1

High-Performance Ternary Polymer Solar Cells Using Wide Bandgap Biaxially-Extended

Octithiophene-Based Conjugated Polymers

Chang-Hung Tsai,1+ Yu-An Su,1+ Po-Chen Lin,1 Chien-Chung Shih,1 Hung-Chin Wu,1 Wen-

Chang Chen,1,2 and Chu-Chen Chueh1,2*

1 Department of Chemical Engineering, National Taiwan University, Taipei 106, Taiwan

2 Advanced Research Center of Green Materials Science & Technology, Taipei 10617, Taiwan

+ These authors are equally contributed to this work.

*Corresponding authors. E-mail: cchueh@ntu.edu.tw

Keywords: Biaxially-extended polymers, wide bandgap, organic solar cell, ternary

Abstract

Ternary organic photovoltaic (OPV) has recently attracted intense research attention since it

has been proven as an effective approach to enhance the device performance. We herein describe

a new strategy to realize high-performance ternary OPVs by using biaxially-extended

octithiophene (8T)-based wide bandgap (Eg) conjugated polymers as the third photoactive

component. Owing to the π-π transition of the conjugated biaxially-extended side-chains, such

polymers exhibit intense absorption in the near-ultraviolet region in addition to the original intra-

charge transfer (ICT) feature arising from the main backbone, revealing a new molecular design

for wide Eg polymers. By further tailoring the polymer backbone with the p-type moieties such as

thiophene (T) or thienothiphene (TT), wide Eg (~2.0 eV) polymers, P8TT and P8TTT, with

absorption wavelengths below 650 nm were prepared, showing very complementary absorption

to the spectra of both state-of-the-art fullerene- (PTB7-Th:PC71BM) and non-fullerene-based

(PBDB-T:ITIC) bulk-heterojunction (BHJ) systems. As providing suitable energy levels, P8TTT

was demonstrated to respectively enable 7.58% and 6.60% enhancement in power conversion

efficiency (PCE) for its derived fullerene- and non-fullerene-based ternary blends with only a

Electronic Supplementary Material (ESI) for Journal of Materials Chemistry C.This journal is © The Royal Society of Chemistry 2018

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small adding amount (10 wt%). This study manifests a new perspective in wide Eg material

design for realizing efficient ternary BHJ systems.

1. Introduction

The progress of solution-processable organic photovoltaic cells (OPVs), as one of the most

promising green photovoltaic techniques nowadays, has been reaccelerated in the past few years

owing to the breakthrough in the exploitation of novel non-fullerene acceptors (NFAs).[1, 2] As

compared to the typical fullerene derivatives, the newly exploited NFAs generally possess more

intense light-harvesting capability and tailorable light-absorption region, which indirectly

promotes the recent fashion of ternary OPVs.1, 2

Originally, the photoactive layer of OPVs consists of a donor (D)/acceptor (A) binary blend,

wherein a nanoscale D-A bulk-heterojunction (BHJ) is formed to facilitate the dissociation of

photoexciton.3,4 However, adding an additional component into a binary BHJ system to either

extend its overall light-harvesting window or optimize its nanoscale phase separation is recently

demonstrated as an effective strategy to further enhance the power-conversion-efficiency (PCE)

of the derived devices.5, 6 Noteworthily, compared to the binary BHJ system, the ternary BHJ

system might also possess higher charge extraction efficiency as considering its better energy-

level cascade for charge transport and dissociation, thus reducing the overall potential loss of

device.7

The ternary OPVs can be classified according to the type of the third component added,

including donors,8-11 acceptors,12-14 inorganic materials,15, 16 and nonvolatile additives17, 18.

Among which, adding a second functional D or A is the most commonly adopted method thus far.

For example, at the earlier stage, owing to the poor light absorption of the fullerene derivatives

3

like [6,6]-phenyl C61/C71 butyric acid methyl esters (PC61BM/PC71BM),19 adding a third

component with complementary absorption to the host donor of a fullerene-based BHJ system is

widely employed to extend its light absorption across the solar spectrum to realize an improved

performance.20-22 Furthermore, the third photoactive component might also prevent the

aggregation of fullerene derivatives to improve device’s thermal stability to a certain degree.20-23

Similar principle can also be applied to the recent surge of NFA-based BHJ systems but with

a slightly different focus. Taking the representative 3,9-bis(2-methylene-(3-(1,1-

dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2’,3’-d’]-s-

indaceno[1,2-b:5,6-b’]dithiophene) (ITIC) derivatives as an example, such NFAs generally

possess a small bandgap (Eg) of ~1.6 eV, providing intense light absorption across the

wavelengths of 600-850 nm, which is complementary to the absorption spectrum of the state-of-

the-art polymers donors with a medium Eg of ~1.7-1.8 eV.1, 2, 22 Therefore, the third component

added for the ITIC-based BHJ systems is generally required to possess a Eg property (>1.9 eV) so

as to realize a panoramic absorption of solar spectrum.24 In addition, such wide Eg component

might afford the Förester resonance energy transfer (FRET) to the pristine photoactive

components, further enhancing the light-harvesting efficiency.25 As the current record PCEs of

OPVs are realized in the NFA-based BHJ systems, the further reduction of energy loss through

the ternary cascade energy levels is also specifically noticed.26, 27

In this regard, various wide Eg third components, including NFAs and polymer donors, have

been recently exploited to realize high-performance ternary OPVs.28-33 Based on similar principle,

we herein manifested a new perspective in wide Eg material design for efficient ternary BHJ

systems by using p-type biaxially extended octithiophene (8T)-based alternating copolymers as

the third photoactive component (Figure 1a). Owing to the π-π transition of the biaxially

extended, conjugated side-chain groups, the derived 8T-based polymers can exhibit intense

4

absorption in the near-ultraviolet region in addition to the original intra-charge transfer (ICT)

feature arising from the main backbone. By further tailoring the polymer backbone with p-type

moieties such as thiophene (T) or thienothiphene (TT), wide Eg (~2.0 eV) polymers, P8TT and

P8TTT, with absorption wavelengths below 650 nm were prepared,29 showing very

complementary absorption to the spectra of both state-of-the-art fullerene- and NFA-based BHJ

systems as shown in Figure 1b and 1c. This result reveals a new molecular design of wide Eg

polymers for pairing with typical BHJ systems. As providing suitable energy levels, P8TTT was

demonstrated as an efficient third photoactive component to simultaneously enhance the

performance of both state-of-the-art binary fullerene- and NFA-based BHJ systems with only a

small adding amount (10 wt%). We also characterized the morphology and optoelectronic

properties of the 8T-based ternary BHJ systems to clarify the roles that the 8T-based polymers

play in performance enhancement.

2. Experimental Sections

2.1. Materials

The polymer donors, PTB7-Th and PBDB-T, were purchased from 1-Material (Canada) and

used without further purification. The 8T-based polymers, P8TT and P8TTT, were synthesized

according to the previous reported procedures.29

2.2. Device fabrication and characterization

The studied inverted OPVs were fabricated in the device configuration of ITO

glass/ZnO/PFN/BHJ/MoO3/Ag. The ITO glass substrates were first cleaned by sonication with

detergent, deionized water, acetone, and isopropyl alcohol for 15 mins each step. Then, the

substrates were dried by N2 flow, followed by plasma treatment for 10 min. The ZnO precursor

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was prepared by dissolving 0.1 g mL-1 zinc acetate in 2-methoxyethanol with 28 μL of

ethanolamine. The ZnO layer was deposited onto the ITO substrates by a spin-coating method

and annealed at 200 oC for 30 min in air. The MeOH solution of PFN (0.5 mg mL-1) containing 2

vol% acetic acid was spin-coated onto the ZnO-coated substrate in a N2 glovebox. The binary

fullerene- and NFA-based BHJ precursor solutions were prepared by dissolving PTB7-

Th:PC71BM and PBDB-T:ITIC in a 1:1.5 and 1:1 weight ratio in CB with DIO additive (CB/DIO

= 97/3 and 99.5/0.5, v/v), respectively. The ternary fullerene- and NFA-based BHJ precursor

solutions were prepared by adding P8TT/P8TFT with weight ratio of 0.1 to the host polymer into

the pristine binary BHJ systems, respectively. All these precursor solutions were vigorously

stirred at 60°C for 8 hr in a N2 glovebox. ~100 nm BHJ layers were spin-coated onto the PFN

layer. For the NFA-based BHJ system, the films were further annealed at 90°C for 10 min in a N2

glovebox. Finally, a 8-nm-thick MoO3 and a 10-nm-thick Ag were thermally deposited under

high vacuum (<10-6Torr) to complete the top electrode. The device’s active area was 10 mm2.

The current-voltage (J-V) characteristics of the fabricated OPVs was recorded using a computer-

controlled Keithley 2400 source measurement unit (SMU) under AM1.5 G, 100 mW cm-2

illumination by a Newport LCS-100 simulator under. The illumination intensity was calibrated

using a Si photo-diode detector with KG-5 filter. The external quantum efficiency (EQE) was

recorded using a monochromatic light from a xenon lamp during the illumination (QE-R,

Enlitech Co., Ltd.). The light intensity at each wavelength was calibrated by using a standard

single crystal Si photovoltaic cell from 300 to 800 nm.

2.3. Morphological characterization

The transmission electron microscopy (TEM) images were obtained using a FEI Tecnai G2

F20 instrument operating at a voltage of 200 kV with a Gatam dual vision charge coupled device

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(CCD) camera. Grazing incidence wide-angle X-ray scattering (GIWAXS) data were conducted

on the beamline BL17A1 with a wavelength of 1.322 Å in the National Synchrotron Radiation

Research Center (NSRRC), Taiwan. Contact angle (CA) was measured for the surface energy

analyses.

3. Results and discussion

3.1. Optical properties of the Ternary BHJs using 8T-based polymers

As reported in the literature, side-chain engineering plays a significant role in polymer

design, which can improve the overall solubility of the prepared polymers, modulate the

intra/inter-molecular packing pattern, and tune the associated optoelectronic properties.30

Recently, Chen et al. have developed a series of biaxially-extended thiophene-based conjugated

polymers, wherein an unique conjugated side-chain is employed with a purpose to form a pseudo

two-dimensional polymer backbone.31, 32 It is interesting to note that owing to the *

electronic transition of the biaxially extended, conjugated side-chain groups, the derived

polymers exhibited intense absorption in the near ultraviolet region (300-450 nm), especially

when the targeted polymers consisted of biaxially-extended octithiophene (8T) moiety.29, 31

It thus will be of great interest if one can develop a wide Eg (~2.0 eV) 8T-based polymer

since it will possess an intense and broad absorption covering the short wavelength region, being

greatly complementary to the absorption spectra of both state-of-the-art fullerene- and NFA-

based BHJ systems.1, 2, 34 Note that the homo-polymer consisting of only 8T moiety is difficult to

obtain due to the large steric hindrance of its bulky conjugated side chains. Therefore, it becomes

a more feasible way to synthesize wide Eg 8T-based polymers by copolymerizing 8T with a

spacer like T or TT units, and thus P8TT and P8TTT are accordingly developed, respectively.

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Presented in Figure 1b are the UV-Vis absorption spectra of PC71BM, ITIC, the host

polymers (PTB7-Th and PBDB-T), and the studied 8T-based polymers (P8TT and P8TTT), and

their absorption coefficient were presented in Figure S1a-b. As shown, besides the prominent

absorption in the near ultraviolet region (300-450 nm), both 8T-based polymers exhibited an

absorption band across from 450 to 650 nm, which is clearly resulted from the intermolecular

interaction (ICT) of polymer backbone. However, their overall light-harvesting window is still

constrained below 650 nm, serving as a promising third photoactive component for both PTB7-

Th:PC71BM and PBDB-T:ITIC BHJ blends (Figure 1b). This advantage is also reflected in the

UV-vis absorption spectra shown in Figure S1c-d, wherein the absorption in the near ultraviolet

region was clearly increased for the ternary BHJ blends incorporating only a small amount (10

wt% relative to the host polymer) of 8T-based polymers as compared to the pristine binary BHJ

blends.

3.2. Electrical and photoluminescence analysis

The highest occupied molecular orbital (HOMO) energy levels of the studied polymers were

measured by the cyclic voltammetry (CV) using ferrocene as a standard reference as shown in

Figure S2. The HOMO level of PTB7-Th, PBDB-T, P8TT, and P8TTT is estimated to be -5.02,

-5.00, -5.29, and -5.17 eV while the corresponding lowest occupied molecular orbital (LUMO)

energy level deduced from the optical bandgap is -3.40, -3.21, -3.31, and -3.16 eV, respectively

(Table S1). Plotted in Figure 2a are the energy-level diagrams of the studied ternary BHJ blends,

wherein the energy levels of PCBM and ITIC are cited from the literature.37, 38

To testify the potential of using 8T-based polymers to constitute efficient ternary OPVs,

photoluminescence (PL) of the binary and ternary blends were compared to probe if there is any

improvement in the photoexciton dissociation rate. As shown in the Figure 2b (top), for the

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fullerene-based BHJ systems, the PL of PTB7-Th exhibited a higher quenching degree in the

ternary blends upon excitation at 550 nm than in the pristine binary blend. Similar phenomena

were also observed in the NFA-based BHJ systems, wherein the P8TTT-based blends showed a

higher quenching degree than the P8TT-based blends (Figure 2b (bottom)). The better PL

quenching observed in all the ternary blends suggesting the facilitated photoexciton dissociation

as compared to the pristine binary BHJ blends that is beneficial for reducing carrier

recombination. In principle, the possible reasons for the improved charge dissociation observed

in the ternary blends can be correlated to better cascade energy level or more optimized

morphology. However, in our case, the 8T-based polymers seem to facilitate the charge

dissociation through the parallel-like BHJ configuration and a more optimized morphology (will

be discussed later) in both fullerene- and NFA-based BHJ rather than through better cascade

energy levels (Figure 2a).39, 40

Besides facilitating the charge dissociation, the wide Eg third component might enable

Förester resonance energy transfer (FRET) to the pristine photoactive components to enhance the

light-harvesting efficiency as mentioned earlier. Figure S3a and S3b illustrated the

superimposition of the UV-vis spectra of PTB7-Th/PBDB-T and the PL spectra of 8T-based

polymers, respectively. As can be seen, the emission of the 8T-based polymers (630 nm for P8TT

and 616 for P8TTT) can be well absorbed by PTB7-Th/PBDB-T, suggesting the feasible FRET

between them.41 Figure S3c and S3d compared the PL spectra of the simplex polymer films and

the studied blends (PTB7-Th/8T-based polymers (10 wt%) and PBDB-T/8T-based polymers (10

wt%)). As shown, only emission from the host polymers (765 nm for PTB7-Th and 680 nm for

PBDB-T) could be observed for the blends and the emission from both 8T-based polymers was

disappeared. This result further confirmed the FRET between them, which is beneficial to raise

the overall light-harvesting efficiency of the derived ternary BHJ blends.

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3.3. Performance of solar cells

We next examined the photovoltaic performance of the studied binary/ternary BHJ blends in

an inverted structure (see Experimental Section). Presented in Figure 3a and 3b were their

measured J-V curves and the resultant photovoltaic parameters including open-circuit voltage

(Voc), short-circuit current (Jsc), and fill factor (FF) were summarized in Table 1. As shown, the

8T-based polymers indeed served as an active third component (10 wt% to the host polymer) to

enhance the performance for both fullerene- and NFA-based systems, especially for P8TTT. For

the fullerene-based system, the P8TTT-based ternary OPV delivered a best PCE of 9.08 % with a

Voc of 0.802 V, a Jsc of 17.26 mA cm-2, and a FF of 65.6 while the P8TT-based ternary cell

yielded a best PCE of 8.59 % with a Voc of 0.811 V, a Jsc of 16.81 mA cm-2, and a FF of 63.0,

exceeding the performance (PCE: 8.44%) of the parent binary device. Similarly, for the NFA-

based system, the P8TTT-based ternary OPV delivered a best PCE of 10.01 % with a Voc of

0.883 V, a Jsc of 16.93 mA cm-2, and a FF of 67.0 while the P8TT-based ternary cell yielded a

best PCE of 9.45 % with a Voc of 0.882 V, a Jsc of 17.01 mA cm-2, and a FF of 63.1,

outperforming the performance (PCE: 9.39%) of the parent binary device.

As compared to the parent binary devices, the Vocs of all ternary devices were clearly

increased owing to the deeper-lying HOMO levels of 8T-based polymers than the host polymers.

In addition, their Jscs were also increased as expected as a result of complementary absorption

and possible FRET contributed from the 8T-based polymers. To confirm this, the external

quantum efficiency (EQE) of the studied devices was measured and the normalized curves were

presented in Figure 3c and 3d for fair comparisons. As shown, the photo-response contributed

from the near ultraviolet region (300-450 nm) was clearly increased, in well congruence with the

UV-vis absorption spectra shown in Figure 3c and 3d. This result clearly validates our

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hypothesis to increase device’s photocurrent by enhancing the absorption in the near ultraviolet

region enabled by side-chain engineered conjugated polymers.

It is worthy to note that the overall adding amount of 8T-based polymers is limited to 10

wt%. The performance of the ternary OPVs will not be clearly increased if the adding amount of

8T-based polymers goes above 10 wt%. Such deficiency might arise from their bulky, large side-

chain groups that might cause certain incompatibility at the associated interface when its loading

amount exceeds a certain degree. Such disadvantage reveals the necessity of further side-chain

engineering of 8T-based polymers, such better side-chain conjugation.

3.4. Charge recombination of device

As seen, the FF of the 8T-based ternary devices showed an obvious increase compared to

the parent binary devices, which might be correlated to better charge dissociation as discussed

earlier. Whereas, the P8TT-based devices only yielded comparable FFs to the parent binary

devices. This discrepancy is plausibly correlated to the spacing between the 8T groups, for which

the larger spacer between 8T moieties in P8TTT than in P8TT is more beneficial to the nanoscale

phase separation in the blend. It has been acknowledged that the FF is a more complicated

function of charge kinetics in device as well as the nanoscale phase separation of the blends.42, 43

In order to better understand the charge recombination behavior in our fabricated OPVs, the

photocurrent density (Jph) as a function of effective voltage (Veff) was investigated and the

corresponding plots in double logarithmic coordinates were shown in Figure 3e and 3f for the

fullurene- and NFA-based systems, respectively. Note that the Jph is calculated from Jph = JL - JD,

where JL and JD respectively represent the current densities measured under AM1.5G

illumination and in the dark, while Veff is defined as Veff = V0 - Vbias, where V0 is the voltage as the

Jph is zero and Vbias is the applied bias.

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In principle, at the high bias region, the Jph reached a saturation current density (Jsat),

representing the condition that charges were fully dissociated and swept out by the high internal

electric field. Therefore, the charge dissociation probability can be evaluated by the ratio of

Jph/Jsat under different external biass. For example, at Veff = 0.1 eV, the estimated charge

dissociation probability for PTB7-Th:PC71BM and P8TT-/P8TTT-based ternary devices was

0.49, 0.55, and 0.63, respectively. While the value for the PBDB-T:ITIC and P8TT-/P8TTT-

based ternary devices was 0.56, 0.59, and 0.74, respectively. As shown, all the ternary OPVs

exhibited better charge dissociation than the parent binary devices, especially for the P8TTT-

based devices, affirming the facilitated photoexciton dissociation in the ternary blends. This

result suggests that the bulky, large side-chain groups can still possess well miscibility with the

parent components when its blending ratio is within the optimized value.

3.5. Morphology of BHJs

The morphology of the blends was next investigated regarding the crucial role that the

molecular order/disorder structural interdigitation of the BHJ films plays in performance. The

molecular packing features and stacking orientations of the studied BHJ films were first studied

by the grazing-incidence wide-angle X-ray scattering (GIWAXS) and Figure 4a depicted their

two-dimensional (2D) GIWAXS patterns. For the PTB7-Th:PC71BM blend, a clear (100) peak

was observed at the in-plane direction, corresponding to the lamellar packing of PTB7-Th.41 Also,

a ring signal at q = ~1.3 Å-1 belongs to the PC71BM aggregates.42 As for the PBDB-T:ITIC blend,

a (100) lamellar diffraction signal of PBDB-T was similarly observed in both binary and ternary

blends.46 Note that there is no noticeable change after adding 8T-based polymers (10 wt%

relative to the PTB7-Th/ or PBDB-T) into the blend.

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To better understand the morphology, one-dimensional (1D) profile extracted from 2D

pattern, full width half-maximum (FWHM) of (100) peak, and pole plot of (100) signal are

subsequently analyzed. Figure 4b and 4c presented the detailed crystallographic properties of the

studied blends and their relevant crystallographic parameters were summarized in Table S2. For

the PTB7-Th:PC71BM BHJ film (left in Figure 4b), the diffraction peak at qy = 0.30 Å-1 is

assigned to the (100) signal of PTB7-Th with a lamellar packing spacing of 20.9 Å while the

peaks at qy = 0.59 Å-1 and 1.34 Å-1 are attributed to PC71BM. These ordering features are

comparable to that of X-ray characteristics in literatures.44, 45 The molecular packing features of

PTB7-Th in the ternary blends were further investigated and both FWHM as well as azimuthal-

angle pole plot analyses were applied to its (100) peak. As shown, similar crystallite size (~ 8 nm)

and packing orientation were observed, indicating the inter-chain organization of PTB7-Th was

not greatly interfered by P8TT or P8TTT.

Similar crystallographic behaviors were found for the PBDB-T:ITIC BHJ film (Figure 4c).

Lamellar packing distance of PBDB-T is estimated to be 21.7 Å (corresponding diffraction signal

at qy = 0.29 Å-1) and the (010) peak of ITIC is detected at qz = 1.56 Å-1 (Figure S4). Alike to the

PTB7-Th:PC71BM case, the stacking ordering (crystallite size of ~ 9 nm) of PBDB-T is

maintained in the ternary blends. However, it is worthwhile to notice that its packing orientation

is slightly improved after blending with the 8T-based polymers, which might facilitate charge

transport in the ternary blends. This result thus suggests there is a compromise between the

loading amount of 8T-based polymers in the ternary blends and its large size of side-chain group.

The hindrance effect arising from the bulky side-chain group of 8T-polymer can be relieved by

optimizing its loading amount in the ternary blend or via better side-chain design.

13

The morphology of these studied blends was then investigated by TEM. Shown in Figure 5a

and 5b were the TEM images of the parent binary blends. For both fullerene- and NFA-based

systems, larger fibrillar structures were observed in the ternary blends (Figure 5c-e and 5d-f),

which might afford more homogenous pathways for charge transport and dissociation at the

associated D/A interface.29, 47 Moreover, the surface energy of the studied BHJ blends was

investigated to understand if there is any surface textural change in the ternary blend. The CA of

each individual component was first measured to assess the surface energies via Owen-Wendt

model.48 For the fullerene-based system, the estimated surface energies for the pristine PTB7-Th

was 43.28 mJ m-2 (Table S3) and the surface energy of the PTB7-Th:PC71BM blend was

decreased to 33.23 mJ m-2. However, after adding P8TT and P8TFT, the surface energies of the

blends was dramatically enhanced to 44.08 mJ m-2 and 50.06 mJ m-2, respectively, validating the

distribution of 8T-based polymers at the pristine PTB7-Th/PC71BM interfaces. A similar

phenomenon was also observed in the NFA-based systems. Combing these results, the positive

role that the P8TT and P8TFT play in the ternary blend in promoting efficient charge generation,

transport, and dissociation can be verified.

4. Conclusion

In this work, we described the effectiveness of wide Eg polymers based on biaxially

extended 8T-based alternating copolymers to serve as an efficient third component to improve

the performance of both fullerene- and NFA-based BHJ systems. Owing to its uniquely biaxially

extended, conjugated side-chain groups, the derived 8T-based polymers show intense absorption

in the near-ultraviolet region. By further tailoring the polymer backbone with the p-type moieties

(T and TT), wide Eg (~2.0 eV) polymers (P8TT and P8TTT) with absorption wavelengths below

650 nm were prepared, showing very complementary absorption to the spectra of the state-of-the-

14

art BHJ systems. As providing suitable energy levels, P8TTT was demonstrated to enable 7.58%

and 6.60% enhancement in PCE for its derived PTB7-TH:PC71BM and PBDB-T:ITIC ternary

blends with only a small adding amount (10 wt%). This study manifests a new perspective in

wide Eg material design for realizing efficient ternary BHJ systems

Acknowledgment

The financial support from Ministry of Science and Technology of Taiwan (MOST 106-2218-E-

002-021-MY2 & 107-3017-F-002-001), the Ministry of Education (107L9006), and Top

University Project from National Taiwan University (106R890703 and 107-S-A09) is highly

appreciated.

Supporting Information Available:

Cyclic voltammetry of polymers. Luminescence characteristics and surface energy of binary and

ternary BHJ blends. 1D-GIWAXS linecuts profile.

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Figure 1. (a) Schematic illustration of the device architecture and the chemical structures of the

studied materials. (b) The corresponding UV-vis absorption spectra of the studied materials: (left)

fullerene-based ternary BHJ system and (right) non-fullerene ternary BHJ system.

18

Figure 2. (a) The energy-level diagram and (b) steady-state PL quenching spectra of the studied

(top) fullerene-based binary/ternary blends and (bottom) non-fullerene binary/ternary blends.

19

Figure 3. (a, b) The J-V curves, (c, d) EQE curves, and (e, f) Jph-Veff characteristic of the studied

(a, c, e) fullerene-based binary/ternary blends and (b, d, f) non-fullerene binary/ternary blends.

20

Figure 4. (a) Two-dimensional GIWAXS patterns of the studied BHJ blends. (b) The

corresponding one-dimensional linecuts (left) and normalized PTB7-Th (100) peak (middle) at

in-plane direction, and pole plot of PTB7-Th (100) signal (right) of fullerene-based BHJ blending

films. (c) The corresponding one-dimensional linecuts (left) and normalized PBDB-T (100) peak

(middle) at in-plane direction, and pole plot of PBDB-T (100) signal (right) of non-fullerene-

based BHJ blending films.

21

Figure 5. TEM images of the studied (a, c, e) fullerene-based binary/ternary blends and (b, d, f)

non-fullerene binary/ternary blends.

22

Table 1. The photovoltaic parameters of the fabricated OPV devices.

Active layer Voc

(V)

Jsc

(mA/cm2)

FF

(%)

PCEmax

(%) a

PTB7-Th:PC71BM (1:1.5) 0.795

(0.795±0.004)

16.67

(16.59±0.20)

63.7

(63.80±0.21)

8.44

(8.36±0.18)

PTB7-Th:PC71BM:P8TT

(1:1.5:0.1)

0.811

(0.811±0.003)

16.81

(16.48±0.23)

63.0

(62.94±0.11)

8.59

(8.39±0.22)

PTB7-

Th:PC71BM:P8TTT

(1:1.5:0.1)

0.802

(0.802±0.004)

17.26

(16.99±0.45)

65.6

(64.20±0.10)

9.08

(8.73±0.17)

PBDB-T:ITIC (1:1) 0.859

(0.859±0.005)

16.88

(16.94±0.24)

64.8

(65.08±0.72)

9.39

(9.07±0.33)

PBDB-T:ITIC:P8TT

(1:1:0.1)

0.882

(0.878±0.006)

17.01

(17.04±0.10)

63.1

(62.94±0.77)

9.45

(9.27±0.18)

PBDB-T:ITIC:P8TTT

(1:1:0.1)

0.883

(0.881±0.003)

16.93

(16.97±0.10)

67.0

(66.72±0.52)

10.01

(9.74±0.26)

a The average PCE shown in the parentheses are based on 15 devices.