生活周遭的熱能無所不在，舉凡太陽熱能、電子產品、工廠、汽機車產業抑或是人體都是熱的發源體，以往這些熱能就被散逸到大氣環境中而消失了，而熱電材料的其中一個特性即能將這些廢熱回收並且轉換成可以利用的電能的有效方法。本研究主題為透過硫化鉛量子點為主體，因其擁有眾多優點例如低熱導率、高席貝克係數、具有很大的波爾激子半徑、可調控的能隙、低成本的液體低溫製程等等。然而，合成之初的硫化鉛量子點表面具有絕緣性的油酸配體，會影響薄膜的電性，因此本研究透過精準的調控配體交換的時間，以碘離子置換掉量子點表面的油酸配體，藉以使得席貝克係數以及導電率大幅提升至-312.6μV/K以及49.56 S/cm，因而使功率因子達到484.92μW/mK2，且使熱電薄膜之ZT值達到0.142，相比於目前的已知文獻，功率因子進而從15.73μW/mK2提升至484.92μW/mK2，其主要的優勢在於精準調控量子點間的距離以及排列，來最佳化載子在量子點間的傳輸，並且透過最大化量子點表面上的碘離子，來達到最穩定的量子點特性，以避免氧化物在量子點表面形成，進而影響薄膜的電性。
在機制探討上，透過FTIR來確定配體交換成功移除表面的油酸配體；並透過UV-Vis-NIR和橢偏儀來確定配體交換完成的時間以及薄膜的光學特性和薄膜厚度的變化；透過XPS來查看硫酸鉛量子點表面的氧化情形以及得知配體交換後處理不但會移除量子點表面的油酸配體，還會移除已經交換上去的碘離子，進而發現配體交換後處理並非越久越好；透過GISAXS/GIWAXS來研究量子點堆疊的結構，並發現配體交換後處理會促使量子點排列的超晶格結構從FCC轉變成BCT，且定量計算晶格扭曲的情形以及量子點間的距離，而得到配體交換後處理會打亂原本量子點的排列的結論；透過laser flash來量測薄膜的熱導率，並發現了多層膜可以降低薄膜的熱導率；透過SEM/TEM檢視量子點堆疊的結構、量子點間距、量子點的形狀及此寸、量子點平面間距、膜況、薄膜厚度等等資訊，最終可以證明精準定量配體交換後處理的時間，才能得到最佳的量子點排列結構，最大化量子點表面的碘離子，最大化油酸配體的移除，以得到最佳的熱電特性表現。

Lead sulfide (PbS) quantum dots (QDs) are promising zero-dimensional materials for contructing n-type thermoelectric applications because of their low-cost solution processability and high potential for self-powered applications. However, the nature of low electrical conductivity arising from the existence of insulating oleate ligands in PbS surfaces critically stands against the enhancement of the thermoelectric power factor. Herein, in this work, PbS QDs with oleate ligands thin film were optimally treated with methylammonium iodide (MAI) counterion in methanol under different immerse durations. We found that the protic solvent, methanol, could largely remove the insulating oleate ligands, which promote bond formation between iodide ions and PbS QDs surfaces. This can highly improve the air-stability of QDs, which can avoid oxide formation. By precisely controlling this ligand exchange immersion time, optimal QDs superlattice structure and interdot spacing can be achieved. Futhermore, electronic coupling within PbS-based thermoelectric films is also greatly promoted, which in-turn improves the electrical conductivity. Through optimization of iodide ligand exchange, the Seebeck coefficient and the electrical conductivity of thin films are substantially improved to -312.6 μV/K and 49.56 S/cm, respectively. Such improvement enables to achieve a high thermoelectric power factor of 484.29 μW/mK2, which is approximately 20.17 times higher other PbS-based thermoelectric devices.

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