新型共軛分子之合成與性質鑑定及其做為聚(3-己烷基噻吩)/二氧化鈦層狀異質界面改質劑之探討

Studies on Synthesis and Properties of Novel Conjugated Molecules as Interface Modifiers of P3HT/TiO2 Layered Heterojunction

張敬賢(Chin-Sien Teo)

指導教授 ： 王立義

國立臺灣大學/工學院/高分子科學與工程學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.01484

摘要

本研究目的為合成出一系列共軛分子做為修飾二氧化鈦之界面改質劑，應用於聚（3-己烷基噻吩)�二氧化鈦層狀異質界面中以改善有機�無機界面相容性。而為了避免改質劑對於界面電荷分離與傳遞產生障礙，其LUMO能階必須位於聚（3-己烷基噻吩)與二氧化鈦之間。為了達到此目標，利用共軛雜環數目（benzathiadiazole和噻吩）調控分子的能隙值，並導入氰基丙烯酸基來降低共軛分子LUMO能階；同時，我們在分子設計中導入己烷鏈於噻吩環上三個不同位置，以提高共軛分子的親油性，並探討不同位置的己烷鏈對於共軛分子的性質影響。
　　在合成部份，我們利用Kumada coupling將己烷鏈接在噻吩環上三種不同位置，並以Stille coupling將兩不同雜環（benzathiadiazole和噻吩）進行鍵結，再透過Vilsmeier-Haack formylation，在共軛雜環中導入單邊醛基，最後進行Knoevenagel condensation將氰基丙烯酸基導入共軛分子中。我們藉由1H NMR、13C NMR、元素分析儀（EA）與電子撞擊質譜儀（EI-MS）鑑定出SL－系列共軛分子結構，並經由UV-vis吸收光譜以及循環伏安法（CV）獲得各別分子的energy band gap、HOMO與LUMO能階性質。同時我們也利用接觸角量測觀察界面改質後的中孔洞二氧化鈦對水的接觸角情形。最後利用聚（3-己烷噻吩）塗佈於改質後的二氧化鈦基材表面，製備FTO/TiO2:IMs/P3HT雙層異質界面結構，並進行螢光光譜量測。
　　由實驗結果我們發現，隨著共軛雜環數目增加，共軛長度的延伸造成改質劑的可見光吸收有明顯的紅位移現象。而在共軛結構中導入己烷鏈除了增加溶解度以外，電子雲密度飽和所造成的推電子特性亦能促使共軛結構的可見光吸收產生紅位移現象。另外當共軛分子吸附在二氧化鈦表面上時，其己烷鏈位置的差異會對分子的吸附聚集產生不同程度的影響，換言之，因己烷鏈破壞分子之間的聚集排列，因此具有己烷鏈的共軛分子吸附在二氧化鈦上的吸收會比無己烷鏈的來得紅位移。而從接觸角量測可以發現，具有己烷鏈的共軛分子能夠提升二氧化鈦表面的疏水性，進而增加改質後的二氧化鈦對有機材料的相容性。
　　由螢光光譜量測結果顯示，具有SL－系列改質後的二氧化鈦，其螢光焠滅比例比無改質的二氧化鈦來得高，此顯示利用共軛分子做為二氧化鈦基材的改質劑能有效促進有機�無機材料界面相容性，並能有效應用於改善異質界面混成太陽能電池。

關鍵字

共軛界面分子 ； 界面改質劑 ； 二氧化鈦 ； 聚己基噻吩 ； 層狀異質界面

並列摘要

The main purpose of this research is to synthesize a series of conjugated molecules serving as an TiO2 modifier in poly(3-hexylthiophene) (P3HT)/titania (TiO2) layer heterojunction devices. By improving the charge separation and transfer between P3HT organic donor and TiO2 inorganic acceptor, the LUMO levels of interface modifiers (IMs) should be located between the LUMO levels of P3HT and conduction band of TiO2. Therefore, combining the strategies of structural design and principle of electronic structure, we developed a series of novel conjugated molecules that composed of three parts: (i) benzathiadiazole and thiophene moieties as the conjugated backbone for energy levels tuning, (ii) a hexyl chain to increase solubility, lipophilicity and inhibit π-stacking aggregation, and (iii) cyanoacetic acid as an electron-accepting and TiO2 anchoring substituents.
We first utilized Kumada coupling to engineer the hexyl chain onto different positions on thiophene thus obtaining various derivative structures, and subsequently combined benzathiadiazole and thiophene moieties through Stille coupling to form conjugated molecules. Next, we performed a Vilsmeier-Haack formylation to yield an additional aldehyde group on the conjugated backbone. Finally, we introduced cyanoacetic acid by Knoevenagel condensation to form SL-series conjugated modifiers. Structural characterization of SL-series was achieved by 1H NMR, 13C NMR, elemental analysis (EA) and electron impact mass spectroscopy (EI-MS). Optical and electronic properties of these molecules were determined by UV-vis spectroscopy and cyclic voltammetry (CV). Furthermore, the contact angle of SL-series modified TiO2 on FTO film were measured by contact angle analyzer. The quenching effect on FTO/TiO2:IMs/P3HT was determined by photoluminescence measurement.
Our analytical studies reveal that the UV-vis spectra exhibit a bathochromic effect with an increment in the conjugated moieties. While introducing the hexyl chain effectively increases the solubility of the conjugated molecules, the electron-density donation of hexyl chain also reflects a bathochromic effect on the UV-vis absorption. We also observed an inhibition toward the formation of π-π stacking aggregation in TiO2:IMs films attributed to conjugated molecules bearing a hexyl chain. Furthermore, contact angle analysis shows that, hexyl chian-containing modifiers form a higher average water contact angle than those without hexyl chain, suggesting a better lipophilicity on the TiO2 surfaces in the presence of conjugated molecules consisting hexyl chain which in turn increases its compatibility with organic materials.
Collectively, our study concluded that modified TiO2 films containing the SL-series compounds have a higher quenching ratio in comparison to their unmodified counterpart. These results can further extend to the notion that conjugated molecules can serve as an interface modifier between organic donor and inorganic acceptor to warrant a better performance in the heterojunction photovoltaic devices.

並列關鍵字

conjugated molecules ； interface modifier ； TiO2 ； P3HT ； layer heterojunction

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