The Wetting Transfer Method Of PEDOT:PSS Films With Highly Conductivity And Influences Of Treatment On Thermoelectric Properties Of The Films

With the development of society,exploiting new energy conversion materials becomes predominant for the shortage in fossil fuels and environmental pollution.Thermoelectric?TE?materials are eco-friendly energy materials with capability to directly convert thermal energy to electricity,which was widely applied to cooling or electrical generation.Traditional inorganic TE materials have excellent energy conversion properties,yet their wide application is severely hindered by toxic nature,high cost and complex preparation process.Nevertheless,flexible organic TE thin film materials present promising potential for their light weight,easy preparation and renewable nature.As one of the most widely studied organic TE materials,poly?3,4-ethylenedioxythiophene?:poly?styrenesulfonate??PEDOT:PSS?become a research hotspot for their high electrical conductivity and low thermal conductivity.TE performance of PEDOT:PSS is closely associated with microtopography,conformation and configuration,oxidation level and crystalline structure of PEDOT chains.Appropriate regulating these factors is of great significance to achieve high TE performance.Especially the configuration of PEDOT chains serve as a dominant factor.The original core-shell structure of PEDOT:PSS would suppress the charge transfer.After interact with organic solvents,alkali,acid or ionic liquids?ILs?,the configuration of PEDOT chains would gradually change from coil to extended or linear structure,consequently leading to a sharp increase of carrier mobility as well as the electrical conductivity and Seebeck coefficient.This current thesis is mainly focused on appropriate regulation of conformation and configuration as well as the oxidation level of PEDOT chains to achieve high TE performance.Furthermore,a new preparation and transfer method of PEDOT:PSS film,which would offer PEDOT:PSS thin film more modification means and even wider application.1.EtOH with low boiling point and dimethyl sulfoxide?DMSO?with high boiling point were employed to dilute aqueous PEDOT:PSS solution,which was subsequently vacuum-filtrated to form homogeneous polymer film with crystal structure.Coulomb interaction between PEDOT and PSS chains were weakened during dilution process,consequently leading to a conformation change upon PEDOT chains from coil to linear.Dilution with organic solution was proven to be a more effective method to regulate PEDOT chains structure compared with traditional doping or organic solvent dipping.Furthermore,as-prepared PEDOT:PSS thin film was transferred to different substrate removing the limitation for post-treatment method.Sulfuric acid dipping would prompt orderly arrangement,crystalline and grain of PEDOT chains,facilitating charge transfer among PEDOT chains.The electric conductivity was effectively elevated(?=2722.41 S cm^-1),consequently leading to an improved power factor(PF=64.3?W m^-1 K^-2).After bended for 1000times,the electrical conductivity maintained almost the same,presenting a good flexibility for wide application.2.Polyethylenimine ethoxylated?PEIE?with abundant imino groups is an effective reductant,whose reducibility can be regulated via hydroxylation to control reaction rate.Meanwhile,sulfuric acid could act as an effective oxidant to control the oxidation level and molecular arrangement of PEDOT:PSS for improving electrical conductivity.In this chapter,we utilize PEIE/ethylene glycol?EG?hybrid solution could obviously prompt Seebeck coefficient of PEDOT:PSS thin film without remarkable sacrifice of electrical conductivity.Combined interaction with concentrated sulfuric acid and PEIE balances the electrical conductivity and Seebeck coefficient.Furthermore,dipping with PEIE/EG and concentrated sulfuric acid could effectively make PEDOT chains as edge-on arrangement,prompting the formation of PEDOT crystalline.The electrical conductivity and Seebeck coefficient are2770.7 S cm^-1 and 21.87?V K^-1 respectively,subsequently leading to an optimal power factor as 133.0?W m^-1 K^-2.Redox post-treatment provides a new way for further improving TE performance of thin film.3.Ionic liquid EMIM:TFSi and lithium salt TFSi:Li with the same lithium ion were employed as modifier for that the exchange of cation and anion would affect the structure of PEDOT:PSS.In this chapter,we investigate the effect of the exchange of cation and anion on TE performance of PEDOT:PSS via optimizing the dipping time with ionic liquid and lithium salt solution.The experimental results shown that imidazolium cation in ionic liquid would obviously prompt the rearrangement of PEDOT chains and lead to an effective ascension of PEDOT:PSS TE performance.The optimal processing time was 5 min.The electrical conductivity and Seebeck coefficient were 999.8 S cm^-1 and 21.87?V K^-1.Power factor was elevated as 46.7?W m^-1 K^-2.4.Hydrazine hydrate and sulfuric as modifier were used to investigate the effect of sequence of acid and base treatment on the TE performance of PEDOT:PSS.It was shown that TE performance of PEDOT:PSS thin film treated with N₂H₄·H₂O-H₂SO₄ was higher than that of thin film treated with H₂SO₄N₂H₄·H₂O.After treat with concentrated sulfuric acid,PEDOT:PSS may interact with reductant more easily via electric charge effect,consequently lowering the electrical conductivity and damaging TE performance.The optimal electrical conductivity,Seebeck coefficient and power factor were 1041.8 S cm^-1,25?V K^-1 and 68 W m^-1K^-2,respectively.