器件结构对激基复合物发光磁效应的影响

The influence of device structure on magneto-electroluminescence in exciplex-based devices

本文制备了一系列基于平面异质结和体异质结的激基复合物发光二极管,在20–300 K温度范围内测量了器件电致发光的磁效应(Magneto-Electroluminescence,MEL).实验发现:在温度较高时,两种不同的异质结器件的MEL呈现出相同的变化趋势,而在低温下(<100 K)却表现出截然不同的变化规律.即:在体异质结器件中,器件的MEL曲线始终未呈现出高场下降的现象;而在平面异质结器件中,当温度降为100 K时,其MEL曲线开始出现高场下降的现象,且温度越低,外加偏压越大,下降越明显.本文通过对两类器件的结构和能级排布分析,得出:平面异质结附近容易聚集大量的三重态激基复合物,从而易发生三重态的湮灭过程,在外加磁场下MEL表现出高场下降;而对于体异质结器件,由于形成的三重态激基复合物浓度较小,故难以发生三重态的湮灭过程.本文通过对激基复合物器件发光磁效应的研究,进一步丰富了激基复合物器件中激发态演化的微观机制,并对提高其发光效率也有一定的指导意义.

A series of organic light-emitting diodes （OLEDs） based on the planar heterojunction exciplex and the bulk hetero- junction exciplex have been fabricated in this letter, and the magneto-electroluminescence （MEL） at different temperature range from 20 to 300 K also has been measured. Results show that two different heterojunction exciplex devices present same variation trend at relatively high temperature, while they show completely opposite change regulations when temperature goes down about 100 K. That is to say, the curve of MEL never show decreases at higher filed in the bulk heterojunction exciplex devices. In the planar heterojunction exciplex devices, on the contrary, the curves of MEL start to decrease at higher field when temperature as long as goes down about 100 K, not only that, The lower the temperature goes down, the greater the applied bias voltage, the curves of the MEL decrease more obvious. By analysing the structure and energy level distribution of two kind of different devices, We find that MEL decreases at higher fields due to the suppression of magnetic on triplet-triplet annihilation process. This is because that a lot of triplet excited states accumulated near the planar heterojunction lead to the relatively large enhancement of triplet-triplet annihilation process （TTA）. While the TTA progress suppressed by the external magnetic field will lead to the curve of MEL decreasing at the higher field. However, this process is hard to happen in the bulk heterojunction devices because of the small concentration of triplet excited states in the bulk heterojunction devices. The MEL in the two kind of different heterojunction exciplex devices has been investigated in our work, and we also analyse the triplet-triplet annihilation process of the evolutionary micromechanism in exciplex-based devices. This work may be helpful for improving the luminescent efficiency of the exciplex-based devices.