界面改質劑與有機添加劑對於聚己基噻吩/無機金屬氧化物太陽能電池之影響與應用研究

Effect of interface modifier and organic additive on photovoltaic properties of poly(3-hexylthiophene)/inorganic metal oxide solar cells

許志偉(Chih-Wei Hsu)

指導教授 ： 王立義

國立臺灣大學/工學院/高分子科學與工程學研究所/博士(2008年)

https://doi.org/10.6342/NTU.2008.00859

摘要

本篇論文的研究中，我們以界面改質的方式來改質無機金屬氧化物並將其與有機導電高分子製備成太陽能電池元件，以此一有機/無機太陽能電池來做一有系統地討論界面改質劑的影響與其在太陽能電池的應用方式:
首先，我們合成出一系列含有不同共軛長度結構(T系列)與含有不同烷基長碳鏈鏈長結構(N系列)之磷酸小分子，並將其以自組裝單層膜的方法應用在一最乾淨簡單的聚己基噻吩/二氧化鈦雙層結構系統中來探討含不同化學結構之界面改質劑對於太陽電池的光伏打效應的影響: 發現這些改質劑的存在並不影響P3HT的吸光行為，但螢光焠滅效率卻隨著界面改質劑的能隙值縮減與LUMO的下降而增加，顯示有機/無機界面間電荷分離的能力受到界面改質劑的影響，並隨著界面改質劑的能隙值縮減與LUMO的下降而有所提升；而這些具有不同化學結構之界面改質劑確實會影響元件的表現行為，尤其是在於開路電壓與短路電流，開路電壓會隨著界面改質劑的能隙值縮減與LUMO的下降而變小，但幾乎不隨界面改質劑的烷基碳鏈長度而變；而短路電流卻會隨著界面改質劑的能隙值縮減、LUMO的下降與烷基碳鏈的縮短而變大。接著，我們進而將此含共軛結構之有機小分子作為界面活性劑，直接應用在溶液製程(solution process)的混掺型太陽能電池系統中以此來改善與探討在混掺型太陽能電池結構中的經界面改質劑改質之無機奈米粒子與有機導電性高分子相容性與光伏打效應的影響: 藉由TEM可發現以界面改質劑改質過之氧化鋅奈米棒狀粒子在P3HT中產生如網狀般之連續通路而沒有各自聚集的現象，由此可知其兩相之相容性變好，因此兩相的接觸面積可以大幅地提升。而藉由改質過之氧化鋅奈米棒狀粒子所製備的混掺元件與無改質的氧化鋅奈米棒狀粒子所製備的元件比較起來，其PCE值均可看出有明顯地提升，另外，我們亦可觀察到界面改質劑改質過之氧化鋅奈米棒狀粒子與P3HT混掺元件的Voc值同樣會隨著界面改質劑能隙值減少與LUMO下降而降低而Jsc值則會增加，此現象與雙層接合結構元件所表現出的現象吻合。
第三部份我們則是利用有機金屬分子copper phthalocyanine (CuPc)直接蒸鍍在太陽能電池元件結構中，利用其在300至400nm之紫外光範圍具有強吸收的特性來當成一有效的紫外光濾光層來減少氧化鋅表面hole trapping level的產生，進而以此來直接取代PEDOT:PSS以及改善元件的光伏打特性及效能。結果發現CuPc濾光層確實能夠避免氧化鋅奈米棒狀粒子因吸收了300至400nm之紫外光而產生元件漏電的現象;並且，於照光情況下我們可知在加入CuPc濾光層後元件之開環電壓與填充因子會隨著CuPc膜厚的增加而有顯著的提昇，不過我們也可觀察到隨著CuPc膜厚的增加，元件的短路電流反而越小。另外，藉由EIS量測我們可知隨著CuPc濾光層厚度的增加R2電阻(並聯電阻)也隨之增大。而根據理論公式我們可知Rp並聯電阻越大，則開環電壓值亦越大；我們的實驗結果完全符合理論公式所述。
因此，藉由以CuPc為濾光層所得的結果與概念，並且結合界面改質劑應用的構想，所以我們更進一部地利用在300至400nm之紫外光範圍具有強吸收的碳六十衍生物(1,2-methanofullerene C60)-61,61-dicarboxylic acid分子及有機染料分子(N3 dye)作為界面改質劑及紫外光濾光器，直接將紫外光濾光層包覆在氧化鋅奈米棒狀粒子表面以期減少氧化鋅表面hole trapping level的產生，進而以此來改善元件的光伏打特性及效能。我們發現對於以(1,2-methanofullerene C60)-61,61-dicarboxylic acid分子改質製備的元件部份，確實有效地改善元件漏電的現象並且以(1,2-methanofullerene C60)-61,61-dicarboxylic acid分子所改質的元件所表現出的光電轉換效率比以N3 dye分子所製備的元件效能來的好，IPCE量測亦顯示(1,2-methanofullerene C60)-61,61-dicarboxylic acid分子所改質製備之元件具有最佳的IPCE效率，可高達17.5%。

關鍵字

有機太陽能電池 ； 自組裝單層膜 ； 界面改質劑 ； 二氧化鈦 ； 氧化鋅 ； 聚己基噻吩 ； 奈米棒狀粒子 ； 紫外光濾光層 ； CuPc ； 碳六十衍生物

並列摘要

In this study, we investigate the effect of interface modification of metal oxide on photovoltaic properties of conducting polymer/metal oxide solar cells, systematically.
First, two series of organic molecules with different chemical structures, 2-oligothiophene phosphonic acid with various thiophene rings (T-series) and ω-(2-thienyl) alkyl phosphonic acid with various alkyl chain lengths (N-series), as interface modifier, to investigate the structural effect of modifiers on the performance of organic/inorganic bilayered photovoltaic devices. The results indicate the interface modifier does not affect absorption behavior of P3HT, but PL quenching efficiency as increased with energy bandgap or LUMO of interface modifier decreasing. It reveals the charge separation of organic/inorganic interface will be affected by chemical structures of interface modifier. Therefore, these interface modifiers that with different chemical structures will affect the photovoltaic properties of devices, especially in Voc and Jsc. Voc will decrease with energy bandgap or LUMO of interface modifier decreasing, but does not be affected by alkyl chain length of interface modifiers changed. In addition, Jsc will increase with energy bandgap, alkyl chain length or LUMO of interface modifier decreasing.
Second, we apply the above interface modifiers as surfactant in solution process of blend device system. TEM image indicate the modified ZnO nanorods without large scale aggregation and form a continued path way in P3HT matrix. Therefore, the increased compatibility and contact area between P3HT and ZnO nanorods has been demonstrated. PCE value of modified ZnO nanorods/P3HT polymer blend devices are higher than without modified ZnO nanorods prepared devices. Furthermore, the trends of Voc and Jsc of modified ZnO nanorods/P3HT polymer blend solar cell are consisted with above layered system.
Third, we demonstrate a low leakage current in a blend ZnO nanorods/P3HT polymer solar cell aided by an inherent UV-cutter layer (copper phthalocyanine CuPc). The power conversion efficiency is found to be appreciated from 0.15% to 0.44% and the open circuit voltage from 0.23 to 0.60 V, at post-introduction of UV-cutter, predominantly due to the growth in the shunt resistance of the device. Impedance spectroscopy studies revealed a strong negative photovoltaic effect of ZnO with UV-induced hole-trapping leading to the degradation of the solar cells performance. The incorporation of UV-cutter in the device, achieved by direct growth of CuPc layer between nr-ZnO and anode, has clearly promoted the efficiency and device operation satiability.
Finally, we synthesize a C60 derivative, (1,2-methanofullerene C60)-61,61-dicarboxylic acid, with a 300-400nm absorption region as surface UV filtered surfactant to apply in blend ZnO nanorods/P3HT polymer solar cell. The decreased leakage current behavior of blend ZnO nanorods/P3HT polymer solar cell has been demonstrated. PCE value and operation satiability of (1,2-methanofullerene C60)-61,61-dicarboxylic acid modified ZnO nanorods/P3HT devices are better than N3 dye (P type) modified devices. In addition, 17.5% IPCE value of (1,2-methanofullerene C60)-61,61-dicarboxylic acid modified ZnO nanorods/P3HT device has been revealed.

並列關鍵字

Organic solar cell ； self-assembled monolayers ； interface modifier ； titanium dioxide ； Zinc oxide ； Poly (3-hexylthiophene) ； Nanorods ； UV cutter ； CuPc ； C60 derivative

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