Degradation of interface between boron subphthalocyanine chloride and fullerene

Apart from external environmental factors, we herein show with ultra-violet photoemission spectroscopy (UPS) studies that degradation in organic photovoltaic (OPV) devices can also be caused by internal deterioration of the donor/acceptor interface. Albeit with impressive initial open circuit voltage (Voc), boron subphthalocyanine chloride (SubPc)/fullerene (C60) device shows a fast Voc decade upon operation. UPS results show that the energy offset between the highest occupied molecular orbit (HOMO) of SubPc and the lowest unoccupied molecular orbit (LUMO) of C60 is reduced from 1.66 to 1.45 eV after aging in ultra-high vacuum (UHV) condition. This result is consistent with the change in built-in voltage of the corresponding device upon operation. The related charge interaction and degradation mechanism in the SubPc/C60 device are discussed.