Photocurrent Enhancement of Copper (II) Phthalocyanine on Nanogap Thin Film Electrodes

Photovoltaic efficiency of organic semiconductors can be improved when the electrode separation distance is below the carrier recombination length. Nanogap electrodes formed by Au/Al₂O₃/Au tunnel junctions were used to study photovoltaic characteristics of Copper (II) phthalocyanine (CuPc) for electrode spacing distance within a 10 nm scale. A large photocurrent enhancement over 50 times that of bulk CuPc film was observed when the electrode gap distance approached 10 nm. CuPc carrier recombination length is seen to be 10 nm, in our evaporation deposited materials, close to its exciton diffusion length in the literature reports. All devices show diode I-V properties due to a large Schotteky barrier contact resistance between the small top Au electrode and CuPc film.