基于石墨烯底阴极的全透明倒置有机发光二极管的研究

Transparent OLEDs have potential applications in see-through displays and lightings. And Transparent OLEDs with bottom cathode（Transparent inverted OLEDs，TIOLEDs)） have better compatibility with n-TFT driving circuitry, inducing an aperture opening ratio of almost 100%. To develop high performance TIOLEDs, the transparent conducting electrode is a key prerequisite. Now, ITO has been widely used as transparent electrode in OLEDs, but it is brittle, and its raw materials are becoming increasingly expensive, rendering it unsuitable for low cost and flexible TIOLEDs. Graphene shows the unique extraordinary properties, such as excellent conductivity, high transparency, good mechanical properties, and low cost, has been widely used as the anode in OLEDs. However, graphene cathode based OLEDs are lacking because of its relatively high work function (4.4 eV)..In this project, graphene will be modified via the physical methods of depositing low work function metal or metal oxide, or active metal salts thin layer in grapheme under a high vacuum, which have been demonstrated to adjust the work function of cathode in commonly bottom-emitting OLEDs. The modified graphene will be studied by electron-only devices and UPS measurement, and objective to obtain a high performance and low work function grapheme cathode, which induce a good electron injection between the graphene cathode and the electron transporting layer because of a lower injection barrier at the interface. Then, combining a commonly transparent top-anode, a series of optical simulation will be carried out for obtaining the optimum structures of red, green, blue, and white grapheme cathode based TIOLEDs. And finally, we expect that a series of red, green, blue, and white TIOLEDs with graphene as bottom cathode can be achieved, which can work well with the n-TFT driving circuitry. The present research achievements will be rich the theory and skills of commercialization processing for TIOLEDs based see-through displays and lightings.

全透明OLEDs在新型See-through显示和照明领域有潜在应用，且阴极在下的倒置器件（全透明倒置OLEDs, TIOLEDs)能与n-TFT很好的匹配，实现几乎100%的开口率。TIOLEDs的关键在于透明电极，常用的透明电极ITO是脆性的，且价格昂贵。石墨烯具有优异的光电性能，且柔韧性好、低成本，已被广泛用作OLEDs的阳极，但其高的功函数（4.4 eV）使其作为OLEDs的阴极报道较少。.本项目拟借鉴常规OLEDs阴极功函数的调节方法，通过在石墨烯上面沉积薄层低功函、强注入的金属及金属氧化物、活泼金属盐类等材料对其修饰，通过单电子器件等测试对修饰后的石墨烯进行表征，研发出与电子传输层能级相匹配的高性能、低成本石墨烯阴极，并阐明石墨烯功函数的调节机理。然后以其为底阴极，选取成熟的透明顶阳极，结合光学模拟设计、优化器件结构，开发适用于n-TFT的一系列高性能单色及白光TIOLEDs。

石墨烯具有优异的光电性能，且柔韧性好、低成本，作为电极在全透明、柔性OLEDs中具有极大潜力。为了提高石墨烯薄膜的导电性，我们设计了银纳米线/石墨烯复合电极，对复合电极的溶液成膜性、导电性、透光率及功函数调节等进行了研究，并将其作为阳极应用在OLEDs中，器件展现出低的起亮电压和高的亮度。在此基础上，我们合成了碎片状的氧化石墨烯，发现其功函数(~4.94 eV)与ITO(~4.80 eV)很匹配，将其使用作空穴注入层制备的绿光OLEDs的最大亮度、电流效率和外量子效率分别达到139700 cd/m2、64.68 cd/A和18.08%，性能参数达到甚至优于PEDOT:PSS基绿光OLEDs。为进一步提高OLEDs的性能，我们提出了三明治主体器件结构，实现了对OLEDs中载流子复合区域的有效管理，开发的蓝、绿、黄、红及白光OLED的最大外量子效率达到21.79%、21.71%、23.85%、23.99%和23.15%，且在5000 cd/m2亮度时，绿、黄、红及白光OLED的外量子效率效率仍达到20.34%、20.95%、20.07%和16.06%。采用新型电荷产生单元（HAT-CN/HAT-CN:TAPC/TAPC）连接上述黄/蓝/黄及红/绿/红两个三明治主体结构的发光单元，开发的叠层四色白光OLEDs的外量子效率和显色指数分别达到34.78%和91，且器件展现出极高的色稳定性。进一步，我们设计了双蓝光发射的器件结构，与磷光超薄层相结合，成功开发了一系列结构简单、高效率及高色品质的白光OLEDs；提出了共给体或受体的激基白光器件设计思路，采用简单的器件结构成功开发出高色品质全激基发射的白光OLEDs。该研究工作对促进OLEDs基础理论完善及产业化发展具有重要意义。