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  • 學位論文

添加層狀奈米矽片於膠態電解質中 以增進染料敏化太陽電池之性能

Enhancing the Performance of Dye-Sensitized Solar Cells by Incorporating Nanosilicate Platelets in Gel Electrolytes

指導教授 : 何國川

摘要


染料敏化太陽能電池(染敏電池)發展至今已可達到10~11%的轉換效率,但由於所使用的液態電解質有易揮發、洩漏與熱穩定性不佳等問題,使得染敏電池的應用受到限制。為了解決這些問題,許多研究團隊以膠態電解質來取代液態電解質以增加長期穩定性。然而,受限於離子導電度低等問題,膠態染敏電池的效率遠低於液態染敏電池。 許多文獻指出,透過無機粒子的添加可以提升膠態系統電池的性能表現,而在本研究中,則是在膠態電解質中添加具有高縱橫比(aspect ratio)的層狀奈米矽片,探討層狀奈米矽片的添加對於電解質以及電池性能的影響。 層狀奈米矽片(Nanosilicate platelet, NSP)是由黏土(clay)經由脫層分散,並加以改質而成,在本實驗中所探討的黏土包含蒙脫土(Montmorillonite, MMT)以及雲母(Mica)兩類。由於天然的黏土為親水性,因此不論是蒙脫土或是雲母皆須要經由改質後才能均勻分散在電解質中。而本章所探討的改質蒙脫土分別是以采酮 (t-Octylphenoxypolyethoxyethanol, C14H22O(C2H4O)n, n=9-10, Triton X-100®) 改質的NSP-Triton® X-100以及十八烷基胺(octadecylamine)所改質的NSP-C18H37NH3+Cl-,改質雲母則是接有烷基的alkyl-nanomica (AMNM)。 在改質蒙脫土的探討上,先以四乙氧基矽烷-采酮(TEOS-Triton® X-100)膠態電解質做為添加對象。透過四乙氧基矽烷-采酮電解質中碘(I2)濃度變化對應效率的變化,可求得在此系統中,在碘鹽(1-Propyl-3-methyl-imidazolium(PMII))為0.6 M時,碘濃度最佳條件為0.05 M。在此基準下,在電解質中加入不同重量百分比的NSP-Triton® X-100,發現在NSP-Triton® X-100添加量為0.5 wt% 時,可將效率從3.60% 提升至4.65%。透過交流阻抗分析得知,I-/I3-於電解質中的擴散阻力(Rdiff.)在0.5 wt% 的NSP-Triton® X-100添加量時有最低值,證明NSP-Triton® X-100在四乙氧基矽烷-采酮膠態電解質中的添加,有正面助益。 同樣以四乙氧基矽烷-采酮電解質做為添加對象,另一改質蒙脫土 NSP-C18H37NH3+Cl- 的添加卻會降低電池的性能表現,而交流阻抗分析的結果顯示,添加NSP-C18H37NH3+Cl-會造成I-/I3-在電解質中的擴散阻力增加,推測是由於C18H37NH3+Cl-為陽離子界面活性劑,使得陰離子的I-及I3-移動受到限制而增加阻抗。 由於四乙氧基矽烷-采酮膠態電解質成分含有二氧化矽粒子,為了減少系統的複雜性並進一步探討NSP-Triton® X-100對於電解質的影響,在後續實驗使用二氟乙烯-六氟丙烯共聚高分子(PVDF-HFP)膠態電解質做為添加對象。實驗結果顯示,NSP-Triton® X-100的添加也可以提升PVDF-HFP膠態電池的效能表現,當添加量為5 wt% 時,可提升效率從4.01提高至5.24%。透過交流阻抗分析,也可以得知NSP-Triton X-100的添加能夠增加電池效能,主要是在於其添加會造成Rdiff.的下降。另外,分析電解質離子導電度(ionic conductivity)的結果中,也發現NSP-Triton® X-100的添加能夠提升離子導電度。透過X光繞射分析(X-ray diffraction analysis, XRD)可得知NSP-Triton® X-100的添加會造成PVDF-HFP膠態電解質結晶度的下降。在長期穩定性的量測中,添加有NSP-Triton® X-100的電池在1000小時後仍有93.4%的初始效率,相對高於不添加的83.3%。 雲母的構造和蒙脫土相似,但片徑較蒙脫土來的大。當AMNM添加量為3 wt% 時,可將電池效率提升至5.7%,Rdiff 從52.1降低至22.1Ω。透過XRD分析也可以看到AMNM的添加會造成PVDF-HFP膠態電解質結晶度的下降。而為了進一步提升此系統的效能,透過分散300 nm的PMMA球於二氧化鈦膠體溶液中來增加孔洞,減少膠態電解質與二氧化鈦/染料間的阻力,可進一步提升效率至6.7%,並在交流阻抗分析、電子壽命量測以及光子-電子轉換效率的量測中都有ㄧ致性的結果。另外,透過cell gap的減少,可以增加fill factor而再提升效率至7.96%。

並列摘要


Dye sensitized solar cells (DSSCs) already could reach about10~11% conversion efficiency, which could comparable with amorphous silicon solar cells. However, there are problems of liquid electrolytes that confine the application of DSSCs, including easy evaporation, leakage and poor thermal stability. In order to solve these problems and improve the long term stability of cells, many research groups try use gel electrolytes to replace with liquid electrolytes. Nevertheless, because the low ionic conductivity, gel-type DSSCs have lower efficiency when compare with liquid-type. Some papers enhance the cell performance of gel-type DSSCs by incorporating nanoparticles. In this study, adding layer nanosilicates which have high aspect ratio into gel electrolyte and discussing the effects on electrolytes and cells. Layered nanosilicates are prepared by exfoliated process from clay and modified. Two types of clay, montmorillonite (MMT) and mica, are being studied. Because nature clay is hydrophilic, they could be dispersed uniformly only after being modified. The modified MMT is NSP-Triton® X-100 modified and NSP-C18H37NH3+Cl-, which is modified by t-Octylphenoxypolyethoxyethanol, (C14H22O(C2H4O)n, n=9-10, Triton X-100®) and octadecylamine, individually. And modified mica is alkyl-nanomica (AMNM), modified by alkyl group. In the study of modified MMT, we first incorporation MMT into tetraethoxysilane-t-Octylphenoxypolyethoxyethanol(TEOS-Triton® X-100) gel electrolytes. We could find the best concentration of iodine is 0.05 M when the 1-Propyl-3-methyl-imidazolium(PMII) is 0.6 M by the results of cell performance with iodine concentration. Under this base, various weight percent of NSP-Triton® X-100 were added into electrolytes, and it was found that the efficiency could be raised from 3.6 to 4.65% when the NSP-Triton® X-100 is 0.5 wt%. From the AC impedance results, the gel-type DSSCs with 0.5 wt% NSP-Triton® X-100 has the lowest I-/I3- diffusion resistance (Rdiff.). These results prove that by incorporating NSP-Triton® X-100 could enhance the cell performance. Also using TEOS-Triton® X-100 as gel electrolytes, adding another types of modified MMT- NSP-C18H37NH3+Cl- into them. However, the incorporation of NSP-C18H37NH3+Cl- would decrease the performance of cells, and from the AC impedance results, they would raise the diffusion resistance of I-/I3- . It might because C18H37NH3+Cl- is a cationic surfactant, which could hinder the motion of I-/I3-, result in the enhancement of diffusion resistance. In order to decrease the complexity of systems due to there are SiO2 particles in TEOS-Triton® X-100 gel electrolytes. Another gel electrolyte, Polyvinyidene fluoride-co-hexafluoro propylene (PVDF-HFP) gel electrolytes were being used. It was found that by incorporating NSP-Triton® X-100 into PVDF-HFP gel electrolytes could also enhance the cell efficiency, which could be raised from 4.01 to 5.24% when the adding amount is 5 wt%. And from the result of impedance, it also could found that the enhancement of efficiency is mainly due to the decrease of Rdiff.. Besides, adding NSP-Triton® X-100 could also raise the ionic conductivity of PVDF-HFP gel electrolyte. By using X-ray diffraction, it could be found that adding NSP-Triton® X-100 would decrease the crystallinity of PVDF-HFP, hence increase the ionic conductivity and decrease the Rdiff.. In the long term stability test, the gel-type DSSCs with 5 wt% NSP-Triton® X-100 have 93.4% initial efficiency which higher than the bare PVDF-HFP gel-type DSSCs (83.3%). Mica has the similar structure with MMT, but it has the larger dimension. It could raise the cell efficiency up to 5.7% and decrease the Rdiff from 52.1 to 22.1Ω when the loading is 3 wt%. It also could be found that the crystallinity would decrease when adding AMNM. To further raise the performance, by dispersing 300 nm PMMA spheres in the TiO2 paste could increase pores of TiO2 electrode, which could decrease the resistance between TiO2/dye and electrolyte, result in the higher efficiency (6.7%). The results could also be confirmed by electron life time and incident light to photon conversion efficiency (IPCE). Also, by decreasing the cell gap, could further enhance the efficiency up to 7.96%.

參考文獻


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