傳統有機發光二極體的特性是由單一主動層組成，藉由載子傳輸至主動層復合後放光；而亞能隙有機發光二極體的特性是主動層由供體與受體(donor/acceptor, D/A)兩種材料構成，載子於界面復合形成電荷轉移態(charge transfer state, CT state)後再將能量轉移至donor的三重態激發態(T1)上最後經由三重態-三重態湮滅(triplet-triplet annihilation, TTA)轉移至高能量單重態激發態(S1)上放光，因此亞能隙系統相對於傳統螢光系統由於載子於界面復合使得所需啟動元件放光的能量小於發光材料的能隙。
本次研究於能階匹配下利用並四苯(tetracene)與 1,2-ADN 兩種亞能隙的主體材料分別搭配不同受體材料分別為富勒烯(C60)與NDI-HF，由於認知亞能隙系統一定會存在界面電荷分離效應(back charge separation, BCS)會將 donor 中 S1 的能量躍遷返回至 CT state 復合造成能量損耗，因此嘗試去減少 BCS 效應對tetracene與 1,2-ADN 系統造成的損耗，並利用磁電致磁電致發光效應輔助觀察元件內部光物理主導機制。
抑制 BCS 的方法有在 D/A之間插入阻擋層浴銅靈(Bathocuproine; BCP)阻擋能量返回界面處以及在donor 摻雜 dopant 藉由 Förster resonance energy transfer(FRET) 與 BCS 效應爭搶S1上的能量。結果顯示 tetracene 亞能隙系統主要受到 BCS 效應影響元件放光，抑制 BCS 效應有效提升元件電性；反觀 1,2-ADN 亞能隙系統中 BCS 效應並不是主導，抑制 BCS 效應無法進一步提升元件電性，反而要以主導元件能量損失的三重態-極化子對湮滅(triplet-polaron quench, TPQ)，想辦法解決此效應才是優化 1,2-ADN 亞能隙系統的前提。

Traditional organic light-emitting diodes generally emit light through carrier recombination in a single active layer. In contrast, sub-bandgap OLEDs use a donor/acceptor (D/A) structure, where carriers recombine at the interface to form charge-transfer (CT) states. The energy is then transferred to the donor triplet state (T1), followed by triplet–triplet annihilation (TTA) to generate the singlet excited state (S1) for light emission. Therefore, sub-bandgap OLEDs can operate at an energy lower than the optical gap of the emissive material. In this study, tetracene/C60 and 1,2-ADN/NDI-HF systems were investigated based on energy-level matching. Since back charge separation (BCS) may cause energy loss by returning the donor S1 energy to the interfacial CT state, BCP insertion and dopant incorporation were used to suppress BCS. Magneto-electroluminescence (MEL) was also applied to analyze the dominant photophysical mechanisms. The results show that the tetracene-based system is mainly limited by BCS, and suppressing BCS effectively improves device performance. However, in the 1,2-ADN-based system, BCS is not the dominant loss mechanism. Instead, triplet–polaron quenching (TPQ) plays a more important role, indicating that reducing TPQ is essential for further improving the 1,2-ADN-based sub-bandgap OLEDs.

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