Research On Flexible Organic Light-emitting Devices Based On Ultrathin Au Grid Electrodes

Flexible electronic technology has developed rapidly in the last decade,in which flexible organic light-emitting devices(OLEDs)have unique advantages in lightness,mechanical stability,transparency and large-area fabrication,and have the potential to become the mainstream display technology in the field of consumer electronics.High mechanical stability and high efficiency are two important performance indexes that determine the practical application of flexible OLEDs,so they have become the focus of scientific research and industry.Transparent conductive electrode(TCE)with excellent optical transmittance and conductivity plays a dual role of charge injection and photon extraction in OLEDs,therefore it is one of the key factors determining the performance of OLEDs.For flexible and wearable applications,the flexibility and mechanical stability of TCEs are crucial.The cost of traditional indium tin oxide(ITO)electrode is increasing year by year,and it suffers from brittleness with poor mechanical performance,which obviously cannot meet the requirements of flexible OLEDs.Ultrathin continuous metal films with a thickness of less than 10 nm are expected to be promising alternatives of ITO transparent electrodes in flexible optoelectronic devices due to their low cost,good mechanical stability and high conductivity.For flexible transparent metal electrodes,the transmittance and mechanical stability need to be further improved.Furthermore,the optical loss caused by the surface plasmon-polariton(SPP)mode associated with the metal electrode/organic layer interface limits the external quantum efficiency of the devices.How to excite SPP resonance in OLEDs and improve the light extraction while obtaining high mechanical stability is still a challenge for flexible OLEDs.In this thesis,we have focused on the transparent ultrathin metal electrodes of flexible OLEDs,and introduced micro-nano structure to realize flexible OLEDs with excellent performance.The main work is summarized in two aspects:1.The ultrathin Au grid electrode has been selected as transparent anode for flexible OLEDs.The grids are introduced into an ultrathin Au film to improve its transmittance and mechanical properties.The optimal ultrathin Au film with a line width of 15?m,gap width of 30?m presents a transmittance of 88.7% at 550 nm and a sheet resistance of 36?/sq.Owing to the reduced tensile stress by the ultrathin grid patterns,the flexible ultrathin Au grid exhibits extraordinary mechanical stability with maintained conductivity after 48 000 bending cycles under a bending radius of 1 mm.Flexible OLEDs with high flexibility and mechanical stability have been obtained using ultrathin Au grid as transparent anode by maintaining an initial efficiency of 92% after 4200 bending cycles.In addition,compared with devices based on continuous Au or conventional ITO anode,the current efficiency of flexible OLEDs has been improved by 30% and 20%,respectively.2.The photons trapped in SPP modes have been recovered effectively by further introducing periodic corrugations into the ultrathin Au grid film to form the ultrathin Au electrode with dual micro-nano structure of grids and corrugations.The fabrication processes of grids and corrugations are compatible.When corrugations are introduced,the morphology,photoelectric properties and mechanical stability of ultrathin Au grid film can be maintained.Owing to the improved light extraction in OLEDs,the current efficiency of the device based on the corrugated ultrathin Au grid electrode has reached 49.2 cd/A,and results in a 30% enhancement.Furthermore,the device still exhibits excellent flexibility by maintaining 91.4% initial efficiency after 5000 bending cycles.