溶液製程高分子太陽能電池之形貌改良與穩定性分析

Morphology Improvement and Stability Analysis of Solution-processed Polymer Solar Cells

楊柏青(Po-Ching Yang)

指導教授 ： 林清富

國立臺灣大學/電機資訊學院/電子工程學研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.10718

摘要

在能源需求的不斷攀升以及石化燃料的逐漸枯竭下，再生能源的發展受到重視。太陽能由於其能量豐沛，且不若核能有廢料處理問題以及潛在危機，因此為未來極有潛力的替代能源候選。在各種太陽能電池中，高分子太陽能電池由於其質輕、可撓等性質，以及可低成本大面積製造的性質，引起了廣泛的注意。為了達到其商業化，必須從三個重點方向來考量：元件效率、穩定性，以及製程成本。
在本論文中，以溶液製程的倒置元件為基本架構，並針對不同的新型施體或受體材料系統進行形貌改良與及界面改質。在溶液製程的策略下，除了元件主動層外，本研究的陰極或陽極的緩衝層，皆以溶液製程的方式來製備。使用溶液製程可大幅簡化製程並降低成本。另一方面，倒置結構的使用是為了改善元件的穩定度問題。避免在ITO電極側塗佈酸性的PEDOT:PSS以及使用高功函數背電極的倒置結構，其穩定性較傳統結構元件高出許多。在論文的最後，我們將使用本質上高空氣穩定性的導電高分子為施體材料，其搭配倒置結構後，元件將具有非常優異之空氣穩定性。
在元件效率的提升上，本論文研究兩種系統下的倒置元件表現：P3HT/ICBA (或PlexcoreR PV2000)系統以及低能隙高分子/PC70BM系統。在P3HT/ICBA系統中，由於ICBA具有較高的LUMO能階，與P3HT的接面可產生較高的元件開路電壓，再利用P3HT自組裝特性，以混合溶劑慢乾法製程最佳化之元件可達到4.7%的能量轉換效率。另一方面，在低能隙系統的研究上，嘗試使用PCDTBT以及a-PTPTBT高分子，搭配在可見光波段有吸收的PC70BM來製備太陽能電池。經過界面修飾後，PCDTBT/PC70BM可達1.8%的效率，而a-PTPTBT/PC70BM可達4.1%，且元件穩定性較傳統的P3HT/PCBM系統高出許多。
在穩定性的測量方面，a-PTPTBT/PC70BM為主動層的倒置結構元件可不經封裝而存放於空氣中超過半年，效率未見明顯衰退。a-PTPTBT之高分子的HOMO層級低於-5.27 eV，因此可抵抗大氣中水氣與氧氣的氧化作用，同時，其高分子內芳香族的單體結構也使其具有化學穩定性，因此以a-PTPTBT為主動層材料的元件可具有高度的穩定性。
在本論文中，我們成功地使用了溶液製程的界面修飾來改善各種主動層系統元件的效率表現，且所有元件皆未經封裝並具有高穩定性。因此，未來將有希望應用此低成本、簡單、元件具有有高度穩定性的生產策略，來實現有機太陽能電池的商業化。

關鍵字

高分子太陽能電池 ； 溶液製程 ； 倒置結構 ； 穩定性 ； 界面修飾

並列摘要

The development of renewable energy technologies has received much attention, because of the increased energy demand and the gradual depletion of fossil fuels. Among those technologies, solar energy has emerged as the potential candidate of alternative energy. Solar energy is seen as the most abundant and cleanest energy source, avoiding the risk of hazardous radiation and the problems of radioactive waste disposal, as the cases for nuclear energy. As one category of solar cells, Polymer photovoltaics have attracted considerable attention due to the potential of achieving flexible and light-weight devices over large area with low fabrication cost. To reach the goal of cells commercialization, three important aspects have to be considered. Efficiency, stability and production cost of the devices should be equally weighed in the development of polymer solar cells.
In this dissertation, we employ the inverted device configuration, based on solution processed, to fabricated polymer solar cells and exploit the use of different donor/acceptor system. For improving device performance, morphology control and interface modification are two major strategies in the processing. The active layer, the cathode and anode interfacial layers are all processed and controlled via solution methods. This solution-based technology can greatly simplify the fabrication procedures, reducing process time and lowering the costs. On the other hand, the use of inverted structure aims at promoting device stability. This device configuration employs the stable high-work-function back electrode and avoids the use of acidic PEDOT:PSS at ITO electrode, therefore showing very high stability over that of conventional devices. In the latter part of this dissertation, we also use the inherently air-stable conducting polymer as the donor material, combined with the inverted structure, to further improve the cell stability.
For fabricating high-performance polymer solar cells, we investigate the effects of using two different types of blend systems: P3HT/ICBA (or PlexcoreR PV2000) and low bandgap polymer/PC70BM. In the P3HT/ICBA system, the high-lying LUMO level of ICBA contributes high open-circuit voltage when ICBA forms the a heterojunction with P3HT. This high Voc combined with the self-organization properties of P3HT can yield device with efficiency up to 4.7% upon process optimization. On the other hand, in the low bandgap polymer/PC70BM system, we attempt to use the low-bandgap PCDTBT and a-PTPTBT conducting polymers as the donor materials, and the PC70BM as the acceptor material. After interface modification, the PCDTBT/PC70BM based device shows a 1.8% power conversion efficiency, while the a-PTPTBT/PC70BM based device can reach 4.1%. In addition, both the systems demonstrates much higher stability than that of P3HT/PCBM system.
In the stability test, the unencapsulated a-PTPTBT/PC70BM based devices can retain its maximum power conversion efficiency even after a six-month storage under ambient conditions. The excellent air stability of the polymer lies in its low-lying HOMO level and the chemically stable aromatic backbone. Therefore, a-PTPTBT can resist the oxidation induced by atmospheric oxygen and water, as well as other possible chemical reactions.
In this work, we successfully employed the solution-processed interface modification to improve the device performance. All the devices studied were not encapsulated and showed high stability. This simple, low-cost, and high device stability process method provides a promising route for achieving commercialization of organic solar cells.

並列關鍵字

polymer solar cells ； solution process ； inverted structure ； stability ； interface modification

參考文獻

Chapter 1

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