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 (VOC) of typical copper phthalocyanine (CuPc) / C60 organic photovoltaic devices are studied. Six fluorescent dyes with progressively increasing ionization potentials (I P) were used to investigate the factors influencing the VOC. The short-circuit current and fill factor of CuPc/ C60 device incorporating dye interlayer are lower than those of standard bilayer device. On the other hand, the VOC 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/ C60 heterojunction is smaller than the C60 exciton binding energy. The findings underscore the importance of energy offsets in photovoltaic responses. © 2009 American Institute of Physics.published_or_final_versio