Flexible And Structured Electrodes For High-performance Flexible Organic Light-emitting Devices

Organic light-emitting devices(OLEDs),with the advantages of light weight,low power consumption,flexibility,and broad color gamut,have gradually occupied the mainstream position in the market.However,the most widely used transparent indium tin oxide(ITO)electrode in the device is no longer suitable for the preparation of flexible wearable devices due to its expensive raw materials,complex preparation process and fragility.And due to the mismatch of refractive index between the functional layers,the waveguide mode and substrate mode are generated.The surface plasmon polariton(SPP)mode at the interface between the organic layer and the metal electrode will also severely restrict the effective emission of photons.All these restrictions will seriously hamper the light extraction,making the final light extraction efficiency less than 20%.In response to the problems of developing flexible OLEDs,we focus on the optimization of silver nanowire electrode and its application in wearable devices.Improving the performance of structured ultra-thin metal electrodes in OLEDs.The research results of this paper include the following aspects:1.Instability and large wire-wire contact resistance of silver nanowires(Ag NWs)have seriously hindered their practical applications as electrodes in optoelectronic devices.Although various methods have been demonstrated to improve the stability and conductivity of the Ag NWs,a simple and low-cost scheme,especially compatible to the flexible substrates for their applications in flexible devices,is still a challenge.Here,perfluorinated sulfonic acid(PFSA)polymer has been employed as a surface-passivation layer on the Ag NWs through a simple surface coating.The PFSA passivation can simultaneously improve the conductivity,thermal stability and mechanical stability of the Ag NWs.As a result,the PFSA-passivated Ag NWs film maintains an almost constant conductivity under ambient condition after heating for30 min at 250 ? or 10 days storage at room temperature,and 600 continuous bending cycles at a bending radius of 1 mm.The PFSA-passivated Ag NWs have been applied to flexibly organic light emitting devices as their electrodes,and both mechanical stability and long-term operational stability have been improved.2.Transparent conductive electrodes(TCEs)have attracted considerable attentions as one of the essential components in optoelectronic devices.High conductivity,transmittance and flexibility are required for the practical applications of the TCEs in wearable and portable electronics.Here,a simple fabrication process of capillary force-induced printing has been developed to realize highly aligned silver nanowires(Ag NWs)film with high flexibility,stretchability and conformability.Ultrathin and skin-attachable OLEDs have been realized based on the aligned Ag NWs electrode.This work has proposed a low-cost and fast fabrication strategy to realize highly aligned Ag NWs electrode for the flexible and stretchable optoelectronic devices.3.A micro/nano structure on the metallic electrode is necessary to outcouple power lost to surface-plasmon polaritons(SPP)in organic light-emitting devices(OLEDs).However,a simple and efficient method to integrate the micro/nano pattern onto the surface of the metallic film is still a challenge.In this work,thermal nanoimprint lithography has been employed to directly imprint periodic corrugation onto an ultrathin metallic film.Both surface morphology and conductivity of corrugated metallic film have been improved by the imprinting process,which is important for its use as electrode in optoelectronic devices.The photons that trapped in SPP modes associated at the organic-cathode interface in the OLEDs have been efficiently extracted by using the periodically corrugated ultrathin metallic film as anode of the OLEDs.A 56% enhancement of current efficiency was achieved compared with the planar device.The corrugated ultrathin anode is further applied to flexible OLEDs,and improved light extraction efficiency has been obtained.In summary,this work focus on the high-performance transparent electrodes based on the development needs of new OLEDs.The use of one-step solution spin coating method and the introduction of a PFSA passivation layer successfully achieved simultaneous optimization of the conductivity and stability of the traditional silver nanowire electrode.Capillary force is used to realize the highly ordered arrangement of silver nanowires on different substrates,and at the same time realize the high conductivity and transmittance of the silver nanowire film.The problem of incompatibility between microstructure preparation and ultra-thin metal film deposition has been successfully solved.Achieve one-step preparation of ultra-thin metal film with nano periodic structure,while ensuring the integrity of the structure and the photoelectric properties of the metal film.And the use of the micro-nano structure to couple out the SPP mode inside the device effectively improves the light extraction efficiency of the device.Through the preparation and optimization of these new electrodes,a certain reference idea is provided for the subsequent preparation of flexible wearable devices.