Photocurrent enhancement in porphyrin-silver nanoparticle composite films using nanostructures of silver nanoparticles

The fabrication of tetraphenyl porphyrin (TPP)-silver nanoparticle (AgP) composite films on indium-tin oxide (ITO) electrodes was carried out by the electrostatic layer-by-layer adsorption technique. Maximum enhancement in photocurrent action spectra as well as in fluorescence emission spectra was observed at an immersion time of 2 h. The effects of AgP on photocurrent and fluorescence suggested the effects of enhanced electric fields resulting from a localized surface plasmon resonance on the enhancement of photocurrent and fluorescence signals. The effect of AgP on the lifetime of the singlet excited state of TPP (1TPP) indicated that the lifetime of 1TPP* decreases as compared with that in the absence of AgP substrate. The results on fluorescence lifetime suggested that the difference between the effects of AgP on photocurrent and fluorescence is most likely ascribed to the notion that the energy transfer from 1TPP* to surface plasmons due to AgP aggregates competes with photoinduced electron transfer from 1TPP* to O ₂during photocurrent measurement.