Dye sensitization of ceramic semiconducting electrodes for photoelectrochemical conversion

TLDR: In this article, the photoresponse of stable electrochemical cells can be extended into the visible region (400-600 nm) using hydroquinone as supersensitizer.

Abstract: 2014 Semiconducting ZnO ceramic electrodes have been sensitized by Rhodamine B and Ru (II) complex dyes. The photoresponse of the stable electrochemical cells can thus be extended into the visible region (400-600 nm) using hydroquinone as supersensitizer. Open circuit voltage of 0.4 V and short circuit currents up to 0.2 mA can be obtained with photons of hv Egap of semiconductor. Revue Phys. Appl. 16 (1981) 5-10 JANVIER 198I,

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Dye sensitization of ceramic semiconducting electrodes
for photoelectrochemical conversion
N. Alonso V., M. Beley, Philippe Chartier, V. Ern
To cite this version:
N. Alonso V., M. Beley, Philippe Chartier, V. Ern. Dye sensitization of ceramic semiconducting
electrodes for photoelectrochemical conversion. Revue de Physique Appliquée, Société française de
physique / EDP, 1981, 16 (1), pp.5-10. �10.1051/rphysap:019810016010500�. �jpa-00244894�

5
Dye
sensitization
of
ceramic
semiconducting
electrodes
for
photoelectrochemical
conversion
N.
Alonso
V.,
M.
Beley,
P.
Chartier
Laboratoire
d’Electrochimie
et
de
Chimie
Physique
du
Corps
Solide,
Université
Louis-Pasteur,
4,
rue
Blaise-Pascal,
67000
Strasbourg,
France
and
V.
Ern
Institut
de
Physique
(*),
Université
Louis-Pasteur,
5,
rue
de
l’Université,
67000
Strasbourg,
France
(Reçu
le
28
juillet
1980,
accepté
le
13
octobre
1980)
Résumé. 2014
Des
électrodes
céramiques
semi-conductrices
de
ZnO
ont
été
sensibilisées
par
des
colorants
Rho-
damine
B
et
complexes
de
Ru
(II).
Ainsi,
la
photoréponse
des
cellules
photoélectrochimiques,
stabilisées
en
utilisant
l’hydroquinone
comme
régénérateur,
peut
être
étendue
au
domaine
visible
(400-600
nm).
Une
tension
en
circuit
ouvert
de
0,4
eV
et
des
courants
de
court-circuit
jusqu’à
0,2
mA
peuvent
être
obtenus
en
utilisant
des
photons
dont
hv
Egap
du
semiconducteur.
Abstract.
2014
Semiconducting
ZnO
ceramic
electrodes
have
been
sensitized
by
Rhodamine
B and
Ru
(II)
complex
dyes.
The
photoresponse
of
the
stable
electrochemical
cells
can
thus
be
extended
into
the
visible
region
(400-600
nm)
using
hydroquinone
as
supersensitizer.
Open
circuit
voltage
of
0.4
V
and
short
circuit
currents
up
to
0.2
mA
can
be
obtained
with
photons
of
hv
Egap
of
semiconductor.
Revue
Phys.
Appl.
16
(1981)
5-10
JANVIER
198I,
Classification
Physics
Abstracts
33.20K -
73.40M -
86.30K
1.
Introduction.
-
Photovoltaic
conversion
of
solar
energy
with
solid
state
p-n
or
metalsemiconductor
Schottky
barrier
junctions
has
found
already
extensive
application
in
low
power
installations.
Efficiencies
near
the
theoretical
values
have
been
obtained,
but
the
cost
of
fabrication
of
reasonably
good
junctions
remains
high,
and
considerable
research
and
develop-
ment
effort,
notably
with
amorphous
matérials
is
still
actively
pursued
to
bring
down
the
cost
of
the
device.
Recently
several
laboratories
throughout
the
world
have
started
parallel
research
on
the
feasibility
of
using
electrochemical
cells.
An
electrochemical
cell
consists
simply
of
a
p-
or
n-type
semiconductor,
an
electrolyte,
and
a
counter-electrode
to
collect
the
charge
carriers.
In
such
a
system
the
cost
of
fabrication
of
the
junction
is
eliminated,
since
the
simple
immer-
sion
of
the
semiconductor
in
the
electrolyte
creates
the
depletion
layer
which
is
necessary
to
obtain
thé
(*) This
work
was
supported
by
grant
PIRDES
ATP
3866
of
the
Centre
National
de
la
Recherche
Scientifique
in
conjunction
with
the
Laboratoire
de
Spectroscopie
and
the
Laboratoire
d’Appli-
cations
Electroniques.
photovoltaic
effect.
Moreover,
with
transparent
elec-
trolytes,
reflection
and
absorption
losses
due
to
the
metallic
contact
on
the
solid
state
device
are
elimi-
nated.
Besides,
scientific
interest
is
accrued
by
the
fact
that,
under
suitable
conditions,
it
could
also
work
as
a
solar
energy-assisted
photochemical
or
photo-
electrochemical
device
which
splits
water
for
the
purpose
of
generating
chemical
energy
in
the
form
of
a
storable
fuel.
An
obvious
problem
with
photoelectrochemica,l
cells
is
their
long
range
stability
since,
in
general,
and
more
like
so
with
low
band-gap
materials,
anodic
dissolution
of
the
electrode
competes
with
the
redox
reaction,
and
a
corrosion
of
the
electrode
takes
place.
The
stability
problem
has
been
object
of
intensive
studies
and
several
stable
electrode-redox
couples
have
been
claimed.
Recent
reviews
can
be
found
in
references
[1,
2,
3].
Other
approach
is
the
use
of
stable
high
band-gap
semiconductor
oxide
electrodes,
e.g.
Egap
>
3
eV,
like
Ti02,
ZnO,
SrTi03,
Sn02,
and
to
extend
the
useful
spectral
response
range
down
into
the
visible
region
by
sensitization
with
organic
dye
molecules.
Photosensitization
with
organic
dyes
has
been
studied
for
some
time
in
conjunction
with
photo-
graphic
and
electrographic
processes.
More
recently,
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/rphysap:019810016010500

6
Fig. 1.
-
Schematic
energy
diagram
of the
photovoltaic
effect
for
a n-type
semiconductor
in
an
electrolyte :
a)
without
sensitization,
b)
sensi-
tized
with
an
organic
molecule
having
energy
levels
D,
D*,
D+
corresponding
to
the
ground,
excited
(triplet
or
singlet)
and
oxidized
states.
The
excitation
D ~
D*
is
obtained
with
photons
with
hv
Egap
of
semiconductor.
The
level
R
symbolizes
the
energy
of a
regenerating
spe-
cies
in
the
electrolyte
which
assures
reduction
of
the
molecule
back
to
its
ground
state.
The
correspondance
of
energy
scales
as
customarily
used
in
solid
state
physics
(zero
at
vacuum
level)
and
in
electrochemistry,
where
the
normal
hydrogen
electrode
(NHE)
is
used
as
reference
is
shown
on
the
left.
In
the
present
work
saturated
calomel
electrode
(SCE)
is
used
as
reference,
the
scale
transformation
being
E(V/SCE)
=
E(V/NHE) -
0.24
V.
an
extensive
research
program
has
been
started
all
over
the
world
to
investigate,
both
from
a
theoretical
and
a
practical
point
of
views,
the
sensitization
by
organic
dyes
of
the
interface
of
semiconductor-
electrolyte
systems
as
potential
candidates
for
solar
energy
conversion
by
stable,
wet
photoelectrochemical
cells.
A
schematic
energy
diagram
of
the
principle
of
operation
is
shown
in
figure
1.
A
review
up
to
1976
has
been
given
by
Gerischer
and
Willig
[4].
Later
work
can
be
found
in
references
[5-21].
Most
of
the
work
has
been
done
on
single
crystals,
with
exception
of
Sno2
films
[18-20]
and
ZnO
[6,
7]
ceramic
elec-
trodes.
With
single
crystals
the
cost
of
the
cell
would
not
likely
be
competitive
with
a
solid
state
device,
so
that
the
most
promising
aspect
of
photoelectro-
chemical
conversion
is
that
using
polycrystalline
semiconducting
electrodes,
e.g.
thin
films
or
ceramics.
Sensitization
of
ZnO
ceramic
electrodes
has
been
performed
[6,
7]
by
using
rose
bengal
dye
which
requires
the
13" jI-
redox
couple
as
regenerator.
Unfortunately,
such
an
electrolyte
absorbs
in
the
visible
region.
It
is
interesting
thus
to
investigate
others
systems
in
which
dyes
in
conjunction
with
a
transparent
electrolyte
can
be
used.
Organometallic
dyes
such
as
Ru (bipy 3
i.e.
tris
(2,2’
bipyridine)
ruthenium
(II),
and
related
complexes
have
been
increasingly
attracting
attention
since
the
first
report
[22]
of
their
ability
to
induce
electron
transfer
reaction
of
the
excited
state,
and
the
work
by
Creutz
and
Sutin
[23]
who
pointed
out
the
possi-
bility
of
decomposition
of
water
induced
by
visible
light.
Recent
research
development
in
this
field
can
be
found
in
references
[24]
to
[26].
The
ground
state
complex
absorbs
visible
light
to
form
a
d
to
03C0*
charge
transfer
excited
state
which
is
relatively
long
lived
(lifetime
0.6
ps
in
water)
[22]
as
compared
to
conven-
tional
organic
dyes
(lifetime
about
10-9
s).
It
seems
that
this
excited
state
is
a
triplet
charge
transfer
state.
Ti02
single
crystals
have
been
already
sensitized
with
the
Ru
(bipy)2+3
dye
by
Clark
and
Sutin
[13]
and
later
by
Hammet
et
al.
[14].
Also,
sensitization
has
been
obtained
on
the
same
electrode
by
chemical
attach-
ment
of
the
dye
on
the
crystal
[12].
Chemically
stable
electrode
was
then
obtained,
but
the
photocurrent
excitation
spectrum
did
not
show
the
characteristic
absorption
peak
of
the
dye
at -
450
nm.
Memming
and
coworkers
[18-20]
have
sensitized
Sn02
films,
one
of
their
techniques
[19]
consisted
of
applying
monolayers
by
the
Langmuir-Bloogett
method
of
the
Ru
(II)
complexes
of
the
type :
where :
or
Also,
recently,
Mackor
and
Schonmann
[15]
have
reported
sensitization
of
pure
and
doped
SrTi03

7
single
crystals
with
the
type
II
dinonadecyl
complex
of Ru
(II)
although
the,
simpler,
complex
Ru
(bipy)2+3
seems
not
sensitize
SrTiO3
single
crystals
[13].
In
this
work
we
wish
to
report
studies
of sensitization
of semiconducting Zn0
ceram ic electrodes
with
Ru
(II)
dye
molecules
of
type
II.
As
this
dye
absorbs
at
~
450 nm,
we
have
also
investigatèd
the
feasibility
of
extending
the
spectral
response
towards
longer
wavelengths
by
using
a
mixture
of
Ru
(II)
and
Rho-
damine
B
(RhB)
dyes
adsorbed
on
the
electrode.
2.
Experimental.
-
Ceramics
of
ZnO
(1.2
cm
in
diameter)
were
prepared
from
commercial
high
grade
zinc
oxide
powder
(Merck
pro
analysi)
by
sintering
in
two
steps.
The
pellets
were
first
moulded
by
compres-
sion
(10
ton.)
before
firing
in
air
at
1 000
°C
for
3 hp
and
quenched.
It
were
then
ground
into
fine
powder,
pressed
again
into
disks
and
heated
at
1 300
°C
for
3
h,
and
quenched.
The
samples
obtained
by
this
method
were
semiconducting
with
a
resistivity
~
103 03A9. cm
at
room
temperature.
Contacts
on
the
back
surface
were
made
by
attaching
a
fine
copper
wire
with
silver
paste
(Degussa
2000)
which
makes
an
ohmic
contact
with
the
ceramic.
The
samples
were
then
mounted
in
glass
tubes
and
moulded
with
an
epoxy
resin.
Prior
to
use,
the
front
surface
of
the
electrode
was
etched
for
3
min.
in
5
N
HCI
solution
which
attacked
the
surface
exposing
grain
(typically
20
p)
boundaries
as observed
by
microscopy.
All
electrolytes
were
made
with
distilled
water.
The
base
electrolyte
was
1.5
M
KCI
with
5
x
10-3
M
hydroquinone
(H2Q)
which
served
as
dye
reducing
agent.
Before
each
experiment
the
electrolyte
was
purged
with
nitrogen.
Prior
to
the
application
of
the
dye
each
electrode
was
tested
for
a
correct
I
V
Schottky
barrier
rectifying
characteristics.
The
electrodes
were
coated
with
the
dye
as
follows.
The
electrode
was
immersed
in
a
10-3
M
acetonitrile
solution
of
the
Ru
(II)
complex,
type
II,
for
30
min,
then
washed
with
distilled
water
in
which
the
dye
is
insoluble,
and
dried.
On
several
electrodes
prepared
in
this
way
RhB
was
deposited
by
dipping
for
few
seconds
in
10-3
M
Rhodamine
B
in
acetonitrile
solution.
After
drying
the
electrode
were
washed
with
dis-
tilled
water
to
eliminate
excess
RhB
deposited
on
the
sample.
Tests
to
sensitize
simultaneously
with
both
dyes
by
immersion
in
a
10- 3
M
Ru
(II)
complex
+
10- 3
M
RhB
acetonitrile
solution
gave
only
elec-
trodes
sensitized
by
the
Ru
(II)
complex
indicating
preferential
adsorption
of
the
organometallic
dye
on
the
ZnO
ceramic
surface.
The
experimental
setup
is
shown
in
figure
2.
The
semiconductor
electrode
and
a
platinum
wire
counter-
electrode
were
placed
in
close
proximity
to
each
other.
A
saturated
calomel
reference
electrode
(SCE)
was
used
to
control the
working
electrode
potential.
A
150
W
xenon
arc
lamp
served
as
a
light
source,
which
was
passed
through
a
water
filter
followed
by
a
monochromator
(Jobin
Yvon
H25).
In
some
experi-
ments
the
monochromator
was
replaced
by
a
C.S.
Fig.
2.
-
Experimental
setup :
1
Cell
(a,
flat
window ;
b,
semicon-
ducting
électrode ;
c,
platinum
counter-electrode ; d,
glass
tube;
e,
saturated
calomel
electrode
(SCE)) ;
2 a
150 W XBO
xenon
arc
lamp ;
3
Lens ;
4
Monochromator ;
5
Filter ;
6
Potentiostat ;
7
Digital
voltmeter
with
analog
output;
8
X Y
recorder.
3-72
Coming
filter
with
which
a
broad
band
excitation
in
the
visible
range
(400-700
nm)
is
obtainèd.
The
potentiostatic
measurements
were
done
in
a
standard
manner
with
a
potentiostat
(Tacussel
type
P.R.T.
2000)
with
which
the
current-voltage
characteristics
were
recorded
on
a
X- Y
recorder.
The
exciting
light
intensity
was
determined
by
means
of
a
thermopile
(Kipp-
Zonen)
together
with
a
microvoltmeter.
An
electrolyte
layer
with
thickness
corresponding
to
the
experimental
distance
between
the
cell
window
and
the
photoelec-
trode
was
inserted
into
the
light
beam
to
correct
for
any
absorbance
or
reflection
so
that
the
actual
intensity
falling
on
the
sample
could
be
estimated.
All
data
were
normalized
to
a
constant,
independent
of
03BB,
incident
light
power.
3.
Results
and
discussion.
-
In
the
dark
the
rest
potential
of
the
ZnO
electrode
in
the
1.5
M
KCI
electrolyte
(pH ~
6.5)
was
reproducibly
found
in
the
N
+
50 mV/SCE
region.
The
value
was
the
same
both
with
the
uncoated
and
with
the
dye-covered
electrodes.
Furthermore,
this
dark
rest
potential
is
unsensitive
to
the
presence
of
hydroquinone
(H2Q)
or
even
of
quinhydrone
(QH2Q)
in
the
electrolyte,
that
is,
the
semiconductor
electrode
doesn’t
pick
up
the
redox
potential
of
the
Q/H2Q
couple.
The
dark
current
was
found
to
be
sensitive
to
the
presence
of
02
in
the
electrolyte.
It
increases
by
a
factor
of
2-3
when
02
is
bubbled
through
a
previously
outgassed
solution.
In
the
photoexcited
experiments
the
platinum
counter-electrode
potential
was
typically
+
0.140
V/
SCE.
This
potential
is
not
well
thermodynamically
defined
because
of the
absence
of quinone
in
the
hydro-
quinone
containing
solution.
Thus,
all
experiments
were
performed
under
potentiostatic
conditions
(vs.
SCE).
The
solutions
were
always
outgassed
and
photo-
current
action
spectra
obtained
with
the
ZnO
electrode
polarized
at
+
50
mV/SCE
so
that
the
dark
current
could
be
considered
as
negligible
in
the
experiment.
Figure
3
shows
the
photocurrent
response
as
a
function
of
wavelength
for
a
ceramic
ZnO
electrode
sensitized
with
the
Ru
(II),
type
II
complex.
For

8
Fig.
3.
-
Photocurrent
action
spectrum
of a
ZnO
ceramic
electrode
sensitized
with
the
dinonadecyl
Ru
(II)
complex
dye
(type
II
shown
in
text).
The
electrode
is
held
at
+
50
mV/SCE
and
excited
at
a
constant
light
power
of 0.28
mW . cm- 2
throughout
the
spectrum.
The
dashed
curve
shows
for
comparison
the
absorption
spectrum
(in
a.u.)
of a
10- 3
M
acetonitrile
solution
of the
dye.
comparison,
the
absorption
profile
(a.u.)
of the
dye
in
a
10- 3
M
acetonitrile
solution
is
also
shown.
Both
curves
show
similar,
well
defined,
structure
but
the
photocurrent
peak
is
shifted
towards
the
longer
wavelengths.
Such
red
shift
is
usually
observed
in
semiconductor
sensitization
responses
and
has
been
attributed
by
Gerischer
[27]
to
a
stronger
polarization
interaction
of
the
molecular
excited
state
with
the
semiconductor
as
compared
to
that
of
the
ground
state.
This
observation
agrees
with
the
results
on
Sn02
films
by
Memming et
al.
[19],
but
contrasts
with
the
results
of
Anderson et
al.
[12]
who
obtained
a
feature-
less
photocurrent
action
spectrum
with
derivatives
of
Ru (bipy)2+3
chemically
attached
to
Ti02
crystals.
Figure
4
shows
the
photocurrent
response
of
the
same
electrode
which
has
been
subsequently
sensitized
with
Rhodamine
B
dye
as
described
previously.
The
photoresponse
extends
now
into
the
yellow
region
showing
the
characteristic
peak
of
RhB
sensitization
at ~
560
nm.
The
insert
gives,
for
comparison,
the
response
of
a
ceramic
ZnO
electrode
coated
just
with
RhB.
This
RhB
excitation
spectrum
is
analogous
to
that
observed
by
Gerischer et
al.
for
ZnO
single
crystals
[4].
The
overall
maximum
monochromatic
quantum
efficiency
(~ 1.5
%)
is
obtained
at
the
Ru‘ (II)
complex
peak
and
is
the
same
whether
or
not
the
electrode
has
been
also
sensitized
with
RhB.
This
seems
to
indicate
that
partial
coverage
by
Ru
(II)
complex
dye
takes
place
at
selective
sites
of the
ceramic
surface
and
that
the
RhB
molecules
adsorb
at
different
sites.
This
may
explain
the
relatively
small
quantum
efficiency
although
other
effects
like
a
high
charge
carrier-recombination
rate
at
the
ZnO-electrolyte
interface
or
a
small
dye-semiconductor
charge
transfer
rate,
as
compared
to
the
direct
to
the
ground
state,
Fig.
4.
-
Photocurrent
action
spectrum
performed
under
the
same
conditions
as
in
figure
3
but
with
the
ZnO
electrode
subsequently
sensitized
with
Rhodamine
B
dye
as
described
in
text.
The
dashed
extension
of the
Ru
(II)
complex
peak
corresponds
to
data
as
obtain-
ed
prior
to
Rhodamine
B
sensitization
(Fig.
3).
The
insert
illustrates
the
photoresponse
of
a
ZnO
ceramic
electrode
when
sensitized
just
with
the
Rhodamine
B
dye.
fluorescent
or
non-radiative,
deactivation
rate
of
the
molecular
excited
state,
cannot
be
yet
ruled
out.
An
important
parameter,
useful
to
compare
the
performance
of
the
ceramic
semiconductor
with
that
of
a
single
crystal,
is
the
flat
band
potential
Efb
which
gives
a
measure
of
the
band
bending
obtained
in
the
depletion
layer
at
the
semiconductor
surface
in
contact
with
the
electrolyte.
As
pointed
out
by
Gerischer
et
al.
[4]
the
flat
band
potential
can
be
obtained
from
the
1-V
characteristics
of the
sensitized
cell,
since
the
potential
(e.g.
vs.
SCE)
for
the
onset
of
the
photo-
current
is
a
mesure
of
Efb
because,
for
dyes
whose
excited
state
lies
above
the
surface
edge
of
the
valence
band,
as
shown
in
figure
1,
injected
electron
flow
will .
start
with
the
onset
of the
bending
of the
band.
Figure
5
Fig.
5.
-
Extended
current-voltage
characteristics
of
a
doubly
sensitized
ZnO
ceramic
in
the
dark
(curve
id)
and
under
broad
band
(400-700
nm)
excitation
in
the
absorption
region
of
the
dyes
(curve
iL).
Subtraction
of
the
dark
current
yields
the
characteristics
iphot
(dashed
curve).
The
onset
of
the
photocurrent
occurs
at
a
flat
band
potential
of E fb
= -
0.3
V/SCE.