Energy band bending induced charge accumulation at fullerene/bathocuproine heterojunction interface

The electronic properties of fullerene (C60)/bathocuproine (BCP)/Ag heterostructures were studied as a function of the BCP layer thickness by photoemission spectroscopy. For the thin BCP layer, the energy levels are flat and gap states exist at the interface. In contrast, energy band bending occurs at the C60/BCP interface when the BCP layer is thick, resulting in a considerable barrier for electron transport and therefore causing charge accumulation in organic solar cells. The results reveal that a thin BCP layer gives a much more favorable energy level structure and conform that charge accumulation is responsible to the anomalous current-voltage (I-V) curve.