Photovoltaic properties of phthalocyanine based p–n diode evaporated onto titanium dioxide

We have investigated the photovoltaic properties of organic p–n heterojunction photovoltaic cells consisting of p-type zinc (or copper) phthalocyanine (ZnPc, CuPc) and various dye materials, such as tetrapyridyl porphyrin (H2TPyP), DCM, Coumarin6, perylene derivative (BP-PTCDI), and Buckminsterfullerene (C60), evaporated on an n-type anatase TiO2 film. The open circuit voltage (Voc) of ITO/TiO2/dye/ZnPc/Au devices lined up in order of DCM > BP-PTCDI > H2TPyP > C60 which corresponds to the order of the energy difference between the Lowest Unoccupied Molecular Orbital (LUMO) values of dye material and the ionization potential of ZnPc. The quantum efficiency also increased effectively by inserting the very thin dye layer (∼ 10 nm) between phthalocyanine (Pc) and TiO2 layer compared to TiO2/Pc double layered device, except Coumarin6, whose LUMO locates higher than Pc, corresponding to the concept of donor–acceptor system. The largest short circuit current density (Jsc) was obtained for the ITO/TiO2/C60/CuPc/Au multilayered structure. Higher values of Voc and Jsc of 0.49 V and 5.42 mA/cm2, under 130 mW/cm2 white light illumination, were obtained by substituting coevaporated layer of C60 and CuPc by C60 layer and by heating the substrate at 120 °C during the deposition.