| Flexible thermoelectric devices can directly convert human thermal energy into electric energy and provide energy for various electronic devices,which is significant to the development of flexible electronics.An efficient thermoelectric device consists of electrodes connecting p-type and n-type thermoelectric arms with matching properties.Conjugated polymers have the characteristics of flexibility,light weight and low cost,and can be used as ideal flexible thermoelectric materials and flexible electrode materials.However,the development of n-type conjugated polymer thermoelectric materials is far behind that of p-type.There are some problems,such as few material systems,low thermoelectric properties and instability,and flexible electrodes need sufficient conductivity and stability.Therefore,this thesis aims to develop n-type thermoelectric materials and electrodes for flexible thermoelectric device applications.The main research contents and results are as follows:In the first part,n-doping and thermoelectric properties of organoborate polymers are studied.A novel organoboron conjugated polymer PBN-19 was selected as n-type thermoelectric material,and molecular dopant 1,3-dimethyl-2-phenyl-2,3-dihydro-1h-benzimidazole（N-DMBI）with good air stability was selected for chemical doping.The effects of doping conditions on the thermoelectric properties and microstructure of the material were studied.It was found that the conductivity of 0.122 S cm-1 and the thermoelectric power factor of 0.08μW m-1 K-2 could be achieved for solution blending doping with the concentration of 140 mol%and the thermal activation time of 2 min.For spin-coating sequential doping,the conductivity of 0.630 S cm-1 and the thermoelectric power factor of 0.22μW m-1 K-2 could be achieved in the dopant solvent system of n-hexane/toluene mixture with volume ratio of 80:20,the dopant concentration of 6 mg m L-1,the infiltration time of 20 s,and the thermal activation time of 10 min.The conductivity of 0.277 S cm-1 can be maintained after 6 days in nitrogen atmosphere at room temperature.The doping stability of N-DMBI is much better than that of tetramethylene（dimethyl amino）（TDAE）vapor sequential doping.It is found that the doping efficiency of spin-coated sequential doping is higher than that of solution blending doping,but the surface morphology and crystallization of the PBN-19 films are slightly affected.In the second part,PEDOT:PSS flexible electrode is prepared and its properties are studied.The conjugated polymer PEDOT:PSS was selected as the material to prepare the flexible electrode,and the influence of preparation method and doping conditions on the conductivity of the electrode was studied,and the stability of the flexible electrode was also studied.PEDOT:PSS nanofiber thin film was prepared by electrospinning technology,and ethylene glycol secondary doping was used to obtain the square resistance of 121Ωsq-1,but the membrane was easy to tear.Then,the PEDOT:PSS films were prepared by spinning coating on flexible substrate of polyethylene terephthalate（PET）film.The square resistance of 280Ωsq-1,159Ωsq-1 and 152Ωsq-1 were obtained by using 1-ethyl-3-methylimidazole diaminitrile exchange doping,glycol secondary doping and methylsulfonic acid protonated doping,respectively.For methylsulfonic acid protonated doped PEDOT:PSS films,the square resistance can be further reduced to 76Ωsq-1by double layer film-making,to meet the conductivity requirements of flexible electrodes.After the electrode was placed in the air for 6days,after 100 bending cycles at the curvature radius of 1.2 cm,and after heating at 120 oC for 2.5 h,the square resistance only increased by 0.27%,6.23%and 9.23%,respectively,showing good air,mechanical and thermal stability.In general,this paper develops high performance n-type thermoelectric materials and flexible electrodes.The research results have guidance and reference significance for the development of this field,and laid the foundation for the development of flexible thermoelectric devices. |
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