在有機太陽能電池的元件結構中，通常是利用塊材異質界面(Bulk-heterojunction)，以P3HT作為電洞傳輸材料、PCBM作為電子傳輸材料，藉由兩者在薄膜中的分布結構來進行電子電洞的傳遞，故薄膜中的結構是有相當的重要性，許多研究會利用加入不同的添加劑來改變薄膜結構，提升太陽能電池的轉換效率，然而先前研究多以分析成膜後的P3HT:PCBM混合系統，對添加劑在薄膜成膜過程的影響的相關研究較少，本研究專注於單一系統P3HT高分子溶液與添加劑的關係，利用臨場垂直射光學干涉儀、低掠角寬角X光散射儀以及低掠角小角X光散射儀來觀察，高沸點添加劑在高分子溶液旋轉塗佈成膜過程中的影響。
先前研究純高分子溶液的例子，可以發現到薄膜成膜過程是由表面開始形成薄殼，而且此層薄殼會決定最後薄膜的型態。在本研究當中則使用不同濃度的添加劑來比較其變化，分別為0 %、3 %和7.4 %體積濃度的高沸點添加劑(OT)於高分子(P3HT)溶液當中，在光學干涉儀的分析中，將旋轉塗佈過程分為三階段:(1)流體主導階段、(2)揮發主導階段以及(3)玻璃態階段，以3% 添加劑溶液為例，我們將薄膜模型假設分成三層，利用干涉圖譜進行曲線擬合，可以觀察到在旋轉塗佈過程中，表面形成約10奈米的低折射率添加劑層，且下層的高分子層相較於純溶液的例子，折光率也較低，隨著時間高分子層折光率提升，進入到玻璃態階段後，則分為兩層，上層有向內正向的折光率差變平緩且上升的趨勢，在低掠角寬角度X光散射儀的觀察下，無添加劑的系統在流體主導與揮發主導階段之間，其高分子結晶度、晶粒大小趨於穩定，然而在加入添加劑以後，結晶度雖然較純的高分子溶液低，不過卻拖長了整體晶粒大小及結晶度成長的時間，特別在(100)結晶方向性部分，加入3%添加劑的系統中明顯有原先長好的晶體方向性被擾亂的行為(繞射峰逐漸強度降低且方向性變差)，由此可推測為表層的添加劑重新擴散回高分子薄膜中且擾亂原先的結晶方向性，在低掠角小角度X光散射儀，可以發現一直到進入玻璃態階段，P3HT聚集體大小不斷在縮小，從橢圓體長軸半徑235奈米至34奈米，短軸半徑由69奈米至10奈米，然而總散射量(Qinv)不斷增加，可以表達出聚集體的總個數不斷在增加以及大小縮小，綜合以上三種實驗觀察，認為加入高沸點添加劑後，因為主溶劑(CB)揮發較為快速，使得不易揮發的添加劑累積於表面，而延後且拖長下層的高分子層成為薄殼的時間，而在進入玻璃態階段後，因為主溶劑幾乎揮發完全，停留於表面的添加劑會因為下層高分子濃度的上升，而重新擴散回下層的高分子薄膜當中，改變結晶方向性以及聚集體大小與數量，而加入濃度越高，則會延後現象發生的時間。

The use of processing additive is a powerful approach for the optimization of active layer performance in organic photovoltaic devices. The researches always focus on the system of P3HT:PCBM system and study the morphology in film state. In this study, we focus on the P3HT system with different amount of OT to investigate the film formation during spin coating by in-situ GIWAXS/GISAXS and normal incident optical interferometry. Analysis (assuming a single liquid layer) of OI results indicates that there are generally 3 stages in the film-forming process: (1) the spin-off or flow-dominated stage, where the film-thinning rate decreases very quickly according to the Meyerhofer equation, (2) the evaporation-dominated stage of plateaued film-thinning rate, and (3) the freezing-in or vitrification stage where the film-thinning rate approaches to zero. In previous case (pure P3HT), we show the formation of a thin layer with high-refractive index at the air-liquid interface in the transition between flow and evaporation dominated stage and it will determine final film’s morphology. Therefore, the air-liquid interface is the significant role during the spin-coating process. In this case, the high-boiling point additive will enhance the air-liquid interface during spin-coating. From the OI observation, the film forms a low refractive index layer at the air/liquid interface (ca. 10 nm in thickness), which indicates that the high boiling OT accumulates on the surface due to CB evaporated soon. Especially, the OT diffuse back to the P3HT-rich layer in the vitrification stage. From the GIWAXS results, it shows the phenomenon that the orientation was randomized and the highest intensity became lower. It may represent the original P3HT crystallites may be disturbed by OT diffusion then randomize the original orientation. In the GISAXS observation, P3HT agglomerates became smaller continuously and invariant keeps increasing even in vitrification stage, may represent that it still grows the new agglomerate makes the average size decrease. Combined all the results, adding a high boiling point additive will prolong the period of film formation. The additive will accumulate on the surface then diffuse back to randomize the crystallites and maybe also make the agglomerates smaller.

致謝 I
摘要 II
ABSTRACT III
LIST OF FIGURES V
LIST OF TABLES VII
1. Introduction 1
1.1 Background 1
1.2. Objective and Approach 2
2. Experimental Details 3
2.1. Material and Specimen Preparation 3
2.2. Instruments 3
2.3 Data Analysis 3
3. Results and Discussion 5
3.1. Evolution of film thinning and additive effect 5
3.2. Additive effect for film-formation during spin coating process. 8
3.2. OT effect on P3HT crystallization during spin-coating 11
3.3. OT effect on P3HT structural developments during spin-coating 14
3.4. A proposed film formation process during spin-coating. 18
4. Conclusion 20
References 21
Appendix A. Instruments and experimental settings 22
Appendix B. Fitting Optical interferograms profiles and parameters 24
Appendix C. In-situ GIWAXS 2D patterns and analysis of profiles in bulk film 28
Appendix D. In-situ GISAXS 2D patterns at incident angle 0.12o 31
Appendix E. Analysis of GISAXS data and fitting curves at incident angle 0.2o 32

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