Chemistry Department Seminar

Extensive efforts have been made in recent years to explore the
photovoltaic and photoelectrochemical properties of electrodes
modified with various donor and acceptor components toward the
realization of highly efficient organic solar cells. In this talk we
present rational molecular design for Photoelectrochemical Devices.
First, we examined substituent effect of meso-tetraphenylporphyrin
(TPP) on the molecular packing with C60 and its photoelectrochemical
properties of SnO2 electrodes modified with the composite clusters of
TPP and C60. In the molecular design of TPP we consider the
following criteria. i) Electron-donating substituents (i.e., methoxy
group) are introduced into meta-positions of the meso-phenyl groups
at the porphyrin ring to strengthen the supramolecular complexation
between TPP and C60 due to the _i-_i interaction. ii) Taking into
account the three-dimensional molecular packing of TPP and C60 in the
TPP-C60 composite film, it is suitable to adopt symmetrical
substitution of the methoxy groups on the meso-phenyl groups against
the porphyrin plane. iii) The methoxy groups between the nearest
porphyrins in the TPP-C60 composite films are expected to interact
each other due to the hydrogen bonding, yielding porphyrin arrays in
the composite films. On the basis of the molecular design, we
prepared novel supramolecular photoelectrochemical device where the
unique molecular arrangement of the porphyrin with the simple,
specific substituent (i.e., meta-methoxy groups) and fullerene on
SnO2 electrodes results in the largest IPCE value (~60%) among this
type of photoelectrochemical devices. In bulk heterojunction solar
cells many researchers have suggested the importance of
nanostructured electron and hole transporting pathways which have
never been confirmed experimentally. Our experimental results are the
first demonstration for the hypothesis. Next, we examined steric
effects of dyes and