Highly Ordered Molecular Orientation in a Phthalocyanine Film Deposited on a Well-Polished Indium-Tin Oxide Substrate

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Metal-free phthalocyanine (H_2Pc) was deposited on an indium-tin oxide (ITO) substrate with a pentacene buffer layer, and the effect of polishing of the ITO surface on the molecular orientation of H_2Pc was studied. By rubbing the ITO surface 10,000 times with a plastic eraser, the average surface roughness of ITO was decreased to 1.0 nm from its initial value of 2.0 nm, and the (313^^-) X-ray diffraction peak of α-form H_2Pc became significantly large. Rocking curves and optical absorption spectra indicated that, by polishing the ITO surface, the disorder in the orientation of the stacking axis (b axis) of H_2Pc was reduced. A Schottky barrier cell of H_2Pc with a highly ordered molecular orientation showed a lower photovoltaic performance than that with a disordered orientation.