Weng Zhichao, Gillin William P, Kreouzis Theo
Materials Research Institute and School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London, E1 4NS, UK.
Sci Rep. 2020 Oct 8;10(1):16806. doi: 10.1038/s41598-020-73953-w.
Organic light-emitting diode (OLED) displays a sign reversal magnetic field effect (MFE) when the applied magnetic field range is reduced to the sub-milliTesla range and the Polaron Pair Model has been successful in explaining the ultra-small MFE. Here, we obtained high resolution (~ 1 µT) magnetoconductance (MC) and magnetoelectroluminescence (MEL) of a tris-(8-hydroxyquinoline)aluminium-based (Alq) OLED within the magnetic field range of ± 500 µT with the earth magnetic field components cancelled. A clear "W" shaped MC with a dip position of ± 250 µT and a monotonic MEL were observed. We demonstrate a fitting technique using the polaron pair model to the experimentally obtained MC and MEL. The fitting process extracts physically significant parameters within a working OLED: the local hyperfine fields for electron and hole in Alq: B = (0.63 ± 0.01) mT (electron), B = (0.24 ± 0.01) mT (hole); the separation rates for singlet and triplet polaron pairs: k = (44.59 ± 0.01) MHz, k = (43.97 ± 0.01) MHz, and the recombination rate for singlet polaron pair k = (88 ± 6) MHz. The yielded parameters are highly reproducible across different OLEDs and are in broad agreement with density functional theory (DFT) calculations and reported experimental observations. This demonstrates the feasibility of this fitting technique to approach any working OLED for obtaining significant microscopic parameters.
当施加的磁场范围减小到亚毫特斯拉范围时，有机发光二极管（OLED）会显示出符号反转磁场效应（MFE），并且极化子对模型已成功解释了这种超小的MFE。在此，我们在消除地磁场分量的情况下，在±500 μT的磁场范围内获得了基于三（8-羟基喹啉）铝（Alq）的OLED的高分辨率（约1 μT）磁电导（MC）和磁电致发光（MEL）。观察到一个清晰的“W”形MC，其凹陷位置为±250 μT，以及单调的MEL。我们展示了一种使用极化子对模型对实验获得的MC和MEL进行拟合的技术。拟合过程提取了工作OLED内具有物理意义的参数：Alq中电子和空穴的局部超精细场：B =（0.63±0.01）mT（电子），B =（0.24±0.01）mT（空穴）；单重态和三重态极化子对的分离率：k =（44.59±0.01）MHz，k =（43.97±0.01）MHz，以及单重态极化子对的复合率k =（88±6）MHz。所得到的参数在不同的OLED之间具有高度可重复性，并且与密度泛函理论（DFT）计算和报道的实验观察结果广泛一致。这证明了这种拟合技术用于接近任何工作OLED以获得重要微观参数的可行性。
