Bi-hierarchical nanostructures of donor-acceptor copolymer ... · Bi-hierarchical nanostructures of donor-acceptor copolymer and fullerene for high efficient bulk ... when the 2-D

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

Electronic Supplementary Material (ESI) for Energy & Environmental ScienceThis journal is © The Royal Society of Chemistry 2013

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.


S3

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


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.


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


S6

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.


S7

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,


S8

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)


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.


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


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.


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


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


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)



I(Q

) (a

.u.)

Qx (Å

-1)


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


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


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.


S18

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


S19

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


S20

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


S21

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)


S22

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