Preparation And Characterization Of PEDOT:PSS-based Thermoelectric Composites

Thermoelectric(TE) material is a kind of materials which can directly convert waste heat into the electrical energy. TE materials can be widely used in power generation by waste heat and solid cooling devices, and now have been applied in aviation and semi-conductor cooling. Generally, the TE performance of inorganic materials is better than organic materials, so researches on TE materials have been focused on inorganic materials. However, inorganic materials suffer from toxicity, high cost and difficult synthesis process. Therefore, organic TE materials are now catching people’s attention. Among organic TE materials, poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)(PEDOT:PSS) is considered as the best organic TE material. Nevertheless, Most of PEDOT:PSS researches are focused on films, not bulk materials. Despite films have made great progress, bulk materials are more practical for device application. So fabrication of bulk TE materials which arecompatible with commercially available TE devices have specific meanings. However, the working efficiency of bulk organic TE materlals is too low to meet the needs of commercial application, so improvement in TE performance must be made. Previous reports indicate introducing inorganic phase in PEDOT:PSS matrix can be an effective way to improve electrical conductivity and Seebeck coefficient, while maintain the feature of low thermal conductivity of PEDOT:PSS. Therefore it becomes a major developing trend of PEDOT:PSS TE materials. In this work, silver nanowires(AgNWs), silver nanoparticles(AgNPs) and Bismuth antimony telluride(Bi0.4Sb1.6Te3) were introduced into PEDOT:PSS to promote electrical conducitivity and Seebeck coefficient respectively. The major works are shown as follow:(1) Bulk PEDOT:PSS TE materials were prepared by hot-pressing technology. The process mechanism was exploredand established by adjusting pressing pressures and temperatures.(2) AgNWs and AgNPs were prepared by polyol reduction of silver nitrate and Bi0.4Sb1.6Te3 powders were obtained by mechanical grinding. The microstructure of samples were characterized by XRD、TEM and FE-SEM. The as-prepared AgNWs possessed a mean diameter of 60 nm and length of 2-4 μm. As-prepared AgNPs possessed cubic shape with the mean diameter of 40 nm. Bi0.4Sb1.6Te3 powders possessed irregular shape with diameter of 100nm-2μm.(3) AgNWs/PEDOT:PSS composite powders were obtained by combining AgNWs and PEDOT:PSS solution through ultrasound technology with different AgNWs weight ratio. Then bulk AgNWs/PEDOT:PSS samples were obtained by hot-pressing composite powders. The micro structure of the samples was studied by XRD、FE-SEM and TEM. The FE-SEM and TEM images confirmed that AgNWs were well dispersed in PEDOT:PSS matrix. TE properties were also studied through ZEM-3, DSC and laser-flash system. The results show that when AgNWs content was 20wt%, the electrical conductivity was greatly enhanced and ZT valuefinally reached2.4×10-3 at room temperature, realized a four-time enhancement.(4) AgNPs/PEDOT:PSS composite powders were synthesised by two methods, they are solution combination and powder combination. Bulk composite samples were synthesised by hotpress process. The microstructure of the samples was studied by XRD、FE-SEM and TEM. The results indicated that AgNPs were well-dispersed in PEDOT:PSS by powder combination method. TE performances were also studied through ZEM-3, DSC and laser-flash system. The results show that TE performance obtained by powder combination method is better than that of solution combination. However, the contribution AgNPs made to ZT is low because of the enhanced carrier scattering effect.The maxium ZT value was 1.3×10-3 at room temperature.(5) Bi0.4Sb1.6Te3/PEDOT:PSS composite powders were obtained by combining Bi0.4Sb1.6Te3 powders and PEDOT:PSS powders through cold grinding, then bulk composite samples were obtained by hot-pressing. The microstructure of samples was studied by XRD, FE-SEMand TEM, which indicated Bi0.4Sb1.6Te3 was successfully dispersed in PEDOT:PSS matrix. TE performance was also studied through ZEM-3, DSC and laser-flash system.The results show that samples realized the simultaneous increase in electrical conductivity and Seebeck coefficient, thus the maxium ZT reached 3.8×10-3 at room temperature, realized a two-time enhancement.