Study On Mechanism And Application Of Doped Poly(3,4-ethylenedioxythiophene):Poly(Styrene Sulfonate)

As a traditional transparent electrode,highly conductive indium tin oxide(ITO)has been widely used in various fields,such as solar cells,luminescent device.With the development of technology,there is an increasing demand for flexible wearable electronic devices.However,ITO has some disadvantages such as poor mechanical properties and hardly to be bended,which leads it unable to be used in flexible devices.In addition,ITO contains the rare metal indium,which increases the cost of the electronic devices.Researchers find new materials to overcome above-mentioned disadvantages,such as metal nanowires,graphene,carbon nanotubes and conductive polymers.Among them,poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)has received wide attention in the field of flexible transparent electrodes.PEDOT:PSS is not only easy to process,but also has good mechanical flexibility,high light transmittance,environmental stability.It has been widely studied and applied in various fields,such as supercapacitors,thermoelectric materials,photovoltaic devices and so on.Nevertheless,the conductivity of pristine films is lower 1 S/cm,which is far behind ITO.Researchers continuously attempt various methods to improve the conductivity of PEDOT:PSS.The practices to improve the conductivity of PEDOT:PSS films focus on treating the films with organic acids,inorganic acids,surfactants and organic agents.The common treated processes include the post-treating and doping of PEDOT:PSS films,which can increase the conductivity of PEDOT: PSS film by about 3 ? 4 orders of magnitude.Most researchers use the particular acid reagent or organic reagent to post-treat PEDOT:PSS films.Although this method can lead to increase the conductivity,the reason why various acid obtained different results is worth further exploring in these researches.In addition,most treated practice is relatively tedious and expensive,and it is incompatible with flexible devices and industrial-scale fabrication.In view of the mechanism and treatment problems existing in the current research,this research chooses a series of representative inorganic acids as the dopant,such as sulfuric acid,phosphorous acid,perchloric acid,phosphate,etc.The optimized PEDOT:PSS films exhibit high conductivity of 2244 S/cm through low concentration doping and simple spin coating method.In addition,its square resistance of 244 K?/sq reduced to 55 ?/sq,and the light transmittance about 87% at 550 nm.Simultaneously,the stability of conductivity can be maintained for 1000 h.Furthermore,organic photovoltaic devices are prepared by using it as a transparent electrode,and a relatively high photoelectric conversion efficiency(3.13%)is obtained,which was more than 80%of the efficiency(3.84%)of the standard organic photovoltaic devices based on ITO.In addition,the efficiency of flexible organic photovoltaic devices based on PET also reached 1.34%,which was also improved compared with the device efficiency(0.58%)based on rigid substrate with pristine PEDOT:PSS film.It is clear that this method has feasibility and application potential.According to the difference of doping results among different acids,this research analyzes the relationship between acid physicochemical properties and conductivity values.We realize that the acid with a low acid dissociation constant(pKa),a high boiling point(Tb)and a low softness parameter of anion is effective in increasing conductivity.Specially,the acid with aforementioned character is effective in inducing phase separation between PEDOT and PSS,which lead the conductive PEDOT long-chain exposed.Simultaneously,it extends from the coil state to the straight chain state,which greatly improves the carrier mobility of PEDOT:PSS film.In addition,if the acid possesses oxidativity,it is able to increase the carrier concentration in PEDOT:PSS film,which could also enhance conductivity of PEDOT:PSS.This research compares the differences among different acids to obtain internal key mechanism,which has a certain reference significance for the subsequent researchers when choosing acid dopants.