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Effects of Porphyrin Substituents on Film Structure and Photoelectrochemical Properties of Porphyrin/Fullerene Composite Clusters Electrophoretically Deposited on Nanostructured SnO 2 Electrodes
Author(s) -
Imahori Hiroshi,
Ueda Masahiro,
Kang Soonchul,
Hayashi Hironobu,
Hayashi Shinya,
Kaji Hironori,
Seki Shu,
Saeki Akinori,
Tagawa Seiichi,
Umeyama Tomokazu,
Matano Yoshihiro,
Yoshida Kaname,
Isoda Seiji,
Shiro Motoo,
Tkachenko Nikolai V.,
Lemmetyinen Helge
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200700446
Subject(s) - porphyrin , photocurrent , substituent , photochemistry , tetraphenylporphyrin , fullerene , materials science , chemistry , crystallography , stereochemistry , organic chemistry , optoelectronics
Abstract We have systematically examined the substituent effects of meso ‐tetraphenylporphyrins on film structures and the photoelectrochemical properties of the composite clusters of free‐base porphyrin and C 60 electrophoretically deposited on nanostructured SnO 2 electrodes. The photocurrent generation efficiency was found to correlate with the complexation ability of the porphyrin for C 60 . Basically, the incident photon‐to‐current efficiency (IPCE) value was increased with increasing relative amounts of the porphyrin versus C 60 in the films. The unique molecular arrangement of the porphyrin with the simple, specific substituents (i.e., methoxy groups at the meta ‐positions of the meso ‐phenyl rings of tetraphenylporphyrins (3,5‐OMeTPP; TPP=tetraphenylporphyrin)) and C 60 on SnO 2 electrodes resulted in the largest IPCE value (ca. 60 %) among this type of photoelectrochemical device. The rapid formation of the composite clusters and microcrystals from the combination of 3,5‐OMeTPP and C 60 in a mixed solvent is unique as the association is accelerated by intermolecular interactions (i.e., hydrogen‐bonding and CH–π interactions) between the methoxy groups of the porphyrins and the porphyrin/C 60 , in addition to the π–π interactions between the porphyrins/C 60 and C 60 molecules. Both the films and single crystals composed of the porphyrin and C 60 exhibited remarkably high electron mobility (7×10 −2 and 0.4 cm 2 V −1 s −1 ), which is comparable to the value for highly efficient bulk heterojunction solar cells. Our experimental results have successfully demonstrated the importance of nanostructured electron‐ and hole‐transporting pathways in bulk heterojunction solar cells. Such a finding will provide basic and valuable information on the design of molecular photovoltaics at the molecular level.