Study of anode modification and thin-film encapsulation of flexible organic light-emitting devices
|摘要:||可撓曲式有機電激發元件(flexible organic light-emitting device, FOLED)的電致發光性質受到氧化銦錫(indium tin oxide, ITO)塑膠基板的表面型態所影響，包括基板表面的圖案化及製程條件。我們提出證據證明FOLED的發光效率可以經由基板的前處理，得到大大的改善。除了使用原子力顯微鏡(atomic force microscope, AFM)及光學顯微鏡進行ITO/PET及ITO/玻璃基板表面分析，也會討論到不同基板前處理對FOLED電致發光性質的影響。我們並且首先加入了陽極修飾層LiF到塑膠基板的ITO上，有效降低元件的操作電壓。
在導電陽極製作方面，室溫下使用負離子束濺鍍技術(negative ion-beam sputtering deposition technology)在polyethersulfone (PES)基板上濺鍍ITO薄膜，在濺鍍時導入Cs蒸氣，ITO/PES薄膜的光學及電特性都獲得改善。在最佳的條件下，ITO/PES薄膜的電阻率可以達到4.3 × 10-4 Ω-cm，比傳統射頻濺鍍(radio frequency sputtering, RF sputtering)的1.58 × 10-3 Ω-cm還低。可見光區域的光學穿透度是85%，ITO/PES薄膜的表面型態在最佳的條件下，表面粗糙度是0.95 nm。除此之外，我們還利用此技術在塑膠基板上沈積氣體阻絶層。在最佳的條件下，我們可以得到SixNy 及 AlxOy的表面平整度(root mean square, Rms)分別為1.54 nm及0.63 nm。
Electroluminescence (EL) performance of flexible organic light-emitting device (FOLED) was found to be highly related to the surface morphology of the indium tin oxide (ITO)/plastic substrate as well as the patterning and processing conditions of the substrate. This thesis presents evidences showing that luminance efficiency of FOLED can be greatly improved by ITO pretreatment. Surface analysis of the ITO/PET by means of atomic force microscope (AFM) and optical microscope was compared with that of the ITO/glass and the influence of flexible OLEDs substrate treatment by various methods on EL performance were discussed. It was found that LiF as modified layer of ITO on plastic substrates led to the decrease of the operating voltage of FOLED devices. In fabrication of anode, ITO thin films were deposited onto polyethersulfone (PES) substrate at room temperature by negative ion-beam sputtering deposition technology of Plasmion Corporation. The optical and electrical properties of ITO/PES thin films were improved by introducing the Cs vapor during sputtering. Under the optimal condition, the resistivity of ITO/PES can reach 4.3 × 10-4 Ω-cm, which is lower than 1.58 × 10-3 Ω-cm of the conventional RF sputtered films. The optical transmittance is 85% throughout visible region. Surface morphology of the optimal ITO/PES films is 0.95 nm of the surface roughness under this condition. In addition, we use negative ion- beam sputtering deposition technology to deposit gas barrier layer on the plastic substrate. Under the optimal condition, we got the Rms of 1.54 nm and 0.63 nm for SixNy and AlxOy, respectively. In thin film encapsulation, we have developed a novel thin film encapsulation method for top-emitting and transparent OLED by introducing organic (not polymer)/inorganic multiple thin films to protect the devices, which is shown to suppress the permeation rate of moisture and oxygen. From the stability test of devices, the projected lifetime of transparent OLED with such a thin film encapsulation technique was similar to that with glass lid encapsulation.
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