染料敏化太陽能電池：無白金對電極與無碘電解質之研究

Dye-sensitized Solar Cells:Study of Pt-free Counter Electrodes and Iodide-free Electrolytes

李君婷(Chun-Ting Li)

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(2015年)

https://doi.org/10.6342/NTU.2015.11328

摘要

本研究論文主要針對無白金對電極進行系統性的開發，與設計新型無碘系統電解質，應用於低成本、高效率之染料敏化太陽能電池。本研究論文主要可分為兩大部分：(1)無白金對電極(第三章至第七章)；(2)無碘系統電解質(第八章)。
無白金對電極之開發主要目的為降低染敏電池之製造成本，透過簡單、非真空、低成本的製程製備多種電催化觸媒材料，用以完全取代昂貴的白金材料。因此，本研究論文首先以碘系統電解質為標準，進行三大類的無白金複合對電極之開發。(一)過渡金屬化合物型：包含第三章中的硫化鈦/導電高分子PEDOT:PSS；第四章中的氮化矽/PEDOT:PSS、氧化矽/PEDOT:PSS、硫化矽/PEDOT:PSS、硒化矽/PEDOT:PSS；第五章中的氮化鋅/PEDOT:PSS、氧化鋅/PEDOT:PSS、硫化鋅/PEDOT:PSS、硒化鋅/PEDOT:PSS等複合薄膜。過渡金屬化合物奈米粒子可提供良好的電催化能力與大的活性面積進行碘還原反應，而硫化鈦、氮化矽、硫化矽、硒化矽、氮化鋅、硒化鋅等材料是第一次應用於染敏電池中。其中，以氮化鋅/PEDOT:PSS為對電極之染敏電池可達到高於白金之效率。(二)碳材型：第六章中製備奈米多孔性之碳黑奈米粒子/磺酸化聚噻吩複合薄膜，可提供高表面積、快速電解質滲透、快速碘離子還原反應。當複合薄膜中含有5 wt%之碳黑奈米粒子時，可達到最佳之染敏電池效率，甚至高於白金。磺酸化聚噻吩是一種噻吩類的水溶性導電高分子，第一次作為染敏電池之對電極材料。在低光照下，此系統下之染敏電池仍可維持良好之效能，表示其可適用於室外或室內之電子元件。(三)導電高分子型：第七章中合成聚二氧乙基噻吩(PEDOT)與六種不同的離子液體修飾PEDOT電極，六種離子液體中包含三種具有不同的碳鍊長度的咪唑陽離子，可改變PEDOT薄膜的表面積；且包含四種不同的陰離子(BF4−, PF6−, SO3CF3−, TFSI−)，可改變PEDOT之共振結構。其中，以1-hexyl-3-methylimidazolium hexafluorophosphate (HMIPF6)修飾PEDOT (8.28%)與1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (HMITFSI)修飾PEDOT為對電極之染敏電池皆可達到高於白金之效率。總而言之，本研究論文開發四種無白金複合薄膜：氮化鋅/PEDOT:PSS、HMIPF6修飾PEDOT、HMITFSI修飾PEDOT、5 wt%碳黑奈米粒子/磺酸化聚噻吩，為可取代白金之替代材料，因為他們皆具有良好的催化碘還原能力、低成本、簡易製程、易於大面積製備等特性。
另一方面，無碘系統電解質之開發主要目的為進一步的提升染敏電池之效率，第八章中透過分子結構之設計，合成具備雙氧化還原通道之離子液體電解質(ITSeCN)，ITSeCN以咪唑修飾之2,2,6,6-四甲基哌啶-1-氧化物作為陽離子氧化還原對，並以硒氰酸根作為陰離子氧化還原對。因此，相較於傳統的碘系統電解質，ITSeCN具備高的氧化還原電位、高擴散係數、良好的異相反應速率常數。為了進一步探討適合驅動ITSeCN氧化還原反應之電催化材料，白金(代表金屬型材料)、PEDOT(代表導電高分子型材料)、硒化鈷(代表過渡金屬化合物型材料)、碳黑奈米粒子(代表碳材型材料)分別做為四大型對電極材料之代表材料。以PEDOT與硒化鈷為對電極之ITSeCN系統染敏電池皆可達到高於白金之效率。可推測過渡金屬化合物型對電極較為適合驅動ITSeCN之氧化還原。

關鍵字

對電極 ； 染料敏化太陽能電池 ； 電觸媒 ； 電解質 ； 無碘 ； 無白金

並列摘要

This dissertation aimed to systematically develop Pt-free counter electrodes (CEs) and to design a novel iodide-free electrolyte for the dye-sensitized solar cells (DSSCs) with low-costs and highly cell efficiencies (η’s). This dissertation is divided into two parts: (1) Pt-free CEs (Chapter 3~Chapter 7) and (2) iodide-free electrolyte (Chapter 8).
In the case of Pt-free CEs, we aim to reduce the costs of the DSSCs using various electro-catalysts for completely replacing the expensive Pt via the simple, non-vacuum, and low-cost fabrication processes. Accordingly, three types of Pt-free composite films were studied using a standard iodide electrolyte. (I) Transition metallic compound-type CEs, including the composite film of TiS2/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (TiS2/PEDOT:PSS) in Chapter 3, the composite films of Si3N4/PEDOT:PSS, SiO2/PEDOT:PSS, SiS2/PEDOT:PSS, SiSe2/PEDOT:PSS in Chapter 4, and the composite films of Zn3N2/PEDOT:PSS, ZnO/PEDOT:PSS, ZnS/PEDOT:PSS, ZnSe/PEDOT:PSS in Chapter 5, were indivitually investigated. In a composite film, the transition metallic compound nanoparticles were separately used to provide attractive electro-catalytic abilities and large active areas for I3- reduction; among those NPs, TiS2, Si3N4, SiS2, SiSe2, Zn3N2 and ZnSe were applied in DSSCs for the first time. Among them, the cell with Zn3N2/PEDOT:PSS CE reached a higher η than that of Pt-based cell. (II) Carbonaceous-type CEs, i.e., the composite films of nano-porous carbon black nanoparticles/ sulfonated-poly(thiophene-3-[2-(2-methoxyethoxy)-ethoxy]-2,5-diyl) (CB NPs/s-PT), were investigated in Chapter 6 to provide large surface area, fast eletrolyte penetratoin, and rapid reaction rate for I3– reduction. When a composite film contains 5 wt% CB NPs, the pertinent DSSC reached best η of 9.02%, which is even higher than that of Pt-based DSSC. The s-PT is introduced as a novel thiophene-based water-soluable conducting polymer for CE in DSSC for the very first time. Under weak sunlight, the cell with CB NPs/s-PT composite CE still maintains good performance, indicating its good compatibility at both outdoor or indoor electronics. (III) Conducting polymer type CEs, including poly(3,4-ethylenedioxythiophene) (PEDOT) and six different ionic-liquid-doped PEDOT films were systematically investigated in Chapter 7. Six different ionic liquids containing three imidazolium cations with different alkyl chains (–C2H5, –C6H13, –C10H21) and four anions (BF4−, PF6−, SO3CF3−, TFSI−) were used as the chemical dopants to increase the surface area of PEDOT films and to ehance the conjugation of the PEDOT films, respectively. Among them, the cell with HMIPF6-doped PEDOT and HMITFSI-doped PEDOT CEs reached higher η’s than that of Pt-based DSSC. In brief, this dissertation explores four Pt-free composite films of Zn3N2/PEDOT:PSS, HMIPF6-doped PEDOT, HMITFSI-doped PEDOT, and CB NPs/s-PT are a promising substitutions of Pt due to their outstanding properties, i.e., good electro-catalytic ability for I3– reduction, low-cost, simple preparation process, and easy for large-scale production.
In the case of iodide-free electrolyte, we designed a novel dual-channel ionic liquid compound (Chapter 8), 1-butyl-3-{2-oxo-2-[(2,2,6,6-tetramethylpiperidin-4-yl)amino]ethyl}-1H-imidazol-3 -ium selenocyanate (ITSeCN), to further improve the cell effiency of DSSCs. ITSeCN is designed to contain dual redox channels of imidazolium-functionalized TEMPO (cationic redox mediator) and selenocyanate (anionic mediator). Thereby, the ITSeCN shows the favorable redox natures, which gave more positive standard potential, larger diffusivity, and better kinetic heterogeneous rate constant than those of iodide. To further investigate a suitable electro-catalytic material for triggering the redox of ITSeCN mediator, several materials were used: (1) Pt (metal type), (2) PEDOT (conducting polymer type), (3) CoSe (transition metallic compound type), and (4) carbon black (carbonaceous type) films were chosen to represent four types of electro-catalytic materials in DSSCs. Finally, the DSSCs with PEDOT and CoSe CEs achieved better performance than that of the Pt-based DSSC. Therefore, it can be infered that the transition metallic compound type CEs would be more suitable for our new synthesized-ITSeCN mediator than the others.

並列關鍵字

Counter electrodes ； dye-sensitized solar cells ； electro-catalyst ； electrolyte ； iodide-free ； Pt-free

參考文獻

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