三氟甲烷之取代烷基硫醇自組裝單分子薄膜修飾於陽極表面對於有機電激發光元件性質之研究探討

Abstract

本篇主要分為兩個部分，第一部份是合成三氟甲烷取代之烷基硫醇分子，其具有相同末端拉電子基（-CF3）但不同長度的碳鏈的硫醇分子，並吸附在金與銀表面形成自組裝單分子薄膜，藉由橢圓儀、紅外光譜儀、接觸角及光電子光譜儀進行表面性質分析，更進一步探討碳鏈奇偶對表面性質及對功函數的影響。第二部分是將三氟甲烷之取代烷基硫醇分子修飾於OLED元件之陽極電極，製備發光元件，研究此修飾對元件之電流、電壓、及發光效率的影響。 第一部分研究結果顯示吸附在金表面時，紅外線的吸收、接觸角及功函數都隨著亞甲基數目依序增加而有大小交替的奇偶效應。但吸附在銀表面時，卻沒有明顯的奇偶效應。第二部分研究結果顯示，經三氟甲烷取代之烷基硫醇分子修飾陽極所製作頂部發光元件，元件結構為Ag/ CF3-SAM/ NPB/ Alq3/ LiF/ Al/ Ag，電流密度隨著修飾硫醇分子之碳鏈長度增加而減少，而發光效率則隨著修飾硫醇分子之碳鏈長度增加而變大，發現奇偶碳鏈的偶極矩變化對電荷的注入影響較小，而碳鏈長度的差異所造成不同的穿遂障礙將是影響發光效率的主因。若元件結構改為Au/ CF3-SAM/ BPAPF/ Alq3/ LiF/ Al/ Ag，其電流密度隨著功函數增加而變大，發光效率以CF3(CH2)11SH所修飾電極的元件最佳。電流效率之變化趨勢可以電洞注入效率的改變而造成電荷平衡改變來解釋。

The thesis is divided into two parts. One is the synthesis of CF3- terminated alkanethiol molecules with different chain lengths and the self-assembled monolayers formed by these molecules on gold and silver. The packing structure and surface property of these SAMs were investigated by ellipsometery, reflection absorption IR (RAIR), contact angle, and photoelectron spectrometer (AC-2), to explore the relationship between surface property and chain length. In the second part, CF3- terminated alkanethiol molecules were used to modify the anode in the fabrication of top-emitting organic light-emitting devices (TOLED). The I-V curve, current density, and current efficiency were investigated.

In the first portion, the results of the reflection absorption IR, contact angle, and work function indicated that the even-odd chain-length effect was observed on the gold surface resulting from the orientation difference of the CF3 group in the SAMs absorbed on the gold surface. Little or no odd-even effect was observed on Ag surface.

In the second part, the performance of the top emitting device composed of Ag/ CF3-SAM/ NPB/ Alq3/ LiF/ Al/ Ag structure with anode modified by different chain length CF3-terminated alkanethiol molecules showed that the current density decreased with increasing chain length. The current efficiency increased with increasing the chain length. This result indicated that the tunneling barrier introduced by the insulating alkyl chains is affecting the charge injection rather than the dipole orientation difference due to chain length. On the other hand, in the device composed of Au/ CF3-SAM/ BPAPF/ Alq3/ LiF/ Al/ Ag, the result showed that the current density increased with increasing workfunction. Otherwise, The highest current efficiency occurred on the anode modified by CF3(CH2)11SH molecules. This result indicated that modulating the dipole orientation of the insulating alkyl chains could optimize the performance of the device. The trend of current efficiency is rationalized in terms of changing charge balance due to charging hole injection.