奈米碳管於染料敏化太陽能電池之應用

The Application of CNTs for Dye Sensitized Solar Cells

汪鑫毅(Hsin-Yi Wang)

指導教授 ： 萬其超

國立清華大學/工學院/化學工程學系/碩士(2010年)

https://doi.org/10.6843/NTHU.2010.00011

摘要

染料敏化太陽能電池因其組裝簡單容易且太陽光電轉換效率不低，故此種電池是下一新世代能源中，頗被看好的一種利用太陽能源產生電力的電池，但現今此種電池仍須利用到貴重金屬箔溅鍍在導電玻璃上做為陰極，其超真空設備與貴重金屬箔無疑大大增加了此電池之成本。

奈米碳管因其高導電度與許多不錯的物理性質，此種材料被許多研究團隊利用來取代箔做為染料敏化太陽能電池之陰極以降低成本。但又因為碳材本身的疏水與黏著力差的特性，我們必須在碳材表面做適當的處理與尋找適當的黏著劑來黏附碳管於電極之上，為了節省使用貴重金屬箔的使用，我們利用濕製程PEDOT電聚合為黏著方式製備出奈米碳管-箔奈米粒子複合物做為染料敏化太陽能電池的陰極催化層，而此種方法現今仍未被討論研究過。

在此研究中，我們使用了兩種不同方式來製備出奈米碳管-箔奈米粒子複合物。因分散方法與接支的官能機不同，我們將碳管接支聚丙烯酸命名為CNTs-PAA，而酸化接支單個梭基的碳管命名為CNTs-COOH，此外，我們利用導電高分子單體EDOT做為還原箔奈米粒子在碳管表面的還原劑。在穿透式電子顯微鏡中，我們發現CNTs-PAA由於表面攜帶較多的梭基，箔奈米粒子可利用較多的負電荷做為穩定生長點因此箔奈米粒子數量較CNTs-COOH多。且此種方法較酸化法不易傷害碳管表面，我們可以從電子顯微鏡中發現CNTs-PAA 結構也相對完整，一般而言，表面保持得越完整的碳管，其電性與物性才能有效的保持。

我們成功利用導電高分子PEDOT電聚合的過程將碳管-箔奈米粒子複合物黏著於導電玻璃上。但由實驗數據顯示，將製備好的電極組裝完電池之後，其效率在CNTs-COOH系統中為2.71％ 在CNTs-PAA系統中為2.34％ 在純PEDOT系統中為1.65％，我們發現，原本應該用來在電池中進行碘離子氧化還原反應箔奈米粒子，在PEDOT電聚合的過程中會幫助PEDOT的生成，這使得碳管-箔奈米粒子複合物的表面被覆蓋一層PEDOT，使其在組裝完電池之後，碘離子氧化還原催化效果與單純使用PEDOT做為陰極相同。因此原本表面生長較多箔奈米粒子的CNTs-PAA系統就表現得比CNTs-COOH系統來的差。

然而，我們也製備當純使用碳管且不改質箔奈米粒子於其表面，使用PEDOT做為黏著劑的催化層的電極，發現組好之電池效率為4.89％，與純使用箔為電極的電池效率5.52％相比幾乎可以匹配，顯示此種電極仍有繼續研究的淺力存在。

我們使用PEDOT做為黏著劑，但接上箔奈米粒子厚的碳管卻會因為箔在電聚合過程中幫助了PEDOT的生長而掩蓋了其原本催化表面，對於此種系統之最適當的組成比例仍需繼續研究。

關鍵字

奈米碳管 ； 染料敏化太陽能電池 ； 白金 ； 對電極 ； 導電高分子

並列摘要

Dye Sensitized Solar Cell (DSSC) has been regarded as a potential candidate for the next generation solar cells owing to their acceptable energy conversion efficiency and facile fabrication methods. However, the noble metal, Pt, is still used as counter electrodes and the required fabrication environment is rigid, which can remarkable increase the cost in DSSC.

Due to the high conductivity, mechanical strength, and several outstanding physical properties, carbon nanotubes (CNTs) are utilized to replace Pt as catalytic in counter electrodes. Because of the poor adhesion ability and the hydrophobic character of CNTs, making they are hardly utilized to prepare coated CNTs electrode, we induce carboxyl groups to make the surface of CNTs hydrophilic and PEDOT is used as binders. To save utilizing Pt, we prepare CNTs-Pt nanoparticles composite catalytic layers by PEDOT electro-polymerization to be the counter electrode of DSSC, and this method is still not discussed yet.

We set two different methods to prepare CNTs-Pt nanoparticles composite. Due to the different functional groups, CNTs grafted with Poly (acrylic acid) is remark CNTs-PAA and CNTs treated with concentrated acid is noted as CNTs-COOH. To fabricate CNTs-Pt nanoparticles composite, the H2PtCl6 is used as precursor and the EDOT monomers are employed as reducing agent. By TEM analysis, we can observe that the Pt nanoparticles are indeed fabricated on CNTs side walls. Moreover, The CNTs-PAA system shows relatively good structural integrity which could still maintain reliable electrochemical properties. With more carboxyl groups of PAA, more negative charge can be utilized to be the spots for growing Pt nanoparticles on the surface of CNTs-PAA.

We prepare CNTs-Pt nanoparticles and fix the composite on FTO glasses by PEDOT with electrophoresis process successfully; however, the PEDOT could cover the CNTs-Pt nanoparticles composite completely compared to those without doping Pt. Although Pt should have catalytic effect of the I-/I3- reaction, because Pt also induces the formation of PEDOT. In this way, all the electrochemical properties of CNTs-Pt nanoparticles composite will exhibit as the same as those of PEDOT. The Cell performances are 2.71％ for PEDOT-(CNTs-PCOOH)-(Pt nanoparticles) electrode, 2.34％ for PEDOT-(CNTs-PAA)-(Pt nanoparticles) electrode, and 1.65％ for PEDOT counter electrode, respectively, showing that with more Pt nanoprticles existing on CNTs, the Cell performance is more like that when only pure PEDOT used as counter electrode. Nevertheless, the PEDOT-(CNTs-COOH) electrode shows comparable efficiency 4.89％ compared to that of sputtered Pt electrode, 5.52％. This electrode is worth for further study.

PEDOT used as binder assists CNTs in increasing adhesion on the FTO glass, but over depositing PEDOT make CNTs-Pt lose its catalytic since PEDOT cover Pt-doped CNTs and shields them completely. How to make CNTs-Pt accessible to external environment and find the optimal composes is the subject that is needed to be explored.

並列關鍵字

CNT ； DSSC ； Pt ； Counter electrode ； PEDOT

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