Optimizing The Thermoelectric Performance Of PEDOT:PSS/Inorganic Films Based On Composite And Solvent-treatment

With the fast development of human economy and society,people are faced with a series of troubles such as environmental pollution and energy shortage.The thermoelectric?TE?conversion technology based on thermoelectric materials,which can directly convert heat energy to electric energy through the directional movement of charge carriers,is a typical representative of clean energy technology.And it has been widely concerned by scientists.Although inorganic TE material due to its high electric transport performance and high Seebeck coefficient has become the main research object in TE field for many years,there still exist some drawbacks such as rarely elements,toxicity,high thermal conductivity and so on.Researchers have shifted their attention to organic TE material with rich resources,low toxicity,and low thermal conductivity.As an important component of organic TE materials,conducting polymers,especiallyforpoly?3,4-ethylenedioxythiophene?:poly?4-styrenesulfonate??PEDOT:PSS?,are playing an increasingly important role in TE materials due to their easy preparation,low weight,good elasticity and good film-forming property.It is noted that conducting polymers have large adjustable electrical conductivity(10^-710³S cm^-1)and Seebeck coefficient(10¹¹0³?V K^-1).It is the key point of conducting polymers to obtain high electrical conductivity and high Seebeck coefficient,simultaneously.Recently,the research of organic/inorganic composites has become an crucial direction for the development of TE materials,based on quantum confinement effect,interfacial energy filtering effect and phonon scattering.Organic/inorganic composites mainly achieve the equilibrium of electrical conductivity and Seebeck coefficient to obtain high TE power factor.However,existing composites and methods inevitably result in the deficiency of low electrical conductivity or low Seebeck coefficient.How to utilize the inorganic high Seebeck coefficient for optimizing the power factor with maintaining or improving the electrical conductivity of the composite film is a difficult problem.In this work,we have fabricated PEDOT:PSS/inorganic composite films via different kinds of film-forming methods.The aim is to improve the Seebeck coefficient of composite film first.Then regulate the surface chemical structure by solvent post-processing to compensate the influence of carrier concentration on the electrical conductivity,so as to further optimize the TE performance of the composite film.The main research contents are summarized as follows:1.In this chapter,a series of PEDOT:PSS/BNNSs composite films were prepared by dilution-filtration method with boron nitride nanosheets?BNNSs?,and their TE performance was further optimized by dual-organic solvent treatment.BN is a typical two-dimensional?2D?structure material with high Seebeck coefficient.In this study,multilayer BNNSs were obtained by organic solvent?DMF?liquid exfoliated method.By optimizing the ratio of conducting PEDOT:PSS to BNNSs,we investigated the effect of BNNSs content on the TE performance of composites films.It was founded that when the content of BNNSs is 5%,the TE performance of the composite film exhibited a significantly improved,which depended on the energy filtering effect improving the interfacial scattering of charge carriers,and the solvent-induced screen effect led the conformation rearrangement of PEDOT:PSS molecules.The electrical conductivity of the composite film was further improved after DMSO solvent post-progressing,resulting from the removal of part of the non-conducting PSS and making the conductive PEDOT particles exposed.In this chapter,2D multilayer BNNSs composite and organic solvent post-treatment were proposed,resulting in a highly enhanced power factor(100.1?W m^-1 K^-2)and ZT value?0.12?.This method provides a new method for improving the TE performance of PEDOT:PSS.2.A series of PEDOT:PSS/SiC-NWs composite films were prepared by dilution-filtration and dip-coating methods.The effects of two kinds of SiC-NWs content on the TE performance of the composite films were investigated systematically.Compared with bulk SiC?b-SiC?,high purity SiC-NWs?p-SiC-NWs?exhibits a better effect on the improvement of the TE performance of PEDOT:PSS.The electrical conductivity and Seebeck coefficient of the composite film increased simultaneously,when 3%content of p-SiC-NWs embedded into PEDOT:PSS matrix.The optimized power factor achieved to be 67.7?W m^-1 K^-2.The results show that the significantly enhanced Seebeck coefficient of the composite films is mainly caused by the quantum confinement effect and the interfacial energy filtering effect at the interfaces.Meanwhile,a small amount of p-SiC-NWs dispersed in the PEDOT:PSS matrix may change the morphology and structure of PEDOT:PSS,thus improving the charge carrier transport performance.Furthermore,we introduced concentrated H₂SO₄and H₃PO₄ post-treatment to optimizing the TE performance of the composite film fabricated by dilution-filtration and dip-coating methods.The results show that the power factor of the PEDOT:PSS/p-SiC-NWs₃ dilution-filtration composite film post-treated by concentrated H₂SO₄ exhibits a higher enhanced than that of H₃PO₄post-treated.The maximum power factor is as high as 128.3?W m^-1 K^-2.With the thermal conductivity measured to be 0.23 W m^-1 K^-1,the figure of merit?ZT?was calculated to be 0.17.Finally,a flexible TE generator consisted by 10 legs of the as-prepared H₂SO₄ post-treated PEDOT:PSS/p-SiC-NWs₃ composite films has been prepared.At the temperature different??35?T?to 100K,the maximum output power of the optimized composite film presents a 5 times higher than that of pure PEDOT:PSS film.The experimental results show that SiC-NWs composite combined with inorganic acid post-treatment can effectively improve the TE performance of PEDOT:PSS.3.In order to further explore the influence of inorganic nano-materials on the TE improvement of PEDOT:PSS,in this chapter,a layered oxide TE material,(Ca_1-xAg_x)₃Co₄O₉,was prepared by sol-gel method.The TE performance of PEDOT:PSS/(Ca_1-xAg_x)₃Co₄O₉ composite films were investigated systemically.The results showed that the TE properties of(Ca_0.85Ag_0.15)₃Co₄O₉ were obviously superior to that of Ca₃Co₄O₉,and had a significant effect on the TE performance of PEDOT:PSS films.When the content of(Ca_0.85Ag_0.15)₃Co₄O₉ is 5%,the TE power factor of the composite film was 42.4?W m^-1 K^-2,which has less effect on the TE performance of PEDOT:PSS composite with BNNSs and SiC-NWs.After that,we compared the TE enhancement of the PEDOT:PSS/(Ca_1-xAg_x)₃Co₄O₉ composite film by concentrated H₂SO₄ and DMSO solvent.Noted that the composite film post-treated by concentrated H₂SO₄ exhibits a better mechanical flexibility.After flexed for 1000 blending times,the power factor was still up to the original 96%.The maximum TE power factor is improved to 75.2?W m^-1 K^-2,which is 3 times of that of pure PEDOT:PSS film.Based on the good flexibility and TE performance of the optimized composite films,a novel palm-power TE generator has been designed and fabricated.The output power of 36 nW is obtained by using the temperature difference between human body and environment,which provides a new idea for the potential application of wearable TE generator.4.In this chapter,a method of integrating composite and solvent treatment was proposed to improve and optimize the TE properties of PEDOT:PSS.A series of PEDOT:PSS/ce-MoS₂ heterostructure films were fabricated by layer-by-layer?Lb L?assembly and spin-coating method.We systematically investigated the chemical exfoliated ce-MoS₂ dispersed in DMSO solvent on the improvement of the TE properties of PEDOT:PSS Lb L assembled films.The experimental results show that the negative charged ce-MoS₂ facilitated the formation of heterostructure TE films with the positive charged PEDOT and reduced the oxidation level of PEDOT.Hence,PEDOT:PSS/ce-MoS₂ composite films achieved a simultaneously enhanced electrical conductivity(0.3⁸67 S cm^-1)and Seebeck coefficient(11.4²1.9?V K^-1).It is because that during the Lb L assembly process,ce-MoS₂ increases the energy barrier at the interface and effectively filters out some low energy charge carriers,leading to an enhanced Seebeck coefficient.Meanwhile,DMSO worked as dispersion solvent not only remove part of the non-conducting PSS chains,but also make the conformation arrangement of PEDOT:PSS,leading to an enhanced electrical conductivity.The significantly enhanced TE performance of PEDOT:PSS was achieved via effective integration of composite and solvent treatment methods,which may provide a new reference for obtaining high performance composite TE films.5.Based on the fact that aerogels often have low thermal conductivity,in this chapter,a series of PEDOT:PSS/Te nanowires?PEDOT:PSS/Te-NWs?aerogel composite films were fabricated by freeze-drying method,and their TE properties were optimized by DMSO vapor annealing post-treatment.Firstly,the effect of different organic solvents addition on the TE properties of PEDOT:PSS aerogel film was investigated.It was found that the PEDOT:PSS aerogel film added with NMP exhibits a large power factor of 1.24?W m^-1 K^-2.Adding 30%content of Te-NWs into PEDOT:PSS aerogel film,the TE power factor increased to 3.6?W m^-1 K^-2.In this complex aerogel composite system,there exists about 80%parallel connected model in charge carrier transport mechanism.The TE properties of the PEDOT:PSS/Te-NWs₃₀ aerogel composite film were further optimized by DMSO vapor annealing treatment.Based on the thermal conductivity measured to be 0.12 W m^-1 K^-1 about one time lower than common composite film,the optimized ZT value reached 2.8×10^-2.The experimental results show that the PEDOT:PSS/Te-NWs aerogel composite film assistanted with DMSO vapor annealing treatment can improve the Seebeck coefficient and electrical conductivity,and decrease the thermal conductivity.It is another effective method to obtain high TE performance composite film.To sum up,in this thesis,we have fabricated a series of PEDOT:PSS-based composite films with different inorganic high Seebeck coefficient materials addition,for optimizing the TE power factor of PEDOT:PSS.Combined with solvent?inorganic acid and organic solvent?treatment,the TE properties of the PEDOT:PSS/inorganic composite films were further optimized.The influences of inorganic nano-materials on the Seebeck coefficient of the composite films and the interfacial barrier of PEDOT:PSS/inorganic on the charge carrier transport mechanism were investigated systematically.The experimental results show that inorganic nano-materials combined with solvent treatment can significantly improve the TE performance of PEDOT:PSS.A preliminary study of wearable flexible TE generator was carried out in order to provide a reference for the application and development of TE generator.