摘要
有機電子元件的發展中，電極與有機半導體介面間的能階相對位modulate
置，對於電荷載子注入效率上一直扮演極其重要的角。其中對於有機發光二極體元件(Organic light emitting diodes, OLEDs)的表現上，起始的電荷載子注入程度對於元件發光效率與元件壽命皆深具影響。並且可經由在電極表面上進行修飾或改質，於電極與有機半導體介面處引入不同方向或強度之電偶極，以調控介面能階相對位置。
在本研究中，我們利用一系列具不同偶極性質之硫醇分子，將其吸附於金屬銀表面以製備出高秩序性之自組裝單層分子薄膜(self-assembled monolayers, SAMs)。其中所使用分子包含不同取代位置之氟取代苄基硫醇、不同鏈長之正烷基硫醇、末端氰基、末端三氟甲烷之取代烷基硫醇與兩種偶極方向相反的烷基硫醇(正癸基硫醇與全氟化癸基硫醇)之二元混合系統，然後將其應用於上發光式有機發光二極體元件之陽極(Top-emitting OLEDs)。並經由元件光電性質的量測與分析，判斷該修飾對元件內電洞載子注入效率的影響。
首先我們顯示相同的取代基因取代位置的不同，造成吸附分子膜偶極方向的不同，可直接有效地調控金屬表面之功函數(work function), 繼而改變載子於陽極與有機半導體介面處的注入能障。其
次我們也顯示除了可藉由改變烷基硫醇分子的末端官能基取代來調
III
整金屬表面功函數外，同時也可藉由絕緣的碳鏈長度的改變來調控位
於介面的穿隧距離(tunneling distance)。經過兩者(極性官能基與穿隧距離)交互調整的過程有效調控介面間的能階相對位置，從而分析元件中電子與電洞平衡狀況及對發光效率的影響。
本研究並進一步以兩種偶極方向相反的烷基硫醇(正癸基硫醇與全氟化癸基硫醇)製備自組裝二元混合分子薄膜(mixed SAMs)修飾於金屬銀表面，藉由混合比例的改變，有效地且連續地調控其功函數變化(4.1 eV~5.8 eV)。後續將其應用於Top-emitting OLED的陽極，並搭配不同電洞傳輸材料(HTL)製作單載子(電洞)二極體元件(Hole-only devices)，或Top-emitting OLEDs 元件，由混合單分子層的混合比例對元件電荷注入效率、發光電流效率影響，分析改善電洞與電子載子數目平衡的方法。
除此之外，針對有機半導體之自身載子遷移率(carrier mobility)普遍不高以及傳統上使用有機薄膜電晶體驅動有機發光二極體在製程上的限制，我們朝向導電通道可大幅縮短的垂直式電晶體方向發展，以期降低電壓提升電流輸出。本研究利用奈米球微影製程技術(Nanosphere lithography, NSL)，同時以聚氧化乙烯(poly(ethylene oxide))進行高分子架橋，以提升聚苯乙烯(polystyrene)奈米球自組裝
的穩定性，從而製作大面積奈米孔洞陣列之鋁金屬閘極，並以聚三己
IV
基塞吩(poly(3-hexylthiophene), P3HT) 做為主動層材料，應用於製備垂直式空間電荷限制電晶體(space-charge limited transistor, SCLT)。本研究所製作之大面積規則陣列鋁基極之空間電荷限制電晶體，於低操作電壓(-2.0V)下可有效獲得高電流密度輸出(平均值為12 mA/cm2)，元件操作最大開關比(on-off ratio)則為2*104，對於有機薄膜電晶體的性質提升有初步著實的成效。
V
Abstract
The energy level alignment between a metal and an organic semiconductor (M/O) is regarded as the dominant factor affecting carrier injection efficiency. In particular, it plays a crucial role in the performances of organic light emitting diodes (OLEDs) including electroluminance efficiency and life-t
ime. Through electrode surface modification, the size and direction of the interface dipole can be introduced to modulate the energy alignment at the interface. In this study, a series of thiol compounds, including fluorine-substituted benzyl mercaptans,n-alkanethiol, cyano-terminated (CN-), trifluoro-terminated (CF3-), perfluroinated substituents and binary mixtures with opposite dipoles, were used to modify the silver anode through the formation of well-ordered self-assembled monolayers (SAMs) and applied in the fabrication of top-emitting electroluminescent devices. The device performances were measured and analyzed to understand the effect of modification on the charge injection.
It is demonstrated that the same substituent placed at different positions on a phenyl ring results in different dipole moment and modulate the work function/charge injection differently. Furthermore we demonstrated that besides the dipolar functional group, the chain length of alkanethiol can be used to tune the tunneling distance for charge injection. Through selection of the two parameters (dipolar functional group and tunneling distance), the energy alignment can be fine-tuned and influence the charge balance and luminescence efficiency.
VI
Furthermore, SAMs of binary mixtures of n-decanethiol and the perfluorinated analogue were formed on silver surface. Through change of mixing ratio, the work function of silver can be tuned continuously over a wide range: from 4.1 eV to 5.8 eV. The mixed SAM-modified Ag surfaces were used as the anode in the fabrication of hole-only devices and electroluminescent devices using different hole-transporting materials (HTL). Through the analysis of charge injection efficiency/luminescence efficiency, strategy of improving hole/electron carrier balance is proposed.
With generally low mobility associated with organic semiconductors and limitations on the fabrication involving lateral transistors as driving component, we also extended our work on vertical type transistors, which uses greatly reduced channel length to lower driving voltage and increase current output. A large-area and periodically patterned nanoporous Al grids with controlled pore size were fabricated by poly(ethylene oxide)-assisted self-assembly of polystyrene nanospheres. This grid layer was used as the base electrode in a space-charge limited transistor (SCLT) with vertical architecture.    A high performance device with poly(3-hexylthiophene) (P3HT) as conducting semiconductor was achieved with a high on-current output of ~12 mA/cm2 and a high on-off ratio of ~2x104 at a collector voltage of -2.0V.
VII

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