Sensitization Effect of Porphyrin Dye on the Photocurrent of Al/Polythiophene Schottky-Barrier Cells

An enhanced photocurrent was obtained in an Al/porphyrin-sensitized regioregular polythiophene (PTh) Schottky-barrier cell when the top energy level of the valence band of PTh solid was more negative than the HOMO energy level of porphyrin. However, when ortho-substituted meso -phenylporphyrins were employed, the photocurrent enhancement decreased to about half compared to the case when nonsubstituted meso -phenylporphyrins were used. We conclude from these results that both a larger thermodynamic driving force for a photoinduced hole transfer from porphyrin to PTh and a closer distance between the two conjugating planes of porphyrin and PTh are necessary to obtain a larger photocurrent.