Study On Flexible And Stretchable Organic Light-emitting Devices Based On Controllable And Ordered Buckles

Recent years,stretchable electronic devices come into people's vision with the development of science and technology.Stretchable light-emitting devices are one important member of stretchable electronics and exhibit extensive application prospect in display and lighting.Stretchable light-emitting devices have attracted much attention due to their great application potential for the rapidly emerging wearable electronics.However,there are still some technical problems to be solved on the way before their commercialization.Stretchability limits the materials selection,structure design and preparation process of the light-emitting devices,which results in the low luminous efficiency of the stretchable light-emitting devices reported to date.Additionally,the luminescence properties of the stretchable light-emitting devices degrade rapidly due to their insufficient mechanical robustness.In my doctoral dissertation,our works mainly focus on buckles-based stretchable organic light-emitting devices(SOLEDs).SOLEDs with controllable and ordered buckles,high efficiency and mechanical robustness have been fabricated by selecting highly efficient small-molecule phosphorescent materials as the light emitter and using various microstructure manufacturing techniques to control the morphology of the buckles;We also fabricated SOLEDs with two-dimensional(2D)stretchability and measured the electroluminescence(EL)performance of the 2D SOLEDs at different stretching states for the first time.Our research results are summarized as follows:(1)Highly efficient and mechanically robust SOLEDs based on a laserprogrammable buckling process.Long period gratings were fabricated on the surface of the elastomeric substrate by a laser ablation process.Ultrathin and flexible OLEDs were fabricated by a template stripping technique.SOLEDs with controllable and ordered buckles were formed by controlling the adhesion regions of the ultrathin OLEDs on the microstructures of the elastomeric substrate.The ultrathin OLEDs were not stretched directly during the stretching process,which provided flexibility for OLEDs in materials selection,structure design and preparation process.At the same time,ordered buckles are beneficial for improving the mechanical stability of the SOLEDs.Consequently,SOLEDs with high efficiency and mechanical robustness have been achieved.The largest current efficiency of the SOLEDs is 70 cd/A at 70% tensile strain by using Ir(ppy)3 as the emitter and the current efficiency degraded about 16% after 15000 stretch-release cycles between 0%-20% tensile strains,which are the highest records for SOLEDs reported at the time.What's more,we mounted the SOLEDs on a finger joint to prove that our SOLEDs have great potential for wearable electronics.(2)SOLEDs with controllable and order buckles based on a roller-assisted adhesive imprinting technique.During the roller-assisted adhesive imprinting process,a metallic spacer layer was coated on the surface of the adhesive and elastomeric substrate to adjust its viscous force without influence on its elasticity.Periodic buckles were directly imprinted by attaching the ultrathin film on the surface of the adhesive and elastomeric substrate with periodic bonding and unbonding regions by using a patterned roller.High temperature or UV irradiation was not involved during the imprinting process.The roller-assisted adhesive imprinting process is simple,fast and suitable for large-area microstructures fabrication.SOLEDs with periodic buckles have been fabricated by this technique.The SOLEDs can be stretched to 100% tensile strain.The largest luminance and efficiency is 15110 cd/m2 and 66 cd/A,respectively,which are both among the best of stretchable light-emitting devices.Additionally,the SOLEDs can keep working after 35000 stretch-release cycles between 0% and 20% tensile strain with the luminance degradation of 27%,which is the best record for the mechanical stability of the SOLEDs reported to date.(3)SOLEDs with controllable and ordered buckles based on a shadow maskassisted deposition and pattern transfer technique.The regions on the surface of the adhesive and elastomeric substrate coated by the metallic spacer layer lose viscidity absolutely.The ultrathin OLEDs could only adhere to the bare regions of elastomeric substrate to form periodic bonding and unbonding regions.Finally,SOLEDs with periodic buckles were formed.The stretchable devices could be stretched to 100% tensile strain.At the same time,excellent EL performance and mechanical stability have been achieved.The largest luminance and current efficiency is 17980 cd/m2 and 73 cd/A,respectively.The SOLEDs can survive 20000 stretch-release cycles between 0% and 20% tensile strain and 6000 stretch-release cycles between 0% and 60% tensile strain with only 10% EL performance variations.(4)Highly efficient 2D SOLEDs based on ultrathin and ultra-flexible polymer substrate.2D SOLEDs with random buckles were formed by attaching the ultrathin OLEDs on a prestretched elastomeric substrate.The OLEDs did not deteriorate under the effect of anisotropic stress during the 2D random buckles forming process due to the ultra-flexibility of the ultrathin polymer substrate and exhibited excellent 2D stretchability.The 2D SOLEDs can bear tensile strain of 50% in area by biaxial stretching and have efficiency of 79 cd/A under 50% strain,which is the largest efficiency to date to the best of our knowledge.The 2D SOLEDs reported here are mechanically robust.The current efficiency degraded only 1.7% after 100 stretch-release cycles with strains between 0% and 25%.