Enhancing The Hole Current Of Organic Light Emitting Diodes

During the past three decades,organic light emitting diodes?OLEDs?have gained enormous attention across the world,due to their appealing merits of being self-emissive,lightweight,and large viewing angle.As of now,OLEDs have been successfully commercialized in the field of flat panel displays and solid-state lighting.Whereas,in order to improve the market competitiveness of OLEDs,the novel architecture designs for making OLEDs more power-efficient are highly solicited.This thesis mainly does the following three aspects of research work:Firstly,the doped organic/organic p-n heterojunctions have been applied as charge generation structure?CGS?in tandem organic light emitting diodes?TOLEDs?.It is found that the field-induced charge generation takes place more efficiently at the interface between BCP:Li₂CO₃ and CBP:MoO₃ than at the interface between BCP:Li₂CO₃ and NPB:MoO₃.Compared to the TOLED using the conventional CGS of 10 nm BCP:Li₂CO₃/20 nm NPB:MoO₃,the one using the CGS of 10 nm BCP:Li₂CO₃/10 nm CBP:MoO₃/10 nm NPB:MoO₃ shows increased device performance.In addition,the interconnecting property of CGS of 10 nm BCP:Li₂CO₃/x nm CBP:MoO₃/20-x nm NPB:MoO₃ shows a strong dependence on the thickness of CBP:MoO₃.Secondly,two hole injection structures incorporating two p-doped hole transport layers have been designed to provide hole current into NPB in OLEDs.The structure of 40nm PEDOT:PSS/10 nm NPB:MoO₃/NPB showed increased device current than that of 20nm NPB:MoO₃/NPB.The structure of 40 nm PEDOT:PSS/10 nm CBP:MoO₃/NPB presented nearly the same device current as that of 20 nm CBP:MoO₃/NPB.The relevant mechanism of this phenomenon was discussed as well.Lastly,OLEDs have been fabricated using various p-doped hole injection structures based on CBP:MoO₃ and NPB:F₄-TCNQ to optimize the hole injection structure and improve the performance.It is found that the improved hole injection structure of ITO/10nm CBP:MoO₃/5 nm NPB:F₄-TCNQ/5 nm CBP:MoO₃ is provided to diminish the hole and exciton losses,greatly increasing the device performance than the other hole injection structures.