高性能對電極觸媒材料於染敏太陽電池之研究:材料製備與電化學分析

High Performance Electro-catalysts for the Counter Electrode in DSSCs: Materials Preparation and Electrochemical Analyses

葉旻鑫(Min-Hsin Yeh)

指導教授 ： 何國川

國立臺灣大學/工學院/化學工程學研究所/博士(2013年)

https://doi.org/10.6342/NTU.2013.10579

摘要

本論文主要為研製高效能對電極觸媒材料於染料敏化太陽能電池(以下簡稱染敏電池)以及量子點敏化太陽能電池(以下簡稱量子點電池)及分析其相關電化學特性；其染敏電池(或量子點電池)結合對電極觸媒材料之光電特性將進一步利用光電化學與光物理進行分析。根據不同的研究課題可將本論文略分為三部分: (1)鉑金修飾對電極材料應用於染敏電池系統 (Chap. 3~5)；(2) 解決非鉑金對電極材料於染敏電池系統中之瓶頸(Chap. 6~9)；(3)利用非貴金屬對電極材料應用於量子點電池系統(Chap. 10~11)。
在使用I-/I3-電解液之染敏電池系統中，一般而言，具有高催化性與穩定性的鉑金為染敏電池之對電極觸媒材料的首選。然而，居高不下的鉑金價格使其整體元件的成本大幅度提高。因此，針對此議題，本研究第一部份採複合材料的概念來提高鉑金利用率。首先，提出具有網狀結構之導電高分子PProDOT-Et2做為鉑金之沉積擔體，製備兼具高比表面積與高催化能力之PProDOT-Et2/Pt複合催化層，使用此複合結構於對電極之染敏電池其元件效能可達6.68%，高於使用傳統鉑金對電極的染敏電池之元件效能(6.43%) (Chap. 3)。為了更進一步提高鉑金利用率，本研究製備鉑金奈米粒子結合具有高導電性與比表面積之石墨烯擔體，成功合成出分散均勻的石墨烯/鉑金奈米粒子複合材料應用於染敏電池對電極之催化層，其優異的催化能力使其元件效能更進一步達到8.64% (Chap. 4)。延續先前的研究，本研究更首度探討鉑金奈米粒子之尺寸效應對於I-/I3-氧化還原反應之影響，結果顯示尺寸過大的鉑金奈米粒子會降低其可反應的活性面積，而過小的鉑金奈米粒子則會大幅提升其反應活化能，降低其反應速率，而適當尺寸之鉑金奈米粒子則能同時兼具高活性面積及合適的反應活化能。使用此鉑金奈米粒子於對電極之染敏電池元件效能可達到9.32% (Chap. 5)。
另一方面，為了完全取代鉑金於染敏電池的使用，碳材、導電高分子及過渡金屬化合物近年來廣泛被應用於取代鉑金催化層。本研究第二部分著重於解決目前過渡金屬化合物與碳材應用於染敏電池之對電極催化層所遭遇的瓶頸。首先，針對改善過渡金屬化合物應用於染敏電池對電極催化層方面，為了有效解決過渡金屬奈米粒子間的連結性，本研究首度提出利用導電高分子PEDOT:PSS做為過渡金屬氮化鈦奈米粒子間的橋梁，有效提高電子於粒子之間傳遞速率並增加粒子於基材之附著性，使用此材料製備之染敏電池其元件效能可達6.67%，遠高於未使用PEDOT:PSS連結之氮化鈦奈米粒子所製備之元件效能(0.17%) (Chap. 6)。此外，本研究所提出的概念可應用於不同奈米材料，並能利用簡易塗佈方式製備複合薄膜，相較於一般傳統的高溫製程，此製程更適合應用於可撓式基材(如ITO-PEN) (Chap. 7)。在針對改善碳材應用於染敏電池對電極催化層方面，本研究提出利用NafionR 做為石墨烯的分散劑，使石墨烯材料能均勻分散在溶液中，並藉由簡單的液滴塗覆法製備厚度均勻且附著性良好的石墨烯薄膜於染敏電池之對電極催化層；其元件效能可達8.19%，遠高於未使用NafionR做為分散劑之石墨烯薄膜所製備之元件效能(4.58%) (Chap. 8)。此外，本研究更首度提出新穎結構之奈米碳管/石墨烯奈米帶應用於染敏電池之對電極催化層。由於奈米碳管/石墨烯奈米帶兼具奈米碳管的優良導電性與石墨烯奈米帶之高催化活性面積，使用此材料製備之染敏電池其元件效能(6.91%)遠高於單獨使用奈米碳管(5.93%)與石墨烯(4.48%)之元件效能(Chap. 9)。
本論文第三部分著重在利用非貴重金屬觸媒材料應用於量子點電池對電極觸媒方面；本研究首度使用導電高分子(Chap. 10)與過渡金屬化合物(Chap. 11)應用於量子點電池之對電極催化層，取代一般應用於催化多硫電解液(S2-/Sx2-)之黃金催化層，結果顯示導電高分子以及過渡金屬化合物對於多硫電解液皆具有良好的催化能力，其元件效能都高於使用一般黃金做為對電極催化層之元件效能，此兼具低成本與高催化能力的導電高分子與過渡金屬化合物將能大幅度降低量子點電池成本並提高其元件效能。

關鍵字

對電極 ； 染料敏化太陽能電池 ； 電化學分析 ； 非貴金屬觸媒 ； 量子點敏化太陽能電池

並列摘要

This dissertation aims to prepare highly efficient catalytic materials on the counter electrodes (CEs) of dye-sensitized solar cells (DSSCs) and of quantum dot-sensitized solar cells (QDSSCs), and to analyze their electrochemical properties. Moreover, the photovoltaic performance of DSSCs (or QDSSCs) with prepared CEs was examined by photo-electrochemical and photo-physical analyses. This dissertation can be divided in three parts: (1) Pt modified catalysts for CE in DSSCs (Chap. 3~5); (2) Pt-free catalysts for CE in DSSCs (Chap. 6~9); (3) noble metal-free catalysts for CE in QDSSCs (Chap. 10~11).
In general, platinum is the most used catalytic material on the CE because of its excellent catalytic ability and stability in the system with iodide/triiodide (I-/I3-) electrolyte. However, the expensive platinum leads to a high cost for the fabrication of DSSCs. To solve this problem, the concept of composite materials was proposed to reduce the usage of platinum at the first part in this dissertation. First of all, a conducting polymer, poly(3,3-diethyl-3,4-dihydro-2H-thieno-[3,4-b][1,4]-dioxepine) (PProDOT-Et2), with three- dimensional (3D) porous structures was applied to be the support for platinum to fabricate a PProDOT-Et2/Pt composite catalytic layer with high specific surface area and good catalytic ability. The DSSC with this composite film on its CE achieved a solar-to-electricity conversion efficiency of 6.68%, which is higher than that of the cell with traditional platinum CE (6.43%). (Chap. 3) In order to further reduce the usage of platinum, a composite film with platinum nanoparticles (PtNPs) and highly conductive graphene supports with large specific surface area was successfully fabricated as the catalytic layer on the CE of DSSCs. The efficiency of the pertinent DSSC was further improved to 8.64%. (Chap. 4) Furthermore, the particle size effect of the PtNPs on the redox reaction of I-/I3- was investigated. It was found that large particle size of PtNPs possesses reduced active area and small particle size of PtNPs owns high reaction activation energy for reducing the I3-. Only suitable size of PtNPs has both properties of high active area and low activation energy. An efficiency of 9.32% was for the DSSC with the suitable size of PtNPs. (Chap. 5)
From the view of reducing fabrication cost, only reduce the usage of platinum is not enough. To completely replace the usage of platinum on DSSCs, carbonaceous materials, conducting polymers, and transition metallic compounds have been widely used recently. The second part in this dissertation aims to solve the problems for applying transition metallic compounds and carbonaceous materials on the CE of DSSCs. Firstly, for improving the catalytic ability of transition metallic compounds on the CE of DSSCs, we applied conducting polymer, poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), as a linker to improve the electrical connection among the titanium nitride (TiN) nanoparticles. The pertinent DSSC showed an efficiency of 6.67%, which is much higher than that of the cell without the linker of PEDOT:PSS (0.17%). (Chap. 6) This concept can also be applied on different nanomaterials and it is easy to fabricate the composite thin film with simple doctor blade coating method. This process is more applicable on flexible substrates, e.g., indium doped tin oxide-poly(ethylene naphthalate) (ITO/PEN), with compared to the traditional high-temperature process. (Chap. 7) On the other hand, we used NafionR as the dispersant for graphene to inhibit the aggregation and applied easy drop-coating method to fabricate a graphene thin film with uniform thickness and good contact with the substrate as the catalytic layer on the CE of DSSCs. An efficiency of 8.19% was obtained for the pertinent DSSC, which is higher for the cell without NafionR as the dispersant for fabricating graphene thin film (4.58%). (Chap. 8) In addition, we proposed a novel structure of multi-walled carbon nanotubes (MWCNT)/reduced graphene oxide nanoribbon (rGNR) and applied it as the catalytic layer on the CE of DSSCs. Owing to the excellent conductivity and high active surface area for MWCNT and rGNR, respectively, the DSSC with this material as the catalytic layer on the CE achieved a higher efficiency (6.91%) than those of the cells with MWCNT (5.93%) or graphene (4.48%). (Chap. 9)
In the third part, we used conducting polymers (Chap. 10) and transition metallic compounds (Chap. 11) as the catalytic layer on the CEs of QDSSCs. Both materials show excellent catalytic abilities and cell performances for the pertinent QDSSCs, with compared to the cell with gold as the catalytic layer. These materials with low-cost and high catalytic ability can largely reduce the cost and enhance the performance of the pertinent QDSSCs.

並列關鍵字

Counter electrode ； dye-sensitized solar cells ； electrochemical analyses ； noble metal-free catalysts ； quantum-dot sensitized solar cells

參考文獻

[1] B. O'Regan, M. Gratzel; "A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films", Nature, 353 (1991) 737-740.

[2] M. Gratzel; "Photoelectrochemical cells", Nature, 414 (2001) 338-344.

[3] M. Gratzel; "Dye-sensitized solar cells", Journal of Photochemistry and Photobiology C: Photochemistry Reviews, 4 (2003) 145-153.

[4] A. Hagfeldt, M. Gratzel; "Molecular photovoltaics", Accounts of Chemical Research, 33 (2000) 269-277.

[5] A. Hagfeldt, G. Boschloo, L. Sun, L. Kloo, H. Pettersson; "Dye-sensitized solar cells", Chemical Reviews, 110 (2010) 6595-6663.