Improved Performance Of OLED Based On Graphene Oxide

Organic light emitting devices?OLED?are considered candidates for next-generation lighting and flat panel display technologies due to their self-illumination,wide viewing angle,light weight,and low power consumption.Graphene oxide?GO?has a two-dimensional structure like graphene and attracted much attention for its unique photoelectric properties.It is used extensively in organic optoelectronic devices,such as organic solar cells and OLEDs,based on its wide band gap.In this thesis,GO functional material was utilized as hole-injection layer?HIL?or composite electrode in the OLEDs.The effects of GO on the emission property of OLED were explored and the mechanism were analyzed.Our work mainly includes the following three parts:Section ?:Organic Light-Emitting Diodes with graphene oxide?GO?as hole injection layer?HIL?have been demonstrated.The OLED devices possess structures of ITO/GO?x nm?/NPB?40 nm?/Alq₃?70 nm?/LiF?0.5 nm?/Al?100 nm?,it is found that as the thickness of GO-HIL is a 3.6 nm an optimal current efficiency of 4.4 cd/A and a brightness of 15770cd/m² were achieved,respectively,which are higher than that of reference device without GO-HIL layer?1 cd/A and 4735 cd/m²?.We reason that the improvement of electroluminescent?EL?intensity would be ascribed to the smoothed ITO surface and the reduced hole-injection barrier due to the high work function of GO layer.In terms of the impendence spectroscopy analysis of hole-only devices?HODs?,for electrical character of device is mainly depends on the bulk resistance of the HODs.As a result,the optimized EL device offers fallen bulk resistances,finally,the improvement in EL performance was obviously realized.Section ?:A highly conductive transparent anode was fabricated by solution method based on poly?3,4-ethylenedioxythiophene?:poly?styrenesulfonate??PEDOT:PSS?/graphene oxide?GO?hybrid film by sulfuric acid?H₂SO₄?treatment.The optimal treated PEDOT:PSS/GO films reach a sheet resistance of 80?per square at a thickness of 40 nm and a high transmittance of 87.7%at 550 nm.Based on the atomic force microscopy,absorption and Raman spectrum,the structures of PEDOT:PSS was changed after the small amount of GO doping and H₂SO₄ treatment,which led to the separation of PSS^-and PEDOT⁺chains and the enhancement of the conductivity of hybrid films.The ITO free OLEDs fabricated with the optimized PEDOT:PSS/GO film as anode has the lowest turn-on voltage and highest current efficiency in comparison with ITO anode and pure PEDOT:PSS anode based OLEDs.At the same time,the brightness of OLEDs with the optimized hybrid film anode is 1.5 times higher than that of OLEDs with pure PEDOT:PSS anode.All of the higher transmittance,higher conductivity and higher HOMO levels,especially the variation of topography,ascribed to the improved efficiency of OLEDs with hybrid film anode.Section ?:Based on silver nanowire?AgNW?,the sheet resistance of hybrid electrode of PEDOT:PSS/GO/AgNW was reduced through optimizing the preparation technology.By using the AgNW ethanol dispersion and poly?3,4-ethylenedioxythiophene?-polystyrenesulfonic acid?PEDOT:PSS?/graphene oxide?GO?mixed solution,the hybrid electrodes were prepared by layered spin coating.The optimized PEDOT:PSS/GO/AgNW hybrid electrode has a low sheet resistance of 19?/?at an average thickness of 45 nm and high transmittance of 87.5%at 550 nm.The OLED using the optimized PEDOT:PSS/GO/AgNW hybrid film as the anode has the lowest turn-on voltage of 2.1 V and the highest current efficiency of 6.2 cd/A and the maximum brightness of 22894 cd/m²,which is much higher than that of OLED using ITO as the anode.