帶丙烯酸基離子液體聚合物及其奈米碳管複合物在染料敏化太陽能電池電解質上的應用

Abstract

本研究主要分為兩部份，第一部分合成出兩種帶有丙烯酸官能基的離子液體單體1-methyl-3- [2-[(1-oxo-2-propenyl)oxy]-ethyl]-imidazolium iodide (DIL)和1-methyl-3- [2-[(1-oxo-2-propenyl)oxy]-ethyl]-benzimidazolium iodide (BDIL)，藉由原子轉移自由基聚合成離子液體高分子，透過液態超導核磁共振鑑定結構。再利用溴化碳管起始聚合離子液體單體，將離子液體聚合物－奈米碳管複合材料，透過高解析穿透式電子顯微鏡觀測型態，再利用熱重分析儀與X光光電子光譜進行材料鑑定。第二部份將複合材料以不同重量比例，加入1-methyl-3-propyl imidazolium iodide (PMII)離子液體電解質中做成太陽能電池元件，分析不同複合材料的光電轉換表現。再利用離子液體高分子配成膠態電解質，製備成元件探討其光電轉換效能。 第一部分研究結果發現帶有咪唑陽離子的離子液體，利用末端基分析純高分子的分子量與其奈米碳管複合物根據熱重分析數據計算所得分子量相同，可知DIL成功地利用溴化碳管起始聚合，產物稱之為MWNT-PDIL。而帶有苯駢咪唑陽離子的離子液體，因單體具有較強的共振結構，使其在利用溴化碳管起始聚合時，單體經由π－π stacking吸附到奈米碳管表面，造成熱重分析所得分子量僅有純高分子聚合的十分之ㄧ，產物稱之為MWNT-BDIL。而純碳管與單體BDIL在室溫下混合，由熱重分析與單體共振結構模擬數據計算，得知BDIL在奈米碳管表面形成單層吸附，混合產物稱之為MWNT(untreated)-BDIL。上述三種奈米碳管-離子液體複合物皆可在離子液體PMII中均勻分散。 第二部分太陽能電池元件測試部分，純PMII電解質測得效率約為5.00%，當加入0.05wt%的MWNT-PDIL可得到5.59%的轉換效率，加入0.5wt%的MWNT-BDIL得到效率為5.09%，而加入0.05wt%的MWNT(untreated)-BDIL所得效率為5.44%。因為我們所改質的奈米碳管，其分散良好，可以幫助電子傳導，提升電流，使得效率有所提升。在高分子膠態電解質系統中，當使用高Tg的PBDIL時，因其分子局部運動性太差，使得離子不易傳遞，造成太陽能電池效率差。而選用Tg較低的高分子PDIL，相較於PBDIL有較好的離子傳遞性，因此可以量得1.16%的效率，當我們添加不同改質奈米碳管複合物時，電流值皆有提升，尤以純碳管系統增加了1.5倍。當增加MWNT(untreated)-BDIL濃度至0.5wt%時，短路電流得到最高值8.51 mA/cm2，光電轉換效率高達3.55%。由此，外層包覆單層離子液體單體的純奈米碳管，可在高分子電解質中分散均勻，吸引負電的奈米碳管不僅幫助碘離子傳導，也提供了較短的路徑，因此對於太陽能電池的電流傳遞有相當好的助益。

This research mainly focused on the fabrication and applications of new type ionic liquid polymers and their carbon nanotube composites on dye sensitized solar cell. There are two major parts in this research. For the first part, we synthesized two kinds of ionic liquid monomer carrying acrylic functional group , 1-methyl-3- [2-[(1-oxo-2-propenyl) oxy]-ethyl]- imidazolium iodide (DIL) and 1-methyl-3- [2-[(1-oxo-2-propenyl) oxy]-ethyl]- benzimidazolium iodide (BDIL), and polymerized them by atom transfer radical polymerization, and then used the brominated carbon nanotube to initiate polymerization under the same condition. All the nano-composites were characterized by high-resolution TEM、x-ray photoelectron spectroscopic and thermo-gravimetric analyzer. For the second part, we added different weight percentage of the nano-composite into ionic liquid electrolyte system for investigating the DSSC performance. Besides, we also used the polymerized ionic liquids to prepare the gel-type electrolyte system for the DSSC. In the first part of the research, both ionic liquid monomers were successfully synthesized and characterized. For the DIL system, the molecular weight estimated from NMR for pure polymer (PDIL) was similar to that estimated from TGA for MWNT-PDIL nano-composite. But for the BDIL system, the molecular weight estimated from NMR for pure polymer (PDIL) was tenfold of that from TGA for MWNT-BDIL nano-composite. It is due to the fact that BDIL was adsorbed on carbon nanotube by π－π stacking resulting from its strong resonance structures. By directly mixing the untreated cabon nanotube with BDIL at room temperature, we found that the BDIL monomer also adsorbed on carbon nanotube in mono-layer on the basis of the TGA data and the simulation result for the resuitng MWNT(untreated)-BDIL nano-composite. All kinds of nano-composites were able to homogeneously disperse in PMII. In the second part, the photon to electron power conversion efficiency of DSSCs with PMII ionic liquid electrolyte system was 5.00%.When adding the proper amouts of different nano-composites into ionic liquid electrolyte system, the efficiency were raised to 5.59%、5.09% and 5.44% for 0.05wt% MWNT-PDIL、0.5wt% MWNT-BDIL and 0.05wt% MWNT(untreated) -BDIL, respectivily. The higher efficiency mainly resulted from the higher photo current, implying that the carbon nanotube could enhance the charge transfer. For the PBDIL-base gel electrolyte system, the high Tg of PBDIL impeded the ion diffusion leading to poor photovoltaic performance. For the PDIL-base system which has lower Tg than that of PBDIL, the power efficiency was 1.16%. On the other hand, adding nano-composite into the PDIL-base system further increased the photo current, implying that carbon nanotube provided a short path for charge transfer. The addition of 0.5wt% MWNT(untreated)-BDIL provided the best performance and the efficiency of fabricated DSSC could reach to 3.55%.