Investigation On Preparation And Performance Of Flexible OLED Using Graphene Conductive Films

Flexible organic electroluminescent diode (FOLED) has been widely studied due to its high luminous efficiency, light weight, low cost, flexibility and high color purity. Graphene has been chosen in this study because of its unique physical characteristics for instance high electrical conductivity, optical transparency and excellent mechanical flexibility. Numerous studies, graphene shows great potential to replace conventional ITO as an anode of the photovoltaic device. However, the high resistivity and rough surface morphology of the graphene limits its practical application. Therefore, we proposed some study to overcome the disadvantages of graphene.In this preliminary study, a layer of PEDOT:PSS film was spray coated on the surface of graphene film to optimize its surface properties. To increase the quality and conductive of the PEDOT:PSS film, different ratio of deionized (DI) water and dimethyl sulfoxide (DMSO) were added into the PEDOT:PSS solvent to obtain 3 difference composite types of graphene/PEDOT:PSS-based transparent conductive film. The performance of graphene film and three different types of graphene/PEDOT:PSS composite films were characterized using SEM, AFM, surface sheet resistance and transmittance measurements. The characterizations showed that graphene/PEDOT:PSS with the ratio of 4:6:0.5 exhibit the optimal surface morphology and optical properties. It has sheet resistance of 320 Ω /m2, highest transmittance of 80%, and maintains stable conductivity and transmittance during multiples bending test.Subsequently, the green, yellow and blue FOLEDs with graphene/PEDOT:PSS-based conductive film were fabricated. All fabricated devices demonstrated uniform light emission and exhibited excellent mechanical flexibility when being bent multiple times. The emitting efficiency of the green flexible device was measured as 1.09 cd/A.Finally, a flexible white phosphorescent organic light-emitting devices (FWPOLED) with graphene/PEDOT:PSS-based conductive film was constructed. The device structure of the FWPOLED was graphene/PEDOT:PSS/NPB/CBP:Ir(ppy)3:Rubrene/NPB(d)/DPVBi/Bphen/ LiF/Al. The device performance was examined with different thickness of each organic layer. When the turn on voltage reached 5 V, the optimal white flexible device was obtained with maximum luminous efficiency 0.91 cd/A and color coordinates (0.31,0.33) which is very close to the standard white point (0.33,0.33). This device also exhibited a stable luminous efficiency after multiples bending at radius of 10 mm.In conclusion, this study demonstrated the optimized ratio of PEDOT:PSS to improve the conductivity of graphene film. With the optimized ratio, the green, blue and yellow monochromatics and white flexible OLEDs with graphene/PEDOT:PSS-based conductive film were fabricated. In addition, it was found that the white emitting color coordinates very close to reported literature. This study suggested that the possible electronics applications of graphene in flexible organic electroluminescent displays and illumination practice.