探討硒化鎘與金奈米粒子的界面性質於光學與光電之影響

Effects of Interface Couplings on the Optical and Photoelectrical Properties of CdSe and Au Nanoparticles

劉翼碩(I-Shuo Liu)

指導教授 ： 林唯芳

共同指導教授 ： 陳永芳

國立臺灣大學/工學院/材料科學與工程學研究所/博士(2008年)

https://doi.org/10.6342/NTU.2008.10176

摘要

界面於奈米材料扮演非常重要的角色，將會影響其物理性質。我們有系統地研究硒化鎘奈米顆粒之表面鍵結不同配合基（ligand）的界面科學、利用不同聯結劑鍵結硒化鎘奈米顆粒與氧化鋅奈米柱之光學性質、和金奈米顆粒與導電高分子之間的界面科學。
使用具有苯環的配合基：α-toluenethiol、thiophenol、和p-hydroxy thiophenol鍵結於硒化鎘奈米顆粒上，我們發現會導致硒化鎘奈米顆粒之螢光強度減弱，但會增強光電性質。且發現使用配合基交換法（ligand exchange）將原本的配合基TOPO （trioctylphosphine oxide）置換成硫醇基分子，使用XRD與HRTEM-SAED發現其晶形並無變差或改變，時間解析螢光衰退光譜暗示著thiophenol和p-hydroxy thiophenol可以有效率地使硒化鎘奈米顆粒之螢光強度減弱，且發現此兩種配合基之螢光壽命大幅地比TOPO和α-toluenethiol的螢光壽命來的小。因此，thiophenol和p-hydroxy thiophenol可以藉由苯環有效率地接收經由光激發硒化鎘奈米粒子產生的電洞，thiophenol為配合基的硒化鎘奈米粒子也顯示出非常好的電荷傳導能力，於光伏特元件(photovoltaic device)中其短路電流密度(short circuit density)十倍於TOPO為配合基的硒化鎘奈米粒子。
接下來我們將硒化鎘奈米顆粒利用不同的聯結劑：3-aminopropyl trimethoxysilane和p-aminophenyl trimethoxysilane鍵結於氧化鋅奈米柱上，研究其硒化鎘奈米顆粒之螢光與光電性質。時間解析螢光衰退光譜暗示著p-aminophenyl trimethoxysilane聯結劑相較於使用3-aminopropyl trimethoxysilane為聯結劑與沒有使用聯結劑（直接將硒化鎘奈米粒子灑在氧化鋅奈米柱上），可以有效率地減低硒化鎘奈米粒子之螢光，其螢光壽命前者遠小於後兩者。因此，p-aminophenyl trimethoxysilane可以有效率地藉由苯環傳送經由光激發硒化鎘奈米顆粒產生的電子至氧化鋅奈米柱上。
最後，我們利用金奈米粒子的表面電漿性質，調控poly(3hexyl thiophene) (P3HT)與poly(2-methoxy-5-(2-ethyl)(hexyloxy)1,4-phenylenevinylene) (MEHPPV)的螢光強度。藉由金奈米顆粒的滅絕光譜（extinction）與導電高分子的的量子產率（quantum yield），可以調控導電高分子的螢光強度。在此我們使用兩種不同型態的金奈米粒子，一種是聚集金（大小約100nm），另一種是分散金（大小約5nm）。當加入聚集金進入導電高分子溶液中（濃度為0.08%重量百分比）可以增強其導電高分子的螢光強度，這是因為聚集金的表面電漿性質產生的散射現象，相反地，分散金表面電漿性質主要是吸收所貢獻，將導致螢光強度的減弱。我們發現加入分散金導致P3HT的螢光強度沒有變化，但對於MEHPPV卻是減弱的現象，這是因為P3HT相較於MEHPPV有較弱的量子效率，P3HT分子間的作用力較大，導致較少的能量從P3HT傳送到分散金上，而沒有減弱螢光強度。當我們將導電高分子的濃度稀釋至無窮稀釋的狀況中（皆1.48×10-5%重量百分比），分子間的作用力可以忽略時，能量從高分子轉移至金奈米粒子成為了主要的機制，導致兩種高分子皆呈現螢光強度減弱的現象。我們因此可以做出結論：導電高分子的螢光強度可以藉由高分子間的作用力、金奈米粒子間的作用力、和高分子與金奈米粒子間的作用力來調控。

關鍵字

界面科學 ； 太陽能電池 ； 螢光 ； 表面電漿 ； 奈米粒子

並列摘要

Interface plays an important role in the physical properties of nanomaterials. We have studied systematically the interface science of CdSe nanoparticle with different ligands, the effect of linkers on the optical properties of CdSe quantum dot coated ZnO nanocolumns, and Au nanoparticles with different conducting polymers.
CdSe quantum dots were encapped with aromatic ligands: α-toluenethiol, thiophenol, and p-hydroxy thiophenol to enhance photoluminescence (PL) quenching and other photoelectric properties of the quantum dots. Both XRD and HRTEM-SAED studies indicate that the crystalline structure of CdSe quantum dots was not only unchanged but also improved by the ligand exchange of TOPO (trioctylphosphine oxide) with thiol molecule. Time resolved PL decay measurements indicate that thiophenol and p-hydroxy thiophenol ligands effectively quench the emission, and the PL lifetime is much shorter than those of TOPO and α-toluenethiol. Thus, both thiophenol and p-hydroxy thiophenol can act as an effective acceptor for photogenerated holes through aromatic π-electrons. Thiophenol capped CdSe quantum dot also exhibits good charge transport behavior showing a 10 fold increase in short circuit current density (Isc) as compared with TOPO capped CdSe quantum dot in the photocurrent study of fabricated photovoltaic devices.
Next, we studied the effect of CdSe quantum dots coated on ZnO nanocolumns with different linkers, including 3-aminopropyl trimethoxysilane, and p-aminophenyl trimethoxysilane for the enhancement of the photoluminescence (PL) quenching and other photoelectric properties of the quantum dots. Time resolved PL decay measurements indicated that p-aminophenyl trimethoxysilane linker can effectively quench the emission of the CdSe quantum dot and induced a much shorter PL lifetime than that of 3-aminopropyl trimethoxysilane and that of no linker between CdSe quantum dot and ZnO nanocolumn. Thus, p-aminophenyl trimethoxysilane can act as an effective transfer for photogenerated electrons from CdSe quantum dot to ZnO nanocolumn through aromatic π-electrons.
Finally, the modulation of photoluminescence of conducting polymers using Au colloids was studied for poly(3-hexyl thiophene) (P3HT) and poly(2-methoxy-5-(2-ethyl)(hexyloxy) 1,4-phenylenevinylene) (MEHPPV). The extent of modulation can be explained by the extinction of Au colloids and quantum yield of polymer solution. Two types of Au colloids were investigated: nanocluster (~100nm) and nanoparticles (~5nm). The addition of the Au nanocluster into either one of the polymer solutions (0.08% by wt.) increased the photoluminescence (PL) of each polymer due to the scattering effect from the Au surface plasmon resonance. In contrast, the addition of Au nanoparticle with surface plasmon resonance coming from the absorption component caused a PL quenching. We have observed the PL intensity remained unchanged for P3HT but decreases for MEHPPV. The low quantum yield characteristic of P3HT has stronger polymer interactions than that of MEHPPV, which reduced energy transfer to Au nanoparticles, and dissipated further into heat with no decrease in PL. The polymer interactions were minimized using a dilute polymer solution (1.48×10-5% by wt. for MEHPPV and P3HT respectively). In this case, the nonradiative decay rate of Au colloids became dominant, and the decrease of PL was observed for both polymers. We therefore conclude that the photoluminescence of conducting polymer can be modulated by controlling the interactions among polymers and Au colloids.

並列關鍵字

interface science ； solar cell ； photoluminescence ； surface plasmon ； nanoparticle

參考文獻

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