三重態-三重態消滅與複合受激態之有機發光二極體研究

Abstract

本研究有兩個主題，其一為複合受激態之有機發光二極體的效率提升。其二為複合受激態觸發三重態-三重態消滅藍色有機發光二極體之效率提升。 複合受激態 (Exciplex) 為兩有機材料，分別具電子施體與電子受體特性，在界面處形成激發態的錯合物。我們針對使用複合受激態之有機發光二極體，調變厚度與混合比例來優化，得到6.57 % 外部量子效率及20.95 lm/W 之功率效率。 再者為研究複合受激態觸發三重態-三重態消滅藍色有機發光二極體 (Exciplex sensitized triplet-triplet annihilation ,簡稱ESTTA)。此系統由複合受激態經能量傳遞給藍色三重態-三重態消滅 (Triplet-triplet annhiliation, 簡稱TTA) 發光體，產生上轉換 (Upconversion) 的放光。其效率可能因單重態激子猝熄而降低。故本章以兩種手段，改善此系統的能量傳遞路徑，增加藍光效率。其一為加入藍色螢光客體材料4,4'-bis[2-(4-(N,N-diphenylamino)phenyl)vinyl]biphenyl) (DPAVBi)，其二為插入 4,7-diphenyl-1,10-phenanthroline (BPhen) 作為三重態傳遞和單重態阻隔層 (Triplet diffusion and singlet blocking,簡稱TDSB)。在既摻雜客體材料亦插 TDSB 層之元件，能提升外部量子效率的藍色分量至2.316%。 上述研究皆屬於延遲型螢光放光，因此我們利用暫態電激發光 (Transient electroluminescence, 簡稱TrEL) 量測系統，來分析這種延遲放光。透過量測電訊號關掉後的電激放光，藉此研究激子於元件中的物理機制，以及能量轉移的過程。

There are two topics in this thesis. The first one is the optimization of exciplex-based organic light-emitting diode (OLED). The second part describes the methods to improve the efficiency of exciplex sensitized triplet-triplet annihilation (ESTTA) OLED. When two organic materials act as electron donor and acceptor respectively and form the excited complexes at their interface, it is called exciplex. We optimized exciplex-based OLED to achieve higher efficiency by means of layer structure tuning. Finally, the power efficiency of 20.95 lm/W and external quantum efficiency (EQE) of 6.57% were obtained. Exciplex generated by two species could transfer its energy to triplet-triplet annihilation (TTA) blue emitter, and created energy upconversion blue emission afterwards. We called this process exciplex sensitized triplet-triplet annihilation (ESTTA). Here, two methods have been adopted to improve the efficiency, which were: (1) doping blue fluorescence dye: 4,4'-bis[2-(4-(N,N-diphenylamino)phenyl)vinyl]biphenyl) (DPAVBi), and (2) inserting 4,7-diphenyl-1,10-phenanthroline (BPhen) as “triplet diffusion and singlet blocking (TDSB)” layer. By employing dopant combined with TDSB layer, ESTTA-OLED increased its blue EQE to 2.316%. In these OLEDs, transient electroluminescence (TrEL) were employed to investigatet the carrier and exciton dynamics by measuring the turn-off responses.