Spray-spin Coating Polymerization And Film Thermoelectric Properties Of Trithienyl π-conjugated Small Molecules

With the increasing environmental pollution and energy shortage,people are beginning to work on the research of green energy materials.Thermoelectric material is a kind of green energy conversion material,which can use internal solid carrier movement to realize the conversion between thermal energy and electrical energy.Considering the existence of a large amount of industrial waste heat and other forms of natural heat,thermoelectric materials that can realize the conversion between thermal energy and electrical energy have great potential research value.At present,thermoelectric materials can be roughly divided into two categories,inorganic thermoelectric materials and organic thermoelectric materials.Compared with traditional inorganic thermoelectric materials,organic thermoelectric materials are gradually being widely studied because of their advantages of rich resources,light weight,good elasticity,easy processing,and low thermal conductivity.Since the research of organic thermoelectric materials is still in the exploratory stage,the performance of existing materials is temporarily unable to meet their practical applications,so it is still crucial for the development and research of new conductive polymer thermoelectric material systems.In addition,although many researchers have studied the relationship between the molecular structure and properties of conductive polymers.But the relationship between the two is still unclear.This makes it impossible for researchers to achieve high performance of materials through precise design of polymer molecules.In order to achieve some relevant properties of conductive conjugated polymer materials,the structure of traditional conductive polymers needs to be complicated,which may usually involve the expansion of the conjugated plane of the polymer molecule.However,polymer molecules that are too rigid usually have the characteristics of insolubility and insolubility,which is not conducive to further thin film processing of polymer molecules and hinders the practical application of materials.Therefore,it is also very important to develop a new and efficient method for manufacturing conductive polymer films.Inspired by the technology of vapor phase polymerization（VPP）,this paper proposes an efficient polymer film manufacturing method,the vapor phase polymer method,which can realize the rigid molecular trithiophene-based polymer film manufacturing in one step.This article also conducted a preliminary study on the relationship between the molecular structure of these polymers and thermoelectric properties.The main contents are summarized as follows:1.In this paper,through further improvement and optimization of VPP technology,we propose a method for preparing polymer films suitable for rigidπ-conjugated monomers,a spray-spin coating polymer method.Then we compared the bithiophene polymer obtained by the traditional solution oxidative polymerization method and the bithiophene polymer obtained by the electrochemical polymerization method,and found that the spray-spin coating polymerization-like preparation method can achieve polymer film preparation in one step.It not only increases the film-forming properties of the polymer,but also has very good uniformity and low surface roughness（RMS≈2.39 nm）.After optimizing the relevant influencing factors of the spray-spin coating polymerization method,the conductivity is improved by 828.6 times compared to the electrochemically prepared bithiophene-based polymer,and the Seebeck coefficient is increased from 17.32μV K^-1 to 23.10μV K^-1.The spray-spin coating polymerization method proposed in this work effectively solves the problem that rigid polymers are difficult to process further,and provides new feasible ideas for the preparation of conductive polymer films.2.In order to further study the relationship between the molecular structure and properties of trithienyl-based polymers,in this study,alkyl side chains of different lengths were introduced in theβposition of the middle thiophene,and the effect of the alkyl side chain length on the thermoelectric properties of the trithienyl polymer film was investigated.As an important functional side chain,alkyl side chains are often used to modifyπ-conjugated polymer molecules.The study found that the introduction of alkyl side chains will basically not affect the spray-spin coating polymerization of trithienyl monomers and doping of thin films.The introduction of alkyl side chains leads to an increase in the steric hindrance of polymer molecules,which reduces the conductivity of polytrithiophene-based films,but there is almost no significant difference in the Seebeck coefficient.3.On the basis of bis（3,4-ethylenedioxythiophene）,theπ-conjugated structure of the precursor is expanded by introducing the conjugated structure of thiophene（Th）and thiophene（TT）.Then these three polymer films were successfully prepared by spray-spin coating polymerization method,and the effect of polymer molecular structure on film morphology and thermoelectric properties was systematically investigated.The study found that the introduction of Th and TT structures can effectively reduce the RMS value of the film,and the introduction of Th can enhance the orderly packing of polymer molecules.The introduction of the TT structure with strong rigidity results in a relatively low effective conjugation length of the polymer molecules due to the relatively poor solubility of the polymer,which causes the polymer molecules to form a network of microcrystalline regions.The introduction of Th and TT structures can greatly increase the material’s Seebeck value while maintaining the high conductivity of poly（bis（3,4-ethylenedioxythiophene））,while the introduction of TT structure,although its Seebeck coefficient has also been considerably improved,but its conductivity is reduced to only two orders of magnitude.