Influence of the donor/acceptor interface on the open-circuit voltage in organic solar cells

The donor/acceptor interface in a standard CuPc/C-60 organic solar cell was modified by insertion of a thin layer of molybdenum trioxide (MoO3). An ultrathin layer of MoO3 between the donor and acceptor increased the open-circuit voltage (V-OC) from 0.45 to 0.85 V. The enhancement in VOC is explained by the increase in the energy level offset between the lowest unoccupied molecular orbital of the acceptor and the highest occupied molecular orbital of the donor (E-HOMO(D)-E-LUMO(A)). The explanation is supported by the energy level analysis of the donor/acceptor interface by ultraviolet photoemission spectroscopy and x-ray photoemission spectroscopy. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3222975]