Preparation And Thermoelectric Properties Of Naphthalimide Composites And Their Devices

Thermoelectric material is a kind of green energy material,which uses the movement of carriers in the solid to realize the mutual transformation between thermal energy and electrical energy.Combining with the advantages of low thermal conductivity of organic materials and high electrical conductivity and Seebeck coefficient of inorganic materials,organic/inorganic composite thermoelectric materials have become a hot topic recently.However,The structure-activity relationship of composite thermoelectric materials is still unclear.Recently,flexible thermoelectric devices have been paid more and more attention by researchers because of their low cost,bending resistance,strong durability and a wide range of applications.Based on the above problems,we designed and synthesized a series of polymers based on naphthalimide(NDI)units.The composite thermoelectric materials were obtained by physical compounding of NDI-based polymers and single-walled carbon nanotubes(SWCNT).The effect of polymer molecular structure on the thermoelectric properties of NDI-based polymer/SWCNT composites was studied systematically.Finally,the P-type thermoelectric material with the best performance is selected and assembled into devices with the existing N-type thermoelectric materials,and the performances of devices are investigated.The details are as follows:1.We designed and synthesized three kinds of NDI-based polymers bridged by alkyl chains of different lengths.It was found that the NDI-based polymers bridged by shorter alkyl chains(NDI-4 and NDI-6)were H-aggregates and the longer alkyl-bridged NDI-based polymers(NDI-10)was J-aggregates due to the intermolecular van der Waals force.By compounding three kinds of polymers with SWCNT,the composite thermoelectric materials have high thermoelectric properties because of the strong?-?interaction between polymers and SWCNT.At room temperature,NDI-10/90%SWCNT has the highest thermoelectric properties with a conductivity of 936±47 S cm^-1and a power factor of 238±21?W m^-1 K^-2.2.Based on the NDI polymers with simple molecular structure and self-assembly in the first part,we designed and synthesized two kinds of donor-receptor NDI-based polymers.Firstly,ethylene?-bridge was introduced into a classical D-A polymer(N2200),and then a strong electron-absorbing group(cyano)was introduced into the conjugated skeleton of one of the polymers.According to the density functional theory(DFT)calculation,ultraviolet-visible absorption spectrum(UV-vis)and cyclic voltammetry(CV)curve test,it is proved that the band gap of the p olymer with cyano group is wider than the other from the point of theory,optics and electrochemistry.The two polymers were compounded with SWCNT in different mass ratios.After the measurement of thermoelectric properties,raman spectrum(Raman),X-ray photoelectron spectroscopy(XPS)and scanning electron microscope(SEM),the strong?-?interaction between cyanide group polymer and SWCNT is attributed to the fact that it is easy to form intermolecular force between cyano group with a pair of lone pair electrons and SWCNT,so the polymer with cyano group/SWCNT composites film has higher thermoelectric properties.3.We prepared simple flexible thermoelectric devices by using the materials which showed great thermoelectric performance in the previous chapters,NDI-based polymer/SWCNT composite thermoelectric materials with superior thermoelectric properties was selected as P-type thermoelectric materials,SWCNT/triethylamine as N-type thermoelectric materials and polyimide(PI)films as flexible subs trates.First of all,we fabricated a pure P-type thermoelectric device.At?T=30 K,the actual open circuit voltage(V_ac)is 5.82 m V and the actual output power(P_ac)is 28 n W.Then the P-N thermoelectric device is fabricated,and the maximum open circuit voltage is 52.9 m V(?T=140 K)and the maximum output power is 2.11?W(?T=84.2 K).