選擇性雷射燒結矽奈米顆粒於柔性基板之機制及其熱電PN接面元件應用

Abstract

伴隨科技的進展，人們對於能源的需求與日俱增，使用能源的同時會產生諸多的廢熱散失，要如何將其回收成為了關鍵課題。在眾多綠色能源中，柔性熱電元件因其輕量、可穿戴及適用於各種表面等優勢而廣受關注。本研究採用選擇性雷射燒結技術，以波長532 nm之脈衝雷射將矽奈米材料於大氣環境下燒結於柔性基板上，並探討其燒結品質及熱電應用。 透過電性、薄膜厚度與電子顯微鏡的表面型態分析，提出矽奈米顆粒燒結的機制。將燒結機制區分為四種情形，以更深入了解矽薄膜的形成機制。接著，分別燒結P型與N型矽奈米顆粒，研究其燒結的能量閾值 (Threshold)、電性及熱電性質，並且藉由冷鑲埋法觀察燒結厚度。由於N型奈米顆粒之粒徑較大，導致兩者燒結程度有所不同。在最佳參數條件下，P型及N型材料皆可達到整層燒結，電阻值分別為3.85 及7.88 Ω-cm。粒徑較大致使N型奈米顆粒燒結程度略遜於P型奈米顆粒，最終之電阻值較高。 我們進一步調整燒結的圖形，使用最佳燒結參數製作柔性熱電元件，探討矽薄膜於熱電應用的潛力。在熱端溫度為338 K時，P型矽奈米顆粒之席貝克係數為53.6 μV/K；N型矽奈米顆粒之席貝克係數為 −80.8 μV/K。接著，我們將P型與N型材料以指定圖形結合成為PN接面，製備熱電PN接面元件。從熱電量測的結果分析中顯示，相同熱端溫度下，PN接面的最大席貝克係數可達156.5 μV/K，證實PN接面有助於提升熱電發電效率。最後，在彎曲測試中，元件的輸出電壓表現證實其良好的可撓性。 本研究成功實現一項快速、低成本且可於大氣環境中燒結矽薄膜的技術，了解其燒結機制後，應用於柔性微型熱電元件 (micro thermoelectric generator, μ-TEG) 的製備，對於能源回收與永續願景極具應用潛力。

With the advancement of technology, the energy demand has increased dramatically. Along with energy consumption, a significant amount of waste heat is generated and dissipated. How to effectively recover this waste heat has become a critical issue. Among various green energy sources, flexible thermoelectric devices have garnered significant attention due to their lightweight nature, wearability, and suitability for multiple surfaces. This study employs selective laser sintering technology, using a pulsed laser with a wavelength of 532 nm to sinter silicon nanoparticles (SiNPs) onto flexible substrates in an atmospheric environment, and investigates the sintering quality and thermoelectric applications. We combine electrical properties, film thickness, and surface morphology analysis using electron microscopy to propose a sintering mechanism of silicon nanoparticles. The sintering mechanism is classified into four regimes to gain a deeper understanding of the formation mechanism of silicon thin films. Subsequently, P-type and N-type SiNPs are sintered separately to study their sintering energy thresholds, electrical properties, and thermoelectric properties, with sintering thickness observed using cold mounting methods. Due to the larger particle size of N-type SiNPs, the sintering extent differs between the two types. Under optimal parameters, both P-type and N-type materials can achieve complete sintering, with resistivity of 3.85 and 7.88 Ω-cm, respectively. The larger particle size results in a slightly inferior sintering extent for N-type SiNPs than P-type SiNPs, leading to higher resistance values. We further adjusted the laser scan patterns and used optimal sintering parameters to fabricate flexible thermoelectric devices, exploring the potential of silicon thin films in thermoelectric applications. At a hot-side temperature of 338 K, the Seebeck coefficient of P-type SiNPs is 53.6 μV/K, while that of N-type SiNPs is −80.8 μV/K. Subsequently, the P-type and N-type materials were combined in a specific pattern to form PN junctions, creating thermoelectric PN junction devices. Thermoelectric measurement indicated that the maximum Seebeck coefficient of the PN junction can reach 156.5 μV/K, confirming that the PN junction enhances thermoelectric power generation efficiency. Finally, in bending tests, the output voltage performance of the devices demonstrates their flexibility. In the research, we successfully achieved a fast, low-cost technique for sintering silicon polycrystalline in an atmospheric environment, elucidated the sintering mechanism, and applied it to the fabrication of micro thermoelectric generators (μ-TEG), demonstrating significant potential for energy recovery and sustainable applications.