具接面結構碲化鉍系化合物之熱電特性量測與模擬分析

Thermoelectric characterization and modeling of junction structured bismuth telluride based compounds

盧孟珮(Lu, Meng Pei)

指導教授 ： 廖建能

國立清華大學/工學院/材料科學工程學系/博士(2016年)

摘要

熱電材料因其能夠直接互相轉換熱能與電能的特性，而被使用於商業化的致冷與發電元件。碲化鉍系列化合物在室溫區段下擁有極佳的熱電轉換效率，於低溫廢熱回收之相關應用範疇具有發展潛力。本實驗以碲化鉍系化合物製備出一種新型的結構，包含兩個不同西貝克係數(Seebeck coefficient)的材料區域，並探討其熱電性質。本論文將系統化的分析與討論下述主題：區域間個別的熱電材料性質、接面結構與接合製程、隨空間變化的電壓效應以及該新型材料的模組之熱電轉換效率。實驗結果之內容分為兩部分，第一部分包含本徵n型碲硒化鉍的基本性質及摻雜性質；第二部分則闡述兩區域之接面試片的特殊性質與對應模組之熱電轉換效應。 首先，實驗初期提出了一個兩階段的退火製程以優化n型碲硒化鉍之冷壓試片的熱電性質，並得到提升30 %的熱電優值。其次，針對銀與銅摻雜效應對於n型碲硒化鉍熱電特性的影響也提出了完整的晶格缺陷機制解釋。銀的摻雜二元特性是由兩種銀雜質缺陷：空隙缺陷(Agi●)與置換缺陷(AgBi’’)，彼此消長所貢獻的。以第一部分本徵與摻雜之n型碲硒化鉍的熱電性質研究為基礎，進一步發展出接合兩個不同西貝克係數材料區域的概念。以本實驗的摻雜與壓錠製程可輕易製備出三種接合試片，包含P+/P、N-/N以及P/N個別兩種區域。比對實驗量測與理論模擬能夠有效預測該種新型結構固有的橫向電壓效應，並得到彼此吻合的結果。最後，本實驗針對接合熱電材料而提出新的模組結構設計，其在特定尺寸下擁有比傳統Π型模組更佳的轉換效果。針對較薄的熱電模組，新型模組的特殊電極導熱配置引入了二維的溫度梯度，能夠使輸出電壓有效提升。額外引入模組上的橫向溫差，能夠有效彌補薄型模組垂直溫差難以建立的不足，以提升薄型模組熱電轉換效率。

關鍵字

熱電材料 ； 碲化鉍系化合物 ； 熱電模組 ； 接面結構材料 ； 摻雜

並列摘要

Thermoelectric materials that enable direct conversion between heat and electricity have been employed in commercial devices for refrigeration and power generation. Bismuth telluride based compounds possess superior thermoelectric efficiency in room temperature regime, showing promising applicability to low temperature waste heat recovery. A novel structure of bismuth telluride based thermoelectric material that contains two regions with different Seebeck coefficients were fabricated and studied. A systematic study including individual thermoelectric transport properties, fabrication of junction structures, spatial voltage effects and thermoelectric power efficiency of corresponding modules has been performed. The study is organized as two parts: the first part contains the basic properties and doping effects of n-type Bi-Te(Se) compounds, and the second part elaborates the thermoelectric effects of junction structured materials and modules. Firstly, a two-step annealing process is proposed to optimize the thermoelectric transport properties on cold-pressed Bi2Se0.21Te2.79 bulk, showing 30 % enhancement in figure of merit. Secondly, in addition to intrinsic Bi-Te(Se) compounds, the effects of doping silver/copper on thermoelectric transport properties are elaborated by the lattice defect mechanisms. The dual electronic nature of silver-related lattice defects is carefully identified with the formation of interstitial (Agi●) and substitutional (AgBi’’) defects. The investigations of intrinsic base and extrinsic doping regions develop the concept of junction structured material with different Seebeck coefficients of two regions. There are three kinds of junction structured materials, including bulks with P+/P, N-/N, and P/N regions, which can be easily fabricated with and without dopants. Thirdly, the transverse voltage effects that are inherent in the novel structure have been well studied with good agreements between experimental and theoretically modeled results. Finally, the novel thermoelectric generation module that is assembled by junction structured materials shows better efficiency than the traditional Π-shape modules under certain dimensional criteria. The special arrangement of electrodes introduces a two-dimensional temperature gradient resulting in a larger voltage output during power generation, especially for thin thermoelectric modules. Introducing a horizontal temperature gradient to complement the insufficient vertical temperature gradient is expected to be the solution of improving the power efficiency of thin junction structured thermoelectric modules.

並列關鍵字

thermoelectric material ； bismuth telluride based compounds ； thermoelectric module ； junction structured material ； Doping

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