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標題: | 原子層沉積薄膜在有機電子元件之應用: 光微影圖樣、封裝以及緩衝層 Applications of Atomic Layer Deposition Films on Organic Electronic Devices: Photo-Patterning, Encapsulation, and Buffer Layer |
作者: | Chih-Yu Chang 張志宇 |
指導教授: | 蔡豐羽 |
關鍵字: | 有機電子元件,原子層沉積,光微影圖樣,封裝, Organic electronics,Atomic layer deposition,Organic light-emitting diodes,Organic solar cells,Photolithography,Encapsulation, |
出版年 : | 2010 |
學位: | 博士 |
摘要: | 本篇研究利用原子層沉積技術 (ALD) 解決有機電子元件欲商業化所面臨的關鍵議題,包括: 在有機發光材料上加入ALD薄膜,使得光微影圖樣製程可適用於有機發光二極體 (OLEDs),並增進元件效率;開發高阻氣性ALD薄膜封裝有機太陽能電池 (OSCs),以及開發兼具高阻氣與電子傳遞功用之ALD薄膜,使得可撓式OSCs在大氣下可保有優異之穩定性。
在OLEDs的研究中,我們在發光材料 (本研究選用MEH-PPV) 上沉積10-Å之ALD氧化鋁薄膜,阻絕製程環境中溶劑或氣體與材料之直接接觸,使材料得以使用光微影技術形成圖樣而不受到任何的損害,此ALD氧化鋁薄膜在完成後可留存在元件中做為增進元件性能的緩衝層。雖然在進行ALD的過程中反應前驅物三甲基鋁會與MEH-PPV上的乙烯基進行加成反應,但此負面效應可藉由在MEH-PPV表面上以異丙醇進行前處理而獲得解決。 在OSCs的研究中,藉由最佳化ALD製程,我們開發了一個可同時對元件進行封裝並適度退火之製程。以聚(3-己烷基噻吩) (P3HT) 混掺6,6-苯基-碳61丁酸甲酯 (PCBM) 為吸光層之電池在經過140 ºC、1個小時之ALD封裝後,元件效率達3.66%。以26-nm之ALD氧化鋁-氧化鉿多層結構薄膜封裝之元件在大氣下可達到與在無水氧環境下相近之衰退速率。氧化鋁-氧化鉿多層結構解決了單一氧化鋁薄膜在大氣下會被水解的問題。除此之外,延長前驅物的曝露時間可以有效改善ALD薄膜在P3HT:PCBM上成核不易的問題。 在可撓式OSCs之研究中,我們開發了低溫製程 (90 ºC) 之ALD氧化鋅薄膜,此氧化鋅薄膜在P3HT:PCBM為吸光層之倒置型太陽能電池中,具有阻氣層以及電子收集層的雙重功用。藉由降低製程溫度至90 ºC以及延長前驅物水蒸氣的抽氣時間 (25秒),所製備的氧化鋅薄膜具有高載子遷移率 (9.6 cm2/V s) 以及低載子濃度(2.1×1017 cm-3),以玻璃為基板之元件效率可達4.06%。而此條件下之氧化鋅薄膜亦具有高阻氣率: 水氣穿透率為低於10-3 g/m2 day,氦氣氣體穿透率為5.03 cc/m2 day。高度吸濕性之聚(亞乙基二氧硫代酚)-聚(磺酸苯乙烯) (PEDOT:PSS) 是造成倒置型太陽能電池在大氣下衰退的主因,而藉由氧化鋅薄膜所提供優異之阻水特性可避免上述問題產生。以70-nm之ALD氧化鋅薄膜與26-nm ALD氧化鋁-氧化鉿多層結構薄膜封裝可撓曲之OSCs,元件效率起始效率為2.77%。元件在大氣下之衰退速率與元件在無水氧環境下相近,在經過1800個小時、65 ºC/60%相對溼度之加速環境下,可維持73%之起始效率。 本論文之研究成果對於OLEDs、OSCs,或是其他對於精細圖樣、電極界面改質或是阻氣封裝有需求之有機電子元件,具有高度參考價值,有利於促進有機電子元件之實用性。 This study utilized atomic layer deposition (ALD) to develop solutions to critical problems of organic electronics, including patterning-enabling and electron-injection- enhancing dual-functioning films for organic light-emitting diodes (OLEDs), gas-permeation barriers for the thin-film encapsulation of organic solar cells (OSCs), and permeation-blocking and electron-collecting dual-functioning films for flexible air-stable OSCs. On OLEDs, we demonstrated that with a 10-Å ALD Al2O3 film overcoated on a poly[1-methoxy-4-(2’-ethyl-hexyloxy)-2,5-phenylenevinylene] (MEH-PPV) electro- luminescent layer, the OLEDs not only withstood an aggressive photolithographic patterning process without any degradation but unprecedentedly showed increased luminous efficiency. Although the ALD precursor, trimethylaluminum (TMA), was found to damage MEH-PPV through addition to MEH-PPV’s vinylene groups, its damaging effect was eliminated by pre-treating the MEH-PPV surface with isopropyl alcohol (IPA), whose hydroxyl groups scavenged TMA throughout the ALD process. On the encapsulation of OSCs, we developed ALD processes that both prevented degradations caused by ambient gases and served as an annealing step that increased the initial power conversion efficiency (PCE) of the cells. With the ALD temperature set at 140 ºC and the deposition time set at 1 hr, OSCs based on blended poly-3- hexylthiophene (P3HT) and [6,6]-phenyl C61 butyric acid-methylester (PCBM), were optimally annealed during encapsulation, achieving a PCE of 3.66%. Encapsulating the cells with a 26-nm Al2O3/HfO2 nanolaminated film overcoated with an epoxy-resin protection layer enabled the cell to obtain an in-air degradation rate that was similar to cell stored in O2/H2O-free atmosphere. The Al2O3/HfO2 nanolaminated structure resolved the problem of hydrolysis-induced aging that occurred in single Al2O3 films, owing to the hydrophobicity of the HfO2 layers. Additionally, extended exposure of the ALD precursors during the ALD process ensured complete coverage of ALD films over the P3HT:PCBM layer at the perimeter of the cells. On flexible air-stable OSCs, we developed low-temperature (90 ºC) ALD ZnO films as both gas barriers and electron-collection layers for P3HT:PCBM-based inverted OSCs. By utilizing a long purge time (25-s) and a low deposition temperature (90 ºC) in the ALD process, we obtained high electron mobility (9.6 cm2/V s) and low carrier concentration (2.1×1017 cm-3) in the ZnO films, thereby optimizing their electron- collecting function and achieving 4.06% PCE in the resultant inverted OSCs. Moreover, when deposited on poly(ethylene terephthalate) (PET) substrates, the ALD ZnO films at 70 nm of thickness showed excellent barrier properties: water vapor transmission rate (WVTR) < 10-3 g/m2 day and helium transmission rate (HeTR) of 5.03 cc/m2 day. This moisture-blocking capability was crucial for achieving air-stable inverted OSCs, as we determined that air-induced degradations of inverted OSCs mainly originated from moisture uptake by the poly(3,4-ethylene-dioxythiophene):polystyrene sulfonate (PEDOT:PSS) layer. Using an 70 nm ALD ZnO film for the electron-collection/barrier dual functions as well as a 26-nm Al2O3/HfO2 nanolaminate as the encapsulation layer, we demonstrated flexible OSCs on PET substrates with initial PCE of 2.77% and with negligible air-induced degradation: the OSCs showed near identical degradation rate as the control devices stored in an O2/H2O-free environment, and they retained 73% of their initial PCE over 1800 hr of storage under a 65 ºC/60% RH accelerated aging condition. The results of my study will facilitate the practical applications of OLEDs and OSCs, as well as other types of organic electronics that require precise patterning, interface engineering and hermetic sealing. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/22808 |
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