模擬與實驗探討有機高分子發光二極體材料之電光性質

Simulation and Experimental Studies of Electro-optical Properties for PLED Materials

蔡安婷(An-Ting Tsai)

指導教授 ： 洪哲文

國立清華大學/工學院/動力機械工程學系/碩士(2012年)

https://doi.org/10.6843/NTHU.2012.00138

摘要

摘要
本研究主要利用量子力學之時間獨立密度泛函理論(time- independent density functional theory, TI-DFT)與時間相關密度泛函理論(time-dependent density functional theory, TD-DFT)兩種方法，模擬高分子發光二極體（polymer light-emitting diodes, PLED）之發光材料，利用微觀分析了解材料特性及其電子與光學性質。
高分子發光二極體，為有機電激發光(organic electroluminescent, OEL)元件的一種，其以高分子材料作為發光層，因此，了解發光層材料之特性在PLED研究中扮演極為重要的角色。本論文為研究PLED之常見高分子發光材料-聚噻吩(polythiophene, PT)及其衍生物，探討其特性。首先，建構噻吩(thiophene, T)之單體(monomer, T1)分子，接著逐步增加單體數量至十個(T10)，十五個(T15)，二十個單體(T20)，利用所計算之各別能隙，線性獲得聚噻吩之能隙與實驗值比較，可獲得適用此類分子的模擬參數，利用此參數計算各單體分子及其衍生物之最佳化結構，振動頻率、單點能量等資訊，可獲得鍵長（bond length）、鍵角(bond angle）、能隙(band gap)、分子軌域(molecular orbital）、游離能(ionization potential)、電子親和力(electron affinity)、電子與電洞重組能(reorganization energy)與紫外/可見光光譜(UV/Vis spectrum)等性質，了解單體增加後，材料性質的改變趨勢，以利預測高分子聚噻吩及其高分子衍生物之性質，此外亦進行激發態計算，可獲得放射光譜(emission spectrum)與史托克位移(Stokes shift)等放光特性。
在實驗部分，利用紫外/可見光光譜儀量測二單體噻吩(2, 2′-Bithiophene, T2)與模擬計算所獲得之吸收光譜進行比對，並可透過吸收光譜圖獲得材料之能隙，可驗證模擬的正確性。最後將聚噻吩及其衍生物各種性質進行比較與探討，推測取代基－Br之聚噻吩衍生物具有較佳的電子/電洞傳輸能力，應可有效增加發光性質，因此，此衍生物可做為未來設計新材料之參考。

關鍵字

密度泛函理論 ； 高分子有機發光二極體 ； 聚噻吩

並列摘要

In this thesis, we employ a time-independent and time-dependent density functional theory (TI-DFT and TD-DFT, respectively) to calculate the performance for polymer light-emitting diodes (PLEDs). Electronic and optical properties of PLEDs emission materials are analyzed and investigated.
PLEDs are one kind of “Organic Electroluminescenc”, OEL, devices. The materials of polythiophene (PT) are used to fabricate the emitting layer in PLEDs. Therefore, it is of prime importance to understand the characteristics of the emitting layer materials which play an important role in PLED research. The first step of this research is to set-up-thiophene (T1) monomer and 2, 2′-Bithiophene (T2, dimer), T3 (trimer), T4 (tetramer)…, T10, T15, T20 molecular models and then calculate their band gap. We can determine the best exchange-correlation functional and basis set for thiophene and thiophene derivatives by using linear extrapolation techniques to determine these band gap values and then performing a comparsion with experimental data. Then, the optimized structures, bond length, band gap, molecular orbital, ionization energies, electron affinities and reorganization energy were calculated by using the DFT. The corresponding UV/Vis spectrum and absorption/excitation energies can be evaluated from the TD-DFT simulation results. The Stokes shift can be observed by comparing the difference between absorption and emission spectrum.
In the experimental part, we took the 2, 2′-Bithiophene (dimer, T2) molecule, and its UV/Vis experimental spectrum data closely matches the simulation results. This is a good indication that we can use B3LYP/6-31G(d) to simulate other molecular units (T3, T4…, T10, T15, T20) and thiophene derivatives. It can be concluded that the derivatives, T_∞Br, may display a better performance than the polythiophene (PT) counterpart and can serve as the design reference for new emission materials of PLEDs devices.

並列關鍵字

DFT ； PLED ； POLYTHIOPHENE

參考文獻

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