Alq_3有机发光二极管中的正负磁电导转变

Positive-negative inversion of magnetoconduce in Alq_3-based organic light-emitting diode

制备了基于Alq3的有机发光二极管,器件结构为ITO/CuPc/NPB/Alq3/LiF/Al,并在不同温度下测量了器件在恒压偏置下传导电流的磁电导效应.当Alq3发光层的厚度为15nm时,在器件的传导电流从双极电流过渡到单极电流的过程中,器件的磁电导发生了明显的正负转变;而当Alq3发光层的厚度为65nm时,在传导电流从双极电流到单极电流的过渡过程中,器件的磁电导呈现随电流减小先上升后下降的变化趋势,但磁电导的值在任何测量条件下始终为正,并未出现正负转变的现象.双极电流的磁电导效应可用电子-空穴对模型和激子-电荷反应模型来进行解释,而单极电流的磁电导效应虽然可归因于器件中的极化子-双极化子转变,但仍需要进一步的研究.

Organic light-emitting diodes （OLEDs） based on Alq3 have been fabricated. The structure of devices is ITO/CuPc/NPB/Alq3/LiF/Al. The magnetoconductance （MC） effect on the current was measured with constant voltage bias. When the thickness of Alq3 layer is 15 nm, an apparent positive-negative inversion of MC occurred during the current transition from bipolar to unipolar. When the thickness of Alq3 layer was 65 nm, the MC values increased firstly and then fell with the decreasing current during the current transition from bipolar to unipolar. However, under any measurement conditions, the MC values were always positive. The inversion of MC form positive to negative was not observed in this device. The MC effect of bipolar current can be explained using the electron-hole pair model and exciton-charge reaction model. While the MC effect of uniploar current still need further study, although it can be attributed to the polaron-bipolaron transition in device.