Flexible Electrodes: Printing Preparation,Functional Regulation And Application

Recently,flexible/stretchable optoelectronics have attracted extensive attention from industry and academia because of their fascinating excellent properties,such as lightweight,portability,bendability,conformability and durability.As the basic components of optoelectronic devices,conductive electrodes have great influence on device performance.Single-crystal silicon semiconductors,printed circuit boards?PCBs?and indium tin oxides?ITOs?are nowadays the most widely used conductive electrodes.However,they are brittle,cost-intensive,and usually fabricated via tedious and complicated process.Thus,they are unsuitable for emerging flexible/stretchable optoelectronic devices.This dissertation is dedicated to developing new electrode materials and novel manufacturing techniques to fabricate conductive electrodes/circuits in a facile,low-cost and scalable way.The research contents mainly include synthesis of electrode materials,formulation of inks,optimization of process,preparation of electrodes,fabrication of devices and characterization of performace.In this work,a facile,low-cost and versatile methodology was developed to enhance the resolution of inkjet printing,involving process optimization as well as substrate modification and treatment.The line width of the inkjet-printed silver lines was successfully reduced to 1/3 of the original value using this methodology.Large-area flexible circuits with delicate pattern and good morphology were thus fabricated.The resultant flexible circuits showed excellent electrical conductivity as low as 4.5?sq^-1 and strong tolerance to mechanical bending.The simple methodology is also applicable to substrates with various wettability,which suggests a general strategy to enhance the printing quality of inkjet printing for manufacturing high-performance large-area flexible electronics.However,the inkjet printed circuits demonstrate very low optical transparency in the visible region and thus are not very suitable for thin-film optoelectronic devices,such as organic solar cells?OSCs?and organic light-emitting diodes?OLEDs?.In this regard,we then prepared high-performance PEDOT:PSS thin-film transparent electrodes.Considering the original PEDOT:PSS shows comparatively low electrical conductivity and is unsuitable for inkjet printing,we firstly modulated the properties of PEDOT:PSS inks.The electrical conductivity of PEDOT:PSS was successfully enhanced by 2³ magnitudes by doping moderate amount of high boiling point solvent,such as ethylene glycol?EG?.Moreover,the viscocity and the surface tension of PEDOT:PSS solution was modulated by adding a fraction of surfactants and its wettability on substrates was also improved,which was desirable for subsequent multi-layer coating and inkjet printing of PEDOT:PSS.In addition,the optoelectronic property(Rs:36?sq^-1,T:82%)and the electrochemical performance(4.72 mF cm^-2)were improved by controlling the number of PEDOT:PSS layers.Besides,the PEDOT:PSS transparent electrodes also showed superior mechanical flexibility.Flexible transparent all solid-state supercapacitors were fabricated using the resultant PEDOT:PSS films as electrodes.The supercapacitors demonstrated comparatively excellent comprehensive performance.We then inkjet printed PEDOT:PSS/Ag grids hybrid electrodes to further enhance the optoelectronic performance of PEDOT:PSS.Hybrid electrodes can not only make full use of the advantages of single materials but also effectively compensate their disadvatages.As a consequence,they demonstrated better comprehensive performance than that of PEDOT:PSS or Ag grids alone,including more superior optoelectronical property(Rs:12?sq^-1,T:89%),better electrochemical performance(7.36 mF cm^-2),higher anti-oxidation capability and comparatively good flexibity.Flexible transparent aesthetic all solid-state supercapacitors were fabricated using the PEDOT:PSS/Ag grids as both current collectors and electrodes.Compared with bendable optoelectronic devices,stretchable optoelectronic devices require transparent electrodes with more excellent mechanical compliance,such as stretchability more than bendability.Thus,we fabricated stretchable AgNWs/PDMS transparent electrodes via transferring AgNWs networks and embedding them beneath the surface of PDMS substrate.The optical transmittance and the electrical conductivity could be optimized via controlling the thickness of the conductive layer.The as-fabricated AgNWs/PDMS transparent electrodes not only exhibited superior optoelectronic performance but also manfesited quite high stretchability,showing great applicability in the emerging wearable optoelectronic devices.