- 學位論文
串聯式有機發光元件連接層之研究
Investigation of Connecting layer in Tandem Organic Light-Emitting Diodes
摘要
近年來在全彩顯示器與固態照明應用技術中，有機發光元件(OLED)之使用上已引發了廣大的矚目，理論上，磷光元件可以有效的使用單重態激發態與三重態激發態的激子，所以其內部量子效率可高達理想的100%，可製備成高效率有機發光元件，儼然成為未來照明之主流，除了有機發光元件高效率外，仍須提高封裝技術、外部光耦合效率、降低操作電壓與售價等等，使有機發光元件在市場上更具競爭力。 本論文提出藉由降低電洞傳輸層與發光層主體之間的注入能障，可以有效降低元件操作電壓。我們以高電洞遷移率的TAPC作為電洞傳輸層，搭配具雙極性傳輸能力的TCz1作為發光層主體，使其形成能階匹配，為達成高效率串聯式元件，首先需考慮穩定度高的連接層材料，例如：不容易水解，還有良好的載子產生特性等等，我們對多種不同結構之連接層(Connecting Layer)進行電性實驗測試，而後採用電性最好的結構進行串聯式元件製作，為求取二個元件單元的載子平衡，我們設計藍綠光色之串聯式元件，利用相異光譜來尋求二發光單元的平衡點，藉以確認連接層適切的載子注入能力，最後，再進行串聯式白色有機發光元件的設計，串聯式白色磷光元件在1000 cd/m2的實用亮度下，其操作電壓為10.1 V，而如此的優異表現，使我們相信串聯式白色有機發光元件未來潛力勢必無可限量。
並列摘要
At present, the organic light-emitting devices (OLEDs) have drawn significant attention because of their potential applications for full-color display and solid-state lighting. In general, the electrophosphorescence can efficiently use both singlet and triplet excited states, and thus its internal quantum efficiency can in principle reach an ideal level of 100%, which is much superior than the 25% upper limit imposed by the formation of singlet excitons in fluorescence. Although the efficiencies and lifetimes of phosphorescent OLEDs (PhOLEDs) have advanced significantly, there should be still plenty of room in improving several critical issues including encapsulation, light extraction, operation voltage, manufacturing cost etc. In addition, in the aspect of OLED for lighting, the device need to operate at higher current density levels to ensure an ample light flux. However, a stressed operation will result in poor performance and limited device lifetime. Recently, a tandem structure has been proposed as a pivotal technique to meet the stringent lighting requirements for OLED commercialization, with a research focus on decreasing the concomitant higher operation voltage. Driving two connected emission units (EMUs) in a tandem structure often requires more than twice the driving voltage for a single EMU. This study investigates bipolar host materials and their effective employment in fabricating tandem white PhOLEDs. Furthermore, the novel design of an energy level aligning mechanism between the hole transport layer/emitting layer is shown to effectively mitigate operational voltages. In sharp contrast to devices using a unipolar host material, we successfully demonstrate that the turn-on voltage of blue PhOLEDs could be decreased from 3.8V to 2.7 V through utilizing a bipolar host. Furthermore, applying the proposed techniques to tandem white PhOLEDs produces a luminance of 103 cd/m2 by a 10.1 V driving voltage.