硫化鉛量子點轉相技術及其在量子點敏化太陽能電池之應用研究

Study on Phase Transfer of PbS Quantum Dot and Its Application in Quantum Dot-Sensitized Solar Cells

陳奕竹(Yi-Chu Chen)

指導教授 ： 周更生

國立清華大學/工學院/化學工程學系/碩士(2012年)

摘要

本研究以水相硫化鉛量子點製程，將硫化鈉滴入硝酸鉛與PVA高分子水溶液中生成硫化鉛量子點，以高分子PVA做為水相分散劑，於製程中調整硫化鈉進料速度與PVA濃度，控制量子點粒徑大小與分布，以TEM分析粒徑結果。研究結果硫化鈉以0.4ml/min 速度進料，於2wt% PVA水溶液中進行合成，可得粒徑4.57 nm，標準差1.2 nm大小量子點，且有80.8%(N%)以上量子點其導帶位置高於陽極基板(TiO2)導帶位置，利於電子傳遞至陽極。
由於水相合成硫化鉛量子點表面被PVA包覆，不利於電子傳輸，另一方面，水溶液表面張力較高，量子點不易滲入陽極材料孔隙中，因此本研究以轉相技術將水相硫化鉛量子點轉至油相，分散於正己烷中，並於轉相過程將PVA去除，研究結果以FTIR觀察量子點改質情形，以吸收光譜分析其莫耳吸光係數之變化。從FTIR中官能基訊號的消長，確定表面PVA被去除，以油酸根取代，量子點轉至油相後波長1155nm處莫耳吸光係數是水相的2.2倍，此外將吸光係數與波長積分，轉相後積分值是水相的1.7倍(波長範圍800-1300nm)。於轉相過程中添加正戊醇，研究對轉相效率之影響，轉相率以AA分析，經最佳化後達到90.6%轉相率。將轉相後硫化鉛量子點應用於量子點敏化太陽能電池達0.26%效率。
研究的另一焦點為氧化鋅包覆銀絲(Ag@ZnO)所構成的一維核殼結構(one dimensional core-shell structure)，以PVP吸附於銀絲表面和鋅離子形成錯合物，經水熱後在表面形成10nm厚氧化鋅殼層，銀絲能作為電子通道使得電子快速傳遞至外電路中。研究討論水熱過程中不同比例之鋅離子和銀絲濃度對表面型態的影響，結果以TEM、SEM和XRD分析，觀察表面型態與分析材料結構，發現氧化鋅進行layer-plus-island成長。

關鍵字

硫化鉛量子點 ； 轉相技術 ； 量子點敏化太陽能電池 ； 氧化鋅 ； 核殼結構

並列摘要

We synthesized the lead sulfide quantum dot by a simple method and by controlling the content of dispersant (2wt%); PVA (polyvinyl alcohol) and the feeding rate of the precursor (0.4ml/min) we could control the exact size quantum dot. Lead sulfide quantum dot was characterized by transmission electron microscopy (TEM), X-ray electron diffraction (XRD) and Ultra violet-visible-near infrared spectroscopy (UV-Vis-NIR). Results show that lead sulfide quantum dot with an average diameter 4.57 nm and the narrow size distributions was obtained. Its standard deviation is 1.2nm. Furthermore, there are above 80.8% (N %) QDs have the higher conduction band than anode material (TiO2). Because aqueous phase QDs have the higher surface tension than organic phase, the QDs is hard to diffusion into the porous of TiO2. Besides, the aqueous phase dispersant (PVA) absorption on the surface of QDs would inhibit the electron transport. Therefore, we desire a phase transfer approach to solve these problems. We prepare the stable dispersion of lead sulfide (PbS) quantum dot in organic solvent by phase transfer. From the FTIR and absorption spectrum, after phase transfer the –OH group signal from the PVA is decrease and the molar absorptivity become 2.2 times. We study the content of the pentanol that affects the phase transfer efficiency, and after optimizing pentanol content the phase transfer efficiency is 90.6%. Afterward we apply the QDs in the quantum dot-sensitized solar cells the efficiency is 0.26%.
On the other hand, we synthesized one dimensional core-shell structure, zinc oxide was coated on the silver nanowire, where the diameter of Ag nanowire was 100 nm and the thickness of zinc oxide coating was 10nm. The polymer PVP (Polyvinylpyrrolidone) assisted the ionic zinc species absorption on surface of Ag. The Ag nanowire provided the high speed channel for electron passing through the anode to arrive to the external circuit. We change the ratio between the Zn2+ and Ag nanowire in the hydrothermal reaction. Observed the morphology of core-shell structure and found the layer-plus-island group.

並列關鍵字

PbS quantum dot ； phase transfer ； quantum dot-sensitized solar cells ； Zinc oxide ； core-shell structure

參考文獻

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