Study On Thermoelectric Properties Of PEDOT/PSS Films

In China,the electricity currently comes from thermal power generation.However,fossil fuel reserves and existing energy technologies are increasingly difficult to satisfy China's growing electricity demand.At the same time,the greenhouse effect,PM2.5 and other issues that may cause harm to human health are not to be ignored.To date,many researchers try to develop clean energy to solve energy and pollution issues.Thermoelectric materials are a magical material that converts heat to electricity directly.Inorganic thermoelectric materials have the advantage of high conversion efficiency,but have drawbacks of high cost and strong toxicity.Organic thermoelectric materials are relatively low cost,non-toxic,environmentally friendly and good flexibility.Organic thermoelectric materials become one of the hot research directions because its potential application in flexible electronic devices.Poly?3,4-ethylenedioxythiophene?/poly?styrene sulfonate??PEDOT/PSS?as an organic thermoelectric materials has attracted much attention due to its high electrical conductivity,good thermal stability,and transparency,as well as good processabilty.Halloysite nanotubes?HNTs?can be used as a dopant of polymers to improve mechanical strength,thermal stability and molecular storage capabilities.Although carbon nanotubes?CNTs?have high electrical conductivity,they are not suitable for thermoelectric materials in theory due to their high thermal conductivity.However,some research groups found that sandwiching organic particles between the CNTs prevented heat conduction through the nanotubes.Therefore,in this thesis,we have investigated on preparation methods and thermoelectric properties of free-standing films of PEDOT/PSS-CNTs or/and HNTs.At the same time,we also have prelimilarily investigated effect of ethylene glycol and poly?ethylene glycol?on durability of PEDOT/PSS film in water in order to develop a patterning method of PEDOT/PSS film.The main contents of this thesis are as follows:1)Firstly,we have prepared the PEDOT/PSS-based thin films on PET substrate by a Bar-coating method.Scondly,the standing film is peeled off in deionized water to obtain free-standing PEDOT/PSS-based films with the help of 7 wt%polyethylene glycol.We have optimized the content of ethylene glycol,CNTs,surfactants,HNTs and liquid film thickness to obtain the optimal film.Typically,the optimizaed conditions for preparation of the free standing PEDOT/PSS-CNTs thin film are Bar-coating with NO.9 rod,by using non-ionic surfactant FS-30 and the PEDOT/PSS dispersion containing 0.2 wt%HNTs and 7 wt%ethylene glycol.As-prepared films were characterized by four-probe conductivity measurement,FT-IR,SEM,UV-VIS-NIR.As a result,the square resistance of the films was decreased with increasing in the content of CNTs in the films.2)We have investigated the thermoelectric properties of free-standing PEDOT/PSS-CNTs thin films with various contents of CNTs.Since the thermoelectric properties of the free standing thin fils were not successfully measured by hamdling problem we have conducted the measurement by using standing thin films to indirectly evalue the free-standing thin films.The results indicated that the power factor?PF?and electrical conductivity???are the largest when CNTs content of 14 wt%.The electrical conductivity and power factor increased roughly with increasing in the CNTs content,i.e.,when the content of CNTs increased from 7 wt%to 14 wt%,the two values increased rapidly from the minum to maximum,and then decreased with increasing in 14 wt%to 24 wt%,finally increased again with increasing in 24 wt%to 28 wt%.On the other hand,the Seebeck coefficient?S?was not much sensitive to CNTs content and temperature.At 328 K,power factor and thermoelectric figure-of-merit?ZT?of the film with CNTs content of 14 wt%were 1.1?W/m K² and 2.2×10^-3,respectively,which are comparable with those of other traditional conductive polymers.3)We have preliminarily investigated the effect of ethylene glycol and poly?ethylene glycol?on the durability of PEDOT/PSS films in water in order to develop a pattering method of PEDOT/PSS.The results indicated that addition or treatment of ethylene glycol or poly?ethylene glycol?improved not only the electrical conductivity,but also durability of the films in water.Furthermore,the durability of the films in water gradually increased with increasing in the addition amount of ethylene glycol,finally,when the addition amount of ethylene glycol is 0.9 wt%,the films were compeletely insoluble in water.In the case of poly?ethylene glycol?,similar trend was observed.When the addition amount of poly?ethylene glycol?increased to 0.5 wt%the films were completely insoluble in water.Moreover,the addition of poly?ethylene glycol?slightly improved tranparency of the film,while the addition of ethylene glycol slightly reduced the transparency.On the other hand,after-treatment of the ethelyene glycol or poly?ethylene glycol?also improved not only the durability in water,but also the electrical conductivity of the films.