合成堆疊石墨烯電極及其在染料敏化太陽能電池之應用

Synthesis and Application of Stacked Graphene Electrodes for Dye-Sensitized Solar Cells

陳豪威(Hao-Wei Chen)

指導教授 ： 王宏文

中原大學/理學院/化學研究所/碩士(2011年)

https://doi.org/10.6840/CYCU.2011.00239

摘要

石墨烯，僅僅由單碳原子層組成的準二維材料，具有良好的機械強度、物理、化學穩定性及快速的電子遷移率，由於現今常用的氧化銦錫導電材料價格日漸上升，而且在軟性導電面板上的應用也較有限，因此，石墨烯的發展及應用逐漸受到重視。

本實驗利用氧化石墨法製備石墨烯薄膜電極，首先把多層堆疊的石墨以硫酸和過錳酸鉀氧化，實驗過程中改變氧化時間(12h、24h、48h、72h)，當氧化時，原本sp2的多層石墨結構會轉為sp3，造成層與層間的分離。氧化完成分別用高溫和冷凍兩種方法乾燥後再進行漿料配製，比較這兩種狀態發現其含水量有明顯的不同。之後用熱處理法將氧化石墨還原成石墨烯，過程中改變熱處理溫度(500oC、550oC、600oC、650oC)，得到的結果顯示出使用高溫乾燥氧化石墨固體調配漿料所形成的薄膜無法長時間穩定存在，容易受到空氣中水分影響而變得不平整，也間接影響到導電率及穿透率，後來改以使用冷凍乾燥氧化石墨配製所得到的薄膜，不僅能穩定存在於玻璃基板上，而且其導電率與穿透率皆有顯著的改善。

以四點探針系統和UV-Vis測得數值發現，在氧化時間48h、熱處理溫度650oC條件下，可以得到導電度(≦100 Ω/□)和穿透度(550 nm 75~80％)的石墨烯薄膜電極，再以SEM和AFM觀測到以化學法製備的氧化石墨皆為小面積剝離，厚度≦1 nm、長寬介於1~5 m之間；石墨烯之所以有良好的導電率在於單碳原子間形成六角形蜂窩狀鍵結且連續無缺陷的平面結構，而氧化石墨碎片間沒有接觸並無法成為平面電子傳遞的通道，因此塗覆厚度上必須達到50~100 nm左右，目的是將分散的碎片以少量堆疊方式形成通路，使電子能順利傳遞。

經由以上的結果整理出一套本實驗室製備堆疊石墨烯薄膜電極的標準流程，接著將此電極應用在染料敏化太陽能電池的工作電極與對電極上，替代目前使用的FTO導電玻璃，實驗數據顯示替代能力不如預期，推測應是石墨烯薄膜的穩定性以及與二氧化鈦薄膜間的親和力差有關，其介面電阻過大導致電池運作時電子無法順利的傳遞，日後會加以改善石墨烯電極的表面性質使介面間阻抗下降，達到取代導電玻璃的目標。

關鍵字

導電薄膜 ； 染料敏化太陽能電池 ； 石墨烯

並列摘要

Graphene, only one single layer of carbon atoms, two-dimensional material, has good mechanical strength, physical, chemical stability and fast transfer rate of electrons. Since the price has been increased, the commonly used indium-tin oxide (ITO) conductive film exhibits its limitation in many applications, especially in soft conductive panel. Graphene is recognized to be an important alternative material for ITO conductive films.
In this study, preparation of graphene thin film electrode through graphite oxide was studied. First, multi-layer stack of graphite was oxidized with sulfuric acid and potassium permanganate. The changes in oxidation time during the experiment (12h, 24h, 48h, 72h) were studied. After oxidation, the solids obtained were dried by two methods, high-temperature drying and freeze-drying, respectively. It was found that significant different water contents existed in these two solids. Heat treatment was used to reduce the GO to graphene. However, Films using high temperature drying were not stable and vulnerable to moisture and therefore become uneven, and poor electrical conductivity and low transparency. Films using freeze-drying result in a stable, good conductivity and transparent conductive films.
It was found that the oxidation time 48h, and heat treatment at 650 oC could result in conductivity (≦100 Ω / □) and transparency of 75 ~ 80% at 550 nm.
From the results, a standard process for a stacked graphene thin film electrodes was developed. The replacement of obtained graphene film for the conventional ITO conductive film and Pt-counter electrode was carried out. The conversion efficiencies of photo-current of DSSCs made by using the synthesized grapheme films were reported and discussed.

並列關鍵字

Conductivity thin film ； DSSC ； Graphene

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