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S1
Supplementary Information
Bi-hierarchical nanostructures of donor-acceptor
copolymer and fullerene for high efficient bulk
heterojunction solar cells
Hsueh-Chung Liao1, Cheng-Si Tsao
2*, Yu-Tsun Shao
3, Sheng-Yong Chang
3, Yu-Ching Huang
2, Chih-
Min Chuang2, Tsung-Han Lin
1, Charn-Ying Chen
2, Chun-Jen Su
4, U-Ser Jeng
4, Yang-Fang Chen
3, and
Wei-Fang Su1*
1 Department of Materials Science and Engineering, National Taiwan University, Taipei 106-17, Taiwan
2 Institute of Nuclear Energy Research, Longtan, Taoyuan 325-46, Taiwan
3 Department of Physics, National Taiwan University, Taipei 106-17, Taiwan
4 National Synchrotron Radiation Research Center, Hsinchu 300-77, Taiwan
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S2
Representative 2D GISAXS, 2D GIWAXS patterns and the integration of GIWAXS patterns
Fig. S1 (a) shows the representative 2D GISAXS pattern of PCPDTBT film processed with 3% DIO,
i.e. P_3%DIO. Fig. S1 (b) and (c) show the 2D GIWAXS images obtained from pristine PCPDTBT
(P_3%DIO) and PCPDTBT/PCBM blend (BL78_3%DIO) films, respectively. The diffractions from
PCPDTBT (100) lamellar layers are indicated by the white arrows in the GIWAXS figures, showing
much more intense diffractions along the out-of-plane direction (Qz). This implies that in both pristine
and blend films, the edge-on polymer crystals with (100) lamellar layers oriented parallel to the substrate
dominates as compared with crystals of other orientations (face-on crystallite). According to the Fig. S1,
it can be observed that the (100) scattering peaks reveal extend arcs (more obvious in P_3% film, Fig.
S1 (a)). This indicates that some of the crystallites are with a small tilted angle relative to the exact
edge-on crystallites, i.e. spread of the crystal orientation. In the present work we also classified these
crystallites as the edge-on crystallites. Therefore, in order to compare the partial crystallinities of edge-
on crystallites among all the sample films, the range of the integration triangle in Fig. S1 is determined
to be capable of covering the arcs of P_3% film which reveals the most extend arc of the (100)
scattering peak than the other film samples. Therefore, most the edge-on type crystallites are included
when the 2-D GIWAXS patterns were reduced to the 1-D GIWAXS profiles.
We have also calculated the missing wedge for the GIWAXS pattern as illustrated by the pole figure
shown in Fig. S2 (b). With the incident angle of 0.2, the missing angle at Q ~ 0.55 Å-1
for the primary
peak (corresponding to a Bragg angle B = 3.33) is ~ 3. The corresponding azimuthal scans of the
GIWAXS patterns are shown in Fig. S2 (c) and S2 (d). In Fig. S2 (d), we have extrapolated the data in
the “missing angle” via a fitted Lorentzian profile. The integrated peak intensity in Fig. S2 (d) is about
30 % larger than that for Fig. S2 (c); this result suggests that the perfect edge-on crystallites, not
accounted for in the triangle integration zone in Fig. S1, may contribute ~30% to the general edge-on
crystallites (with an orientation angle spread of 20 from the meridian line, as shown in Fig. S1).
Nevertheless, the systematic approximation can still correctly provide the relative crystallinity for the
studied samples.
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Fig. S1. (a) 2-D GISAXS patterns of pristine PCPDTBT processed with 3% DIO, i.e. P_3%DIO. The
red rectangle indicates the integration area used to reduce the 1-D GISAXS profile.2-D GIWAXS
patterns of (b) P_3% DIO and (c) BL78_3% DIO films. The white arrow indicate diffraction of
PCPDTBT (100) lamellas. The red inverse triangles in (b) and (c) represent the integration area used in
reducing the 2-D patterns into 1-D GIWAXS profiles.
Qz
Qx
a
PCPDTBT (100) c
P_3% DIO
BL78_3%DIO
b
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S4
-50 -40 -30 -20 -10 0 10 20 30 40 50
100
200
300
400
500
600
700
800
900
1000
detector meridian cut
fitting curve
Inte
nsit
y (
a.u
.)
Azimuth angle (degree)
(c)
-50 -40 -30 -20 -10 0 10 20 30 40 50
100
200
300
400
500
600
700
800
900
1000
pole figure
fitting curve
Inte
nsit
y (
a.u
.)
Azimuth angle (degree)
(d)
Missing wedge
Fig. S2 (a) GIWAXS pattern shown in Fig. S1 and (b) the corresponding pole figure. (c) and (d) are the
azimuthal scans of (a) and (b) at Q = 0.55 Å-1
, respectively, for the primary peak.
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S5
The background effect and PEDOT:PSS effect on the GISAXS profiles and the resolved
nanostructures of the sample films
There’s a concern of multiple scattering1-2
in GISAXS experiment which affects the background
subtraction. We have a detailed discussion as follows. The GISAXS results in the present work were
obtained from the film samples which were directly spin coated on bare silicon (Si) substrate. The 1-D
GISAXS profiles were taken along the in-plane direction as shown in Fig. S1 (a), with the scattering
intensity corrected for background scattering from bare Si measured separately with the same GISAXS
geometry. For the background subtraction purpose, sample film transmission in the GISAXS geometry
was also obtained from the ratio of the specular beam intensities measured with sample on Si wafer and
that with pure Si wafer, under the same GISAXS geometry. The results indicates that the background
subtraction a minor effect in the present work owing to the much smaller background scattering intensity
(Fig. S3 (a), discuss later).
Fig. S3. (a) GISAXS profiles purely obtained from silicon substrate in comparison with GISAXS
profiles purely from P_w/o DIO film and BL78_w/o DIO film (subtracted by the background of Si as
substrate). (b) GISAXS profiles purely obtained from Si+PEDOT:PSS in comparison with GISAXS
profiles purely from P_w/o DIO film and BL78_w/o DIO film (subtracted by the background of
Si+PEDOT:PSS as substrate).
a b
0.01 0.1
1E-3
0.01
0.1
1
10
100
I(Q
) (a
.u.)
Qx (Å
-1)
Silcon
P_w/o DIO
BL78_w/o DIO
0.01 0.1
1E-3
0.01
0.1
1
10
100
I(Q
) (a
.u.)
Qx (Å
-1)
PEDOT:PSS
P_w/o DIO
BL78_w/o DIO
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According to the study by Renaud et al.,2 the typical multiple scatterings are most significant along
the out-of-plane direction. The 2-D GISAXS patterns show substantially varied multiple streaks (beams)
in out-of-plane direction (resulted from multiple scatterings) with different exit angles; these multiple
beams (resulted mainly from the interferences inside the film in the Qz direction), however, carry similar
in-plane structural information hence similar in-pane scattering patterns. To avoid the multibeam
complication, in our data analysis, we have strategically select the most strong in-plane scattering strip
associated with the specular beam, with a narrow Qz step (Fig. S1 (a)) to minimize the multibeam
scattering effect. Furthermore, it can be seen that the 2-D patterns (Fig. S1(a)) in our present work
illustrate largely concentrated scattering strips in the in-plane direction along Qx; the narrow scattering
distribution in the Qz direction leads to small coupling of the multi-beam scattering.
Before the comparison of adopting Si substrates or Si+PEDOT:PSS in GIWAXS/GISAXS
characterization, we first examined if the PEDOT:PSS film deposited on Si has the similar quality to
that of on ITO (structure of solar cell device). Both the ITO substrates (for device fabrication) and Si
substrates (for GIWAXS/GISAXS characterization) were cleaned through an identical process prior to
PEDOT:PSS deposition, i.e. ultrasonically cleaned by a series of solvents, ammonia/H2O2/DI water,
methanol, and isopropanol and subsequently treated by oxygen plasma for 20 minutes. For the wetting
issue addressed by the reviewer, we have measured the water contact angle (the PEDOT:PSS is
dissolved in water) of the ITO and Si substrates respectively. Both the substrates show < 5o contact
angle which indicates the extremely hydrophilic of the substrate surfaces after oxygen plasma treatment.
Moreover, we used the atomic force microscope (AFM) to observe the surface morphology (meso-scale)
of PEDOT:PSS deposited on ITO and Si respectively (Fig. S4). It can be observed that the PEDOT:PSS
films reveal very similar topography and surface roughness either spin coated on ITO or Si substrate.
The results imply that the PEDOT:PSS film on Si substrate is of the analogous quality to that on ITO
substrate. Hence the GIWAXS/GISAXS characterization adopting the Si+PEDOT:PSS substrate can be
correlated to the photovoltaic properties of solar cell devices on the ITO+PEDOT:PSS substrate.
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For quantitatively justifying the effect from PEDOT:PSS (multiple scatterings), we compared the
GISAXS results of the film samples deposited on Si substrate and PEDOT:PSS (~15 nm)-coated Si
substrate (Si+PEDOT:PSS), respectively. The GISAXS profile purely from Si substrate (as background
file) is presented in Fig. S3 (a) together with the GISAXS profiles of pristine PCPDTBT (P_w/o DIO)
and PCPDTBT/PCBM blend (BL78_w/o DIO) subtracting the Si background. The P_w/o DIO and
BL78_w/o DIO films have the lowest GISAXS intensities compared to the other film samples.
Nevertheless, it can be observed that the subtracted GISAXS intensities of both films are much larger
than that of the Si substrate by an order. It indicates the background from silicon would have little effect
on the final reduced profiles.
Similarly, the GISAXS profiles reduced from the samples with Si+PEDOT:PSS as the substrates are
shown in Fig. S3(b). They are reduced by subtracting the scattering intensity of Si+PEDOT:PSS as the
background profile. The GISAXS profile purely from the Si+PEDOT:PSS substrate is also shown in Fig.
S3(b). It can be also observed that the GISAXS profile intensity contributed purely from the
Si+PEDOT:PSS substrate is much lower than those purely from the sample films by an order.
Consequently, we can conclude that when adopting Si or Si+PEDOT:PSS (~15 nm) as substrate, the
background (multiple reflections off interfaces) has relatively little effect in this case. However, We
have also showed that the GISAXS background purely from the Si+PEDOT:PSS (Fig. S3(b)) is slightly
larger than that from Si (Fig. S3(a)).
For extensive comparison, the background subtracting GISAXS profiles of all the film samples on Si
and Si+PEDOT:PSS, respectively, are shown in Fig. S5 (a-c; Si substrate) and Fig. S5 (d-f;
Si+PEDOT:PSS substrate). The GISAXS profiles of the films from the same processing condition but
on different substrates are similar to each other. Moreover, the structural parameters of the films
extracted by model fitting from the same processing condition on the Si and Si+PEDOT:PSS substrates,
respectively, are also found to be close to each other. The discrepancy in GISAXS intensities due to the
additional PEDOT:PSS is so little that the effect to the model fitting can be ignored in this case. It
implies that the thin films show similar morphology regardless the presence of PEDOT:PSS. Actually,
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in our previous study3 we also compared the phase separated morphologies of P3HT/PCBM blend films
on Si and Si+PEDOT:PSS substrates. (Please see the Supporting Information of ref 3.) The local phase
separation in the bulk of the annealed P3HT/PC60BM films (of ~100 nm thickness) away from the
interface is largely not affected by the PEDOT:PSS layer, leading to the similarly observed morphology
(GISAXS and GIWAXS profiles). Therefore, the GISAXS characterization performing on silicon
substrate can be rationally employed to investigate the nanostructure of the sample films and directly
correlated to the solar cell performances.
Fig. S4 Atomic force microscope image of PEDOT:PSS thin film deposited on (a) Si and (b) ITO
substrate.
Fig. S5 GISAXS profiles obtained from all film samples with (a-c) Si and (d-f) Si+PEDOT:PSS
substrates, respectively. (a,d) Pristine PCPDTBT processed without and with different amounts of
additive DIO. (b,e) PCPDTBT/PCBM blend films with 78 wt% PCBM processed without and with
different amount of DIO. (c,f) 3%DIO-processed pristine PCPDTBT film and PCPDTBT/PCBM blend
films with 33%, 50%, 78 wt% PCBM, respectively.
a
b
0 nm
10 nm
1 um 1 um
b a c
d e f 0.01 0.1
0.1
1
10
100
1,000
P_w/o DIO
P_0.5% DIO
P_3% DIO
P_5% DIO
P_10% DIO
I(Q
) (a
.u.)
Qx (Å
-1)
0.01 0.1
0.1
1
10
100
1,000
I(Q
) (a
.u.)
Qx (Å
-1)
BL78_w/o DIO
BL78_0.5% DIO
BL78_3% DIO
BL78_5% DIO
BL78_10% DIO
0.01 0.1
0.1
1
10
100
1,000
P_3% DIO
BL33_3% DIO
BL50_3% DIO
BL78_3% DIO
I(Q
) (a
.u.)
Qx (Å
-1)
0.01 0.1
0.1
1
10
100
1,000
P_w/o DIO
P_0.5% DIO
P_3% DIO
P_5% DIO
P_10% DIO
P3HT
I(Q
) (a
.u.)
Qx (Å
-1)
0.01 0.1
0.1
1
10
100
1,000
I(Q
) (a
.u.)
Qx (Å
-1)
BL78_w/o DIO
BL78_0.5% DIO
BL78_3% DIO
BL78_5% DIO
BL78_10% DIO
0.01 0.1
0.1
1
10
100
1,000
P_3% DIO
BL33_3% DIO
BL50_3% DIO
BL78_3% DIO
I(Q
) (a
.u.)
Qx (Å
-1)
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S9
Estimation of the Δρ value in model fitting
In the typical GISAXS characterization (not absolute measurement), the measured scattering intensity
is indeed a relative intensity. The GISAXS measurement itself is very difficult to be normalized to the
absolute intensity due to the complex scattering geometry. Additionally, the absolute scattering contrast
cannot be determined. The value of scattering length density (SLD) difference (Δρ; scattering contrast)
between targeted particle and matrix significantly affects the determination of absolute volume fraction
(φ). Therefore, the estimated Δρ value herein is only valid for determining the relative volume fraction
for a series of GISAXS data. However, basically the resolved domain sizes are reliable because they are
insensitive to Δρ or the absolute intensity. In the present work, the adopted strategy is to rationally
estimate the Δρ values, which leads to physically reasonable φ values. On the other hand, the volume
fraction is also a parameter in the structural factor of fractal model. It can be partly confined by the
shape of GISAXS profile, reducing the uncertainty caused by the estimated contrast value. It also
implies that the volume fraction determination cannot be freely manipulated by any assumed Δρ value.
For pristine PCPDTBT films (two phases system), the Δρ is the SLD difference (contrast) between
PCPDTBT fractal-aggregated domain/network comprised of crystallites (ρc-PCPDTBT) and surrounding
amorphous PCPDTBT matrix (ρa-PCPDTBT). It is fixed at 0.3 × 10-6
Å-2
for all the pristine PCPDTBT
films, (P_w/o DIO, P_0.5%DIO, P_3%DIO, P_5%DIO, and P_10%DIO), leading to reasonable volume
fractions of fractal-aggregated domains (crystallinity) of 2% ~ 20%. For the ternary phase system of
PCPDTBT/PCBM blends, two Δρ values are estimated. One is between PCPDTBT fractal-aggregated
domains (ρc-PCPDTBT) and the surrounding matrix of amorphous PCPDTBT chains that are
heterogeneously mixed with PCBM molecules (ρa-PCPDTBT+PCBM). The other is between PCBM fractal-
aggregated domains (ρPCBM) and the surrounding matrix (ρa-PCPDTBT+PCBM). The spatially distributed
PCBM in amorphous PCPDTBT is expected to have a larger scattering length density (ρa-PCPDTBT+PCBM)
than that in pristine PCPDTBT film (ρa-PCPDTBT). Hence the Δρ of PCPDTBT crystallites (ρc-PCPDTBT)
relative to surrounding matrix is estimated to a smaller value in the blend films (ρc-PCPDTBT - ρa-
PCPDTBT+PCBM = 0.2 × 10-6
Å-2
). The estimated Δρ values are summarized in Table S1.
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S10
The estimated Δρ values lead to the resultant 13%, 18% and 34% volume fractions of PCBM
aggregated domains when 33 wt% (BL33_3%DIO), 50 wt% (BL33_3%DIO), and 78 wt%
(BL78_3%DIO) PCBM were mixed with PCPDTBT respectively. These volume fractions are physically
reasonable for electron transport in solar cell devices. Additionally, they are also close to the values of
P3HT/PCBM cases reported elsewhere,4-5
indicating the rationally estimated Δρ values.
Table S1 Estimated scattering length density difference between different phases.
Δρ between two phases Δρ values
(Å-2
)
ρc-PCPDTBT - ρa-PCPDTBT 0.3 × 10-6
ρc-PCPDTBT - ρa-(PCPDTBT+PCBM) 0.2 × 10-6
ρPCBM - ρa-(PCPDTBT+PCBM) 0.4 × 10-6
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S11
Discussion of the polymer morphology
It was reported by several groups that the AFM and TEM observations reveal conventional P3HT
polymer crystal has (1) long nanofibril or (2) irregular nodule-like (or grainy) morphologies, depending
on the molecular weight (Mw), annealing condition, solution-casting process, etc.6-8
Low molecular
weight P3HT crystals have nanofibril morphology due to their extended packing of inter-chains. High
molecular weight P3HT crystals (3 kDa) have nodule-like domains because of the folded intra-chain.9
The AFM study pointed out that the long fibril morphology is formed by the self-assembled nanorod
grains with boundaries.9 Basically, controlling the film morphology from fiber-like, nanorod to grainy
and further interconnected network depends on the molecular weight and the associated annealing
temperature.9 However, for D-A copolymer or D-A copolymer/fullerene blend film, various
spectroscopic observations of the polymer crystal morphologies can be categorized into (1) fractal-like
aggregation or dispersion of spherical-like crystallites,10-13
(2) short fibril-like or rod assembled by
spherical-like crystallites14-16
and (3) long nano-fibril crystallites.17-18
For the structure (2), we used the cylinder model19
which can fit well the GISAXS profile in the
middle- and high-Q region also show in Fig. S6 (model (I)). However, the upturn of intensity in the low-
Q region describing the interaction of rod-like particles cannot be fitted using the other structure factor
model. For the structure (3), we used the model of fractal network aggregated by long channels19-20
to fit
the GISAXS profiles as shown in Fig. S6 (model (II)). However, the fitting result cannot support the
existence of long fibril-like polymer crystal. Hence we conclude that the PCPDTBT has very different
crystallization behavior as compared to that of conventional P3HT based on the excluded possibility of
long fibril morphology. Therefore, the analysis model of fractal-aggregation of spherical-like crystallites
(structure (1)) we proposed here is the most reasonable and can provide the best fit on multi-length scale.
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S12
0.01 0.1
Q (A-1)
0.1
1
10
100
I (Q
) a
.u.
PCPDTBT+0.5%DIO
Model_Fit (I)
Model_Fit (II)
o
(b)
0.01 0.1
Q (A-1)
0.1
1
10
100
1000
I (Q
) a
.u.
PCPDTBT+3%DIO
Model_Fit (I)
Model_Fit (II)
o
(a)
Fig. S6 Model fitting of pristine PCPDTBT film processed with (a) 0.5% and (b) 3% DIO, i.e.
P_0.5%DIO and P_3%DIO respectively by models of:
Model (I):19
consistence of (1) fractal network comprised of channel with the fractal dimension DP and
the channel width Lch, and (2) cylinder form factor with the radius R and length H:
dQR
QRjQHjILQQLIQI ch
D
chPP
2/
0
2101
22 sin])sin(
)sin()cos
2(2[)20/exp(])2/(1[)(
Model (II):19-20
only fractal network comprised of channel:
)20/exp(])2/(1[)( 22
ch
D
chP LQQLIQI P
All fitting lines are the best fit using the nonlinear least-squares calculation.
a b
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S13
Cross examination of model fitting of PCPDTBT/PCBM (78% PCBM) films processed with x%
DIO (x3)
There are two approaches generally used for model fitting the PCPDTBT/PCBM (78% PCBM) films
processed with x% DIO (x3):
(I) The GISAXS profile purely contributed from the PCBM (main phase) can be obtained by
appropriately subtracting the GISAXS profile of the minor phase (from a separate sample; regarded as a
concentration-normalized background profile) from that of the blend. For example, the GISAXS profile
purely contributed by aggregated PCBM clusters of the blend film processed with 3 % of DIO can be
determined by subtracting the concentration-normalized GISAXS profile of the P_3%DIO film from
that of the BL78_3%DIO blend film. Then, this profile can be directly modeled by the PCBM structure.
The error source of this approach is the assumption of the scaled GISAXS intensities of pristine
PCPDTBT as the basis of subtraction. Its advantage is a direct method providing an approximated
GISAXS profile scattered from the PCBM clusters.
(II) The contribution of minor phase (polymer) in the GISAXS profile can be assumed as a simple
model with flexible but least variables which is incorporated into the model. The advantage of this
approach is that the structure of minor phase in the blend as background is flexibly adjustable but keeps
the least variables (for avoiding the artificial interference). The fixed parameter of particle size
(2RPCPDTBT) is necessary to keep the least variables because it is relatively less sensitive to the profile.
Additionally, this approach is free of error source of scaled or normalized factor and can simultaneously
and flexibly determine their real contributions in relative volume fraction from both phases. This
approach was also adopted by Lou et al. in investigating the PCBM aggregations in PTB7 polymer
solution but using a much simpler model as background part.21
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S14
Fig. S7 GISAXS profiles that are from pure PCBM clusters of PCPDTBT/PCBM (78 wt% PCBM)
blend films processed with 3%, 5%, and 10% DIO, i.e. BL78_3%DIO, BL78_5%DIO, and
BL78_10%DIO respectively. The solid lines represent the model-fitted intensities.
Table S2 PCBM structure parameters of BL78_x%DIO (x 3) films obtained from indenpent model
fitting approaches of (I) and (II) respectively, where in approach (I) the contribution purely from PCBM
clusters are resolved and model fitted while in approach (II) the structure of PCBM clusters and
PCPDTBT polymer crystals are simultaneously modeled in a nonlinear least-squares fitting.
Thin films φPCBM (I)
(%)
ξPCBM (I)
(nm)
Rg-PCBM (I)
(nm)
φPCBM (II)
(%)
ξPCBM (II)
(nm)
Rg-PCBM (II)
(nm)
BL78_3%DIO 35 5.0 11.3 34 6.1 14.9
BL78_5%DIO 37 6.1 14.9 37 6.6 16.1
BL78_10%DIO 36 6.7 16.4 37 6.7 16.4
0.02 0.04 0.06 0.08
0.1
1
10
Pure PCBM (BL78_3% DIO)
Pure PCBM (BL78_5% DIO)
Pure PCBM (BL78_10% DIO)
I(Q
) (a
.u.)
Qx (Å
-1)
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S15
Scattering intensities calculated by various terms of SAXS models
Fig. S8 (a) GISAXS intensity calculated by model fitting for the BL78_w/o DIO film (red square
scatter) constituted of the intensities determined by Debye-Bueche model (blue line) and Fractal
aggregation model (green line). (b) GISAXS intensity calculated by model fitting for the BL78_3%DIO
film (green trangle scatter) constituted of the intensities of PCPDTBT fractal aggregation (blue line) and
PCBM fractal aggregation model (red line).
a b
0.01 0.1
0.1
1
10
100
I(Q
) (a
.u.)
Qx (Å
-1)
BL78_w/o DIO
Debye-Bueche model
Fractal aggregation model
0.01 0.1
0.1
1
10
100
I(Q
) (a
.u.)
Qx (Å
-1)
BL78_3% DIO
PCPDTBT fractal aggregation
PCBM fractal aggregation
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S16
The additive effect based on different D-A copolymer/fullerene BHJs
Fig. S9 Scheme of different D-A copolymer/PCBM BHJ nanostructures processed without (a,b) and
with (c) additives. Different structures (a) and (b) would evolve to the similar structure (c). The (a)
represents a BHJ of lower crystallinity polymers such as PCPDTBT, which shows uniformely dispersed
PCBM in PCPDTBT amorphous matrix. The (b) represents a BHJ with higher crystallinity polymer
such as that of ref.11,14-15 which reveals large-scaled PCBM domains with ~hundreds of nanometers
(confined by polymer aggregated crystallites). When processed with additive, both of BHJs would attain
optimized nanostructure with 10-20 nm polymer and PCBM aggregated domains. Microscopic
observation of (a) and (c) concludes the growth of PCBM clusters10,17
while that of (b) and (c)
oppositely concludes the suppresssed PCBM clusters due to the additive effect.11,14-15
Additive effect
a
b
c
Large-scale PCBM domains
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S17
Interaction among additive molecules, PCBM and polymer during solvent evaporation
In the early stage of drying process, the dominating high-boiling additives facilitate the larger polymer
crystal network with dense fractal structure. In solution the spatial distribution of the remaining
polymers (amorphous chains) and the additive molecules (surrounding around polymer crystals or partly
intercalated with amorphous chains) are still fractal like within the formed polymer crystallites.
Therefore, the PCBM molecules are arranged to the fractal domain because they are selectively
dissolved in the additive molecules. In the late stage, the additives evaporate and finally the bi-
hierarchical structures of polymer and PCBM form. According to the above mechanism, the intrinsic
properties of polymer such as crystallinity, solubility, etc. would affect the nanostructural evolution. For
example, the lower the solubility of polymer in host solvent or additives, the more significant
segregation of polymer crystallites (from solution to dense fractal structure) during the early stage of
drying process. Such significant fractal-aggregation of polymer crystals would affect the subsequent
arrangement of PCBM (selectively dissolved in additives) to the fractal domains surrounding the
polymer crystals. Hence the solubility of polymer may also be a critical factor affecting the optimized
loading ratio of PCBM for constructing continuous electron transporting pathway.
Fig. S10 Schematic representation of the fractal-like additives (red circles) which selectively dissolve
PCBM confined within the polymer crystallites. The PCBM is then subsequently arranged into fractal-
like aggregation during additive evaporation.
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Correlation between the quantitative bi-hierachical nanostructures and optoelectronic and
photovoltaic properties
Fig. S11 Photocurrent density-voltage curves of PCPDTBT/PCBM (78% PCBM) solar cells processed
without and with different amount of DIO, i.e. 0.5%, 3%, 5% 10% respectively.
Table S3 Photovoltaic characteristics of PCPDTBT/PCBM (78%PCBM) solar cells processed without
and with different amounts of DIO.
Devices Voc (volts) Jsc (mA/cm2) FF PCE (%)
BL78_w/oDIO 0.67 11.0 0.44 3.2
BL78_0.5%DIO 0.65 12.5 0.44 3.6
BL78_3%DIO 0.62 14.9 0.56 5.2
BL78_5%DIO 0.62 14.1 0.56 4.9
BL78_10%DIO 0.61 13.0 0.51 4.0
0.0 0.2 0.4 0.6-16
-12
-8
-4
0
4
Cu
rre
nt
De
ns
ity
(m
A/c
m2)
Voltage (volts)
BL78_w/o DIO
BL78_0.5% DIO
BL78_3% DIO
BL78_5% DIO
BL78_10% DIO
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Fig. S12 Pictures of PCPDTBT/PCBM (78%PCBM) film processed with 10% DIO, i.e.
BL78_10%DIO. (a) as-cast film and (b) stored in golve box overnight. The inset in (b) shows the optical
microscopic image of the micro-scale segregated particle on the film.
Fig. S13 UV-Vis absorption spectrum of PCPDTBT/PCBM (78% PCBM) blend films processed
without and with different amounts of DIO, i.e. 0.5%, 3%, 5% 10% respectively.
400 500 600 700 800 900 1,000
0.2
0.3
0.4
0.5
0.6
Ab
so
rban
ce
Wavelength (nm)
BL78_w/o DIO
BL78_0.5% DIO
BL78_3% DIO
BL78_5% DIO
BL78_10% DIO
250 μm
250 μm
a
b
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Fig. S14 Current density-voltage curves of (a) electron only and (b) hole only device of BL78_w/oDIO
and BL78_3%DIO respectively. The solid line represent the fitting curves following the field-dependent
space carrier limited current (SCLC) method as shown below:22
where J is the current density, ε is the relative permittivity, ε0 is the vacuum permittivity, Veff is the
effective voltage, L is the film thickness, E0 is the characteristic electric field, and μ is the mobility.
Table S4 Electron and hole mobility obtained from SCLC measurement of BL78_w/oDIO and
BL78_w/oDIO films respectively.
Thin film μe (cm2/Vs) μh (cm
2/Vs)
BL78_w/oDIO 2.3×10-5
1.4×10-5
BL78_3%DIO 3.8×10-4
2.6×10-5
a b
0 1 2 310
-5
10-4
10-3
10-2
10-1
100
101
102
BL78_w/o DIO
BL78_3% DIOC
urr
en
t D
en
sit
y (
mA
/cm
2)
Veff
(volts)
0 1 2 310
-5
10-4
10-3
10-2
10-1
100
101
102
BL78_w/o DIO
BL78%_3% DIO
Cu
rren
t D
en
sit
y (
mA
/cm
2)
Veff
(volts)
LE
VV
LJ eff
0
2
3
0 89.0exp8
9
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Photovoltaic properties of PCPDTBT/PCBM blend films with different PCBM loading amounts
Fig. S15 Photocurrent density-voltage curves of PCPDTBT/PCBM solar cells with different
PCPDBT/PCBM blending ratios, i.e. 33%, 50%, 78% PCBM and processed with 3% DIO.
Table S5 Photovoltaic characteristics of PCPDTBT/PCBM solar cells processed with different blending
ratios and processed with 3% DIO.
Devices Voc (volts) Jsc (mA/cm2) FF PCE (%)
BL33_3%DIO 0.55 6.7 0.52 1.9
BL50_3%DIO 0.63 11.5 0.50 3.6
BL78_3%DIO 0.62 14.9 0.56 5.2
0.0 0.2 0.4 0.6-16
-12
-8
-4
0
4 BL33_3% DIO
BL50_3% DIO
BL75_3% DIO
Cu
rre
nt
De
ns
ity
(m
A/c
m2)
Voltage (volts)
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References
1. Y.-S. Sun, S.-W. Chien and J.-Y. Liou, Macromolecules, 2010, 17, 7250.
2. G. Renaud, R. Lazzari and F. Leroy, Surf. Sci. Rep., 2009, 64, 255.
3. Y.-C. Huang, C.-S. Tsao, C.-M. Chuang, C.-H. Lee, F.-H. Hse, H.-C. Cha, C.-Y. Chen, T.-H. Lin,
C.-J. Su, U.-S. Jeng and W.-F. Su, J. Phys. Chem. C 2012, 116, 10238.
4. H.-C. Liao, C.-S. Tsao, T.-H. Lin, C.-M. Chuang, C.-Y. Chen, U.-S. Jeng, C.-H. Su, Y.-F. Chen
and W.-F. Su, J. Am. Chem. Soc. 2011, 133, 13064.
5. W.-R. Wu, U.-S. Jeng, C.-J. Su. K.-H. Wei, M.-S. Su, M.-Y. Chiu, C.-Y. Chen, W.-B. Su and C.-H.
Su, A.-C. Su, ACS Nano, 2011, 5, 6233.
6. A. Zen, M. Saphiannikova, D. Neher, J. Grenzer, S. Grigorian, U. Pietsch, U. Asawapirom, S.
Janietz, U. Scherf, I. Lieberwirth and G. Wegner, Macromolecules, 2006, 39, 2162.
7. W. Ma, J. Y. Kim, K. Lee and A. J. Heeger, Macromol. Rapid Commun., 2007, 28, 1776.
8. A. Zen, J. Pflaum, S. Hirschmann, W. Zhuang, F. Jaiser, U. Asawapirom, J. P. Rabe, U. Scherf and
D. Neher, Adv. Funct. Mater., 2004, 14, 757.
9. H. Yang, T. J. Shin, Z. Bao and C. Y. Ryu, J. Polym. Sci., Part B: Polym. Phys. 2007, 11, 1303.
10. J. K. Lee, W. L. Ma, C. J. Brabec, J. Yuen, J. S. Moon, J. Y. Kim, K. Lee, G. C. Bazan and A. J.
Heeger, J. Am. Chem. Soc., 2008, 130, 3619.
11. M.-S. Su, C.-Y. Kuo, M.-C. Yuan, U.-S. Jeng, C.-J. Su and K.-H. Wei, Adv. Mater., 2011, 23, 3315.
12. M. Morana, H. Azimi, G. Dennler, H.-J. Egelhaaf, M. Scharber, K. Forberich, J. Hauch, R.
Gaudiana, D. Waller, Z. Zhu, K. Hingerl, S. S. van Bavel, J. Loos and C. J. Brabec, Adv. Funct.
Mater., 2010, 20, 1180.
13. M. R. Hammond, R. J. Kline, A. A. Herzing, L. J. Richter, D. S. Germack, H.-W. Ro, C. L. Soles,
D. A. Fischer, T. Xu, L. Yu, M. F. Toney and D. M. DeLongchamp, ACS Nano, 2011, 5, 8248.
14. Y. Liang, Z. Xu, J. Xia, S.-T. Tsai, Y. Wu, G. Li, C. Ray and L. Yu, Adv. Mater., 2010, 22, E135.
Electronic Supplementary Material (ESI) for Energy & Environmental ScienceThis journal is © The Royal Society of Chemistry 2013
S23
15. J. S. Moon, C. J. Takacs, S. Cho, R. C. Coffin, H. Kim, G. C. Bazan and A. J. Heeger, Nano. Lett.,
2010, 10, 4005.
16. S. lbrecht, W. Schindler, J. Kurpiers, J. Kniepert, J. C. Blakesley, I. Dumsch, S. Allard, K.
Fostiropoulos, U. Scherf and D. Neher, J. Phys. Chem. Lett., 2012, 3, 640.
17. Y. Gu, C. Wang and T. P. Russel, Adv. Energy Mater., 2012, 6, 683.
18. S. Cho, J. K. Lee, J. S. Moon, J. Yuen, K. Lee and A. J. Heeger, Org. Electron., 2008, 9, 1107.
19. C.-S. Tsao, M. Li, Y. Zhang, J. Leao, W.-S. Chiang, T.-Y. Chung, Y.-R. Tzeng, M.-S. Yu and S.-H.
Chen, J. Phys. Chem. C, 2010, 114, 19895.
20. P. Pfeifer, F. Ehrburger-Dolle, T. P. Rieker, M. T. Gonzalez, W. P. Hoffman, M. Molina-Sabio, F.
Rodriguez-Reinoso and P. W. Schmidt, D. J. Voss, Phys. Rev. Lett., 2002, 88, 11502.
21. S. J. Lou, J. M. Szarko, T. Xu, L. Yu, T. J. Marks and L. X. Chen, J. Am. Chem. Soc., 2011, 133,
20661.
22. M. Lenes, M. Norana, C. J. Brabec and P. W. M. Blom, Adv. Funct. Mater., 2009, 19, 1106.
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