摻合型高分子發光層之型態對其電激白光發射行為的影響

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研究生：	張永政 Yung Cheng Chang
論文名稱：	摻合型高分子發光層之型態對其電激白光發射行為的影響 white light emission via manipulation of phase heterogeneity in light-emitting layer of immiscible blends
指導教授：	蘇安仲 An Chung Su
口試委員:
學位類別：	碩士 Master
系所名稱：	工學院 - 化學工程學系 Department of Chemical Engineering
論文出版年：	2007
畢業學年度：	95
語文別：	英文
論文頁數：	77
中文關鍵詞：	白光、高分子發光二極體、摻雜、溶劑影響
外文關鍵詞：	white light, PLED, blend, solvent effect
相關次數：	點閱：2 下載：0
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本研究主要由聚芴系高分子(PFO)或其共聚物(Cz75PF)混摻另一高分子(P3HT)來達成白光發光。其中以發藍光的材料PFO或Cz75PF當主體高分子(host)而發紅光材料P3HT則為客體(guest)，主體高分子的發光光譜與客體高分子的UV吸收光譜有著很好的重疊。而這些共軛高分子本質上傾向於不互相混合，因此熱力學上的溶解或動力學上的捕捉(trapping)現象將限制P3HT鏈在PFO或Cz75PF基材上的存在量。這理應完全是由於相的不均勻度所影響，我們亦能從熱力學上以及動力學上來調控，分別是調整摻雜程度在低客體的組成與選用不同蒸氣壓溶劑而使之在成膜過程中具有迥異的揮發速率。
在第一個部分，我們探討的是P3HT在Cz75PF上的不同組成(0.15到0.5 wt%)，其餘參數則保持固定；尤其氯仿(chloroform)在這始終被採納當主要溶劑。至於第二部分便固定P3HT在PFO基材上的組成(0.5 wt%)；所選用的溶劑其蒸氣壓由高到低分別是氯仿(chloroform)、四氫夫喃(THF)以及氯苯(chlorobenzene)，根據UV吸收光譜(UV-vis)、光激發螢光光譜(PL)、電激發光譜(EL)與時間解析光譜(TREL)對溶液及膜的分析可得到以下幾個結論，恰巧能夠描敘元件效能在EL光譜上的變化：(1)能量的轉移(推測是Förster-type的型式)從PF主鏈到散佈於其中之P3HT鏈在這些摻雜系統是固有的，(2)在電激發的狀態下，載子在P3HT鏈(散佈於PF基材)上的捕捉與再結合(recombination)是影響其發光的主要因素，(3)宏觀上被分離出來的P3HT區域會使得載子不易跑出去，(4)低揮發速率會導致在PFO基材上有β相出現，因而造成捕捉與能量轉移會發生在PFO基才上。

Here we report experimental results of tuning towards white light emission from blends of poly(9,9-di-n-octyl-2,7-fluorene) (PFO) or its copolymer Cz75PF (in which ca. 67 mol% of the monomers are grafted with a carbazole group at the end of its alkyl side-chain) with regio-regular poly(3-n-hexyl-2,5-thiophene) (P3HT). The blue-emitting PFO or Cz75PF serves as the host, whose emission spectrum significantly overlap with absorption spectra of the red-emitting P3HT guest. As these conjugated polymers are inherently immiscible, there should be limited presence of P3HT chains thermodynamically dissolved or kinetically trapped in the PFO or Cz75PF matrix. One would expect clear effects from phase heterogeneity, which can be manipulated thermodynamically by adjusting blend composition at low guest levels and kinetically by choosing solvents of different vapor pressures and hence different evaporation rates during film formation.
In the first approach, we used different levels (0.15 to 5.0 wt%) of P3HT doping for the Cz75PF. Other processing parameters were kept fixed; specifically, chloroform was consistently adopted as the main solvent. In the second approach, we used a fixed level (0.5 wt%) of P3HT doping for the PFO matrix; the solvent used was then varied from chloroform, tetrahydrofuran (THF), to chlorobenzene in the order of decreasing vapor pressure. By means of ultraviolet-visible (UV-vis), phololuminescence (PL), excitation (PLE), electroluminescence (EL), and transient electroluminescence (TREL) spectroscopic analysis of the solutions and the cast films, we reach the following conclusions that satisfactorily describe variations in EL device performance. (1) Energy transfer (presumably the Förster-type) from PF chains to P3HT chains molecularly dispersed within the PF matrix is inherent in these blends. (2) Trapping and recombination of carriers on P3HT chains molecularly dispersed in the PF matrix exerts dominant effects in electroluminescence. (3) Macroscopically separated P3HT domains serve as in efficient drains of carriers. (4) Slow solvent evaporation results in formation of beta phase in the PFO matrix, which also allows for trapping and energy transfer from the PFO matrix composed dominantly of nematic glass.

Chapter 1. Background    1
1-1 Introduction    1
1-1-1 Polymer light-emitting diodes    1
1-1-2 Basic device structure    1
1-1-3 White light emission    2
1-2 Unresolved Issues    11
1-2-1 Complex device structure    11
1-2-2 Interfacial mixing    11
1-2-3 Phase separation and compatibility    11
1-2-4 Bias-dependent and color stability    12
Chapter 2. Experimental Details    17
2-1 Materials    17
2-2 Instruments used    17
2-2-1 Ultraviolet-visible spectroscopy (UV-Vis)    17
2-2-2 Photoluminescence spectroscopy (PL) and Electroluminescence spectroscopy (EL)    17
2-2-3 Surface profiler    17
2-2-4 Atomic force microscope (AFM)    17
2-2-5 Time-resolved electroluminescence (TREL)    18
2-3 Sample preparation    18
2-4 Experimental procedures    18
2-4-1 Surface modification    18
2-4-2 Devices fabrication    19
2-4-3 Devices testing    20
Chapter 3. Color tuning via control of the P3HT doping level in Cz75PF host    22
3-1 Spectroscopic characteristics    22
3-2 Morphological features    24
3-3 Device performance    25
Chapter 4. Effects on emission behavior from the choice of solvents    35
4-1 Spectroscopic characteristics    35
4-2 Device performance    37
4-3 Morphological features    39
4-4 Time resolved electroluminescence    39
Chapter 5. Conclusion    67
References    68
Appendix    70

                                

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