[[alternative]]Fabrication and Characterization of Bi2Te3 nanoparticle-Polythiophene Nanocomposite for Thermoelectric Materials

[[abstract]]ZT為評估材料熱電性能的一個數值， 這是由Seebeck係數，導電率，熱傳導率和所使用的溫度。熱電材料的ZT在1960年代已經接近1，但是直到最近十年才有顯著的突破。 在1993年，Mildred S. Dresselhaus提出以低維度的材料來提升ZT，並為熱電材料帶來希望。本研究即使用這個概念製備奈米熱電複合材料。 我們透過複合材料工程提出一種新的熱電材料，由導電高分子和常見的熱電材料所組成。因為常見的熱電材料具有好的導電率和Seebeck係數，而導電高分子則具有低的熱傳導率，將兩者製備為複合材料可以增加聲子散射，破壞其熱傳導，並維持其導電率。並可透過複合材料工程調整熱電性能。我們選擇導電高分子 P3HT 和在室溫下擁有最好ZT的熱電材料Bi2Te3。 為了改善在P3HT和Bi2Te3之間的可溶混性，首先我們合成與P3HT結構相似的保護劑3-MHT來製備Bi2Te3奈米柱。由1 H-NMR和FTIR 鑑定保護劑3-MHT結構正確，並可調整實驗參數製備出長350~1500 nm和直徑25~150 nm的奈米柱。TEM、XRD和EDS結果證明Bi2Te3奈米柱結構及組成正確。而奈米柱外為所包覆的保護劑保證其在P3HT溶液中的可溶混性。第二我們將奈米柱加入P3HT溶液中，製備出奈米熱電複合材料。由TEM圖證明奈米柱良好分散在P3HT中。接著我們量測能階、導電率及Seebeck係數，但是導電率並不如預期，由於保護劑3-MHT是電的絕緣體所致。在加入Bi2Te3奈米柱後導致導電率變差，導電率由原先P3HT的218 Ω-1 m-1變成76~113 Ω-1 m-1，對Seebeck係數而言是稍微地從32 µV/K增加到37 ~39 µV/K。而所製備的P3HT-Bi2Te3奈米熱電複合材料，最好的ZT預估約為0.045。 The thermoelectric performance of a material could be evaluated by its figure of merit ZT which is consisted of Seebeck coefficient, electric conductivity, thermal conductivity and applied temperature. The ZT of the thermoelectric materials has approached the value of 1 in the 1960s, but does not have the significant breakthrough until the recent decade. In 1993, Mildred S. Dresselhaus proposed a new concept that the low-dimensional materials could have improved ZT and brought a hope to thermoelectric materials. In this study, we used this concept to prepare nanocomposites for thermoelectric materials. Here we proposed a new thermoelectric material by composite engineering, which was composed of conducting polymers and the conventional thermoelectric materials. Since the conventional thermoelectric materials have good electric conductivity and Seebeck coefficient, the conducting polymers with low thermal conductivity could increase the phonon scattering to ruin the thermal transportation in the prepared composites and maintain their electric properties. The thermoelectric performance could be adjusted by composite engineering. We chose the conducting polythiophene P3HT and the thermoelectric material Bi2Te3 which owned the best ZT at room temperature. In order to improve the miscibility between P3HT and Bi2Te3, firstly, we synthesized the protection agent 3-MHT with similar structure of P3HT to prepare Bi2Te3 nanorods. The protection agent 3-MHT identified by 1H-NMR and FTIR could fabricate Bi2Te3 nanorods with 350~1500 nm in length and 25~150nm in diameter dependent on their experimental parameters. TEM、XRD and EDS results identified and characterized Bi2Te3 nanorods correctly. The Bi2Te3 nanorods capped with 3-MHT guaranteed their miscibility with P3HT polymers. Secondly the designed nanocomposites were manufactured by a simple mixing of Bi2Te3 nanorods and P3HT polymer in solution. TEM image demonstrated a well-dispersed morphology of the Bi2Te3 nanorods in P3HT polymer matrix. We measured the bang-gap, electric conductivity and Seebeck coefficient of the prepared nanocomposites but the electric properties were not good as expectancy due to the electric-insulating protection agent 3-MHT. The addition of Bi2Te3 nanorods led to worse electric conductivity from 218 Ω-1m-1, the value of pristine P3HT polymers, to 76~113 Ω-1m-1 ¬and the Seebeck coefficient slightly increased from 32 µV/K to 37~39µV/K. The best ZT was estimated to be the value of 0.045 for the prepared P3HT-Bi2Te3 nanocomposites.[[notice]]補正完