本論文以紅螢烯亞能隙有機發光二極體為研究對象，透過光電特性與磁場效應探討亞能隙發光機制中的非輻射復合損耗。亞能隙發光機制是由供體/受體界面產生電荷轉移態，並透過能量轉移與三重態-三重態煙滅上轉換至單重態激子實現低啟動電壓，然而界面電荷分離產生的非輻射復合會使元件發生損耗。為了深入探討亞能隙中損耗機制，本研究中透過電容-亮度-電壓關係，探討元件的界面載子動力學，分析電荷復合的過程。研究中發現，當電荷注入並發生復合時元件未觀察到發光，與界面電荷分離中電荷轉移態非輻射復合損耗高度相關。研究中透過與並四苯系統的比較，確認當亞能隙發光機制中界面電荷分離效果較強時，單重態激子回到電荷轉移態後，會以非輻射復合的方式損耗。為抑制發光機制中損耗，本研究透過摻雜與中間阻擋層方式阻擋界面電荷分離路徑，結果顯示，元件效率與發光啟動電壓皆有提升，有效抑制界面電荷分離產生的電荷轉移態非輻射復合。此結果為高效率亞能隙有機發光二極體設計，提供新的方向與途徑。

This thesis focuses on rubrene-based sub-bandgap organic light-emitting diodes (OLEDs). Through optoelectronic characteristics and magneto-electroluminescence (MEL) effects, the non-radiative recombination losses in the sub-bandgap emission mechanism are investigated. This mechanism originates from the generation of charge-transfer (CT) states at the donor/acceptor interface, which then achieve a low turn-on voltage via energy transfer and triplet-triplet annihilation (TTA) up-conversion to singlet excitons. However, the non-radiative recombination resulting from back charge separation (BCS) leads to losses within the device. By exploring the loss mechanisms in the sub-bandgap region, interfacial carrier dynamics is investigated using the capacitance-luminance-voltage (C- L-V) relationship, the charge recombination process is analyzed. Our findings reveal that when charges are injected and undergo recombination, no luminescence is observed from the device, which is highly correlated with the non-radiative recombination loss of the charge-transfer states during back charge separation. By comparing with a tetracene-based system, the back charge separation effect is stronger in the sub-bandgap emission mechanism, the singlet excitons return to the charge-transfer states and are subsequently lost through non-radiative recombination. In addition to suppress the losses within the emission mechanism, doping and an intermediate blocking layer can be applied to obstruct the pathways of back charge separation. Device efficiency and turn-on voltage are improved. Especially non-radiative recombination of charge-transfer states caused by back charge separation is suppressed. These results provide a new direction and approach for the design of high-efficiency sub-bandgap OLEDs.

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