Study On Organic Light-emitting Diodes(OELDs) With Small Size Graphene Oxide(GO) And Its Composites As Hole-injection Layers(HIL)

Organic light-emitting diodes（OLEDs）have attracted considerable attention owing to their unique advantages,such as self-luminous,big color gamut,fast response speed,low power consumption,and flexibility.After several decades of efforts,significant advances have been achieved in OLEDs,and they have been widely applied in lighting and display fields.To fabricate OLEDs,there are two frequently used methods:vacuum thermal deposition method and solution-processed techniques.Compared to the vacuum thermal deposition method,solution-processed techniques have some advantages such as low equipment cost,simple preparation process,and low materials consumption,which make them have great development potential in the future.Because of its good solubility and film-forming property,Poly（3,4-ethylenedioxythiophene）:Poly（styrenesulfonate）（PEDOT:PSS）is currently the most frequently used hole injection layer（HIL）material in solution-processed OLEDs.Unfortunately,PEDOT:PSS possesses some undesirable properties such as natural acidity and hygroscopicity,make it damage the ITO and easily be undermined by moisture and oxygen in the air.These defects of PEDOT:PSS not only limits the performance but also affect the long-term stability of the devices.The shortage of high-performance hole injection materials that can be processed by solution methods has become a problem,which limits the development of solution-processed OLEDs.To resolve this problem,we plan to use the small-size graphene oxide（GO）and its composites that can be processed by solution methods as the HIL.The electroluminescence performance of the corresponding devices was studied to analyze the working mechanism of small-size GO and its composite HIL.The specific research work is as follows:1.Firstly,the small-size GO was used as HIL to fabricate the tris（2-phenylpyridine）iridium（III）（Ir（ppy）₃）based green phosphorescent OLEDs.The maximum luminance,current efficiency and external quantum efficiency of the optimal device reached131600 cd/m²,73.14 cd/A,and 20.63%,respectively,which indicated that the device with small-size GO as HIL are better than that of controlled device with PEDOT:PSS as HIL.The related mechanism for the improvement of small-size GO based devices was analyzed,and the results show that the small-size GO has great potential as a high-performance hole injection material to replace PEDOT:PSS for solution-processed OLEDs.2.Two-dimensional antimonene quantum sheets（AMQSs）were synthesized and doped in the small-size GO to form composite HIL.Then the GO/AMQSs composite HIL was used to fabricate OLEDs,and its influence on the device performance was studied.Through the optimization of GO/AMQSs composite HIL and device structure,the optimal device was obtained.The maximum luminance,current efficiency and external quantum efficiency of the optimal device reached 78930 cd/m²,71.20 cd/A and 20.15%,respectively.Compared with PEDOT:PSS device or small-size GO device,the performance of GO/AMQSs device was greatly improved.This can be attributed to the introduction of AMQSs,which further improves the hole injection and transport capabilities of the GO/AMQSs composite HIL.These results prove the feasibility of GO/AMQSs composite HIL and its great potential in replacing PEDOT:PSS.3.A new type of two-dimensional material—exfoliated black phosphorus（EBP）nanosheets were synthesized and doped in small-size GO to form composite HIL.The GO/EBP composite HIL was prepared and applied to OLEDs.By adjusting the doping concentration of EBP,a series of different GO/EBP composite HIL were obtained.The maximum luminance,current efficiency,and external quantum efficiency of the optimal device reached 128100 cd/m²,85.94 cd/A and 24.13%,respectively.The improvement of GO/EBP composite HIL device performance can be attributed to its good film-forming properties,high transmittance,and excellent hole injection ability.It was proved that the GO/EBP composite hole injection layer has excellent performance and is suitable for solution-processed OLEDs.