臺灣博碩士論文加值系統

有機發光二極體 (OLED) 較傳統的LED 具備了低耗損功率及零視角的優勢，因此使OLED這個題目的研究漸趨熱烈。 Alq3 是最被廣泛應用作為OLED中有機電子傳輸層之材料，其分子結構式為三個quinoline 官能基和一個鋁原子螯合而成。 在Alq3 的電子結構中，它的最高電子佔據態 (HOMO) 以及最低電子位佔據態 (LUMO) 分別坐落於 phenoxide 和pyridrl 上。 我們的研究著重於Alq3 和陰極金屬的接面。 其接面的位能障影響著金屬注入電子至有機層的效率，並影響了整個元件的發光性能。 本實驗利用同步幅射光來探討不同厚度的Ag 對Alq3 的反應，主要觀測期化學反應與能帶接面。
根據我們的數據,我們可以將Ag鍍覆在Alq3上的過程分為兩個步驟。在步驟一時，銀原子由鬆散的Alq3 表面擴散進去，進而和Alq3分子產生些許反應造成Alq3能帶的彎曲。到了步驟二，銀的數量越來越多，銀原子便不再擴散並以cluster的型態堆疊在Alq3之表面。在這個步驟中，我們發現銀的增加減少了原本極厚的不良導體Alq3膜造成的charging 效應。 同一時間銀將電子轉移至Alq3的 N 原子上，形成了一個 interface dipole。這個dipole 也加入了影響真空能階 (vacuum level) 之不連續的因素當中，因此我們在實驗中發現真空能階有著0.6 eV的不連續，其中包括了0.24 eV 的dipole 及 0.36 eV的銀和Alq3之功函數之差。 另外，在銀的cluster 巨大的體積影響下，Alq3中的Al – O鍵會被拉長，而使氧的核層能譜中多了一個新波峰。

Organic light emitting devices (OLEDs) has superiority to traditional LEDs by its low power consumption and wide viewing angle. Alq3 is the most popular material for the electron transport layer in OLED, which was constructed by three quinolines and an aluminum atom. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of Alq3 band are located on the phenoxide site and pyridrl site on Alq3 molecule, respectively. We have focused on the interface between Alq3 and the metal cathode in this research, which dominates the barrier of electron injection from metal cathode to the organic layer. We used the synchrotron radiation to take our data and investigate the how Alq3 interact with Ag with different thickness.
According to our experiment, we differentiate Ag deposition on Alq3 into two stages. In stage I, Ag atom diffuses into thick Alq3 film and causes band bending of Alq3. In stage II, the Ag dopant grows as clusters on the top of the Alq3 than diffusing into it. In the process of Ag dopant becomes more to decrease the inevitable charging effect of thick organic layer. On the other hand, the Ag donate charge to the N atom in Alq3, which forms the cluster-induced dipole with magnitude 0.24 eV. This leads us to detect the vacuum level (VL) difference between Ag and Alq3 including work function difference and cluster-induced dipole, which with magnitude 0.6eV. By the way, the large cluster size of Ag would elongate the Al - O bond and make a new component appear in O 1s spectrum.

Contents

摘要..…………………………….……………………………………...……………I
ABSTRACT……………………..………………………………………………..…II
ACKNOWLEDGES……………………………………………………………..…III

CHAPTER 1: INTORDUCTION…………………………………………..……..1
1.1. Introduction of OLED…………………………………………………1
1.2. The molecular and electronic structure of Alq3………..…………..7
1.3. Motivation…………………………………………………………….14
1.4. Literature review ……………………………………………….…...15
1.4.1. Ag clusters on C60/Si(111)……………………………………15
1.4.2. Gaq3 on Ag…………………………………………………….20
1.4.3. Distinguishing between interface dipoles and band bending at Alq3 at Alq3/Ag interface…………………………………...25

CHAPTER 2: EXPERIMENTAL………………………………………………………………….29
2.1 Introduction of photoemission spectroscopy……………………..29
2.2 Synchrotron radiation………………………………………………34
2.3 Beam-line specifications……………………………………………36
2.4 Pumping system…………………………………………………….37
2.5 Hemispherical electron analyzer…………………………………..37
2.6 Sample preparation…………………………………………………44
2.6.1. n-Si(100) surface preparation……………….……….…......44
2.6.2. Silver evaporation……………………………………………44

CHAPTER 3: PHOTOEMISSION SPECTRA OF the Ag/Alq3 INTERFACE……………………………………………………..48
3.1 Valence band
3.1.1. The HOMO and the cuoff spectra…………………………48
3.1.2. Ag 4d and EF edge shift…………………………………….50
3.2 Core-level Shift……………………………………………………….50
3.2.1. N 1s………………………………………………………….58
3.2.2. O 1s………………………………………………………….59
3.2.3. C 1s…………………………………………………………..59
3.2.4. Ag 3d…………………………………………………………71
3.2.5. Al 2p………………………………………………………….71
3.3 Proposed model……………………………………………………….74
3.3.1. Stage I: Ag Atom on Alq3………………………………………………..…..74
3.3.2 Stage II: Ag cluster grows and become bulk-like……......75
CHAPTER 4: Conclusions………………………………………...…………..81
REFERENCES………………………………………………………...…………..82

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