半導體奈米材料於發光二極體之研究

Fabrication of Organic Light-Emitting Diodes Using Semiconductor Nanocrystal as Emitting Materials

李勇志(Yung-Chih Lee)

指導教授 ： 陳家俊

國立臺灣師範大學/理學院/化學系/碩士(2000年)

摘要

我們以二甲基鎘、硒和(TMS)2S (bis-trimethylsilane sulfide) 在TOPO (tri-n-octylphosphine oxide) 微胞溶液中合成出硒化鎘和硒化鎘/硫化鎘奈米晶體。奈米晶體表面所接的界面活性劑，可以用來控制奈米晶體的形狀，也能修飾奈米晶體的表面性質。並藉由改變實驗條件來控制奈米晶體的體積及大小分佈。由穿透式電子顯微鏡來觀察奈米晶體，發現所合成的奈米晶體的粒徑大約是3 nm。並以吸收及放光光譜來鑑定其性質，發現半導體奈米晶體因其特有的量子限量化效應(quantum confinement effect )，使得其能隙會隨著晶體大小不同而改變，不必經由改變其化學結構就可以改變其能隙的特點備受矚目。
將所合成的硒化鎘、硒化鎘/硫化鎘奈米晶體搭配有機發光材料，研究奈米晶體於有機發光二極體所具有的光電特性。我們發現元件中奈米晶體膜厚將影響到電激發光(electroluminescence；EL) 的放光位置及強度。於元件ITO/PEDOT-PSS/PVK/CdSe(CdS)/BCP/Mg:Ag中的奈米晶體層過薄時，使得電子電洞不易結合於奈米晶體層內，所以會在600nm和400nm的位置分別產生奈米晶體及PVK的電激發光的波峰，其放光波峰的強度會隨著所施加電壓的不同而改變。於元件ITO/PEDOT-PSS/PVK /CdSe/BCP/Mg:Ag中，依據量子限量化效應關係，硒化鎘奈米晶體的能隙會隨著體積的不同而變化，所以將不同粒徑的硒化鎘奈米晶體應用於發光二極體中，既可產生不同波長發光。

關鍵字

硒化鎘奈米晶體 ； 硒化鎘 ； 有機發光二極體 ； 量子限量化效應

並列摘要

We have synthesized CdSe and CdSe(CdS) core/shell nanorcrystals in tri-n-octylphosphine oxide (TOPO) micellar solution using dimethylcadmium (Cd(CH3)2), selenium (Se) powder and bis-trimethylsilane sulfide ((TMS)2S) as the reactants. The sizes of the nanocrystals were controlled by varying the experimental conditions such as the concentration of Cd(CH3)2, reaction temperature, and reaction time. The nanocrystals were characterized using UV-Vis absorption and fluorescence spectra. The absorption and fluorescence spectra suggested that the band edges of the resulting nanocrystals shift to higher energy than that of the bulk CdSe crystals. The transmission electron microscopy images indicated that the CdSe nanocrystals are about 3 nm.
We have demonstrated the electrical and optical characteristics of the organic light emitting diode (OLED) devices using nanocrystals as the emitting layer, Poly (9-vinylcarbazole) (PVK) as the hole-transport layer, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) as the electron-transport layer, and poly(3,4-ethylenedioxythiophene) -poly(4-styrenesulphonate) (PEDT-PSS) as the hole-injection layer. We have investigated the characteristics of CdSe for ITO/PEDT-PSS/PVK/CdSe/BCP/Mg:Ag structure and CdSe(CdS) for ITO/PEDT-PSS/PVK/CdS(CdS)/BCP/Mg:Ag structure. Then, we change the thickness of CdSe for ITO/PEDT-PSS/PVK/CdSe/BCP/Mg:Ag structure. We found that emission wavelength of these heterostructure devices was affected by the thickness of the light emitting layer of LED. The intensity of the electroluminescence (EL) at the position of 600 nm from nanocrystals and at 400 nm from PVK change with different voltages applied to the devices. We also found that ITO/PEDT-PSS/PVK/CdSe/BCP/Mg:Ag structure using CdSe nanocrystals in their emitting layer can provide emission tunable in the visible spectrum, because of the size-dependent luminescence of the quantum dots.

並列關鍵字

CdSe nanocrystals ； Cadmium Selenide ； Organic light emitting diodes ； Quantum confinement effect

參考文獻

43. Heeger, A. J.; Parker, I. D.; Yang, Y., Synth. Met., 1994, 67, 23.

1. Alivisatos, A. P., Science, 1996, 271, 933.

3. Tolbert, S. H.; Alivisatos, A. P., Annu. Rev. Phys. Chem., 1995, 46, 595.

8. Wang, Y.; Herron, N., J. Phys. Chem., 1991, 95, 525.

10. Gleiter, H., Prog. Mater. Sci., 1989, 33, 223.