利用有机磁效应研究热活化延迟荧光量子阱器件中的微观机制

Investigation of micro-mechanism in thermally activated delayed fluorescence quantum well devices by utilizing organic magnetic effects

采用具有反向系间窜越(reverse intersystem crossing,RISC)特性的热活化延迟荧光(thermally activated delayed fluorescence,TADF)材料制备了量子阱有机发光二极管,测量了器件的磁电导(magneto-conductance,MC)和磁电致发光(magneto-electroluminescence,MEL),由此还可得到器件效率的磁效应(Mη),并利用这些磁效应特征曲线来研究器件中的微观过程.实验发现:室温下,尽管无量子阱参考器件的MC表现出RISC特性和载流子对三重态激子的解离机制,但量子阱器件的MC则只表现出三重态激子对载流子的散射机制;而且,无量子阱参考器件的MEL和Mη都表现出了系间窜越(ISC)和三重态激子对的湮灭(TTA)的过程,但量子阱器件的MEL则表现出ISC和三重态激子对载流子的散射机制,且其Mη只表现出了ISC属性.随着温度从室温降至20 K,量子阱器件和参考器件的ISC都增强,但量子阱器件在20 K还出现了TTA过程,而参考器件的TTA则在100 K后消失.我们提出根据量子阱器件和无量子阱器件的结构特性以及温度对F?rster能量转移和三重态激子的浓度与寿命的影响可以较好地解释这些实验现象.显然,研究量子阱器件的磁效应,不仅为发光器件提供设计思路,同时还可加深对有机磁效应的认识.

The quantum well organic light-emitting diodes（OLEDs） based on thermally activated delayed fluorescence material with reverse intersystem crossing（RISC） characteristics have been fabricated in this paper. Meanwhile, the magneto-efficiency（Mη） was obtained by measuring the magneto-conductance（MC） and magneto-electroluminescence（MEL） of the devices, and we research microscopic process of devices by analyzing the characteristic curves of magnetic field effects. Surprisingly, we found that the MC curves of nonquantum-well device showed typical RISC property and the dissociation of triplet excitons by holes at room temperature, but the MC curves merely exhibited the mechanism of electron scattering by triplet excitons in quantum well device. In addition, although the MEL and Mη curves of non-quantum well device demonstrated intersystem crossing（ISC） and triplet-triplet annihilation（TTA）process, the MEL of quantum well device showed the mechanism of electron scattering by triplet excitons and the Mη only displayed the typical ISC curves. As decreasing the temperature from 300 K to 20 K, the ISC processes of quantum or non-quantum well devices increased, however, the TTA process occurred in quantum well device at 20 K and the TTA process of non-quantum well device gradually vanished at 100 K. We propose that the structure property of quantum or non-quantum well devices, temperaturedependent F？rster energy transfer, and the lifetime and concentration of the triplet excitons can explain the experimental phenomena very well. Obviously, the research of magnetic effects in quantum well devices not only provides ideas for designing high efficient light-emitting devices, but also can deepen the understanding of organic magnetic effects.