改良花青素染料敏化太陽能電池之性能

On the performance improvement of the dye-sensitized solar cells based on anthocyanin.

李堃源(Lee, Kun Yuan)

指導教授 ： 徐邦達

國立清華大學/生命科學院/生物資訊與結構生物研究所/碩士(2016年)

摘要

染料敏化太陽能電池(dye sensitized solar cells, DSSCs)是目前新穎的一種薄膜太陽能電池。在本論文中我們使用來自紫高麗菜的花青素作為太陽能電池的染料來源。有別於化學染料，天然染料具有無毒性、成本低廉、容易取得、對自然環境友善等優點。本論文中嘗試使用二氧化鈦電極退火及添加促進劑的方式，希望將染料敏化太陽能電池的光電轉換效率及其他各項數值有更進一步的提升。
我們在組裝太陽能電池前先將二氧化鈦電極進行退火，二氧化鈦電極以460°C活化30分鐘，而白金電極亦用高溫爐以350°C溫度放置30分鐘。經過退火過後的染料敏化太陽能電池在光電轉換效率的表現可以提升75.9%，而與光電轉換效率有關的幾項數據如短路電流密度 (short current density, Jsc in mA/cm2) 改變最為明顯，從2.56 mA/cm2提升至4.34 mA/cm2上升了69%。填充因子 (FillFactor)從0.66提升至0.7。開路電壓 (open-circuit voltage, Voc in V)的改變則不大。
另外在電極的浸泡上我們發現了在40°C的溫度下浸泡10分鐘時染料敏化太陽能電池的光電轉換效率會達到最大值。我們也繼續嘗試醣類 (carbohydrates)中的兩種寡醣類來做促進劑 (enhancer)，分別是異麥芽寡糖(isomaltooligosaccharide)及木寡糖 (xylooligosaccharides)，我們發現在木寡糖濃度達到300 mg/mL時染料敏化太陽能電池的效率表現會來到最大值2.145%。
脫氧膽酸 (deoxycholic acid)常被用來當作花青素的共同吸附劑 (coadsorbent)，因其可以有效的提升光電轉換效率。在上述木寡糖濃度達到300 mg/mL的狀況下加入脫氧膽酸使其濃度達到40 mM時，光電轉換效率可以再被提升到2.366%。總合上述一連串的方法可使光電轉換效率從原先無退火的1.034%提升至2.366%，增加128.8%。
我們也將從花青素萃取液中分離出來的impurity fraction (IPF-1)進行濃縮，並且以促進劑的方式加回到花青素萃取液中，發現濃縮後的IPF-1對於光電轉換效率亦有相當程度的提升，從1.501%提升至1.732%上升了15.3%的效率，證實了紫高麗菜的花青素萃取液含有可以提升染料敏化太陽能電池效率之物質，它們很可能也是某種醣類。因此我們可以直接使用天然染料並不需要添加其他物質，只需在製程上加以改良即能有效率上的提升。希望這些研究在一切崇尚自然的訴求下，能為太陽能電池的製造提供一個更天然、成本更低的新選擇。

關鍵字

染料敏化太陽能電池 ； 花青素 ； 醣類 ； 退火 ； 紫高麗菜

並列摘要

Dye-sensitized solar cells (DSSCs) is a relatively new thin film solar cells. In this study DSSCs were fabricated using anthocyanin as natural dye which was extracted from red cabbage (Brassica oleracea var. capitata f. rubra). Naturally pigments are friendly to environment, abundant in supply, easily accessible and highly absorptive in the visible region, all make them good candidates as alternative photosensitizers. In order to obtain a better performance of dye sensitized solar cells, several means to enhance the efficiency of DSSCs were explored.
Activation of electrode was done before assembly. TiO2 electrode was activated at 460oC for 30 mins and platinum electrode at 350 oC for 30 mins. Electrode activation can improve the efficiency by 75.9%. Here the short current density (Jsc in mA/cm2) was raised form 2.56 mA/cm2 to 4.34 mA/cm2, and fill factor was elevated from 0.66 to 0.7. No significant change in open circuit voltage.
An optimal soaking conditions for electrode were found to have a duration of 10 min and temperature at 40°C. In addition, carbohydrates have been shown to be performance enhancers. Two oligosacchrides, isomaltooligosaccharide (IMO) and xylooligosaccharides (XOS) were tested. The highest efficiency (2.145%) was reached when 300 mg/mL of XOS was used.
Deoxycholic acid (DCA) is a common coadsorbent used along with anthocyanin, for it can act as an effective efficiency enhancer. A combination of 300 mg/mL XOS and 40 mM DCA together could boost the efficiency of DSSCs form 1.034% to 2.366% (an accumulative improvement of 128.8%).
Impurity fraction (IPF-1) obtained from anthocyanin extract during purification was concentrated, and added back to anthocyanin extract as enhancer. The efficiency was raised from 1.501 to 1.732% (an improvement of 15.3%), indicating that anthocyanin extract contained unknown substances that can enhance the performance of DSSC. They are most likely some kinds of carbohydrates. It seems that we can effectively promote the efficiency using this natural dye without adding anything else, provided an improved process is employed. With the prevailing demand for being natural, our research may provide a good choice for making solar cells in a more natural way and at lower cost.

並列關鍵字

dye sensitized solar cells ； anthocyanin ； red cabbage ； annealing ； saccharide

參考文獻

nanoparticles in dye-sensitized solar cells. Dalton Transactions(45), 10078-10085.

Treatment of TiO2 Nanoparticles on Photovoltaic Performance of Fabricated

Aswani Yella, Hsuan-Wei Lee, Hoi Nok Tsao,Chenyi Yi,Aravind Kumar Chandiran,Md.Khaja Nazeeruddin,Eric Wei-Guang Diau,Chen-Yu Yeh,Shaik M Zakeeruddin,Michael Grätzel. (2012). Porphyrin-Sensitized Solar Cells with Cobalt (II/III) – Based Redox Electrolyte Exceed 12 Percent Efficiency. SCIENCE,334(629-634).

Bang, So Yeon, Ko, Min Jae, Kim, Kyungkon, Kim, Jong Hak, Jang, In-Hyuk, & Park, Nam-Gyu. (2012). Evaluation of dye aggregation and effect of deoxycholic acid concentration on photovoltaic performance of N749-sensitized solar cell. Synthetic Metals, 162(17-18), 1503-1507.

sensitizers for dye-sensitized solar cells. Solar Energy, 84(10), 1833-1837.