low manufacturing cost of Sn O₂nanoparticles also contribute to the industrialisation of stacked devices.The theoretical experiment of using a polymer heterojunction P3HT:PC₆₁BM as a charge-generating layer in the CGU of the laminated device,and selecting octylamine as the protective layer of the lower organic film through orthogonal solvent,results of the prepared tandem yellow OLED show that the device performance is improved compared with the laminated device made of Al/C₆₀/Cu Pc/NPB:F4-TCNQ structure.In addition,the effect of the thickness of the octylamine film on the performance of the stacked devices was investigated.The results and analysis show that the P3HT:PC₆₁BM polymer heterojunction can be used as a charge generation layer for high performance tandem OLEDs.The incorporation of a suitable solvent as a protective layer into the CGU structure can effectively improve the efficiency of the polymer photovoltaic heterojunction and hence the overall performance of the stacked devices.