Study On Self-healing Flexible Alternating Current Electroluminescent Devices For Wearable Electronics

Flexible wearable electronic technology has changed the physical form of traditional rigid electronics.It shows wild application in the fields of flexible display and lighting,chemical and biological sensing,artificial intelligence,human-computer interfacing,and wearable devices,which greatly promotes the integration of manmachine-object.Flexible alternating current electroluminescent(ACEL)devices have the characteristics of lightweight,portability,large-area processing,and high flexibility.As an essential part of the flexible wearable system,it promotes the development of the Internet of things(Io T).Nevertheless,the inevitable external stimulation can lead to equipment damage,and then lead to device performance failure and service life reduction.Therefore,the development of multifunctional ACEL devices with selfhealing function can not only ensure the rapid recovery of the device performance under external damage,but also increase the service life of the device and reduce the maintenance cost.At the same time,the trend of miniaturization,flexibility,and ubiquity of modern wearable systems not only puts forward higher requirements for the preparation process,luminescent performance,flexibility,compatibility,reliability and stability of devices,but also brings great challenges to the traditional energy driving mode.TENG based on triboelectrification and electrostatic induction coupling effect can collect all kinds of low-quality energy from the surrounding environment in real-time to drive miniaturized electronic devices.It has the advantages of simple structure,wide material sources,simple operation,strong mobility and environmental friendly.It has great application prospects in the fields of information communication,self-powered sensing,and flexible display.In this paper,the self-healing ACEL device and TENG are integrated to realize the self-powered and self-healing multi-color display system.The luminous intensity of the ACEL device is enhanced by adjusting the dielectric constant of emissive layer with MXene.The relevant results are as follows:(1)Highly transparent,stretchable and self-healing material(SSH-PDMS)was prepared by introducing the dynamic imine bond into PDMS.The transmittance of the film was as high as 96% in the entire visible range;an ultra-high stretchability of 2500%at the uniaxial tensile rate of 20 mm/min and high healing efficiency of 96% at room temperature have been realized.The existence of imine bonds in self-healing elastomer,as confirmed by Fourier transform infrared spectroscopy(FTIR),might be responsible for this excellent self-healing performance.(2)A stretchable and self-healing electrode(SSH-electrode)was prepared by loading the single-walled carbon nanotubes(SWCNTs)thin films on SSH-PDMS;three Zn S based electroluminescent phosphors(B-Zn S,G-Zn S,O-Zn S)were dispersed in SSH-PDMS to prepare emission layers with different luminescence colors.The surface morphology,crystal structure,chemical composition,and luminescence properties of the SSH-electrode and Zn S-based electroluminescent powder were investigated,as well as their self-healing performance.The self-healing ACEL device with a sandwich structure was fabricated,and the factors affecting the EL performance were studied.The EL intensity increases with the increase of voltage and phosphor concentration;while exhibits a volcano-shaped curve with the increase of tensile strain.When stretched to 200% of its original length,the brightness of the ACEL device reaches its maximum value.The ACEL device remains stable EL output even after1000 repetitive stretch-release cycles.(3)Contact-separation TENG was fabricated by using Cu and PTFE films as positive and negative friction layers,respectively.The output open-circuit voltage and short-circuit current are 175 V and 10 μA,respectively.With the increase of external load resistance,the output voltage increases while the current decreases.As for the optimized external resistance of about 100 MΩ,the output power of TENG reaches its maximum of 150 μW.This well matches the impedance value of the ACEL device in our work.Multi-color ACEL arrays were realized by utilizing the patterned electrodes and multiple phosphor-containing dielectric layers.The self-healing ACEL device is integrated with TENG to obtain a self-healing and self-powered multi-color display device.(4)The influences of MXene concentration(0 wt% ～ 1 wt%)on the EL intensity of self-healing ACEL devices were investigated.Compared with those without MXene,the EL intensity of MXene-doped ACEL devices is significantly enhanced;and the EL intensity reaches its maximum value when the MXene concentration is 0.25 wt%,regardless of the driving voltage.For an optimized situation,the ACEL device with0.25 wt% MXene driven at 250 V delivers an enhanced EL intensity approximately 5times higher than that of the ACEL devices without MXene.In order to further understand the role of incorporated MXene to enhance the EL output,the spatial distribution of the electric potential and field strength have been studied by finite element analysis simulation.The dielectric constants of emission layers with different concentrations of MXene were calculated.The relative dielectric constant increases when the MXene concentration is increased from 0 wt% to 0.25 wt%;for the MXene concentration greater than 0.25 wt%,the relative dielectric constant decreases due to the percolation limit induced by high MXene loading ratio.