以聚電解質/奈米碳管複合材料製作軟質固態電解質在染料敏化太陽能電池上之應用

Abstract

由於目前固態染料敏化太陽能電池的效率普遍不高，加上具有可撓曲性的太陽能電池已成為趨勢，為了提升效率，考量電子的傳導機制，本研究希望利用低玻璃轉移溫度的高分子，來製作軟質固態電解質，除了藉由良好的離子流動特性來提高效率外，期許能應用於可撓曲電池元件。因此，我們利用Butyl acrylate(BA)與帶有羧酸基的單體Acrylic acid(AA)、Methacrylic acid(MAA)以無乳化劑聚合方法聚合出共聚高分子。透過DSC儀器分析證實上述共聚物的玻璃轉移溫度均低於室溫25℃，屬於具離子性軟質共聚高分子，並將這些共聚高分子應用於DSSC的電解質中，製成軟質固態電解質。 實驗第一部分：改變三種BA與AA、BA與MAA單體之間的比例，製成軟質固態電解質後，其DSSC在1.5AM 100mW/cm2太陽光照射下，實驗結果發現在P(BA1-co-AA1)的系統中，其光電轉換效率可達3.29±0.09％，開路電壓與短路電流分別為0.65±0.05V和9.01±0.10 mA/cm2。在P(BA1-co-MAA1)的系統中，其光電轉換效率可達3.71±0.06％，開路電壓與短路電流分別為0.68±0.05 V和 11.11±0.12 mA/cm2。 實驗第二部分：由於利用具離子性高分子共聚物作為軟質固態電解質的DSSC，效率不及於膠態與液態電解質，因此第二部分將藉由引入MWCNT來改質上述軟質固態電解質。實驗結果發現，添加MWCNT於上述軟質固態電解質可提升光電轉換效率，在P(BA3-co-AA2)的系統中，當加入0.3 wt％的MWCNT時，其光電轉換效率可提升至5.09±0.08％，開路電壓與短路電流分別提升至0.70±0.09 V和13.27±0.12 mA/cm2。在P(BA3-co-MAA2)的系統中，加入0.3 wt％的MWCNT，光電轉換效率可提升至5.15±0.11％，開路電壓與短路電流分別提升至0.72±0.05 V和12.55±0.09 mA/cm2。顯示添加0.3 wt％的MWCNT，開路電壓與短路電流均大幅提升，軟質固態電解質的導電度也顯著增加，由DSC測試結果發現P(BA3-co-AA2)的系統當加入0.3 wt％的MWCNT時，Tg由9.89℃降到6.90℃。而在P(BA3-co-MAA2)的系統，Tg由15.48℃降到-0.79℃。顯然MWCNT可經由羧基陽離子-π作用力吸附P(BA3-co-AA2)的AA鏈段和P(BA3-co-MAA2)的MAA鏈段，不但降低共聚物的Tg而且可以增加MWCNT在軟質固態電解質的分散性。透過SEM及TEM照片證實MWCNT在軟質固態電解質的分散性相當好，因此可以提供一個很好的電解質氧化還原電子傳遞的管道。

The power conversion efficiency of solid-state dye-sensitized Solar Cells (DSSCs) reported in the recent literature is still low and the flexible solar cells is deemed to be the trend of future. Therefore, to improve the power conversion efficiency of solid-state DSSCs and achieve the goal of flexibility, this research tried to use the copolymers with the glass transion temperatures lower than the room temperature to fabricate the soft solid-state electrolytes for DSSC. We used butyl acrylate (BA) to copolymerize with two kinds of monomers containing carboxylic acid group, acrylic acid (AA) and methacrylic acid (MAA), through emulsifier-free emulsion polymerization. The glass transion temperatures of resulting copolymers measured by differential scanning calorimetry (DSC) were all below room temperature (25℃). Then we used these soft copolymers to prepare the soft solid-state electrolyte for DSSCs. In the first part of this resreach, we changed the molar ratio of BA and AA (MAA) monomers for copolymerization. By using 1.5AM 100mW/cm2 sunlight, we found the power conversion efficiency of DSSC using P(BA1-co-AA1) electrolyte system was 3.29±0.09％, and its open circuit voltage (Voc) and short circuit current density (Jsc) were 0.65±0.05V and 9.01±0.10 mA/cm2. Whereas, the DSSC using P(BA1-co-MAA1) electrolyte system had power conversion efficiency of 3.71±0.06％, open circuit voltage value of 0.68±0.05 V , and short circuit current density of 11.11±0.12 mA/cm2. In the second part of this research, due to lower power conversion efficiency for the DSSCs using ionic copolymer systems as a solid-state electrolyte compared to liquid and gelled-type electrolytes, we incorporated MWCNT with above soft solid-state electrolyte to increase the electric conductivity. The results showed that the DSSCs using P(BA1-co-AA1) system containing 0.3 wt% MWCNT had the best performance with the power conversion efficiency increasd to 5.09±0.08％. Voc and Jsc were 0.70±0.09 V and 13.27±0.12 mA/cm2 respectively. Moreover, the DSSCs with P(BA1-co-MAA1) system containing 0.3 wt% MWCNT also showed the best result with the power conversion efficiency increased to 5.15±0.11％. Voc and Jsc were 0.72±0.05 V and 12.55±0.09 mA/cm2 respectively. Apparently, addition of 0.3wt% MWCNT to the solid-state electrolyte increased both Voc and Jsc and also elevated the electric conductivity. The glass transion temperature of P(BA3-co-MAA2) measured by DSC decreased from 9.89℃to 6.90℃ by adding 0.3wt% MWCNT . The glass transion temperature of P(BA3-co-MAA2) containing 0.3wt% MWCNT also decreased from 15.48℃ to -0.79℃. It implies that MWCNT could adsorb the AA segment of P(BA3-co-AA2) and MAA segment of P(BA3-co-MAA2) through carboxylic cationic-π interaction.