液態製程之高效率有機發光元件

Abstract

本論文開發一種能與捲對捲製程結合且能製作多層有機半導體元件的液態製程方法-刮刀塗佈法，本方法能適用於塗佈有機高分子及小分子材料。此方法有效的於5 cm × 5 cm 尺寸內塗佈達10％的均勻性。目前利用此方法製作之磷光發光元件，各色光之效率分別達：綠光 33 cd/A, 橘光 40 cd/A, 藍光 20cd/A, 以及白光 34 cd/A。 此外，本論文亦開發出轉印低功函數之有機發光二極體陰極的方法，利用聚苯乙烯薄膜作為犧牲層置於用來轉印的軟性基板於陰極之間，並於轉印時加熱至150℃使聚苯乙烯薄膜融化而轉印至有機發光層上，目前利用此方法製作之元件效率約達蒸鍍製程下的七成，而操作電壓約高五伏。本論文亦開發出無ITO陽極的元件，利用不同長度的自組裝單分子層混合能有效調變銀的功函數及濕潤程度，能製作出高效率的上下發光的有機發光二極體，且效率及亮度與一般常用的ITO/PEDOT:PSS相近。另一方面，我們亦開發出高電流輸出及高開關比的有機垂直式電晶體，開關比可高達104。最後我們也結合有機發光二極體及有機垂直式電晶體製作成有機發光電晶體。電晶體能透過柵極電極來調變通過有機發光二極體的電流。有機發光電晶體的最高亮度可達1208 cd/m2，且發光效率可達10 cd/A。此外因此發光電晶體是由重直式電晶體與發光二極體垂直堆疊而成的，因此有達100％的開孔率。

In this thesis, a continuous roll-to-roll compatible blade-coating method for multi-layers of general organic semiconductors is developed. This method succeeds for polymers and small molecules. Uniformity is within 10% for 5 cm by 5 cm area with a mean value of tens of nanometers with little material waste. For phosphorescent OLED 33 cd/A is achieved for green, 40 cd/A for orange, 20 cd/A for blue, and 34 cd/A for white. In addition, a low work function cathode of blade-coated organic light-emitting diode is transferred from a soft polydimethylsiloxane (PDMS) mold by lamination without vacuum. A sacrificial layer of polystyrene with low Mw 1,500 and melting point of 120 ℃ is inserted between the cathode and PDMS for the subsequent mold removal at 150 ℃ by melting polystyrene. The efficiency is about 70 percent of the devices with thermally evaporated cathode. The turn-on voltage is about 5 volts higher. Furthermore, ITO-free anode of OLED is achieved by mixed self-assembled monolayers (SAM) modified Ag. Using a longer carboxyl-terminated component, which may shield or and bury the shorter fluorinated component in the SAM allows higher amount of fluorinated component to be used for increasing the work function of silver, without compromising the wetting property of the substrate needed for spin-coating of emissive conjugated polymer for PLED. PLED with high efficiency and brightness close to the case of ITO/PEDOT:PSS anode are achieved for both top and bottom emission PLED. On the other hand, a polymer vertical transistor with an on/off current ratio higher than 104 is demonstrated. The proposed space-charge limited transistor (SCLT) uses a metal-grid base containing high-density submicron openings to modulate the vertical space-charge-limited current (SCLC). Finally, polymer light-emitting transistor is also realized by vertically stacking a top-emitting polymer light-emitting diode on a polymer space-charge-limited transistor. The transistor modulates the current flow of the light-emitting diode by the metal-grid base voltage. As the cathode is fixed at −12 V and the grid base voltage varies from 0.9 V to −0.9 V the light emission is turned on and off with on luminance up to 1208 cd/m2. The current efficiency of the light-emitting transistor is 10 cd/A. The aperture ratio is basically 100 % because the light emitted upward is not shielded by the vertical metal-base transistor underneath with roughly the same area.