有機發光二極體小分子材料Mq3(M=Al, Ga)之電子結構和光學性質分析

Analysis of Electronic Structure and Optical Properties in Mq3(M=Al, Ga) as Emitting Materials for OLEDs

陳琮凱(Tsung-Kai Chen)

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(2011年)

https://doi.org/10.6843/NTHU.2011.00404

摘要

本研究旨在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）方法，模擬有機發光二極體（Organic Light Emitting Diodes, OLED）之材料特性與光學性質的微觀分析。
發光層材料特性在有機發光二極體研究中扮演著最重要的角色，本論文的內容在於研究以Mq3、Mq2p(M=Al, Ga)與其衍生物做為有機發光二極體之發光層材料，討論其光學及材料特性。首先建立出meridional-Mq3的分子模型，接著將meridional-Mq3中的qb（8-hydroxyquinoline）配體用啶 (picolinate, p)配體取代，建構出Mq2p，最後以Mq2p為基礎，根據六種不同位置的“CH”/N取代（意指將qa與qc的C-H鍵用N原子取代），建立其相對應之分子模型，接著利用建構好的分子模型來計算最佳化之結構，並計算分子間之振動頻率、單點能量，再將模擬出來的結果進行分析，最後得到所需要的鍵長（bond length）、鍵角（bond angle）、偶極矩(dipole moment)、能隙(band gap)、分子軌域（molecular orbital）、游離能（ionization potential）、電子親和力（electron affinity）、重組能（reorganization energy）、紫外線可見光光譜（UV/VIS spectrum）等有機材料特性。
激發態部份，針對各個不同分子模型，進行激發態能量及其結構最佳化，計算出螢光發射光譜（fluorescence spectrum）和史托克位移（Stokes shift）之光學特性及電性。最後將Al與Ga之模擬結果做出優劣性的比較，並進一步與實驗數據做比對。由於Ga與Al光電性質極為接近，但Ga相對於Al較為穩定，可以延長OLED壽命，故預計未來可以作為新的有機發光材料。

關鍵字

有機發光材料

並列摘要

This thesis employs a quantum simulation technique to analyze how the materials that are used to fabricate the emitting layer affect the electronic and photonic properties of the final product - an organic light emitting diode (OLED). The materials of interest that are used to fabricate the emitting layer in OLEDs are Mq3, Mq2p (M=Al, Ga) and their “CH”/N (i.e., replace the C-H bonds in both qa and qc with N atoms) derivatives.
he first step before the quantum simulation takes place is to set-up meridional-Mq3 molecular models which included Mq2p and its “CH”/N substitution derivatives. Both time-independent and time-dependent density functional theory (TI-DFT and TD-DFT, respectively) techniques are employed. The former is used to optimize the molecular structures, and the latter to determine the electronic excitation energy. Then, the ground state structures to calculate the bond length, bond angle, dipole moment, band gap, molecular orbital, ionization energy, electron affinity, reorganization energy, were optimized using the DFT. The corresponding UV/VIS spectrum and absorption/excitation energies are evaluated from the TD-DFT technique. With the resulting fluorescence spectrum, the Stokes shift can be observed. Quantum simulations were carried out with the Gaussian09 software package which makes use of the hybrid exchange-correlation functional B3LYP and the 6-31g(d), 3-21g* basis sets. Finally, simulation results and experimental data were compared for both Alq3 and Gaq3 derivatives. It was concluded that Gaq3 derivatives displayed a better performance than the Alq3 derivatives. It is hoped that with the fundamental academic design tool provided here, future investigations on the performance of novel materials for fabricating OLEDs can be continued.

並列關鍵字

OLED

參考文獻

[2] M. Pope, H. P. Kallmann and P. Magnante, “Electroluminescence in organic crystals”, J. Chem. Phys., Vol. 38, pp. 2042-2043, 1963.

[3] C. W. Tang and S. A. VanSlyke, “Organic electroluminescent diodes”, Appl. Physics Letters, Vol. 51, pp. 913-914, 1987.

[4] C. W. Tang, S. A. VanSlyke and C. H. Chen, “Electroluminescence of doped organic thin films”, J. Appl. Phys., Vol. 65, pp. 3610-3616, 1989.

[6] J. P. Zhang and G. Frenking, “Quantum chemical analysis of the chemical bonds in Mq3(M=AlIII, GaIII) as emitting material for OLED”, Chemical Physics Letters, Vol. 394, pp. 120-125, 2004.

[7] J. P. Zhang and G. Frenking, “Quantum chemical analysis of the chemical bonds in Tris(8-hydroxyquinolinato) aluminum as a key emitting material for OLED”, J. Phys. Chem. A, Vol. 108, pp. 10296-10301, 2004.