See-through amorphous silicon solar cells with selectively
transparent and conducting photonic crystal back reflectors
for building integrated photovoltaics
Yang Yang, 1 Paul G. O’ Brien, 2, 3 Geoffrey A. Ozin, 3,a) and Nazir P. Kherani 1, 2, a)
1
The Edward S. Rogers Sr. Department of Electrical and Computer Engineering,
University of Toronto, 10 King’s College Road, Room GB254B, Toronto, ON M5S 3G4,
Canada
2
Department of Materials Science and Engineering, University of Toronto, 184 College
Street Room 140, Toronto, ON M5S 3E4, Canada
3
Materials Chemistry Research Group, Department of Chemistry, University of Toronto,
80 St. George Street, Toronto, ON M5S 3H6, Canada
Supplementary Information
I.
Angular and Polarization Dependence of STCPC Reflectance
We measured the angular and polarization dependence of the reflectance of the
STCPC samples BR460, BR520 and BR620, which is shown in FIG S1, S2 and S3
respectively. For both the p- and s-polarized incident light, the Bragg peak position
experiences a blue shift with increasing angle of incidence. For p-polarized light, the
reflectance peak intensity decreases when the angle of incidence increases from 8 degrees
to 40 degrees. The FWHM of the Bragg reflectance peak decreases for p-polarized light
with increasing angle of incidence, indicating a decrease in the stop bandwidth, while the
FWHM of the Bragg reflectance peak is essentially unchanged for s-polarized light with
a
) Authors to whom correspondence should be addressed. Electronic mail: kherani@ecf.utoronto.ca;
gozin@chem.utoronto.ca
increasing angle of incidence. The angular dependence of the reflectance spectra of the
STCPCs for different polarizations shows a similar trend as that reported in the literature
for 1-D holographic photonic crystals.1, 2
It is noteworthy that the critical angle ϴc at which the stop band disappears for ppolarized incident light is defined as
c  arctan(
 a b
)
( a   b ) v   a b
(1)
where εa and εb are the dielectric constants of the layers comprising a 1-D photonic crystal
and εv is the ambient dielectric constant (εv =1 for air).3 For our STCPC samples, the
dielectric constants of the ITO and SiO2 nanoparticle layers which comprise the 1-D
photonic crystal at Bragg peak wavelengths of 460nm, 520nm and 620nm are listed in
Table I. For the STCPC samples used in this study, it can be shown by simple calculation
that the argument in equation (1) is not real and hence the condition for observing the
critical angle is not satisfied.
Table I. Dielectric constants of ITO layer and SiO2 nanoparticle layer at wavelengths
corresponding to the Bragg peak positions of the STCPC samples. The dielectric constants
were determined using spectroscopic ellipsometry.
Wavelength
(nm)
εITO
εSiO2
460
4.24
1.82
520
3.96
1.81
620
3.76
1.79
FIG.S1. Reflectance of BR460 with (a) p-polarized light, (b) s-polarized light and (c)
unpolarized light at incident angles of 8, 20 and 40 degrees, respectively.
FIG.S2. Reflectance of BR520 with (a) p-polarized light, (b) s-polarized light and (c)
unpolarized light at incident angle of 8, 20 and 40 degrees, respectively.
FIG.S3. Reflectance of BR620 with (a) p-polarized light, (b) s-polarized light and (c)
unpolarized light at incident angle of 8, 20 and 40 degrees, respectively.
II.
Calculation of Jsc with Different Bragg Peak Positions
The extinction coefficient and absorption coefficient of a-Si:H films are well
documented in the literature. In order to study the effects of different STCPC reflectors
we designed Bragg reflectors with reflection peaks at 460 nm, 520 nm and 620 nm.
Using the scattering matrix method we calculated the Jsc of the 135 nm a-Si:H cell on
STCPC rear contacts with Bragg peaks at 460 nm, 520 nm and 620 nm. The comparison
of the calculated and the experimental results is shown in FIG.S4.
FIG.S4. Comparison of experimental Jsc (solid black square) and calculated Jsc (solid red
circle) using the scattering matrix method. The relative increase of experimental Jsc (open
black squares) and the relative increase of calculated Jsc (open red circles) relative to the
200 nm ITO back reflector reference is also shown.
III.
a-Si:H deposition parameters
The deposition gas flow rate for the n, i and p layers in the a-Si:H n-i-p cell are
listed in Table II. The substrate temperature during the deposition for each layer is 200°C.
The RF power used for all the three layers are 2.0W.
Table II. Gas flow rate for n, i and p layers in the a-Si:H deposition.
Silane
(sccm)
Diborane
(sccm)
Phosphine
(sccm)
n-layer
8
0
20
i-layer
30
0
0
p-layer
8
20
0
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