Jang Eun-Bi, Choi Geun-Su, Bae Eun-Jeong, Ju Byeong-Kwon, Park Young-Wook
Nano and Organic-Electronics Laboratory, SunMoon University, Asan 31460, Republic of Korea.
Display and Nanosystem Laboratory, Department of Electrical Engineering, Korea University, 145, Anam-ro, Seoul 02841, Republic of Korea.
Nanomaterials (Basel). 2023 Aug 18;13(16):2366. doi: 10.3390/nano13162366.
We report the electroluminescence (EL) characteristics of blue ultra-thin emissive layer (U-EML) phosphorescent (PH) organic light-emitting diodes (OLED) and thermally activated delayed fluorescence (TADF) OLED. A variety of transport layer (TL) materials were used in the fabricated OLEDs. The well-known FIrpic and DMAC-DPS were used with a thickness of 0.3 nm, which is relatively thicker than the optimal thickness (0.15 nm) of the blue phosphorescent ultra-thin emissive layer to ensure sufficient energy transfer. While FIrpic showed overall high efficiency in various TLs, DMAC-DPS exhibited three times lower efficiency in limited TLs. To clarify/identify low efficiency and to improve the EL, the thickness of DMAC-DPS was varied. A significantly higher and comparable efficiency was observed with a thickness of 4.5 nm, which is 15 times thicker. This thickness was oriented from the TADF itself, which reduces quenching in a triplet-triplet annihilation compared to the PH process. The thinner optimal thickness compared with ~30 nm of fluorescent OLEDs suggests that there still is quenching taking place. We expect that the efficiency of TADF U-EML OLEDs can be enhanced through further research on controlling the exciton quenching using multiple U-EMLs with spacers and a novel material with a high energy transfer rate (ΔE).
我们报告了蓝色超薄发光层（U-EML）磷光（PH）有机发光二极管（OLED）和热激活延迟荧光（TADF）OLED的电致发光（EL）特性。在所制备的OLED中使用了多种传输层（TL）材料。使用了著名的FIrpic和DMAC-DPS，其厚度为0.3 nm，这比蓝色磷光超薄发光层的最佳厚度（0.15 nm）相对更厚，以确保足够的能量转移。虽然FIrpic在各种传输层中总体上表现出高效率，但DMAC-DPS在有限的传输层中效率低三倍。为了阐明/识别低效率并改善电致发光，改变了DMAC-DPS的厚度。观察到厚度为4.5 nm时效率显著更高且相当，该厚度是原来的15倍。这个厚度源自TADF本身，与PH过程相比，它减少了三重态-三重态湮灭中的猝灭。与荧光OLED约30 nm的厚度相比，更薄的最佳厚度表明仍存在猝灭现象。我们期望通过进一步研究使用带有间隔层的多个U-EML和具有高能量转移速率（ΔE）的新型材料来控制激子猝灭，从而提高TADF U-EML OLED的效率。
