Photovoltaic Properties of Organic p–n Junction Devices Consisting of Phthalocyanine and n-Type Porphyrin Deposited on an n-Type TiO₂Layer

Abstract

We have investigated the photovoltaic properties of organic p–n junction photovoltaic cells deposited on an n-type TiO2 layer. The p-type and n-type compounds used were donor-like metallo-phthalocyanine (ZnPc or CuPc) and acceptor-like metal-free (or Zn) 5,10,15,20-tetra (4-pyridyl) porphyrin (H2TPyP or ZnTPyP). The p or n-type characteristics of each material were interpreted in terms of the photovoltaic and the rectification properties of the organic semiconductors sandwiched between a wide gap n-type semiconductor TiO2 and Au. The characteristics of materials was summarized as (n-type) H2TPyP > ZnTPyP > CuPc > ZnPc (p-type). We then investigated the photovoltaic properties of an organic p–n junction on TiO2 composed of ITO/TiO2/H2TPyP (x nm)/ZnPc (50 nm)/Au structure. It was found that the photovoltaic properties in this structure were optimized when the thickness of the H2TPyP layer, x, was 6 nm. The quantum efficiency was improved considerably, especially at the Soret band of H2TPyP (x=6 nm). The open circuit voltage VOC was also improved up to 0.7–0.8 V which is larger than the 0.45 V of an ITO/TiO2/ZnPc/Au device.