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 $(IP)$ 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 $IP$ of dye material and falls off when the $IP$ 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.