Fabrication And Application Of Flexible Electronics Based On Porous Materials

Flexible electronics technology is an emerging electronic technology in which thin-film electronic components are fabricated on flexible substrates.Flexible electronic devices can be bendable,compressible or stretchable,thus,they can meet the requirement of the deformation on the human body and machine.They have the functions of wearable,conformal contactable with skin,and even implantable.They are expected to be applied in mobile communications,health monitoring,human bionics,education,and entertainment.Flexible electronics start from bendable devices to stretchable and epidermal devices,which present the challenges for materials such as electronic components materials and electrode materials.Recently,conductive materials with intrinsic flexibility,such as metal nanomaterials,carbon nanomaterials,and organic conductive polymers,have been rapidly developed,providing strong support for the construction of various flexible electronic devices.On the other hand,the design of traditional rigid functional materials into stretchable geometry has also brought new method for flexible electronics.Porous materials have been widely investigated result in the advantages such as low relative density,high specific strength,high specific surface area,lightweight,sound insulation,heat insulation,and good permeability.In particular,porous materials can achieve good transparency,gas permeability,and stretchability,which are adapt to the fabrication procedure of flexible electronic devices.In this dissertation,flexible transparent electrodes,stretchable electrodes,breathable ultra-thin stretchable electrodes,and breathable dielectric materials are prepared from two-dimensional and three-dimensional porous materials and applied to organic optoelectronic devices,strain sensors,electrophysiology?EP?monitoring electrodes,and pressure sensor,respectively.These porous materials are fabricated by the breath figure method and template leaching method.The main research contents and results of this dissertation are as follows:?1?Preparation of porous flexible transparent electrode by breath pattern method and its application in organic optoelectronic devices:In order to increased the uniformity of the pore structure of the metal grid flexible transparent electrode prepared by self-assembly template method,in this session,we proposed honeycomb structure copper mesh transparent electrode prepared by the selective etching the coppe film.The porous polymer membrance prepared by the breath figure method is used as a template for etching.The flexible transparent electrode has good transmittance and low sheet resistance.It has the transmittance of 83.5%with the sheet resistance.28.7?/sq.And The line width is invisible to human eyes?<1?m?and does not generate moire effect.In addition,the haze factor is less than 1%.By depositing an Ag layer and performing surface treatment by ultraviolet-ozone?UV-Ozone?,the work function of the flexible transparent electrode is modifide and applied in the preparation of flexible organic solar cell.The solar cell exhibited a photoelectric conversion efficiency?PCE?of 2.04%,which was similar to that of the device using indium tin oxide?ITO?as an electrode.In addition,the metal mesh flexible transparent electrode can also be used to prepare flexible organic light emitting diodes,which showing its application potential in organic optoelectronic devices.?2?Preparation of stretchable electrode of porous metal thin film by breath figure method nd application in strain sensors:Metal mesh is a stretchable geometric structure.It can be applied in stretchable electrode when compounded with elastic substrates.In this session,a silver grid stretchable transparent electrode with a two-dimensional honeycomb structure was prepared by transfer a metal mesh structure prepared by breathing figure method to a polydimethylsiloxane?PDMS?substrate.The transparent stretchable electrode has the transmittance of 79%with the sheet resistance.26?/sq and a maximum elongation of 35%.The strain sensor prepared with this structure has very high sensitivity.In the range of 0-15%stretching,the resistance changes linearly with strain,and the gauge factor is about 14.3.And the multi-domain phenomenon of the honeycomb metal mesh structure makes the electrode isotropy with strain,so the sensor has an omnidirectional test capability.The sensor demonstrates high sensitivity and quick response ability in real-time detection of finger and muscle movements,detection of fixed frequency and even complex mechanical vibrations?such as vibrations caused by striking glass?.?3?Preparation of porous,breathable,ultra-thin,stretchable electrodes by breath figure method and the application in bioelectrical monitoring:The epidermal electronic needs to have good breathability in the long-term application,but the traditional non-porous substrates do not have this characteristic.In this session,a two-dimensional porous thermoplastic polyurethane elastomer?TPU?film with a through-hole structure is prepared by a breath figure method and the silver nanowires were loaded on the surface by dip coating to prepare a gas-permeable,ultra-thin,stretchable electrode.This electrode has good gas-permeability,and its water vapor permeability reaches 23 mg/cm²·h under the conditions of the ambient temperature of 35?and relative humidity?RH?of 40%±5%.At the same time,it has the sheet resistance of 7.3?/sq with the transmittance of 61%.The resistance change versus strain shows a"programmable"property.This electrode has a good application in epidermal electrodes and human-machine interfaces.The ultra-thin nature of the film enables it to achieve conformal contact with the skin,which can improve the quality of recording biological signals and the comfort of long-term wearing.In electrocardiogram?ECG?and electromyography?EMG?recording,the signals obtained by porous electrode can be comparable to commercial Ag/Ag Cl electrodes.At the same time,it has achieved good results as the electrode of the touch sensor in self-capacitance mode.?4?Preparation of porous dielectric elastomer by template leaching method and its application in pressure sensors:The gas permeability is limited in traditional capacitive pressure sensors.In this session,the template leaching method was applied to prepare a three-dimensional porous dielectric elastomer with high permittivity.The three-dimensional porous dielectric elastomer is composed of polydimethylsiloxane/barium titanate/graphite powder?Graphite/Ba Ti O₃/PDMS?mixed material.The three-dimensional porous dielectric elastomer has high dielectric constant,high gas permeability,and a low compressive modulus.The relative permittivity of this elastic dielectric is about 34,and during the compression process,its permittivity continues to increase.The water vapor permeability of the porous material is about 17 mg/cm²·h,under the ambient temperature of 35?and relative humidity?RH?of 40%±5%,it was applied it to a capacitive pressure sensor to achieve more sensitive pressure sensing.At the same time,the high dielectric constant is also conducive to reducing the working area of the capacitive pressure sensor,allowing us to prepare a 6×6 pressure sensor array on the area of the size of the fingernail,which is used to distinguish the pressure distribution on the surface.