Synthesis Of Stretchable Electronic Composite Materials And Their Applications In Electroluminescent Devices

Stretchable electronic devices are an important area in the development of current electronic technology.It surpasses the limitation of traditional rigid electronic devices,maintaining stable performance even when the device is subjected to bending,twisting,and stretching.Thanks to the skin-like deformability of stretchable electronic devices,stretchable electronic devices are widely applied in many fields such as electronic skin,soft robots,and biomedical devices,which compensates for the shortcomings of traditional rigid devices.Among them,stretchable electroluminescent devices are an important part of stretchable electronic devices,serving as the information output window of stretchable electronic systems.Among the stretchable light-emitting devices,the ZnS:Cu-based AC electroluminescent device employs a parallel plate capacitor structure,and it will not affect the overall light emission of the device even if the electrode and the fluorescent material are microscopically separated,rendering its natural reliability and durability.However,due to dome disadvantageous factors such as low brightness,high driving voltage,and monotonous display function,the application of ZnS:Cu-based electroluminescent device is restricted beneath the wearability.Accordingly,lowering the driving voltage and completing the display applications of the devices are of great significance to the development of stretchable light emitting devices.This paper starts from the preparation of patterned stretchable transparent electrodes and high-dielectric elastomers,and then the preparation process of stretchable light-emitting display devices is further developed.Finally,a low-voltage driven epidermal display that can be directly attached to the human body is obtained.The main research work of this paper is described as follows:1.Research on preparation of stretchable transparent electrode based on silver nanowires(Ag NWs)and its screen-printing patterning process.The thermal treatment on thermoplastic elastomer-based Ag NW electrode exhibits a double post-treatment effect.On the one hand,it reduces the resistance at the nodes of Ag NWs,while on the other hand,it increases the adhesion between the substrate and the Ag NWs.An inverted patterning technology of Ag NW electrode on the basis of screen-printing is further developed.Screen printing the thermoplastic elastomer solution to obtain the protective layer of the Ag NWs effectively reduces the influence of the polymer on the contact resistance of the Ag NWs.The maximum precision of the Ag NW electrode prepared by this process is 60μm and when the square resistance is 4Ω/sq,the light transmittance reaches 70%.2.Preparation and performance optimization of elastic composite dielectric materials filled with ceramic particles.Focusing on the low dielectric constant of the silicone rubber system widely used in current stretchable AC electroluminescent devices,the dielectric constant of the thermoplastic elastomer system is explored.Among them,the intrinsic dielectric constant of fluoroelastomers exceeds 10,which is much higher than that of commonly used silicone rubber.The dielectric properties of the composite material can be further improved by doping high dielectric barium titanate nano particles.Being modified with polyvinylpyrrolidone(PVP),the barium titanate particles exhibit better dispersibility and polymer affinity.The prepared high-dielectric composite material achieves a dielectric constant between 11 and 65according to the filling volume ratio of the particles,and it shows excellent mechanical properties as well.3.The preparation of stretchable light-emitting devices and the study of the influence of dielectric materials on their light-emitting characteristics.Stretchable electroluminescent devices are prepared using the aforementioned thermoplastic dielectric material.The stretchable device prepared using the pure phase thermoplastic elastomer with higher dielectric constant exhibits higher brightness,and the electroluminescent device prepared using the fluoroelastomer with the highest dielectric constant shows the highest brightness exceeding 1000 cd/m~2.The luminance of devices based on two-phase composite material prepared by mixing the fluororubber with barium titanate will increase with the increase of the dielectric constant,and the highest luminance is obtained when the volume ratio is 30%and meanwhile the dielectric constant reaches 35.When the volume ratio surpasses 30%,the brightness decreases due to the reduced light transmittance of the light-emitting layer and increased dielectric loss of the light-emitting layer resulting from the filling particles.The luminescence characteristics of the light-emitting device prepared with 30%barium titanate filling volume ratio were further studied.The highest brightness is obtained with a driven voltage frequency of 13k Hz,and it firstly realized the luminance more than 100 cd/m~2 with a driven voltage of 35V,satisfying the safety requirement for wearable application.4.Research on the manufacturing process of stretchable AC display.Combing with the softening characteristics of thermoplastic elastomers at high temperatures,the stretchable light-emitting display can be conveniently prepared using layer by layer hot pressing.A butterfly-shaped electroluminescent device is then fabricated employing the above technology,and it can exhibit stable display under various pneumatic conditions.At the same time,an epidermal clock display that can be directly attached to the skin is prepared.Combining with the solution processability of thermoplastic elastomers,a low-cost preparation process for stretchable AC devices based on screen-printing has been developed.Different luminescent inks can be printed accurately by overprinting,and finally a three-color luminous stretchable display device is successfully prepared.The prepared multi-color device can be dynamically displayed during the stretching cycle,showing the great potential of such devices in the practical application of wearable displays.