低溫製程之高效鉑奈米結構與新穎鉑/石墨烯複合材料於染料敏化太陽能電池之應用

Abstract

多元醇合成法可製備出形貌控制良好之金屬奈米結構，我們利用此法並搭配溶液酸鹼度的調整，在未加保護劑的情況下成功製備出尺寸極小且分散均勻之鉑奈米結構。在此論文中，我們利用浸泡法製備染料敏化太陽能電池之鉑對電極，此法具有低溫及低成本的優勢並可應用至軟性基材。藉由硫醇官能化之導電基材與鉑奈米結構連結，鉑奈米結構可自組裝於基材表面形成單層薄膜。由SEM上視圖可發現自組裝之鉑奈米結構均勻分布於FTO導電玻璃上，由TEM剖面圖我們觀察到此鉑奈米結構具有高度的結晶性並且整齊規律地單層排列於基材上，其尺寸僅有2 nm。將此自組裝鉑對電極與最佳化的TiO2陽極材料結合，我們可發現製備於ITO基材之自組裝鉑對電極可達到9.2%的光電轉換效率，優於傳統熱還原法製備於FTO基材之鉑對電極9.1%，而製備於FTO基材之自組裝鉑對電極也可達到9.0%。 在本論文的第二部分，利用電化學循環伏安法沉積均勻的鉑奈米結構於覆有石墨烯之FTO基材表面，發展出新穎的鉑/石墨烯複合材料作為對電極觸媒。我們發現，藉由含氧官能基與缺陷結構的增加，石墨烯薄膜經後處理可改善其催化活性。將鉑/石墨烯複合材對電極進行元件光電轉換效率量測，其達到8.0%，略高於傳統鉑對電極的7.9%，此效能的提升主要來自於FF的增加。有別於單純石墨烯或鉑組成之對電極，鉑/石墨烯複合材對電極具有更多的優點與發展性，其中由電化學交流阻抗量測的結果顯示，其電荷轉移阻抗僅1.8 Ω，相對於傳統鉑對電極3.5 Ω及石墨烯對電極23 KΩ，更凸顯出其優異的催化特性，是非常有潛力的對電極材料。

Polyol synthesis is a successful method to generate metal nanostructures with well defined and controllable shapes. Here we report the fabrication of Pt nanostructures as transparent counter electrode (CE) for dye-sensitized solar cells (DSSC) via a dip-coating process suitable for flexible devices. A self-assembled monolayer (SAM) of Pt nanostructures was fabricated by linking Pt nanoparticles with thio functionalized transparent conducting oxide (TCO) substrate. Scanning electron microscope (SEM) top-view images show the Pt nanoparticles homogeneously distributed on the surface of a fluorine doped tin oxide (FTO) conductive glass. Ttransmission electron microscopic (TEM) cross-section images reveal that the Pt nanopaticles are highly crystalline and self-organized on the substrate with a uniform size of 2 nm in diameter. The DSSC device made of SAM CE and optimized TiO2 photoanode attained an overall power conversion efficiency 9.2% on indium tin oxide (ITO) substrate, which is slightly higher than the device with a conventional thermal cluster Pt (TCP-Pt) CE on FTO substrate (9.1%) ；the device made of SAM CE on FTO substrate gives the efficiency 9.0%. As second part of this thesis, a novel structure of Pt/Graphene nano-composite was developed as CE materials for DSSC applications. Using cyclic electro-deposition (CED) approach previously developed in this laboratory, Pt nanostructures were deposited uniformly on a graphene thin film, dispersed on the surface of FTO substrate. Post-treatments of graphene nanosheets to increase the amount of oxygen-containing functional groups and the defect sites were performed to improve the catalytic activity. In our study, the device incorporating Pt-grafted graphene CE showed a power conversion efficiency 8.0%, which is slightly higher than that of a device made of conventional TCP-Pt CE (7.9%), due to an improvement of FF. The CEs made of Pt/Graphene composite are superior to other electrodes that consist solely of graphene or Pt films. Based on the results obtained from the impedance spectral measurements, the charge transfer resistance of Pt/Graphene CE is 1.8 Ω, which is smaller than that of TCP-Pt CE (3.5Ω) and that of graphene CE (23KΩ). Our results indicate that the Pt/Graphene composite materials have excellent electro-catalytic performance, perfectly suitable for use as CE for DSSC.