有機高分子發光二極體材料能隙 之量子模擬與電化學實驗

Quantum Simulation and Electrochemical Experiment on Band Gaps of PLED Materials

鄭雅方(Cheng, Ya Fang)

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(2015年)

摘要

本研究主要是利用循環伏安法、紫外可見光譜法等實驗方法，量測高分子發光二極體（polymer light emitting diode, PLED）之能隙(band gap)，並同時以時間獨立與時間相依密度泛函理論（time- independent and time-dependent density functional theory, TI-DFT and TD-DFT）模擬此發光材料之材料特性及光學性質，並做微觀分析。
有機電激發光(organic electroluminescent, OEL)的元件中，以高分子材料作為發光層的高分子發光二極體，其材料特性在PLED研究中極為重要。而在有機發光二極體中，發光層材料特性亦扮演著最重要的角色。本論文為研究PLED常見高分子發光材料-聚噻吩(polythiophene, PT)，探討其材料特性。
量子模擬部分先建構噻吩(thiophene, T)之單體(monomer, T1)分子，接著逐步增加單體數量至十個(T10)，甚至到二十個單體(T20)，再利用所計算之各別能隙，迴歸分析獲得聚噻吩之能隙，利用建構好的分子模型來計算最佳化之結構，再將模擬出來的結果進行分析，獲得分子軌域(molecular orbital）、吸收光譜等材料特性，並與實驗值比較，了解材料性質在單體增加後的改變趨勢，分析實驗與模擬的可信度。
電化學實驗方面，使用多變電位施加於含有微電極之電化學電池的循環伏安法(cyclic voltammetry, CV) 量測化合物之氧化還原系統，對於有機半導體微量分析上估計能帶，測量此材料的氧化電位Eox與還原電位Ered，並加以換算得到氧化過程電子所需的能量(最高佔據分子軌道，highest occupied molecular orbital, HOMO)，與還原過程電子注入到一個分子所需的能量(最低未佔分子軌道，lowest unoccupied molecular orbital, LUMO)。最後進行模擬與實驗的結果分析比較，確定實驗與模擬數據的可靠度及正確性。

關鍵字

高分子發光二極體(PLED) ； 循環伏安法 ； 紫外可見光光譜 ； 能隙

並列摘要

In this thesis, I mainly use the cyclic voltammetry (CV) and UV-Visible spectrum to measure the optical properties of polymer light emitting diodes (PLEDs) to compare with the quantum simulation results which are based on time-independent and time-dependent density functional theories (TI-DFT & TD-DFT) for microscopic analysis.
PLEDs play an important role in organic electroluminescent (OEL) especially the emitting layer in PLEDs. One of the basic materials to fabricate the emitting layer is the polythiophene (PT). Therefore, it is important to exploit the material properties by experiments and appropriate simulations. In the quantum simulation part, since Gaussian function is not capable of representing periodically molecular structure, the first step is to set up T1(monomer), T2(dimer), T3(trimer), until T20 molecular models and then use the regression analysis to predict the band gap of the polythiophene. The absorption energies are then evaluated from the DFT and TD-DFT simulations.
In the experimental part, using the cyclic voltammetry by varying the input potential is able to analyze the redox system of the emitting materials and to estimate their band gaps from the V-I plots. The oxidation potential (Eox) and the reduction potential (Ered) can be obtained, and are transformed to the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) accordingly. Finally, through experimental result verifications, this quantum simulation technique is concluded to be reliable and accurate for predicting the optical properties of modern PLEDs.

並列關鍵字

polymer light emitting diode (PLED) ； cyclic voltammetry ； UV-Visible ； band gap

參考文獻

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