https://scholars.lib.ntu.edu.tw/handle/123456789/64219
標題: | 高表面積白金對電極及具光子晶體結構之導電玻璃在染敏太陽電池之應用 Platinum Counter Electrode with High Surface Area and FTO Photonic Crystals for Dye-Sensitized Solar Cells |
作者: | 王俊傑 Wang, Chun-Chieh |
關鍵字: | 循環伏安法;染料敏化太陽能電池;電化學電鍍法;光子晶體;鉑金屬薄膜;Cyclic Voltammetry;Dye-sensitized solar cell;Electrodeposition;Photonic crystals;Platinum | 公開日期: | 2011 | 摘要: | 本文分為兩個部分。第一個部分為,具有高表面積之新穎白金結構應用於染料敏化太陽能電池(以下簡稱染敏電池),第二個部分為,導電玻璃之光子晶體週期結構,應用於染敏電池之光電極基材。 具有低成本、容易製作等特性之染敏電池,至今其光電轉換效率已可達到11%。其中,染敏電池的對電極,以使用鉑金屬薄膜為居多。雖然鉑金屬較為昂貴,但其具有相當優異的催化特性,以及穩定性。鉑金屬對電極薄膜昂貴的原因主要是因為傳統的製備方法較無效率,以濺鍍法(sputter)來說,其使用時腔體需要抽真空、鉑鈀材純度需要極高等等,使得製備出來的鉑金屬薄膜昂貴。以熱還原法 (thermal decomposition)來說,雖然在高溫燒解中,鉑金屬粒子間具有更高的附著力,但是因為熱力學平衡的結果,使得鉑粒子聚集,產生團簇現象(cluster),使得鉑薄膜表面積降低,催化能力也降低。文獻中,取代濺鍍法與熱還原法的方法為電鍍鉑薄膜法(electrochemical deposition method)。電鍍鉑薄膜法是以電化學方法還原鉑前軀鹽,電鍍鉑金屬粒子於導電基材上,具有相對低廉的製備價格,但是卻較低的附著力。在本篇論文第一部分中,結合了電鍍鉑薄膜法的低成本性質,以及熱還原法的高附著力,使用居有週期性結構模版 (templates),避免鉑粒子聚集產生之團簇現象,維持鉑金屬薄膜之表面積,製備出具有高表面積之新穎結構鉑薄膜,應用於染敏電池之對電極。 本文使用之週期性結構模版之材料為聚苯乙烯(PS)奈米球。聚苯乙烯奈米球先以毛細力方法沈積於導電玻璃(FTO)表面上,形成週期性結構模版,再浸泡於鉑前軀鹽之乙醇溶液中,進行鉑金屬電鍍。然後,鉑粒子於是沈積於聚苯乙烯奈米球之間的孔隙中。經過高溫處理、熱分解聚苯乙烯奈米球後,可得到具有高表面積之鉑金屬薄膜。根據不同的鉑電鍍電鍍,可得到不同新穎結構之鉑金屬薄膜。 首先,以循環伏安法(Cyclic volatammetry),可電鍍出分布均勻、含有次微米孔洞鉑金屬薄膜。此次微米孔洞提供了較高的表面積與催化活性,和一般平板式電鍍鉑金屬粒子電極比較,當應用於正照式染敏電池之對電極,含有次微米孔洞鉑金屬薄膜可提供較高之光電流以及光電轉換效率。由於裸露的導電玻璃表面太多,電解質氧化還原之逆反應增加,使得填滿因子(Fill factor)較低。於是,使用了微量的鉑金屬濺鍍後處理,增加鉑金屬薄膜表面粒子間的連結性,在AM 1.5照光狀態下,可達到將近8.89%的光電轉換效率,大幅提昇填充因子。因此,含有次微米孔洞鉑金屬薄膜成功了取代一般平板式鉑金屬粒子薄膜。 深入研究發現,使用定電流還原法,可製備出更明顯之孔洞鉑金屬薄膜,在電子顯微鏡下發現,其結構為含有大量孔洞之鉑金屬球體團簇薄膜(PtSCMP)。在沒有微量的鉑金屬濺鍍後處理下,由於含有大量孔洞之鉑金屬球體團簇薄膜具有高表面積、較佳的催化特性,當作為正照式染敏電池之對電極時,在同樣照光狀態下,可達到8.67%之光電轉換效率。當作為背照式染敏電池之對電極時,其較高之穿透度與催化特性,相對於一般平板式鉑金屬粒子薄膜,也可達到較佳之光電轉換效率。 以外,若是使用脈衝電流法(pulse current method),在還原電流週期性的開關電鍍之下,可得到具有反式蛋白石結構(inverse opal)之鉑金屬薄膜。此結構於文獻中,尚未應用於染敏電池,本文創新應用於正照式之染敏電池,發現相對於一般平板式鉑金屬粒子薄膜,也有顯著的光電流與光電轉換效率的提升。但是由於其不透光性,此結構並不適合使用於背照式之染敏電池。 另外,在第二部分中,本文另以二氧化矽奈米粒子為模版,以感應耦合電漿離子蝕刻技術(ICP),創造出蝕刻導電玻璃之光子晶體週期結構,應用於染敏電池之光電極基材中。當應用於正照式之染敏電池,由於其獨特光學性質,光電流與光電轉換效率可明顯的提昇。更多光學性質的分析與應用於染敏電池之最適化條件,將是未來研究的重要課題。 This thesis is divided by two parts. The first part is novel Pt counter electrodes used in dye-sensitized solar cells (DSSCs), and the second part is novel FTO photonic crystals used as the substrate of photoanodes in DSSCs. Among several solar cells, the dye-sensitized solar cells (DSSCs) with low cost and easily fabricated process have been developed with the highest efficiency of 11%. For the DSSCs, up to date, Pt remains the most common catalyst material of the counter electrode because of its superior electro-catalytic activity, stability, and DSSC performance, despite lots of Pt alternatives were prepared to solve the cost-down issue. However, the cost of Pt fabrication is expensive since the conventional methods, such as sputtering and thermal decomposition, are not efficient. Compared with sputtering and thermal decomposition methods, the electrodeposited Pt is simple with low cost possibility, but with poor adhesive property. In the first part of this thesis, the advantages of electrochemical deposition with lost cost and thermal treatment with better Pt adhesive property were combined to fabricate Pt films with high surface area as the counter electrode of DSSCs. A monodispersed polystyrene (PS) nanoparticles were deposited on the fluorine-doped SnO2 (FTO) glass to be used as a template for the Pt electrochemical deposition. During the electrodeposition, the Pt nanoparticles were deposited into the void of the template, and the Pt films with high surface area and better adhesive property were created after removing the template by thermal treatment. Then, the Pt films with high surface area, including several novel morphologies, were obtained. Using cyclic voltammetry method, a novel Pt sub-micron structure with favorable high-surface-area pores was firstly successful fabricated by H2PtCl6 electrodeposited PS template, with diameter of 300 nm. After heat treatment at 385oC to remove the PS particles, the Pt sub-micron structure led to higher electro-catalytic ability and higher JSC due to its higher surface area, when compared with the direct-electrodeposited Pt without PS template. Although the fill factor (FF) of the DSSC composed of Pt sub-micron structure is lowered, the Pt-sputter post-treatment compensated the FF and achieved an excellent photovoltaic performance with the cell efficiency (η) of 8.89% in a front-illuminated DSSC. Therefore, a unique Pt morphology with novel Pt sub-micron structure was created and a significant improvement of the DSSC performance has been executed for using a high surface area counter electrode of novel Pt sub-micron structure with Pt-sputter post-treatment in the cell fabrication. The novel Pt sub-micron structures were further investigated. By means of constant cathodic current method, novel high-surface-area Pt films composed of spherical clusters with multiple nanopores in each cluster (PtSCMP films) has been successfully electrodeposited on FTO glass and applied as the counter electrodes of DSSCs. Without Pt-sputter post-treatment, the front-illuminated DSSC made with the PtSCMP film, deposited at 3.0 C/cm2 with a 300 nm PS templates, exhibits a better photovoltaic performance with an η of 8.67% due to its favorably high surface area. Besides, among different sizes of PS particles, the PtSCMP film, deposited at 0.5 mA/cm2 and 3.0 C/cm2 with a 300 nm PS template, possesses the highest electrocatalytic ability, electroactive area, JSC and conversion efficiency in a front-illuminated DSSC. Thus, the PS template with a diameter of 300 nm is the most suitable size for PtSCMP film in front-illumianted DSSCs. For back-illumination, the DSSC with PtSCMP film, deposited at 1.0 C/cm2 with a 300 nm PS templates, on its CE, shows improved JSC and η compared with the cell made with a Pt nanoparticles (PtNP) film (without PS template) due to the higher transmittance. By way of the pulse cathodic current method, the Pt films with inverse opal structures (PtIO) were electrodeposited on FTO glass and firstly applied to the counter electrodes of DSSCs. The PtIO films, formed with a 450 nm PS template and deposited at 3 C/cm2, possessed the highest electrocatalytic ability, electroactive surface area, and photovoltaic performance while assembling in a front-illuminated DSSC among various sizes of PS templates. Compared with the pulse-current platinum nanoparticles (p-PtNP) film (without PS template), the electroactive surface area of PtIO film with a 450 nm PS templates was largely improved. Besides, the PtIO films are not suitable for back-illuminated DSSCs due to its unfavorable fully-Pt-coverage and lowered transmittance. Hence, the front-illuminated DSSC with PtIO film successfully achieved a comparable η with a value of 7.04 %. In the second part, using photonic crystals as templates, a novel photonic crystal made of FTO glass have been successfully fabricated. Using a SiO2 nanoparticles monolayer as a mask, the FTO was etched by the inductively coupled plasma (ICP) and was a periodically structure and possessed optic characteristics, resulted in an increased JSC when used as the substrate of a photoanode in a front-illuminated DSSC. Further, the optical characteristics would be analyzed and be discussed in the future. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/252195 |
顯示於: | 化學工程學系 |
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