Abstract
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.
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