聚（3-己基噻吩）在溶液態與固態的結構研究

Structures of Poly(3-hexylthiophene) in Solution and Bulk State

高魁佑(Kao, Kuei Yu)

指導教授 ： 陳信龍

國立清華大學/工學院/化學工程學系/博士(2015年)

https://doi.org/10.6843/NTHU.2015.00564

摘要

具有剛性主鏈和柔性側鏈的共軛高分子，在光電產業相當受矚目，包括太陽能電池，發光二極管和薄膜晶體管（TFT）。由於良好的電荷傳輸性和溶液加工性，聚（3-己基噻吩）（P3HT）已被認為在本體異質結（BHJ）聚合物太陽能電池是最有前途的材料之一。由於共軛聚合物的澆鑄膜受到記憶效應的影響，而導致BHJ聚合物太陽能電池的功率轉換效率有所差異。因此，調查共軛系列聚合物的溶液結構及其對隨後流延膜的形態效果的結構是一個重要的基本任務。
本文的重點是說明P3HT結構在溶液與固體的相轉化過程狀態。我們有系統地研究了P3HT在二甲苯引起的凝膠化。在老化的過程中發現巨觀的相分離，產生P3HT富域相和微米尺度的溶劑富域相，通過了成核和生長機制奈米鬚晶形成驅動，進而有穩定的機械強度在P3HT富域相導致有凝膠屬性。因此，P3HT/二甲苯凝膠在不同尺度特徵的分層結構具有獨特形態加入PCBM的發現大大減慢的凝膠化，這暗示P3HT和PCBM二甲苯之間有利的相互作用的存在。
對結晶動力學和相關結構的發展在P3HT的隨後鑄膜溶液結構的效果進行了研究，以解決潛在的形態形成共軛聚合物膜的記憶效應。我們比較P3HT在膜澆鑄從凝膠（稱為“凝膠鑄膜”）的結晶度與在膜澆鑄從液體溶液（稱為“溶液鑄膜”），以了解對溶液結構的效果在共軛聚合物的隨後流延膜的結構發展。同步SAXS測量和熱分析表明，P3HT在凝膠鑄膜既寒冷和熔融結晶均較溶液鑄對應慢很多。P3HT的結晶主要發生在個別納米晶須和晶須，在那裡它們有限的尺寸在至少一個維度上施加的強大的空間約束的晶體生長。
最後，我們試圖解析區域規整對P3HT的自組裝過程中的作用。 P3HT的區域規整通常特徵在於定義為頭 - 尾（HT）對子規整度（RR）值。我們發現了凝膠化速率和結晶動力學會影響自組裝。結果發現，略小的RR值有更快的凝膠化，顯示更快的結晶動力學和較高的熔點。在構結構核譜核磁共振（NMR）的詳細特徵表明，較小的RR值的樣本包含了一個顯著較高的人口HT-HT序列。因此，除了HT對子由RR值所表示的量， HT序列對於P3HT的形態的微妙控制非常重要。本文也因此提供了P3HT的兩個解決問題，結構和結晶行為的系統的解析。結果形態的控制形成誘導結晶的光電應用的P3H膜極其重要。

關鍵字

聚（3-己基噻吩） ； 溶液 ； 凝膠 ； 結晶動力學 ； 奈米鬚晶

並列摘要

Conjugated polymers composed of semirigid backbone and the flexible side chains for facilitating their solubility in common organic solvents are the key materials of polymer-based optoelectronics, including solar cells, light-emitting diodes and thin-film transistors (TFTs). In the case of bulk heterojunction (BHJ) polymer solar cells, poly(3-hexylthiophene) (P3HT) has been considered as one of the most promising donor materials due to a good combination of charge transport properties, solution processability and the ease of synthesis with controllable regioregularity and molecular weight. The morphology of the active layer, which has a significant impact on the power conversion efficiency of the BHJ polymer solar cell, is strongly influenced by the dissolution condition of the conjugated polymer for film casting due to the existence of the memory effect; therefore, investigating the structure of the solution structure of conjugated polymer and its effect on the morphology of the subsequently cast film is an important fundamental task.
This thesis is focused on elucidating the structures and phase transformation processes of P3HT in the solution and bulk state. We systematically studied the gelation process of the semidilute solution of P3HT with xylene induced by prolonged aging. A macrophase separation generating P3HT-enriched phase and solvent-rich phase of μm in length scale occurred during the aging. Phenomenologically, the phase separation took place via the nucleation-and-growth mechanism driven by the formation of nanowhiskers in the P3HT-enriched domain. The P3HT-enriched macrodomains were mechanically stabilized by the networking of the nanowhiskers and their jamming in the system led to the gel property. Therefore, P3HT/xylene gel was characterized by a hierarchical structure with distinct morphological entity at different length scales, namely, the macrodomains with μm length scale composed of the nanowhiskers assembled by the crystallites. The addition of PCBM was found to greatly slow down the gelation, which implied the existence of favorable interaction between P3HT and PCBM in xylene.
The effect of the solution structure on the crystallization kinetics and relevant structural development in the subsequently cast films of P3HT has been studied to resolve the memory effect underlying the morphological formation of conjugated polymer films. We compared the crystallization rate of P3HT in the film cast from the gel (called “gel-cast film”) with that in the film cast from the liquid solution (called “solution-cast film”) to understand the effect of solution structure on the structural development in the subsequently cast film of conjugated polymer. The in-situ SAXS measurement and thermal analysis revealed that both the cold and melt crystallization of P3HT in the gel-cast film were much slower than those in the solution-cast counterpart. The retardation of crystallization rate in the gel-cast film was attributed to the abundance of the nanowhiskers, which remained largely undisrupted even when the temperature was higher than the crystal melting point. In this case, the the crystallization of P3HT occurred predominantly within the individual nanowhiskers and the meshes in the networks of the whiskers, where their limited sizes in at least one dimension imposed a strong spatial constraint to the crystal growth and chain motion for crystallization.
Finally, we attempt to resolve the role of regioregularity on the self-assembly process of P3HT. The regioregularity of P3HT is normally characterized by the regioregularity (RR) value defined as the mole percentage of head-to-tail (HT) dyad in the backbone. Here we revealed that the by the content of HT-HT triad also plays an important role governing the self-assembly of P3HT in solution and bulk state by investigating the gelation rate and crystallization kinetics of two P3HT samples bearing almost identical RR value and average molecular weight. It was found that the semidilute xylene solution of the sample with slightly smaller RR value exhibited a faster gelation driven by the formation of crystalline nanowhiskers. In the bulk state, this sample also displayed a faster crystallization kinetics and higher melting points. Detailed characterization of the configurational structure by nuclear magnetic resonance (NMR) spectroscopy showed that the sample with smaller RR value contained an obviously higher population of HT-HT triad sequence. Therefore, in addition to the amount of HT dyad represented by the RR value, the population of the consecutive HT sequence along the polymer chain plays a significant role in the self-assembly processes of P3HT. Knowledge on this system parameter, which can be deduced conveniently from 13C NMR spectroscopy, is hence essential for the delicate control of the morphology of P3HT.
This thesis has thus provided a systematic understanding of the structures and crystallization behavior of P3HT in both solution and bulk state. The results shall be fundamentally important for understanding and controlling the morphological formation of the P3H film induced by crystallization for opto-electronic applications.

並列關鍵字

P3HT ； solution ； gel ； crystallization kinetics ； nanowhisker

參考文獻

Chapter 1

6. Huang, Y.; Cheng, H.; Han, C. C. Macromolecules 2011, 44, (12), 5020-5026.

7. Huang, Y.; Cheng, H.; Han, C. C. Macromolecules 2010, 43, (23), 10031-10037.

13. Chen, P. Y.; Rassamesard, A.; Chen, H. L.; Chen, S. A. Macromolecules 2013, 46, (14), 5657-5663.

15. Chen, C. Y.; Chan, S. H.; Li, J. Y.; Wu, K. H.; Chen, H. L.; Chen, J. H.; Huang, W. Y.; Chen, S. A. Macromolecules 2010, 43, (17), 7305-7311.