Research And Application Of PEDOT:PSS Flexible Transparent Electrode

Printed electronics that utilizes a set of functional inks and printing techniques to manufacture electronic devices is becoming an emerging technology,with advantages in mass producing large-area,flexible,light weight,and portable devices at low cost.In many of these printed electronics,at least one electrode required to be transparent in order to emit or harvest light by the devices.Currently indium tin oxide?ITO?coated on rigid glass is used as the standard transparent electrode,LED,light emitting diodes and other electronic devices.However,the mechanical properties of ITO are poor.If it is bent,it will break,which limits its application to flexible devices.And indium of ITO is a rare metal,resulting in high cost of some optoelectronic devices.In summary,ITO can not meet the new requirements of people on the flexibility of the device,so it is urgent to find new materials to replace it.Now many researchers are studying graphene,thin-film metals,metal mesh and carbon nanotubes and other materials to replace ITO.Among them,poly 3,4-ethylenedioxythiophene/polystyrene sulfonate?PEDOT:PSS?is a new material which have potential to replace ITO.PEDOT:PSS is a stable suspension.The suspension can be prepared on a glass substrate or a flexible substrate to form a light blue transparent conductive film.The film is not only easy to process,but also has good mechanical properties,high transmittance,heat resistant,environment-friendly and other advantages.However,the original film suffer a low conductivity less than 1S/cm,so it is necessary to find a suitable method to improve its conductivity.A large number of studies have shown that the use of organic acids,inorganic acids,surfactants and salt solutions to treat PEDOT:PSS,which can increase the conductivity of PEDOT:PSS film by about 2-3 orders of magnitude.In this paper,we use of chloroplatinic acid,dimethyl sulfoxide?DMSO?and ethylene glycol?EG?to modify the PEDOT:PSS solution,and use this flexible electrode to a flexible touch screen.Through a large number of experiments,we have found the best parameters of the process,such as the stirring speed and stirring time of the solution,as well as the rotational speed of the gluing machine and the temperature of the heating table.The experimental data show that when PEDOT:PSS solution is treated with 0.035 mol/L chloroplatinic acid,The film formed by the sizing machine and finally the PEDOT:PSS film annealed at110°C,it can increase the conductivity of the film by four orders of magnitude.The conductivity of the film reached 1194 S/cm.The sheet resistance of the PEDOT:PSS film decreased from 116 K?/sq to 41?/sq,and the transmittance at 550 nm was 85%.If the film use in commercial,the FoM must higher than 35,and the FoM of the H₂PtCl₆-doped PEDOT:PSS film can reach 47.This conductive film was prepared on a flexible substrate,and the stability of the film was tested for one month,and it was found that the sheet resistance of the film unchanged.The mechanical properties of the film were also tested by bending the film with different times.The reasons for the increase in conductivity of the PEDOT:PSS thin film were analyzed by characterization methods such as microscopy,X-ray photoelectron spectroscopy,Raman and Fourier transform infrared spectroscopy.The results show that H₂PtCl₆ can oxidize PEDOT to create more charge carriers when it is reduced to PtCl₂.On the other hand,H₂PtCl₆ is effective in reducing the Columbic interaction between PEDOT and PSS,thus causing phase separation and conformational change of the PEDOT chains,which change from coiled to a linear/extended-coil morphology,and from a benzoid to a quinoid conformation.This work paves the way to directly print highly conductive transparent electrode in high-throughput and low cost.This article also investigated the application of conductive film on flexible touch screens.First,we investigated the preparation and cleaning process of flexible substrates.A method for preparing a flexible conductive film by using a screen printing technique was studied.We can get a rough surface through screen printing technology,and the shetet resistance of the film is 130k?/sq.In the later period,the original solution was improved by doping with sulfuric acid,and the film was prepared using a coating technique.Through the improvement of the solution and the optimization of the preparation process,a uniform flexible transparent conductive film can be prepared by the coating technique.We apply this film to touch screens,which perform well in mechanical and stability tests.The sheet resistance of the film is 120?/sq,and the transmittance of the film can reach 89%.This shows that the PEDOT:PSS film has good potential as a flexible transparent electrode.