Photoelectrochemical and optical properties of porphyrin thin films prepared by the electrolytic micelle disruption method

Abstract

Photoresponses for various porphyrin films prepared by the electrolytic micelle disruption (EMD) method have been investigated in the indium-tin oxide / porphyrin / I 3 – , I – / Pt cell. The EMD film of an n-type porphyrin, 5, 10, 15, 20-tetra(4-pyridyl)porphyrin (T(4-py)P), exhibited a clear optical filtering effect (OFE), while not for the EMD films of p-type porphyrins such as (5, 19, 15, 20-tetraphenylporphyrinato)zinc(II) (ZnTPP). For the EMD-ZnTPP film, the photocurrents at 500–700 nm were remarkably enhanced by increasing the film thickness. These photoelectrochemical properties were explained in terms of the electrolyte-permeability of the EMD films, which were confirmed by the electrochemical measurements and electron microscopic observations. The high conversion efficiency of the EMD-ZnTPP film was explained on the same basis. The difference in the thickness dependence of OFE between T(4-Py)P films prepared by the EMD and physical vapor deposition method was elucidated by the differences in diffusion lengths of excitons and in widths of photoactive layers in the films. In addition, a modified version of the EMD method was described in conjunction with a morphology control of the porphyrin solids. Key words: porphyrin, organic thin film, photoresponse, micelle, electrochemistry.