Y. Harima et al., LIGHT-ABSORPTION IN THE NEAR-INFRARED AND PHOTOCURRENT SYNERGISM OBSERVED WITH VACUUM-SUBLIMED FILMS OF ZINCTETRAPHENYLPORPHYRIN, Thin solid films, 307(1-2), 1997, pp. 208-214
Photocurrent peaks are found in the near-infrared (NIR) as well as in
the visible for zinc(LI) tetraphenylporphyrin (ZnTPP) films contacting
redox solutions, in contrast to no appreciable photocurrent in the NI
R for a sandwich-type cell of Al/ZnTPP/Au. The spectral responses of p
hotocurrents in the NIR for the wet cells resemble that of photocurren
t synergism reported earlier for the sandwich-type cell, although the
ZnTPP solid is almost transparent in this wavelength region. The obser
ved electronic transition in the NIR is ascribed not to a singlet-to-t
riplet excitation which is commonly observed with phthalocyanine solid
s, but to the absorption of the NIR light due to a trace of a ZnTPP ph
otoproduct, most probably an isoporphyrin. The photoproduct, which dim
inishes a generation efficiency of photocurrents by acting as a recomb
ination center, is responsible for the increase in photocurrents due t
o Soret band excitation by simultaneous illumination with the NIR ligh
t. The difference in the Ic?NIR photoresponse between the wet cells an
d the dry cell is explained on the basis of an energy-level considerat
ion. (C) 1997 Elsevier Science S.A.