of 16
Supplemental Information for
Photoelectrochemistry of Core
Shell Tandem
Junction n
-­‐
p
+
-­‐
Si/n
-­‐
WO
3
Microwire Array
Photoelectrodes
,
¢
Matthew R. Shaner,
,
¢
Katherine T. Fountaine,
Shane A. Ardo,
Robert H. Coridan,
,
¢
Harry A. Atwater*,
,
¢
Nathan S. Lewis*
Division of Chemistry and Chemical Engineering, M/C 127
-
72
Thomas J. Watson, Sr. Laboratories of Applied Physics, M/C 180
-
32
¢
Joint Center for Artificial Photosynthesis, M/C 13
2
-
80
1200 E. California Blvd.
California Institute of Technology
Pasadena, CA 91125, USA
Electronic Supplementary Material (ESI) for Energy & Environmental Science
This journal is © The Royal Society of Chemistry 2013
Table S
1
:
Refractive index source for light absorption modeling
Material
n,k source
Si
Asp
ne
s
1
WO
3
Ellipsometry
(
Figure S
1
)
ITO
Ref.
2
SiO
2
Palik
3
Electronic Supplementary Material (ESI) for Energy & Environmental Science
This journal is © The Royal Society of Chemistry 2013
Table S
2
:
Geometr
ic parameters
for
the
Si/WO
3
microwire
structure in Figure 1b
used for the optical
modeling
Si Microwire diameter (d)
1.8 μm
Si Microwire height (h)
80 μm
Si Microwire pitch (p)
7 μm
Si substrate thickness (t
Si
)
Infinite
SiO
2
boot height (h
boot
)
20 μm
SiO
2
boot thickness (t
boot
)
100
nm
SiO
2
base thickness (t
base
)
500
nm
ITO thickness (t
ITO
)
50
nm
WO
3
coating thickness (t
WO3
)
500
nm
WO
3
top thickness (t
WO3top
)
2.3 μm
Electronic Supplementary Material (ESI) for Energy & Environmental Science
This journal is © The Royal Society of Chemistry 2013
Figure S
1
:
Refractive index data for WO
3
.
T
he real
component of the refractive
index
, n,
was obtained by
fitting
ellipsometry data and extrapolating above the
bandgap
with
a Lorentzian
function
.
G
iven the
n
obtained by
ellipsometry
, a
n
adapted form of a multilayer material transfer matrix program was used to fit
integrating sphere transmission
data
to extract
the imaginary component of the
refractive index,
k
.
Electronic Supplementary Material (ESI) for Energy & Environmental Science
This journal is © The Royal Society of Chemistry 2013
Figure S
2
:
C
o
n
centration
profile
of boron
in
an
n
-­‐
Si planar wafer after BCl
3
drive in
,
from
a secondary ion mass spectrometry (
SIMS
)
measurement
(see experimental
section). This shows an emitter thickness of
~
2
5
0
nm.
Electronic Supplementary Material (ESI) for Energy & Environmental Science
This journal is © The Royal Society of Chemistry 2013
Figure S
3
:
a) SEM image captured by the EDX instrument of a tandem microwire
cross section. The line scan performed is overlaid on this image with the beginning
and end indicated. b) Line scan data as reported by the Oxford Aztec software. It
shows a clear transit
ion from a Si rich area (<0.35
μ
m
) to an indium rich area (0.35
μ
m
-­‐
0.45
μ
m
) to a W and O rich area (>0.45
μ
m
). This further verifies the presence
of the layered structure as described in the main text.
Electronic Supplementary Material (ESI) for Energy & Environmental Science
This journal is © The Royal Society of Chemistry 2013
Figure S
4
:
(
a
)
,
(
c
)
,
(
e) SEM images captured by the EDX software that indicated the
point where data was taken at.
(
b
)
,
(
d,
)
(
f) Corresponding EDX data the points
depicted in
(
a
)
,
(
c
)
,
(
e.
)
These data also confirm the layered structure described in
the text.
Electronic Supplementary Material (ESI) for Energy & Environmental Science
This journal is © The Royal Society of Chemistry 2013