有机发光二极管的光致磁电导效应

制备了结构为ITO/CuPc/NPB/Alq₃/LiF/Al的常规有机发光二极管, 之后对器件采用波长为442 nm和325 nm的激光线进行照射产生激子, 并在小偏压下(保证器件没有开启)对激子的演化过程进行控制, 同时测量器件的光致磁电导(photo-induced magneto-conductance, PIMC). 实验发现, 不同于电注入产生激子的磁电导效应, PIMC在正、反小偏压下表现出明显不同的磁响应结果. 当给器件加上正向小偏压时, 器件的PIMC在0-40 mT范围内迅速上升; 随着磁场的进一步增大, 该PIMC增加缓慢, 并逐渐趋于饱和. 反向小偏压时, 器件的PIMC随着磁场也是先迅速增大(0-40 mT), 但达到最大值后却又逐渐减小. 通过分析外加磁场对器件光生载流子微观过程的影响, 采用'电子-空穴对'模型和超精细相互作用理论对正向偏压下的PIMC进行了解释; 反向偏压下因各有机层的能级关系, 为激子与电荷相互作用提供了必要条件, 运用三重态激子与电荷的反应机制可以解释PIMC出现高场下降的实验现象.

Light-induced magnetoconductance effect in organic light-emitting diodes

Organic light-emitting diode with a structure of ITO/CuPc/NPB/Alq₃/LiF/Al is fabricated. The excitons of the device are produced by laser irradiation using two kinds of laser beams which are at 442 nm and 325 nm, and the evolutions of the excitons are controlled by a small bias (which is either positive or negative, and ensures that the device does not turn on). The photo-induced magneto-conductance (PIMC), which is the dark current of the device showing no magnetic response at a small bias, is also measured at the same time. It is found that unlike the magneto-conductance in the electrical injection case, the PIMC presents significantly different results at the positive and negative small bias. The PIMC of the device increases rapidly in a range of 0-40 mT at a small forward bias, then increases slowly with the further increase of magnetic field, and finally becomes saturated gradually. But in the case of small reverse bias, although the PIMC of the device also first increases rapidly with the increase of magnetic field (0-40 mT), but it decreases after its maximum value has been reached. By using a composite model of electron-hole pairs and the theory of hyperfine interaction, the PIMC effect at the forward bias can be explained by analyzing the effects of the applied magnetic field on the micro-processes of the light-generated carrier of the device. When the device is in the case of reverse bias, due to the fact that the relationship of the energy-band of each organic layer provides the necessary conditions for the interactions between exciton and charge, the decrease of PIMC in high magnetic-fields can be attributed to the mechanism of reaction between triplet exciton and charge.