Enhanced Photoanodic Output at an Organic p/n Bilayer in the Water Phase by Means of the Formation of Whiskered Phthalocyanine

The photoelectrode characteristics of an organic p/n bilayer in the water phase were studied with respect to film; 3,4,9,10-perylenetetracarboxylic-bisbenzimidazole (PTCBI, an n-type semiconductor) was used in combination with 29H,31H-phthalocyanine (H2Pc, a p-type semiconductor). When H2Pc was vapor-deposited on top of the PTCBI layer on a heated substrate (cf. degree of pressure, ca. 5.0 x 10(-4) Pa; temperature at the substrate, 120 degrees C), a transmission electron microscopic image showed an enhanced contact area of the p/n interface in comparison with that prepared at r.t., due to the formation of a whisker H2Pc. The PTCBI/H2Pc bilayer can work as a photoanode along with photophysical events in its interior. The rate-limiting charge transfer at the H2Pc/water interface was kinetically analyzed assuming the Langmuir adsorption equilibrium at that interface. Kinetic analysis demonstrated that the increased contact area can successfully lead to efficient photoinduced carrier generation; particularly, when a thick whisker of H2Pc was formed, the magnitude of the oxidation kinetics at the H2Pc/water interface was approximately 2.5 times higher than that without thermal treatment.