Research On Fabrication Of High-Performance Ultra-thin Au Electrode And Its Application In Organic Light-Emitting Devices

During the last decades,extensive attention has been paid to transparent conducting electrodes owing to their widespread applications,including transparent display devices,touch screen panel,organic optoelectronic devices,and transparent film heaters.The most commonly used transparent electrode is indium tin oxide?ITO?with high electrical conductivity and optical transmittance in visible wavelength region.However,ITO suffers from the increasing price with limited indium resource,insufficient conductance for large-area devices,and incompatibility with flexible devices due to its poor mechanical flexibility and high annealing temperature during fabrication processing.In order to break through the limitations of ITO,many new kinds of potentially alternative transparent electrodes have been developed,such as conductive polymers,graphene,carbon nanotubes,metal nanowires,patterned metal nanostructure grids,and ultrathin metallic films.Despite of the flexibility of carbon-based materials and conductive polymers,the low conductivity limits their applications as electrodes.Metal nanowires and patterned metal nanostructure grids need complex synthetic and fabrication processing,which restrict the electronic performance of device based on this kind of electrodes.A continuous and transparent ultrathin metal film with high electrical conductivity and good mechanical flexibility is considered as a promising candidate to replace ITO electrodes.Unfortunately,it is well known that the thermally evaporated or sputtered ultrathin metal film?<10 nm?follows the Volmer-Weber growth mode usually exhibiting a discrete granular and rough morphology due to poor adhesion with the substrate,which dramatically decreases the optical transparency and directly deteriorates their electrical conductivity.Therefore,a novel transparent conducting electrodes with high transmission,good conductivity and mechanical flexibility,as well as,low costs and low-temperature processing,is still a challenge.In the paper,we have demonstrated an ultrasmooth and ultrathin Au transparent film with the thickness of 4.4 nm based on hybrid nucleation layer by a low-cost and simple method.The hybrid nucleation layer,which consisted of the S-1805 film as the substrate modification layer and 0.6 nm Ag film as the seeding layer,suppressed the three-dimensional?3D?islands formation of the ultrathin Au film due to the Volmer-Weber growth mode.Based on the combined effects of Ag wetting behavior and chemical binding between S-1805 and Au atoms,the 4.4 nm ultrathin Au film with the structure of S-1805/Ag/Au exhibited extremely smooth and continuous surface morphology with a very good root-mean-square roughness?RMS=0.365 nm?,high conductivity with the sheet resistance of R_s=70.4?sq^-1,and high transparency of T=78.4%at the wavelength of 550 nm.Application of the high performance Au electrode as anode in OLEDs,A 25%current efficiency enhanced in OLEDs.Moreover,the flexible OLEDs based on the hybrid anode with NOA-63 flexible substrate have also shown superior flexibility and mechanical robustness by bending texting.