SUPPLEMENTARY
Surface plasmon excitation in semitransparent
inverted polymer photovoltaic devices and their
applications as label-free optical sensors
Byoungchoo Park*1, Soo Hong Yun1, Chan Youn Cho1, Young Chan Kim1, Jung Chul
Shin1, Hong Goo Jeon1, Yoon Ho Huh1, Inchan Hwang2, Ku Youn Baik1, Young In Lee1,
Han Sup Uhm1, Guang Sup Cho1 and Eun Ha Choi1
1
Department of Electrical and Biological Physics, Kwangwoon University,
2
Department of Electronic Materials Engineering, Kwangwoon University,
Wolgye-Dong, Nowon-gu, Seoul 139-701, Republic of Korea
*e-mail: bcpark@kw.ac.kr
(Supplementary Information)
1
SUPPLEMENTARY FIGURES
Fig. S1 Energy-level diagram of the semitransparent IPSCs studied and optical
properties of the functional multilayers used in the IPSCs. (a) Schematic illustration of
the energy-level diagram of the semitransparent IPSCs. The inset shows the molecular
structures of P3HT and PCBM. (b) The optical absorption spectra of the P3HT:PCBM
layer. The inset shows a photograph of a P3HT:PCBM layer on a glass substrate. The
P3HT:PCBM PV layer used for the IPSCs exhibited optical absorption with a peak at
around 495-510 nm, which is mainly attributed to the π-π* transition of the P3HT (band
2
edge: ~650 nm). (c) Upper panel: The transmission spectra (T) of the IPSCs investigated
(dashed curves), together with T for the single thin (~45 nm) Ag and Au metal films
(solid curves). The inset shows a photograph of a pair of semitransparent IPSCs. Lower
panel: The reflectance spectra (R) of IPSCs investigated (dashed curves), together with
R of the single thin (~45 nm) Au and Ag metal films (solid curves). The lowest
transmission of the IPSC with a thin Au anode (Au-IPSC) occurred at around 500 nm
due to the strong absorption of the P3HT:PCBM layer, in contrast with the thin Au layer,
which reaches its maximum transmission at this wavelength. The low transmission of
the Au-IPSC at wavelengths longer than the absorption edge (~650 nm) of the
P3HT:PCBM layer is mainly attributed to the strong optical reflection of the Au-IPSC.
Although the transmission and reflection spectra differ between the Au and the Ag films,
the optical characteristics of semitransparent IPSCs with a thin Ag anode (Ag-IPSC)
were found to be similar to those of the Au-IPSC.
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Fig. S2 Complex refractive indices of the functional multilayers used in the
semitransparent IPSCs. (a) Left: A typical example of spectroscopic ellipsometry
measurement results of a P3HT:PCBM layer on a Si wafer coated with SiO2 (300 nm)
for a range of different incidence angles (60° ~ 80°). Ellipsometric alpha (α) and beta (β)
parameters were analyzed using the Fresnel model and were found to be in good
agreement with the experimental data, as shown in the figure (solid curves). Right:
Estimated real (n) and imaginary () refractive indices of the P3HT:PCBM layer, which
are comparable with the n values of Reference 25 in the manuscript. (b) Complex
refractive indices of the ITO, PEO:Cs2CO3 and MoO3 functional layers obtained from
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ellipsometry measurements. Ellipsometric parameters were acquired for the polarization
change (𝝆 = 𝐭𝐚 𝐧 𝝍 𝐞𝒊∆ = 𝒓𝑷 ⁄𝒓𝑺) of the incident light wave as reflected at the different
interfaces in the films, where the ellipsometric angles Delta (∆) and Psi () are related
to α and β: 𝐭𝐚𝐧 𝝍 = 𝐭𝐚𝐧 𝑷 ∗ {(𝟏 + 𝜶)⁄(𝟏 − 𝜶)}𝟎.𝟓 and 𝐜𝐨𝐬 ∆ = 𝜷 (𝟏 − 𝜶𝟐 )−𝟎.𝟓 .
Here, P is the polarizer azimuth angle (45o) in the rotating analyser ellipsometer (RAE),
and ‘𝒓𝑷 ’ and ‘𝒓𝑺 ’ are the complex Fresnel reflection coefficients of the sample film for
TM (transverse-magnetic or p-) and TE (transverse-electric or s-) polarized lights,
respectively.1 The optical constants obtained show good agreement with those published
previously.2,3 (c) Complex refractive indices of the thin Au and Ag metal layers (ca. 45
nm, sputter-deposited), obtained from variable wavelength attenuated-total-reflection
(ATR) measurements (symbols). The curves show the results fitted using an analytical
model of the frequency (𝝎)-dependent Drude-critical points model for the electric
permittivity (𝝐) of gold and silver4:
𝝐𝐃𝐂𝐏 (𝝎) = 𝝐∞ −
𝝎𝟐𝐩
𝟐
𝝎 +𝒊𝜸𝝎
+ ∑𝟐𝒑=𝟏 𝑨𝒑 𝜴𝒑 (𝜴
𝐞𝒊𝝋𝒑
𝒑 −𝝎−𝒊𝒑
+𝜴

𝐞−𝒊𝝋𝒑
𝒑 +𝝎+𝒊𝒑 
),
where the first and second terms are the standard contribution of a Drude model5 with a
high-frequency limit dielectric constant 𝝐∞, a plasma frequency 𝝎𝐩 and a damping
term 𝜸, while the last two terms are the critical point transition contributions6 from the
5
interband transitions (gap) with critical point amplitude 𝑨𝒑 , interband transition
frequency 𝜴𝒑 , phase 𝝋𝒑 and broadening 𝒑 4. Here, we used 𝝐∞ = 1.1431, 𝝎𝒑 =
1.320×1016 rad s-1, 𝜸 = 1.7306×1014 rad s-1, 𝑨𝟏 = 0.26698, 𝜴𝟏 = 3.8711×1015 rad s-1,
𝝋𝟏 = -1.2371, 𝟏 = 3.7693×1014 rad s-1, 𝑨𝟐 = 3.0834, 𝜴𝟐 = 4.1684×1015 rad s-1, 𝝋𝟐
= -1.0968, 𝟐 = 2.5419×1015 rad s-1 for the thin Au film, and 𝝐∞ = 15.833, 𝝎𝒑 =
1.3861×1016 rad s-1, 𝜸 = 19.8847×1013 rad s-1, 𝑨𝟏 = 1.0171, 𝜴𝟏 = 6.6327×1015 rad
s-1, 𝝋𝟏 = -0.93935, 𝟏 = 6.685×1014 rad s-1, 𝑨𝟐 = 15.797, 𝜴𝟐 = 9.2726×1017 rad s-1,
𝝋𝟐 = 1.8087, 𝟐 = 1.2258×1017 rad s-1 for the thin Ag film.
Fig. S3 Optimum thickness of the Au anode in IPSCs. (a) To determine the optimum
thickness of the Au anode in the semitransparent IPSC for resonant excitation of SPs,
the optical absorptions of the Au anodes were calculated numerically by FDTD as a
function of the thickness of the Au electrode for an incident light of  = 632.8 nm at
6
three incident angles (θs) of the SPR angle of 43.8 o (θ = θR), the lower off-resonance
angle of 42.0 o (θ < θR) and the higher off-resonance angle of 48.0 o (θ > θR). The figure
clearly shows that the most appropriate thickness of the Au anode to cause resonance
of SPs is about 45 nm. (b) In order to confirm the optimum thickness (ca. 45 nm) of
the Au anode in the semitransparent IPSC studied, the optical absorptions of all the
functional multilayers used in the Au-IPSC were also calculated as a function of the
incidence angle  for an incident light of  = 632.8 nm at the given Au thickness of 45
nm. The figure clearly shows that at the SPR angle (θ = θR), the optical absorption of
the Au anode is strongest among the functional layers and the total absorption of the
all multilayers almost reaches 1.0. This result indicates that the main origin of the
sharp dip in the R() spectra (e.g., Figure 2b) is the strong absorption of the Au anode
due to SPR excitation, and is not attributed to the effects of any destructive
interference or transmission of incident light.
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Fig. S4 Optical dispersion relationships between the frequency f and the in-plane
wavevector kX for the TM-polarized modes in the IPSCs studied. Optical dispersion
relationships of an Au-IPSC (left panel) and an Ag-IPSC (right panel) for the
TM-polarized modes as determined by means of the finite difference time domain
(FDTD) method. In the FDTD calculations, as input parameters we used the refractive
indices of the multilayers in the IPSCs, as determined by optical measurements
(Supplementary Fig. S2). In the figures, the dotted lines labelled “air-mode” and
“glass-mode” represent the frequencies and wavevectors accessible by light
propagating in air and in the glass substrate, respectively. The solid curves labelled
“ITO-mode” and “P3HT:PCBM & MoO3-mode” represent the waveguide modes in
the ITO and P3HT:PCBM/MoO3 layers, respectively. The dispersion relationships
clearly show that the semitransparent IPSC structure under investigation supports two
TM-polarized resonant modes, arising from the strong coupling of the incident photons
8
with the SPs at the two metal/dielectric interfaces, i.e., the metal anode-air (SP1 mode)
and metal anode-(MoO3)-PV (SP2 mode) interfaces.
Fig. S5 PV performance of the Ag-IPSC. (a) Semilogarithmic plot of the dark J-V curve
of an Ag-IPSC. (b) J-V curve of the Ag-IPSC under bottom illumination (open
symbols), together with the curve under top illumination (closed symbols). (c) IPCE
spectral curve of the Ag-IPSC under bottom illumination (open symbols), together with
the curve under top illumination (closed symbols).
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Fig. S6 Optical power absorbed by the functional layers in an Au-IPSC. Plots of the
calculated fraction of the optical power absorbed by the functional multilayers in an
Au-IPSC, as a function of the angle of incidence for TM- (upper) and TE-polarized
(lower) incident light with wavelengths of 633 nm (a), 500 nm (b), and 750 nm (c). The
data were obtained from FDTD simulations.
The optical power absorbed by the multilayers in the Au-IPSC from the incident light
was investigated by means of FDTD simulations with the optical parameters of the
layers (see Supplementary Fig. S2). Supplementary Fig. S6 shows that for incident light
of = 633 nm, which corresponds to the wavelength just above the bandgap of the PV
layer, the amount of power absorption in the IPSC can be split into five regions; Region
1 (Transmission) and Region 2 (Reflection) represent the light transmitted directly
through the IPSC and the light reflected from the IPSC, respectively. The other regions
represent the amount of light-absorption of the PV layer, the Au anode (‘Surface
plasmons’), and other functional layers including the MoO3, ITO, and PEO:Cs2CO3
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layers. At normal incidence, for both TM- and TE-polarized incident light, 45.7% of the
incident light is absorbed into the PV layer, 9.6% is absorbed into the Au layer, and
7.1% is absorbed into the other stacks. As  increases, for TM-polarized incident light,
SP coupling in the Au absorption begins to increase at angles just above the critical
angle (θC) of 41.3°, with a more rapid rise at an SPR angle (θR) of 43.7°, showing the
highest fraction of SP-coupled light (about 60.4%). While the absorption of the other
layers decreases at this SPR angle, above this SPR angle the SP coupling decreases and
the absorption levels of the other layers recover to their high values. For TE-polarization,
however, as increases the absorption of each layer changes continuously without any
contribution from SP excitation. We therefore note that at θ = θR for TM-polarized
excitation light, the power absorption of the Au-IPSC probably has two main
contributors: PV absorption and SP excitation. For comparative purposes, the
wavelength-dependent absorption of light by the Au-IPSC was also investigated
(Supplementary Figs. S6b and S6c). For incident light of = 500 nm, which
corresponds to the wavelength of maximum absorbance of the PV layer, most of the
incident light is absorbed directly into the PV layer, implying a very small contribution
of SP, even for TM-polarization. In contrast, for incident light of  = 750 nm, which
corresponds to the wavelength just below the bandgap of the PV layer, most of the
incident light is reflected at θ < θR due to the high n and small  of the PV layer on the
highly reflective Au anode. Alternatively, it is absorbed by the Au anode layer when θ ≈
θR (only for TM-polarized light), with a small amount of absorption by the PV layer. It
is also noted that the strong reflection at θ ~ 0° for incident light of λ = 750 nm is the
main reason for the low transmission of the Au-IPSC at wavelengths longer than the
absorption edge of the PV layer (~650 nm).
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Fig. S7 Excitation of SPs on Ag-IPSC. Excitation characteristics of SPs on the Ag-IPSC
and their effects on the PV characteristics were investigated using the ATR
prism-coupling technique as a function of angle of incidence (θ). (a) Angular
TM-polarized reflectivity spectra (R) of the Ag-IPSC assembled with an ATR coupling
prism (Ag-IPSC/prism) for an incident light of  = 632.8 nm. The symbols represent the
experimental data, and the solid curve represents the theoretical simulation. The SPs are
excited at a resonant angle of θR = 43.4o. (b) Simulations of depth profiles of electric
field intensity (|E|2) in the Ag-IPSC structure as functions of incident angle  and depth
z. The colours show the strength of the electric field intensity. (c) Measured J-V curves
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of the Ag-IPSC/prism at the resonance angle (θ = θR = 43.4o), together with the curves
at the lower off-resonance ( = 41.7o < θR) and the higher off-resonance ( = 48.6o > θR)
regions for a monochromatic incident light (λ = 632.8 nm, 0.35 mW cm-2). In the J-V
curves, it is clear that the observed JSC values depend strongly on the excitation of SPs.
(d) Dependence of normalized JSC of the Ag-IPSC/prism on the angle of incidence  for
the 632.8 nm excitation. The circles represent the experimental data, and the solid curve
represents the normalized optical absorption of the PV layer, calculated by the FDTD
simulation. It is noted that the SPR angle of the JSC(θ) spectra (APG) is nearly identical
to that of the R(θ) spectra (ATR, Fig. S2a), confirming that the observed results of the
Ag-IPSC exhibit similar behaviour to those of the Au-IPSC, as described in the main
text.
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Fig. S8 Comparison of stabilities and lifetimes for the semitransparent IPSCs studied. In
order to investigate the stabilities of the fabricated semitransparent IPSCs, we measured
the relative PCEs as a function of storage time. After fabrication, the IPSCs were not
encapsulated. Because the devices were exposed to ambient air, they degraded, mainly
as a result of the presence of oxygen and water in the air.7 The operational lifetimes of
the devices were measured under intermittent illumination (solar simulator, 100 mW
cm-2, AM 1.5G) at a temperature of 26.1 ± 2.0 °C and a relative humidity of 31 ± 9.7%.
Between measurements, the devices were kept in the dark under open-circuit conditions.
The symbols represent experimental data, and the dotted lines show curves fitted using
bi-exponential decay functions.7 As shown in the figure, the Ag-IPSC (closed circles)
clearly exhibits a pronounced bi-exponential decay with 𝐏𝐂𝐄(𝒕)⁄𝐏𝐂𝐄(𝟎) =
𝟎. 𝟏𝐄𝐱𝐩[− 𝒕⁄𝒕𝟏 ] + 𝟎. 𝟗𝐄𝐱𝐩[− 𝒕⁄𝒕𝟐 ], where the fast lifetime (t1) is about 3 hrs and the
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slow lifetime (t2) is about 950 hrs. In contrast to the relatively rapid degradation of the
Ag-IPSC, it is clear that the Au-IPSC (open circles) exhibits a nearly single-exponential
decay of 𝐏𝐂𝐄(𝒕)⁄𝐏𝐂𝐄(𝟎) = 𝟎. 𝟕𝐄𝐱𝐩[− 𝒕⁄𝒕𝟏 ] + 𝟎. 𝟑𝐄𝐱𝐩[− 𝒕⁄𝒕𝟐 ] with t1 ~ t2 ~ 2800
hrs, indicating that the Au anode has the advantage of long term stability. This long
term stability of the Au-IPSC is mainly due to the higher ionization energy (or higher
work function) of Au than Ag (See Supplementary Fig. S1a). Note that the PCE values
obtained are averages of more than four individual devices on different substrates.
Fig. S9 Surface morphologies of the bi-adlayers on Au-IPSC. AFM morphologies (10 ×
10 μm2) for the formation (upper) and desorption (lower) of the Cytop and BSA
bi-adlayers on the Au-IPSC were observed using an atomic force microscope set to scan
15
in the static force mode (AFM, Nanosurf EasyScan2 AFM, Nanosurf AG, Switzerland
Inc.). (See also Figs. 3a-b). The root mean square (RMS) surface roughnesses of the
single Cytop adlayer and the Cytop/ BSA bi-adlayers on the Au anodes decreased to
3.23 and 2.17 nm, respectively, from a relatively high surface roughness of 5.21 nm of
the bare Au anode. After washing with water, the surface roughness (ca. 3.26 nm) of the
washed surface was similar to that of the single Cytop adlayer, implying redissolution
of the BSA adlayer in water. This result is consistent with the estimated layer thickness
of ca. 20.4 nm for the bi-adlayers after washing with water, which is close to that (17.1
nm) of the single Cytop adlayer (See Figure 3b), confirming that the upper BSA was
almost removed by the wash water. After successive exposure to the pure Ar plasma,
the roughness (ca. 3.69 nm) of the treated surface is still similar to that before the
exposure of the Ar plasma, implying little influence of the pure Ar plasma on the
adlayers. In contrast, in the areas re-exposed to the Ar/O2 plasma, an area with a rough
surface (ca. 5.55 nm) may clearly be seen in the AFM images, indicating that the
adlayers were almost etched out by the plasma. These AFM results are also consistent
with the SPR observation that the thickness of the adlayers exhibited a slow decrease
(ca. 1.7 nm) for the pure Ar plasma, while showing a rapid decrease (ca. 17.1 nm) for
the Ar/O2 plasma (See Fig. 3b), due to the enhanced reaction of adlayers with ozone,
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hydroxyl radicals and oxygen atoms in the Ar/O2 AP plasma. The AFM results thus
confirmed the results of the SPR investigations described above for the nanoscale
formation and/or desorption of adlayers.
Fig. S10 In-situ monitoring ATR (R) and APG (JSC) signals. (a) Comparison of real
time in-situ monitoring ATR (R) and APG (JSC) signals at four different incidence
angles (s) of 43.50°, 45.15°, 45.80° and 46.60° for Cytop/ BSA adlayers on Au-IPSC
during an Ar plasma treatment process using an AP plasma jet.8 The adlayers were
treated using an Ar plasma jet and the ATR (R) and APG (JSC) signals were recorded as
a function of treatment time. As shown in the figure, time-dependent changes in the R
curves (ATR) during the treatment are almost identical to those (APG) in the JSC curves.
(b) A photograph of an operating Ar plasma jet treating the Cytop/ BSA bi-layers on the
Au-IPSC/prism. To generate the AP plasma jet, we used a needle-type plasma jet source
17
derived from a dc–ac inverter of several tens of kHz in the voltage range 1–3 kV.8 We
generated the plasma jet (plume length of about 10 mm), treating the bi-adlayers using a
flow of Ar gas (2.5 ml min-1), and investigated the ATR and APG signals as a function
of treatment time.
Table S1: Summary of the device performance of the Au-IPSC after each step in the
formation and desorption processes for the bi-adlayers of Cytop and BSA on Au anodes.
VOC
JSC
FF
PSC
(V)
(mA cm-2)
(%)
(%)
Virgin Au-IPSC
0.59±0.01
9.68±0.42
49.55±1.30
2.82±0.10
Cytop coating
0.59±0.01
9.21±
50.12
2.72±
0.38
±2.99
0.05
0.61±
9.59±
49.46
2.87±
0.01
0.63
±2.72
0.16
0.60±
9.33±
50.45
2.84±
0.01
0.88
±2.04
0.35
0.61±
9.41±
47.97
2.76±
0.01
0.98
±4.14
0.33
Ar/O2 plasma
0.61±
8.87±
51.87
2.79±
treatment
0.01
0.86
±1.29
0.25
Step
BSA coating
Washing with water
Ar plasma treatment
18
* The values shown are the averages and standard deviations obtained from several (more than
five) individual PSCs on independent substrates for the device studied.
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