Negative magnetoconductance effects in amorphous copper phthalocyanine thin film: trap-assisted bipolaron formation

Abstract

Negative magnetoconductance (MC) effects have been observed over a large temperature range from room temperature to 20 K in amorphous copper phthalocyanine (CuPc) thin film. It is found that the negative MC increases when the temperature decreases. The corresponding current density–voltage characteristics of the device at different temperatures reveal that this negative MC is related to the presence of traps in CuPc thin film. Moreover, the magnitude of negative MC scales with current density for nearly three orders. Based on these results, trap-assisted bipolaron formation, a developed mechanism based on bipolaron, has been proposed. We suggest that traps existing in CuPc thin film can assist the formation of bipolarons through lowering the formation energy. This model is further confirmed by the negative MC responses with light illumination.