PPE(聚對苯乙炔)和P3HT(聚3-己基噻吩)之 高分子形貌與光譜關係的探討

Abstract

化學小分子間彼此堆疊排列，進而形成團簇或結晶時，不只是外觀形貌上有所變化，分子-分子間的作用力更可以影響分子軌域的能量間隙(HOMO-LUMO gap)，使得許多光譜上的特性改變；例如說，未溶解的結晶和分散在溶劑中的孤立分子，通常都有很明顯的顏色差距，這是因為能量間隙改變後所吸收的光波長不同所導致。反向來說，我們也可以利用光譜的變化的特性，來研究小分子微觀上的堆疊排列。 對於共軛高分子而言，高分子鏈和鏈之間的糾纏交疊，遠較一般小分子的堆疊排列更複雜，多向性和多點式的鏈間作用力對能量間隙的影響也更難以分析，極需要有極高空間分辨率並帶有能量解析度的工具。對固態材料來說，XRD或TEM再加上ARPES就是絕佳利器；但對分子材料來說，絕大多數材料的結晶性都非常差，都無法使用以上的分析工具，能用於”軟”材料的非破壞性的分析工具就極為重要。 本論文研究PPE (Poly(para-phenylene ethynylene))與P3HT (Poly(3-hexylthiophene) 兩種高分子其形貌與光譜關係的探討。最終目標是希望能用近場光學顯微鏡，在局域上同時量測高分子形貌和對應的光譜。並且利用溶劑蒸氣退火的方式改變高分子的排列和形貌，再進行同步量測。 文獻中普遍認為，將高分子進行溶劑蒸氣退火的過程，可以使高分子在空間上進行重新排列，會重排趨向較為有序的結構。目前溶劑蒸氣退火的處理，已經大量應用於有機太陽能電池的製程中，但基礎的研究卻非常很少。我們透過自製光學監測系統，針對高分子溶劑蒸氣退火的過程，進行即時的螢光光譜分析；並且在溶劑蒸氣退火前後，都使用原子力顯微鏡量測表面形貌，以確認在何種尺度下，可以觀察到高分子樣品的結構形貌變化。 我們發現溶劑退火的過程中，高分子的螢光光譜會從固態的光譜，轉換至接近液態的光譜，且在轉換的過程螢光訊號強度會先大幅下降，再回升最後達到平衡狀態。在溶劑退火過後，沒有溶劑的光譜則會接近固態狀態的光譜。我們也利用近場掃描顯微鏡(SNOM)系統針對PPE高分子進行探討，透過不同溶劑的PPE溶液塗布在基體表面，我們可以製造出不同形貌的高分子結構。針對細微的形貌我們可以同時瞭解不同形貌對於光譜的影響。

When small molecules stack on top of each other to form clusters or crystals, not only the appearance and morphology change, but also the molecular-molecular interactions can affect the molecular orbital energy gap (HOMO-LUMO gap), so that many spectral characteristics change; for example, undissolved crystals and isolated molecules dispersed in a solvent usually have a clear color difference. It is caused by the difference in the wavelength of light absorbed after the energy gap is changed. Conversely, we can also use the characteristics of spectral changes to study the microscopic stacking arrangement of small molecules. For conjugated polymers, the entanglement and overlap of polymer chains and chains is far more complicated than the stacking arrangement of ordinary small molecules. The effect of multidirectional and multipoint inter-chain forces on the energy gap is also more difficult to analyze. Tools with extremely high spatial resolution and energy resolution are needed. For solid materials, XRD or TEM plus ARPE is an excellent weapon; but for molecular materials, the crystallinity of most materials is very poor. The analysis tools above cannot be used. Therefore, non-destructive analysis tools which can be used for 'soft' materials are extremely important. This thesis studies the relationship between the morphology and spectrum of two polymers, PPE (Poly (para-phenylene ethynylene)) and P3HT (Poly (3-hexylthiophene). The ultimate goal is hoping to simultaneously measure the morphology and corresponding spectrum of the polymer in the local area by near-field optical microscopy. On the other hand, using solvent vapor annealing (SVA) to change the arrangement and morphology of the polymer, and then perform a simultaneous measurement. It is generally considered in the literature that the process of SVA of polymers can rearrange the polymers in space, and the rearrangement tends to a more ordered structure. At present, the treatment of SVA has been widely used in the manufacturing process of organic solar cells, but the basic research is rare. We use an home-made optical monitoring system to perform real-time fluorescence spectrum analysis of the polymer in SVA process. Before and after SVA, we confirm the changes in the structure and morphology of the polymer samples can be observed at what scale by measure the surface morphology by atomic force microscopy. We found that during the process of SVA, the fluorescence spectrum of the polymer will be converted from the solid state spectrum to a spectrum close to the liquid state. During the conversion process, the intensity of the fluorescence signal will first drop sharply, then rise again and finally reach an equilibrium state. After the SVA process, the spectrum without the solvent will approach the spectrum of the solid state. We also use a scanning near-field microscope (SNOM) system to study PPE polymers. By coating PPE solutions with different solvents on the surface of the substrate, we can produce polymer structures with different morphologies. From the detail of topography, we can understand the effect of different topography correlated with the spectrum at the same time.