以自組裝單層膜修飾的氧化銦錫為陽極之高分子太陽能電池

Polymer solar cell using self-assembled monolayer modified ITO as anode

許舒涵(Shu-Han Hsu)

指導教授 ： 芮祥鵬 ； 王立義

國立臺北科技大學/工程學院/有機高分子研究所/碩士(2011年)

摘要

高分子太陽能電池近幾年成為大家爭先研究的領域，但是成本以及生命周期長短一直是個還需再改善的部分。用來當作電洞傳導層的PEDOT:PSS，具酸性且易吸水，因此我們將一系列具有羧酸、苯環結構及不同強度的推拉電子基團 (-CN、-CF3、-OCH3、-NH2) 之分子自組裝在ITO表面成為自組裝單層膜(self-assembled monolayer, SAM)，取代PEDOT:PSS作為電子阻擋材料以建構高分子太陽能電池。
在第一階段的實驗，我們以測量表面的接觸角(contact angle)來觀察分子膜的成長情形；使用X射線光電子能譜儀(XPS)了解分子在表面的元素分佈；利用AFM測量表面的粗糙度變化及分子的聚集情況。另外，應用光電子譜分析儀(AC-2)分析經有機分子修飾後的功函數(work function)，數據顯示表面的功函數與苯環上取代基的拉電子能力強弱相關。最後，我們進一步以這些SAM-modified ITO為陽極，製備成P3HT/PCBM-based太陽能電池。其中，使用帶有-CN或-CF3官能基的分子時，元件的開環電壓可做到近似於PEDOT:PSS-based元件，而且其光轉換效率可達3.64%。使用成本較低的carboxylic acid取代PEDOT:PSS，將可降低元件的製備成本，並可能增加電池的有效周期。
在一般高分子太陽能元件裡，電洞的載子位移率比電子的載子位移率低，所以第二階段實驗我們將ITO陽極蝕刻微米尺度的凹槽，期許凹槽能夠深入P3HT
:PCBM主動層，加速電洞載子位移率，但是因為PEDOT:PSS無法順著形狀塗佈，因此我們進一步將自組裝單層膜能夠順著形狀成長的特性運用於此，使得此實驗設計能夠達到提升電洞載子位移率的功效。

關鍵字

高分子太陽能電池 ； 自組裝單層膜 ； 羧酸

並列摘要

Polymer solar cells have gained wide interest in recent years, but how to further cut down the fabrication cost and increase the device lifetime is still an important issue for their commercialization. In this study, a series of assembled monolayers (SAMs) of benzoic acid with various para-substituted groups on ITO was employed to replace PEDOT:PSS as the electron blocking layer of polymer solar cells.
In the first part of this thesis, contact angle, X-ray photoelectron spectroscope, and AFM were applied to study the SAMs of benzoic acid derivatives on ITO. AFM images showed the presence of SAMs slightly reduced the surface roughness of ITO. In addition, the effect of SAMs on the work function of ITO was examined using AC-2. The experimental results indicated that the electron donating ability of the para-substituent on benzoic acid had decisive effect on the work function of ITO. An electron donating moiety will up-shift the work function but an electron withdrawing group will down-shift the work function of ITO. Finally, the SAMs-modified ITO was used as transparent anode to fabricate P3HT/PCBM bulk heterojunction solar cells. I-V measurements demonstrated that as the para-substituent was –CN or –CF3 group, the SAMs-based device reached a power conversion efficiency of 3.64%, which is comparable to that of a conventional solar cells with PEDOT:PSS as electron blocking layer.
In the second part, the SAMs-covered ITO which was patterned with ordered line-shaped groove was utilized as the anode of solar devices to shorten the transport pathway of hole. Preliminary results showed this patterned ITO is helpful in rising the short-circuit current. Further optimization on the thickness of photoactive layer and the dimension of groove is still undertaking by our group members.

並列關鍵字

organic solar cells ； self-assembled monolayer ； carboxylic acid

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