- 學位論文
可用於增進有機發光顯示器效能之像素結構研究
Studies of Pixel Structures for Enhancing Organic Electroluminescent Display Performances
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摘要
主動式有機發光二極體 (active-matrix organic light-emitting diode, AMOLED) 因為其在顯示技術與應用中具有各種吸引人的優點，已成為主流的顯示技術之一，對於許多 AMOLED 的應用（例如，移動和可穿戴式裝置），功耗是一個十分關鍵的議題，因此盡可能地實現 OLED像素的最高外部量子效率 (external quantum efficiency，EQE) 至關重要。然而，目前AMOLED的內部發光仍僅少部分能萃取出來，而與理想值之外部量子效率相去甚遠。迄今為止，仍然缺乏一種高效且可行的光萃取技術/結構，能夠同時提高OLED顯示器的效率和節能，又能保持影像品質及製程相容性。 有鑑於此，我們實驗室先前提出了一種三維像素結構作為有效提升OLED顯示器出光效率的方法。此方法順勢利用傳統AMOLED的像素凹槽結構，將底部的金屬反射陽極延伸擴展到像素定義層(pixel definition layer，PDL)邊坡之上，並用高折射率填料(filler)選擇性地填充在像素開口處(凹槽區域)以形成光學反射凹面結構，透過此三維結構可以提升數倍的光萃取增益。在本論文研究的第一部分，我們透過光學模擬軟體更加詳細地評估所設計之AMOLED三維像素結構，包括在實際製程下像素凹槽的邊坡會呈現出有弧度/梯度的情況(graded bank slope)，並與連續平直的像素凹槽邊坡(straight bank slope)做比較；同時考慮製程難度較小的非選擇性填充高折射率填料(non-patterned filler)在像素結構中，並與理想情況下選擇性填充高折射率填料(patterned filler)在像素凹槽區域中做比較；以及使用實際的OLED疊層結構，並探討上述情況下所造成的效果與影響。根據光學模擬的結果可以明確地得知，透過實際製程下具有弧度/梯度的像素結構(graded bank)以及非理想情況下(但製程難度較小)的非選擇性填充高折射率填料(non-patterned filler)在像素結構中仍然可以保持並提供顯著的光萃取增益。此外，具有弧度/梯度的像素結構(graded bank)還提供了對於觀看特性上有益的影響。 本論文的第二部分，透過光學模擬研究薄膜封裝(thin film encapsulation, TFE)對上述反射式三維OLED像素所造成的光萃取影響，而模擬結果顯示TFE疊層將會導致光萃取效率大幅地降低。因此我們在像素和封裝層之間引入了額外的角度選擇性光學膜(angle-selective optical film, ASOF)結構，以此控制耦合到封裝層中的光角度分布，以大幅降低封裝層引起的光學損耗，保持大部分(一定程度)的光萃取效率。本研究成果對於開發更高效率、更省電的AMOLED提供有用的見解與指南。
並列摘要
Active-matrix organic light-emitting diode displays (AMOLEDs) have become one of the major display technologies due to their various attractive merits for display applications. Power consumption is a critical issue for many AMOLED applications (e.g., mobile and wearable applications); thus, achieving the highest possible external quantum efficiency (EQE) of pixel OLEDs is essential. However, current AMOLEDs still suffer poor light extraction and far from ideal EQEs. Thus, to date, a highly effective and feasible light extraction technique/structure that can boost efficiencies and power saving of OLED displays and yet keep image quality and manufacturing compatibility is still lacking and remains a grand challenge. Recently, through optical simulation, we proposed a three-dimensional (3D) pixel configuration as a potential and promising way to boost light out-coupling of OLED display pixels. By taking advantage of the conventional concave pixel structure in AMOLED, extending the bottom reflective electrode onto the bank slope of the pixel definition layer (PDL) and selectively filling the bank opening (concave area) with high-index filler to form the optically reflective concave structure, it is possible to give several-fold light extraction enhancement. In the first part of this dissertation, we further extend the simulation work by evaluating the effects of more realistic graded bank slope vs. straight bank slope, less challenging non-patterned (blanket) high-index filler vs. patterned filler, and real OLED layer stacks and properties. The optical simulation clearly reveals that light extraction enhancement can be mostly kept with more realistic graded bank profiles and even less ideal (but also less challenging) non-patterned filler can provide substantial extraction enhancement. Besides, the graded bank structure also provides beneficial effects on viewing characteristics. In the second part of this dissertation, influences of thin film encapsulation (TFE) on light extraction of such reflective 3D OLED pixels are considered as well by simulation studies. Unfortunately, the optical simulation reveals strong reduction of the light extraction efficiency induced by TFE layers. As such, an additional angle-selective optical film (ASOF) structure between the pixel and the encapsulation layers is introduced to control the angular distribution of the light coupled into the encapsulation layers and to solve TFE-induced optical losses. As a result, TFE-induced losses can be substantially reduced to retain much of light extraction efficiency. The results of this study are believed to provide useful insights and guides for developing even more efficient and power-saving AMOLEDs.
參考文獻
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