Impact of dye interlayer on the performance of organic photovoltaic devices

The influences of buffer interlayer at the donor/acceptor interface on the open circuit voltage (V-OC) of typical copper phthalocyanine (CuPc)/C-60 organic photovoltaic devices are studied. Six fluorescent dyes with progressively increasing ionization potentials (IP) were used to investigate the factors influencing the V-OC. The short-circuit current and fill factor of CuPc/C-60 device incorporating dye interlayer are lower than those of standard bilayer device. On the other hand, the V-OC increases linearly with the I-P of dye material and falls off when the I-P is equal to or greater than 5.6 eV, in which the energy offset between the highest occupied molecular orbitals at the interlayer/C-60 heterojunction is smaller than the C-60 exciton binding energy. The findings underscore the importance of energy offsets in photovoltaic responses. (C) 2009 American Institute of Physics. [doi:10.1063/1.3243991]