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論文名稱 Title |
MEH-PPV/ Short-Length Carbon Nanotubes 光伏薄膜混摻Alq3的研究 Study on the Effect of Blending Alq3 into MEH-PPV/ Short-Length Carbon Nanotubes Photovoltaic Thin Film |
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系所名稱 Department |
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畢業學年期 Year, semester |
語文別 Language |
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學位類別 Degree |
頁數 Number of pages |
61 |
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研究生 Author |
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指導教授 Advisor |
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召集委員 Convenor |
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口試委員 Advisory Committee |
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口試日期 Date of Exam |
2006-06-26 |
繳交日期 Date of Submission |
2006-07-19 |
關鍵字 Keywords |
有機太陽能電池、光吸收、小分子、高分子、光電荷產生 charge photogeneration, light absorption, small molecular, polymer, organic solar cell |
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統計 Statistics |
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中文摘要 |
激子的產生、激子的漂移、電荷的轉移和電荷的傳輸,是有機太陽能電池產生光電流的四個重要的關鍵機制。在本篇論文,我們採用小分子材料Alq3 增加poly [2-methoxy-5-(2'-ethyl-hexyloxy)-1,4- phenylene-vinylene]:short-length carbon nanotubes (MEH-PPV:SLCNTs) 薄膜在太陽光譜中 300至450 nm 波段的光吸收,亦是增加激子的產生。比較有添加和沒有添加電子接受(Acceptor)材料時,電子貢獻(Donor)材料的光激螢光(PL)強度是一項檢測電荷轉移現象的簡單方法。除此之外,藉由觀察Donor材料PL強度驟滅的程度,亦可以粗略得知電荷轉移效率的消長。 [1-6] 利用此一原理和方法,我們觀察到在SLCNTs濃度為33 wt.%時,可能有最大的電荷轉移效率。為了更進一步的確認,我們同時也採用時間解析螢光生命週期的檢測方法。量測後的結果顯示,SLCNTs濃度為33 wt.%時,MEH-PPV高分子材料有最短的生命週期。此一結果和我們先前的猜測有高度謀合。為了簡化分析接下來的實驗結果,我們在此一濃度,下了二個假設,分別為:(1) 電荷轉移效率是一高值,其它的機制與電荷轉移機制相比可以忽視。因完成電荷轉移機制所需的時間是在次兆分之一秒等級。(2) 在複合薄膜中,激子的擴散效率接近1。基於此假設,MEH-PPV:Alq3 和MEH-PPV:Alq3:SLCNTs PL體系有相對較高的PL驟滅的程度,說明了混摻Alq3的薄膜會有相對較高的光電荷產生。藉由吸收光譜和PL光譜的分析,我們也證實了Alq3 和MEH-PPV之間的能量轉移現象。當MEH-PPV:Alq3薄膜被Alq3最大的吸收波長380 nm的光激發時,不見Alq3的PL光譜,卻只見MEH-PPV的PL光譜強度隨著Alq3的濃度增加而增加,顯示Alq3將能量轉移給MEH-PPV。由SEM照影發現,有添加Alq3的MEH-PPV薄膜,薄膜表面的孔洞有明顯的減少。這意味著採用有添加Alq3的MEH-PPV薄膜作為光反應層的元件,可能會有較小的接觸電阻。由以上的實驗結果,我們相信添加Alq3的光反應薄膜,應用在太陽能電池也許可以提升元件性能。 |
Abstract |
For organic solar cells: exciton generation, exciton diffusion, charge transfer, and charge transport of a photoactive layer are the important factors in photocurrent generation. In this thesis, we blend small molecular material tris(8-hydroxyquinoline)aluminum (Alq3) into poly [ 2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene-vinylene ]:short-length carbon nanotubes (MEH-PPV:SLCNTs) films to increase the light absorption, in the range of 300 to 450 nm, and hence increase the exciton generation. The comparison of the photoluminescence (PL) of a donor with that of the Donor-Acceptor composite provides an important and simple method to detect the charge transfer phenomenon. Furthermore, the degree of photoluminescence quenching may be representative of the efficiency of charge transfer. [1-6] Using this concept and method, we obtain that at the mix ratio of 1:0.5 (MEH-PPV:SLCNTs) by weight, 33 wt.% SLCNTs, probably have the maximum of charge transfer efficiency. To further check that at this concentration might have the maximum efficiency of the charge transfer, we also used time-resolved fluorescence spectrometer to measure the fluorescence lifetime of MEH-PPV. The shortest MEH-PPV fluorescence lifetime of 0.15 ns at 33 wt.% SLCNTs corresponds with our conjecture. For simplicity to discuss next experiment results, we make two assumptions at this mix ratio: (1) The efficiency of the charge transfer process is very high, so the competing processes can be neglected. Because of the forward electron transfer process occurs in the sub-picosecond time domain; (2) The exciton diffusion efficiency is approximately unity in the bulk heterojunction photoactive layer. Based on this assumption, the higher degree of photoluminescence quenching of MEH-PPV:Alq3 and MEH-PPV:Alq3:SLCNTs system demonstrates blending alq3 into MEH-PPV:SLCNTs films maybe can increase the charge photogeneration. The PL and UV/VIS absorption spectra are employed to examine the energy transfer process between Alq3 and MEH-PPV. When MEH-PPV:Alq3 films are excited at the wavelength of 380 nm which is in the main absorption region of Alq3, the increase in PL intensity of MEH-PPV at 577nm and the absent emission spectra of Alq3 illustrates Alq3 transfer its energy to MEH-PPV. By scanning electron microscopy, we observed that the surface pinholes became less than that of MEH-PPV films. This result suggests the devices utilizing the MEH-PPV:Alq3 composites as electron donor materials may have smaller electrode contact resistance. From all above the experiment data, we believe using MEH-PPV:Alq3:SLCNT as a photoactive layer perhaps can enhance the device performance. |
目次 Table of Contents |
誌 謝 I Abstract II 中文摘要 V List of Figures IX Chapter 1: Overview and Motivation 1 1.1 Organic photovoltaic cells 1 1.2 Polymer OPVs 2 1.2.1 Single-layer device 2 1.2.2 Bilayer heterojunction device 3 1.2.3 Bull heterojunction devices 4 1.3 Motivation for study 5 Chapter 2: Basic theories for Solar Cell 8 2.1 Solar radiation 8 2.2 External quantum efficiency 10 2.3 Charge transfer and energy transfer 11 2.4 Characterization of solar cell 18 Chapter 3: Experimental Details 22 3.1 Theory of time-resolved fluorescence kinetics 26 Chapter 4: Results and Discussion 30 4.1 Charge transfer between MEH-PPV and SLCNTs 30 4.2 Energy transfer from Alq3 to MEH-PPV 35 4.3 Blending with Alq3 37 Chater 5: Conclusion 45 Reference 46 |
參考文獻 References |
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