PEDOT:PSS Flexible Thermoelectric Material And Its Applications

In industrial production and our daily lives,emissions from factory boilers,car exhaust and large amounts of generated heat energy cannot be effectively used.How to effectively recycle these low-quality heat continues to receive widespread attention.however,The heat from the human body is also a huge potential energy and is usually ignored.Compared with other energies,the heat generated by the human body is very stable and easy to recycle.Thermoelectric functional material can directly convert heat into electricity through internal carrier movement.It has a good application prospect in solving waste heat recovery.Thermoelectric devices made of thermoelectric materials display a variety of advantages,such as absence of moving parts,no noise pollution,and long operating lifetime,over most other energy devices.Compared with inorganic thermoelectric materials,organic thermoelectric materials have the advantages of light weight,non-toxicity,abundant raw materials and easy industrial large-scale preparation,which is beneficial to the development of portable and wearable thermoelectric devices.Among them,poly 3,4-ethylenedioxythiophene/polystyrene sulfonate(PEDOT:PSS)is a new material with potential in high conductive polymers.PEDOT:PSS can be stably dispersed in water,and its aqueous solution can be easily prepared onto a glass substrate or a flexible base.The formed thermoelectric film has good mechanical properties and is environmental friendly.However,the original film has low thermoelectric properties,whose conductivity is less than 1 S/cm,and the Seebeck coefficient is only 15?V/K.Thus,it is urgent to find a suitable way to improve its thermoelectric performance.A large number of previous studies have shown that the conductivity can be improved by removing excess PSS,so that the thermoelectric performance is significantly improved.In addition,the Seebeck coefficient of the material can be improved by reducing the doping level or electrochemical methods.In this paper,simply add the appropriate amount of sulfonic acids solution in the PEDOT:PSS aqueous solution,such as:methanesulfonic acid,benzenesulfonic acid,4-chlorobenzenesulfonic acid,p-hydroxybenzenesulfonic acid,p-toluenesulfonic acid,ethylbenzenesulfonic acid naphthalene sulfonic acid and camphorsulfonic acid have different conductivity enhancement,while the Seebeck coefficients remain basically unchanged.Among them,the benzenesulfonic acid solution has the best effect on the conductivity improvement.After extensive experiments,we found the best filmmaking process parameters,such as the stirring speed and stirring time of the doping solution,and the annealing temperature after film formation.The highest electrical conductivity reaches 1996 S/cm when doped with 0.06 mol/L benzenesulfonic acid.At the same time,in order to explore the difference in conductivity of different sulfonic acids,we investigated whether the pH of and the acidity coefficient(pKa)of the sulfonic acid have an effect on its conductivity.Finally,studies have shown that sulfonic acids with different functional groups have a significant effect on the conductivity caused by functional groups.The PEDOT:PSS film doped with benzenesulfonic acid was further treated with a mixed solution of water and hydrazine and a mixed solution of dimethyl sulfoxide and hydrazine to adjust the oxidation level.The carrier concentration of the conductive polymer is brought to an optimum value to obtain the maximum power factor.An optimal PF of 203.1?W/(m K~2)is achieved when treated with DMSO/HZ mixed solution.Analysis of the experimental results by atomic force microscopy,Raman spectroscopy,cyclic voltammetry,UV-Vis spectrophotometer and UV photoelectron spectroscopy,it shows the doping of benzenesulfonic acid increased the mobility and oxidation level of the carrier,resulting in conductivity enhancement.The post-treatment of HZ allows the carrier concentration of the PEDOT:PSS film to be debugged to an optimum level,thereby optimizing the power factor of the material.This paper also studies the applicability of the thermoelectric performance improvement method in the application of thermoelectric devices.We used a vacuum filtration method to prepare a pre-doped PEDOT:PSS solution on a filter paper to form a film,and then perform the above post-treatment.The film has excellent flexibility and mechanical properties and is made into a flexible thermoelectric wristband.When attached to human skin,a thermal voltage of 4.6 mV can be generated.As the temperature difference increases,it also exhibits a good linear response.This also confirms our approach to great potential for high performance organic thermoelectric materials for large scale industrial applications.