有機發光二極體顯示器之畫素結構優化應用於效率增益

Abstract

有機發光二極體應用於顯示器為目前市場上一主流技術，其相較於傳統液晶顯示器具有諸多優點，如更輕薄、反應速度更快及更高對比度等，然而其高折射有機材料疊層結構及顯示器結構所造成之穿透損耗，使得最終耦合進入空氣之出光效率低落，而現有之諸多研究對於提升出光效率所採用之方法也不完全適用於顯示器結構，因此基於顯示器架構需提出一方法來優化其出光效率。 在本研究之模擬計算中針對有機膜層及畫素結構所構成之多重尺度結構，採用結合波動光學與幾何光學之計算，對於波長尺度之膜層結構採用傳輸矩陣法來計算光源資訊及表面反射特性，並將結果匯入至光線追跡模型中，以光線追跡法計算大尺度之畫素結構，達到嚴謹計算且減少時間成本之效果。 在本研究中基於上發光式有機發光二極體顯示器之基本結構提出一改善方法，藉由一折射率匹配材料以選擇性方式填入畫素中，並調整畫素之結構，最終達到優化出光效率之成效，以常見之CBP(折射率約為1.81)作為填充層材料並配合其最佳之畫素定義層底角可達到43.7 %之出光效率，若提高填充層材料之折射率達到2，配合其最佳之畫素定義層底角則可達到50.2 %之出光效率，相較於基本平面元件具有90 %以上之效率增益，且增加結構高寬比更可進一步提升出光效率，故此一設計可有效優化顯示器之出光表現。

Applying organic light-emitting devices (OLEDs) as displays is a mainstream technology today. Compared with conventional liquid crystal display (LCD), OLED displays have thinner structure, faster response time, and higher contrast ratio. However, it suffers from low external quantum efficiency (EQE) duo to the stacked structure with high-index organic materials and the penetration loss in the pixel definition layer (PDL). Therefore, the optimization of EQE based on display structure is needed. In order to save the simulation time, combination of wave optics and ray optics is introduced to deal with multi-scale structure including organic stack (nm-scale) and pixel structure (μm-scale). Transfer-matrix method is used to calculate emission profiles and surface properties of the organic stack. Then ray-tracing method is used to calculate pixel structure with imported results of transfer-matrix method. In this study, an optimization method based on display structure is introduced. The EQE can be enhanced by selectively filling an index-matching material into pixel’s opening area and adjusting the pixel structure. The EQE can reach 43.7 % by using CBP as filler and can reach 50.2 % by using the filling material with refractive index of 2. The EQE enhancement compared to the basic top-emitting device is more than 90 %, and the EQE can further increase by increasing height to width ratio of the pixel structure. Therefore, the design can significantly enhance the performance of OLED displays.