Synthesis And Performance Study Of Small-sized Anion Doped Poly(3,4-ethylenedioxythiophene)-Based Thermoelectric Materials

As one of the novel energy materials,polymeric thermoelectric materials exhibit lighter weight,lower cost,better flexibility and lower thermoconductivity compared to conventional inorganic thermoelectric materials,which have a wide application prospect.Among which,poly?3,4-ethylenedioxythiophene??PEDOT?exhibits the highest performance and draws great attention among researchers.Compared to the commercially available PEDOT:polystyrenesulfonate?PEDOT:PSS?,small-sized anion doped PEDOT?S-PEDOT?exhibits lower steric effect and more ordered structure and is more capable of being a base material for thermoelectric applications.However,due to some factors such as bad reaction controllability,inhibitor dependence,low film thickness and negative increment of electrical conductivity with increasing film thickness,S-PEDOTs are currently not suitable for practical applications.Furthermore,synthesizing polymer-inorganic composite materials is a commom route to optimizing the performance.However,PEDOT-based composites suffers problems such as particle sedimentation,oxidation and agglomeration and exhibit limiled performance enhancement.Focusing on these problems,this work begins with developing a self-inhibited polymerization?SIP?method,which realized the facile synthesis of high performance S-PEDOT thick film.After that,focusing on role of anion,we systematically studied the influence of anion basicity and steric effect on the polymerization and the structure of the polymer.And standards for optimized counter-ion/oxidant are established.Finally,by applying SIP method in a novel Te?IV?-based oxidant,high performance S-PEDOT-Te nanoparticle?quantum dot?composite films with high density are successfully synthesized,which brings new strategies for the synthesis of PEDOT-based composite materials.1.Self-inhibited polymerization and chemical reduction of weakly basic acid doped PEDOTsS-PEDOTs are synthesized via solution casting polymerization?SC?or vapor phase polymerization?VPP?using novel highly soluble oxidants containing weakly basic anions.The weakly basic anion can substitute the role of base inhibitor and ensure the stability of the reaction,while the high solubility of the oxidant can avoid the crystallization of the oxidant and substitute the role of anti-crystallization inhibitor.The resulted purer film exhibits?m-scale thickness,which was almost 10 times thicker than the films synthesized through conventional methods.The films exhibit a maximum power factor of 69.6?W/m K²,which was higher than the power factors of most of the reported fully doped S-PEDOT films.Finally,the power factor of the film is optimized to 77.2?W/mK² by reducing with acidified phenylhydrazine.2.Study of the mechanism of influence of anion on the structure and performance of S-PEDOTsAnion plays a key role in both the polymerization and the structure of PEDOT.As a precursor,anions greatly influence the reaction rate and oxidant solubility.In its role as a counter-ion,the anions also affect chain conductance and crystal growth.Higher anion basicity brings about greater inhibition on H⁺and Fe³⁺concentrations and the reaction is more controllable.Therefore,the doping level and electrical conductivity will increase.On the other hand,lower basicity results in enhanced stability of bipolaron and the higher potential of electrical conductivity.Besides,the steric effect of anion will affect the degree of structural order and the crystallization of the polymer.The electrical performance dropped with increasing steric effect.As a result,the facile synthesis of high performance S-PEDOT thick film requires doping anion with low steric effect,weak basicity and high solubility.3.Synchronized production and performance optimization of PEDOT-Te nanocomposite filmsBased on SIP method,by introducing TeCl₄ as another oxidant,one-step synthesis of high performance PEDOT:DBSA/Cl-Te thick film is achieved.The synchronized production of PEDOT and Te results films containing evenly distributed and well-protected nanoparticles.The concentration and particle sized of Te are adjusted through controlling the Te?IV?/Fe?III?ratio and<5 nm Te quantum dots are formed.Through the effective phonon scattering by the quantum dots,the Seebeck coefficient is significantly increased at low Te loading.The Cl^-/DBSA^-codoping results in higher doping level and electrical conductivity than single anion doping.As a result,at low Te concentrations as 2.1-5.8 wt%,the films exhibits high power factors¹00?W/mK²,which are 50%higher compared to a pure PEDOT:DBSA film and is the higer than most PEDOT-based composite materials.