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博碩士論文 etd-0719106-233414 詳細資訊
Title page for etd-0719106-233414
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
系所名稱
Department
畢業學年期
Year, semester
語文別
Language
學位類別
Degree
頁數
Number of pages
61
研究生
Author
指導教授
Advisor
召集委員
Convenor
口試委員
Advisory Committee
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
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
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