Thioether Bond Modification Enables Boosted Photovoltaic

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Thioether Bond Modification Enables Boosted Photovoltaic Performance of Non-Fullerene Polymer Solar Cells Youdi Zhang, Ying Wang, Tao Yang, Tao Liu, Yiqun Xiao, Xinhui Lu, He Yan, Zhongyi Yuan, Yiwang Chen, and Yongfang Li ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b11700 • Publication Date (Web): 14 Aug 2019 Downloaded from pubs.acs.org on August 14, 2019

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ACS Applied Materials & Interfaces

Thioether Bond Modification Enables Boosted Photovoltaic Performance of Non-Fullerene Polymer Solar Cells Youdi Zhang,a, b Ying Wang,a Tao Yang,d Tao Liu,*, e Yiqun Xiao,f Xinhui Lu,f He Yan, *, e Zhongyi Yuan, *, a, b Yiwang Chen, *, a, b, c Yongfang Lig a College

of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031, China

b Institute

of Polymers and Energy Chemistry (IPEC), Nanchang University, 999 Xuefu

Avenue, Nanchang 330031, China c

Institute of Advanced Scientific Research (iASR), Jiangxi Normal University, 99 Ziyang

Avenue, Nanchang 330022, China d Key

Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology,

Chinese Academy of Sciences, China e

Department of Chemistry and Hong Kong Branch of Chinese National Engineering

Research Center for Tissue Restoration & Reconstruction, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong f

Department of Physics, Chinese University of Hong Kong, New Territories, Hong Kong,

China. g Beijing

National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids,

Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China

E-mail: [email protected], [email protected], [email protected], [email protected]

1 ACS Paragon Plus Environment

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Abstract A

small-molecule

nonfullerene

acceptor,

ITIC-S,

bearing

fused

heptacyclic

benzodi(cyclopentadithiophene) core with thioether bond substituted thiophene, is designed, synthesized, and compared with its alkyl substituted analog, ITIC2. Compared with ITIC2, ITIC-S with thioether bond exhibits higher electron mobility, slightly larger optical band gap, and similar absorption. The active layer incorporating ITIC-S and the wide-bandgap polymeric donor PBDB-T-SF displays a smaller crystalline coherent length of - stacking, more balanced mobilities, weaker bimolecular recombination, and more effective charge collection than its PBDB-T-SF:ITIC2 counterpart. Accordingly, polymer solar cells incorporating ITIC-S and PBDB-T-SF demonstrate a fill factor (FF) of 66.8% and a champion power conversion efficiency (PCE) of 11.6%, exceeding those of PBDB-T-SF:ITIC2 blend (PCE = 10.1% with FF = 59.7%), which shows that the thioether bond substitution strategy is an easy yet viable way for designing high-performing electron acceptor.

Keyword: small molecular acceptor; thioether bond; n-type organic semiconductor; organic photovoltaics; polymer solar cells


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INTRODUCTION Polymer solar cells (PSCs) offer unique advantages of short energy payback time, sufficient raw materials, eco-friendliness, light weight, semi-transparency, flexibility, coupled with the ease of high-throughput processing.1-15 The active layer in bulk-heterojunction (BHJ) PSC device comprises donors and acceptors.16-19 Fullerene derivatives like PC71BM are the dominating acceptors, benefiting from good electron-accepting capability, high electron mobility, as well as three-dimensional charge transport.20-23 Nevertheless, fullerenes suffer from deficiencies of limited adjustability of chemical structures and energy levels, weak light absorption, and thermal instability.24, 25 Consequently, nonfullerene acceptors gain favor in the study of polymer solar cells.26-40 The small-molecule nonfullerene acceptors (NFA) with fused-ring, like ITIC,41 typically comprise electron-donating fused-ring core substituted by side chains, flanked with two termini of strong electron-accepting ability. Fused-ring core, termini, and side chain could be altered to boost the acceptor’s performance.42-45 Although side chains exert minor influence on the optoelectronic potentials, they have a more evident influence on intermolecular interactions, which existed between adjacent acceptor molecules and between donor and acceptor. Side chains, hence, can alter solubility, mobility, crystallinity, as well as active-layer morphology. Polymeric donors bearing conjugated substituents, namely, 2D conjugated polymeric donors, are extensively utilized in PSCs, as they usually outcompete their 1D conjugated analogs.46,

47

Encouraged by the effectiveness of 2D-conjugation strategy in donors, ITIC2

was designed by introducing conjugated side chains into the core of ITIC1, which extended the intramolecular conjugation, and promoted intermolecular interaction and π–π overlap.

42

ITIC2 displayed a PCE of 11.0% with FF of 63.0% using polymer FTAZ as the donor, as opposed to FTAZ: ITIC1 with PCE of 8.54% and FF of 56.4%. However, the FF of 63.0%, 3 ACS Paragon Plus Environment


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far from ideal value, still limited the overall PCE. 2D conjugated acceptors have potential in constructing high-performance solar cells but still lacks concern and investigation. Herein, we designed a new NFA, ITIC-S (Scheme 1), by replacing the alkyl substituent of ITIC2 with thioether substituents. This strategy was reminiscent of the evolvement of 2D-conjugated donor from PBDTT-TT to PBDTT-S-TT,[42] which demonstrated the multiple roles of thioether substitution. On one hand, thioether donated some electron density to the polymeric donor’s conjugated main chain, and on the other hand, the sulfur atom is of electron-accepting capability, as the overlap of the pπ(C)-dπ(S) orbitals enables divalent sulfur atom to obtain electrons from the p-orbital of C-C double bond

[43].

Compared with ITIC2, ITIC-S with

thioether substituents exhibited a slightly wider optical band gap, similar light absorption, coupled with higher electron mobility. The introduction of thioether bond disrupted the - stacking of ITIC-S pure film and PBDB-T-SF:ITIC-S blend. PSCs incorporating PBDB-T-SF and ITIC-S exhibited a champion efficiency of 11.6% with a high FF of 66.8 %, surpassing those of PBDB-T-SF:ITIC2 (PCE of 10.1% with FF of 59.7%). The introduction of thioether bond provides an easy and resultful solution to explore high-performance non-fullerene acceptors.

Fused-Ring Electron Acceptors

R1

R1 SR

CN CN S

S

2

O

CN S

S S S

O

ITIC2

R1 =

C 2H 5

R2

O

F

R1

S

S R2 S

S

NC CN

S

R1 O

O

S R2

CN

2

S

O

NC

R2 R2 S R1

SR

CN R2

Donor

R1

S

S

S S

S

n S

S R2 =

C 4H 9

C6H13

R1

ITIC-S

F

S R1

PBDB-T-SF

Scheme 1. Chemical structures of ITIC2, ITIC-S, and PBDB-T-SF.

RESULTS AND DISCUSSION Synthesis and Charicteristics. Scheme 2 depicted the synthetic routes to ITIC-S. ITIC-S was carefully characterized by NMR spectra in Supporting Information (SI). At room 4 ACS Paragon Plus Environment

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temperature, ITIC2 and ITIC-S dissolved well in chloroform (CF) and ortho-dichlorobenzene. The decomposition temperatures (defined as the temperature of 5% weight loss) of ITIC2 and ITIC-S are 319 and 308 ºC, respectively, illustrative of their excellent thermal stability (Figure S1 in SI).

C 2H 5

C 2H 5

C 2H 5

S

S

S COOC2H5 S

+

Sn

S

Br

S

S

toluene ,110 oC

S S

S

(2)

C2H5OOC

Amberlyst 15 toluene , 110 oC

R R

S

45%

S C 2H 5

S

C 2H 5

C 4H 9

C 2H 5

C 4H 9

BDT-S-2Sn

C 4H 9

BDT-T-S

C 4H 9

S

S CN

R R

S (1) POCl3, DMF

S

CHO

S

S

OHC

+

O

pyridine NC

CN

CHCl3, 70 oC

S R R

IT-S

C 4H 9

C 2H 5

C 2H 5

(2) 1,2-Dichloroethane reflux, 18 %

S S

S

78%

S

THF , reflux

S

S

S

C6H13

(1) BrMg

COOC2H5

Pd(PPh3)4

R R

S

S

S Sn

C 4H 9

C 4H 9

C 4H 9

S

CN

O

80%

S

R R

S

S

S

R R

O

S

NC

S

S

S C 2H 5

C 4H 9

C 4H 9

IT-S-CHO

R=

CN

C6H13

C 2H 5

ITIC-S

0.8

a

ITIC2 solution ITIC-S soluton ITIC2 film ITIC-S film

0.6 0.4 0.2 0.0 300

400

500

600

700

Wavelength (nm)

Figure 1.

800

900

5

4

1.0

Absorption Coefficient / 10 cm

-1

Scheme 2. Synthetic routes of small mocular acceptor ITIC-S.

Abs. (a. u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


4

b

PBDB-T-SF:ITIC2 PBDB-T-SF:ITIC-S

3 2 1 0 300

400

500

600

700

800

Wavelength (nm)

UV-vis absorption of (a) ITIC2 and ITIC-S (in solution and as films) and (b)

PBDB-T-SF:ITIC2 and PBDB-T-SF:ITIC-S blend films.

Optical and Electrochemical Properties. Absorption of ITIC2 and ITIC-S in the extremely dilute CF solution with concentration of ~10−6 M and as thin film were displayed in 5 ACS Paragon Plus Environment


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Figure 1a. In solution, ITIC2 showed a max molar absorptivity of 1.5 × 105 M−1 cm−1 at 716 nm. By contrast, ITIC-S showed a blue-shifted absorption maximum at 708 nm with a higher molar absorptivity of 1.9 × 105 M−1 cm−1. ITIC2 and ITIC-S films displayed absorption maxima at 738 and 736 nm, which red-shifted 22 and 28 nm compared with those in solution, respectively. Estimated from thin film’s absorption onset, the optical bandgaps of ITIC2 and ITIC-S were 1.53 and 1.55 eV, respectively. Obviously, the absorption intensity of 104

PBDB-T-SF:ITIC-S blend (ɛ = 4.50 × PBDB-T-SF:ITIC2 blend (ɛ = 3.38 × 104

nm cm-1) was stronger than that of

nm cm-1) (Table 1), beneficial for the Jsc of

photovoltaic device (Figure 1b).

Table 1. Physicochemical properties of ITIC2 and ITIC-S. Materials

Td

λmax (nm)

Ega)

(°C) solution film (eV)

εb)

HOMOc)

LUMOc)

(M−1 cm−1)

(eV)

(eV)

ITIC2

339

714

738

1.53

1.5 × 105

5.48

3.84

ITIC-S

308

708

736

1.55

1.9 × 105

5.50

3.86

a)Calculated c)measured

from the absorption onset of pure film; b)Molar absorptivity at λmax in solution.

from the cyclic voltammograms.

We use cyclic voltammetry (CV) to investigate ITIC-S’s energy levels (Table1 and Figure S2 in SI). Compounds ITIC-S exhibited definitely and highly irreversible oxidation waves and reduction waves. The reduction potentials and onset oxidation are measured to estimate LUMO and the highest occupied molecular orbital (HOMO) energy levels.48 The LUMO and HOMO of ITIC2 were 3.84 and 5.48 eV. In comparison, ITIC-S with alkylthio substitution exhibited slightly downshifted energy levels (LUMO: 3.86 eV and HOMO : 5.50 eV). Photovoltaic Properties. The polymeric donor PBDB-T-SF with optical bandgap of 1.80 eV exhibited strong absorption from 300 to 700 nm, which complemented well with ITIC2 6 ACS Paragon Plus Environment

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and ITIC-S (Scheme 1 and Figure 1a). The HOMO and LUMO of PBDB-T-SF were −5.40 and −3.60 eV, which matched well with ITIC2 and ITIC-S, and contributed to exciton dissociation; and its low-lying HOMO helped to obtain large open-circuit voltage (Voc). We prepared a set of PSC devices with a conventional architecture.

32, 49

PCE of the

best-performing devices, and corresponding parameters including the Voc, FF and short-circuit current density (Jsc) are summarized in Table 2. Figure 2a depicted the J - V curves of the best PSC devices. The PBDB-T-SF:ITIC2 blend provide a efficiency of 10.1%, together with a Voc of 1.085 V, a Jsc of 15.65 mA cm−2 and a FF of 59.7%. PBDB-T-SF:ITIC-S blend, by contrast, afforded a optimal PCE value of 11.6% with a Voc of 1.057 V, a higher Jsc of 16.43 mA cm−2

3

2

80

a

0

b

60

-3

IPCE (%)

Current Density (mA/cm )

coupled with a higher FF of 66.8%.


-6 -9 -12

40 PBDB-T-SF:ITIC2 PBDB-T-SF:ITIC-S 20

-15 -18

0.0

0.2

0.4

0.6

0.8

0 300

1.0

400

Voltage (V)

c

0.1

0.1

Veff (V)

600

700

800

d

2

2


1

500

Wavelength (nm)

Current Density (mA/cm )

10

Jph (mA/cm )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

10

1


1

10

2

100

Light Intensity (mA/cm )

Figure 2. (a) J - V curves under the simulated AM1.5G illumination with the light intensity of 100 mW cm-2, (b) EQE spectra, (c) Jph versus Veff characteristics, and (d) Jsc versus Plight characteristics. 7 ACS Paragon Plus Environment


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Table 2. Photovoltaic parameters and mobilities of the PBDB-T-SF:acceptor devices.

Acceptorsa)

ITIC2

ITIC-S a)

Vocb)

Jscb)

calc. Jsc

FFb)

PCEb)

(V)

(mA cm2)

(mA cm2)

(%)

(%)

1.069±0.011

15.49±0.19

58.6±1.5

9.70±0.28

(1.085)

(15.65)

(59.7)

(10.1)

1.046±0.009

16.4±0.16

66.3±0.4

11.4±0.2

(1.057)

(16.43)

(66.8)

(11.6)

15.49

16.27

The weight ratio of PBDB-T-SF and acceptor was 1:1.

μh

μe

(cm2

(cm2 V−1

V−1 s−1)

s−1)

7.81 × 10−4

4.17 × 10−4

7.51 × 10−4

4.41 × 10−4

b)

Average value together with

standard deviation were calculated from twenty independent PSC devices. The value in parentheses belonged to the best-performing device.

As Figure 2b illustrated, the optimized PBDB-T-SF:acceptor devices exhibited broad photoresponse in the region of 300-850 nm. PBDB-T-SF mainly contributed to the photoresponse of 300 to 650 nm, and the acceptors mainly harvested photons with wavelengths

of

650-850

nm.

The

EQE

maxima

of

PBDB-T-SF:ITIC2

and

PBDB-T-SF:ITIC-S blends were 62.7% and 65.9%, respectively, located at ~ 580 nm. PBDB-T-SF:ITIC-S blend exhibited higher EQE than PBDB-T-SF:ITIC2 blend in the whole range of 300 - 850 nm. According to the integration of EQE spectra, the Jsc of PBDB-T-SF:ITIC2 and PBDB-T-SF:ITIC-S blends were 15.49 and 16.27 mA cm−2, respectively, which agreed with that directly measured from J – V curves. The error is less than 5% (Table 2). The photocurrent density (Jph) as a function of the effective voltage (Veff) was measured to probe the charge generation and charge collection properties (Figure 2c).50 Here, Jph is given by Jph= JL − JD, where JL and JD are the photocurrent densities under illumination and in the dark, respectively; Veff is given by Veff = V0 − Va, where V0 is the compensation voltage at Jph = 0 and Va is the applied bias voltage. When the Veff is higher than 3 V, it can be assumed that 8 ACS Paragon Plus Environment

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all of the excitons in active layer are totally dissociated into free holes and electrons, followed by thorough collection by anode and cathode. In this scenario, Jsat, short for the saturation photocurrent

density,

illustrates

the

amount

of

absorbed

incident

photons.

PBDB-T-SF:ITIC-S blends exhibited similar Jsat (17.51 mA cm−2 ) with PBDB-T-SF:ITIC2 blends (17.56 mA cm−2 ), indicating that these blend have similar amount of absorbed incident photons under the simulated AM 1.5 G irradiation. The exciton dissociation efficiency (ηdiss = Jph/Jsat) and charge collection efficiency (ηcoll = Jsc/Jsat, where Jsc is the compensation electric current under maximizing the power output) can be calculated under the short-circuit and maximum power output conditions, respectively. PBDB-T-SF:ITIC-S exhibited higher ηdiss of 93.8% and higher ηcoll of 76.9% than those of PBDB-T-SF:ITIC-2 (ηdiss of 89.1% and ηcoll of 67.9%), which indicated more effective charge transfer and extraction in the former blend. Charge recombination was probed via measuring Jsc under different Plight (Figure 2d).51 The formula Jsc ∝ PS can describe the relationship between Jsc and Plight. S = 1 indicates free carriers are fully collected by the corresponding electrodes before recombination. S < 1 shows the existence of bimolecular recombination. The PBDB-T-SF:ITIC-S-based device displayed larger S of 0.93 than that of the PBDB-T-SF:ITIC2 counterpart (0.87), indicative of the suppressed bimolecular recombination in PBDB-T-SF:ITIC-S device. It is in accord with the more efficient charge collection and thus higher FF of PBDB-T-SF:ITIC-S device. The carrier mobilities of ITIC2 and ITIC-S pristine films, together with PBDB-T-SF:ITIC2 and PBDB-T-SF:ITIC-S blends were measured via the SCLC method. ITIC-S neat film exhibited an electron mobility (μe) of 6.98 × 10−4 cm2 V−1 s−1, exceeding ITIC2 (6.41 × 10−4 cm2 V−1 s−1), (Figure S3 in SI). PBDB-T-SF:ITIC2 blend presented a hole mobility (μh) of 7.81 × 10−4 cm2 V−1 s−1, which is slightly higher than that of PBDB-T-SF:ITIC-S (7.51 × 10−4 cm2 V−1 s−1), and displayed a μe of 4.17 × 10−5 cm2 V−1 s−1, which is slightly lower than PBDB-T-SF:ITIC-S (4.41 × 10−4 cm2 V−1 s−1) (Figure S4a and Figure S4b in SI). The balance 9 ACS Paragon Plus Environment


of μh and μe (μh/μe = 1.70) in the PBDB-T-SF:ITIC-S blend favors the weaker bimolecular recombination, higher charge extraction efficiency and higher FF (66.8%). Morphologies Studies. To further investigate the relationship between two acceptor materials’ chemical structures and morphology, AFM, and GIWAXS were carried out. As the AFM height images shown in Figure S5a-d in SI, both blends displayed uniform nano-fibrillar network morphology, which is conductive to charge transport.13, 52 PBDB-T-SF:ITIC-2 and PBDB-T-SF:ITIC-S blends displayed similar root-mean-square surface roughness (Rq) of 1.03 and 1.12 nm, respectively.

Figure 3. (a) 2D GIWAXS patterns of PBDB-T-SF:ITIC2 and PBDB-T-SF:ITIC-S blends. (b) The corresponding GIWAXS intensity profiles along the out-of-plane (red and solid line) direction and in-plane (black and dotted line) direction.


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GIWAXS were utilized to study molecular packing and orientation in films.42,

53

The

two-dimensional (2D) GIWAXS patterns and the corresponding intensity profiles of PBDB-T-SF, ITIC2 and ITIC-S pure films, and PBDB-T-SF:ITIC2 and PBDB-T-SF:ITIC-S blend fims were presented in Figure 3 and Figure S6 in SI, respectively. PBDB-T-SF pure film displayed the lamellar peak at qr = 0.27 Å−1 (d = 23.3 Å) and qz = 0.31 Å−1 (d = 20.3 Å), and the π-π peaks at qz = 1.70 Å−1 (d = 3.69 Å). The lamellar diffraction peaks of ITIC2 and ITIC-S appeared at qr = 0.31 Å−1 (d = 20.3 Å) and qr = 0.32 Å−1 (d = 19.7 Å), and their corresponding - peak appeared at qz ≈ 1.72 Å−1 (d = 3.7 Å) with crystalline coherence length (CCL) of 14.3 Å, and qz ≈ 1.53 Å−1 (d = 4.1 Å) with obviously smaller CCL of 4.4 Å. Both ITIC2 and ITIC-S showed a face-on orientation, contributing to charge transport in the vertical direction. The larger d-spacing and smaller CCL of the - peak in ITIC-S neat film, presumably indicated the thioether bond in the BDTT motif reduced the crystallinity of pure ITIC-S film.54 This trend was weakened but still observed in PBDB-T-SF:acceptor blends. PBDB-T-SF:ITIC2 blend exhibited a - peak at qz ≈ 1.71 Å−1 with CCL of 17.9 Å, while PBDB-T-SF:ITIC-S blend displayed a - peak at the same qz with smaller CCL of 13.9 Å in the out-of-plane direction. The incorporation of the thioether bond into the BDTT motif disrupted of the blend film’s - stacking and crystallinity. CONCLUSIONS To summarize, we designed a 2D conjugated NFA, ITIC-S, by replacing alkyl substituents with thioether substituents on the central BDTT moiety of ITIC2, and investigated the influences of the thioether/alkyl substituents on optoelectric properties, charge-transport ability, photo-active layer’s morphology, and photovoltaic performance. Compared with ITIC2, ITIC-S with thioether bond exhibited slightly larger optical band gap, similar light harvest, and higher μe. The smaller CCL of out-of-plane - peaks in ITIC-S pure films and blend films than their counterparts indicated that the introduction of the thioether substituents 11 ACS Paragon Plus Environment


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into the BDTT motif disrupted the - stacking and the crystallinity of ITIC-S based pure film and blend film. The PSCs incorporating PBDB-T-SF:ITIC-S active layer exhibited a champion PCE of 11.6% and a FF of 66.8%, outcompeting those with PBDB-T-SF:ITIC2 blend (FF = 59.7%, PCE = 10.1%). The weaker bimolecular recombination and the more efficient charge extraction boosted Jsc and FF, accounting for a better PCE of PBDB-T-SF:ITIC-S PSCs. Our results demonstrated that the introduction of thioether bond is a easy yet viable gateway to high-performance electron acceptors. EXPERIMENTAL SECTION Materials. Unless stated otherwise, all the solvents and chemical reagents were obtained commercially and used without further purification. All monomers and target molecule were characterized by 1H NMR and

13C

NMR to notarize their chemical

structures (Figue S7-S14). Compound ITIC2 and PBDB-T-SF were synthesized according to previously published procedures, respectively.42, 55 Synthesis

of

BDT-T-S.

BDT-S-2Sn

(3

g,

3.10

mmol),

ethyl

2-bromothiophene-3-carboxylate (2.91 g, 12.39 mmol), Pd(PPh3)4 (214.73 mg, 0.185 mmol) and toluene (25 mL) was heated in a 110 ºC bath for 12 hours under the protection of an argon atmosphere. The reaction mixture was cooled to at room temperature, after dichloromethane and water extraction, the organic layer was dried over anhydrous MgSO4 then filtered. After solvent evaporate from filtrate, the residue was purified by silica gel (200 – 300 mesh) column chromatography. Using dichloromethane/petroleum ether (1:4) as the eluent, 2.30 g (yield 78%) of target product was obtained as yellow solid. 1H NMR (400 MHz, CDCl3) δ 7.88 (s, 1H), 7.51 (d , 1H), 7.35 (d, 1H), 7.27 (d, 1H), 7.19 (d, 1H), 4.28 (s, 2H), 2.93 (d, 2H), 1.65 (d, 1H), 1.53 – 1.37 (m, 4H), 1.35 – 1.18 (m, 8H), 0.89 ppm (s, 7H);

13C

NMR (100

MHz, CDCl3) δ 162.87, 141.84, 141.47, 139.80, 137.91, 136.72, 135.76, 132.45, 130.73, 129.63, 128.58, 125.30, 124.97, 123.38, 77.30, 60.92, 43.52, 39.21, 32.11, 28.74, 25.32, 22.92, 12 ACS Paragon Plus Environment

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14.05, 10.75 ppm; HRMS (MALDI-TOF) m/z: [M + H]+ calcd for C48H54O4S8 950.2; found, 950.7. Synthesis of IT-S. BDT-T-S (2.3 g, 2.42 mmol) and THF (85 mL) were stirred together in a 250 mL round bottom flask at rt under the protection of argon. A THF solution (65 mL) of fresh 4-hexylphenyl-1-magnesium bromide which prepared from magnesium turnings (700 mg, 29.2 mmol) and 1-bromo-4-hexylbenzene (7 g, 29.2 mmol) was added dropwise to the mixture. The mixture was stirred for 14 h at 70 ºC. The reaction mixture was cooled to at room temperature and 60 mL saturated NH4Cl aqueous solution was added to it, after dichloromethane/water extraction, the organic layer was dried over anhydrous MgSO4 then filtered. After solvent evaporate from filtrate, the yellow residue was added into a 250 mL round bottom flask. Toluene (115 mL) and Amberlyst 15 (4.5 g) were added under the protection of an argon atmosphere. The mixture was stirred for 15 h at 110 ºC. The reaction mixture was cooled to at room temperature and filtered. After solvent evaporate from filtrate, the residue was purified by silica gel (200 – 300 mesh) column chromatography. Using petroleum ether as the eluent, 1.60 g (yield 45%) of target product was obtained as light yellow solid. 1H NMR (400 MHz, CDCl3) δ 7.36 (s, 1H), 7.30 – 7.24 (m, 2H), 7.12 – 7.01 (m, 7H), 6.95 (d, 8H), 6.85 – 6.75 (m, 6H), 6.68 (s, 3H), 6.21 (s, 2H), 2.81 (s, 5H), 2.56 (d, 8H), 1.62 (s, 10H), 1.54 – 1.40 (m, 10H), 1.38 (s, 8H), 1.30 (d,79H), 0.92 ppm (d,34H); 13C NMR (100 MHz, CDCl3) δ 164.92, 141.74, 141.33, 141.09, 140.74, 136.29, 133.92, 131.30, 130.84, 130.20, 128.53, 128.25, 127.83, 124.35, 123.74, 123.46, 122.51, 43.48, 39.05, 35.64, 35.49, 32.11, 32.03, 31.85, 31.47, 30.13, 29.70, 29.37, 29.23, 28.98 – 28.77, 25.30, 23.00, 22.68, 14.17, 10.81 ppm; HRMS (MALDI-TOF) m/z: [M + H]+ calcd for C92H110S8 1470.6; found, 1471.2. Synthesis of IT-S-CHO. IT-S-CHO was synthesized by two steps: firstly, anhydrous DMF (4.76 mL, 51 mmol) was added to a 25 mL round bottom flask at rt under the protection of argon. then POCl3 (6 mL, 78 mmol) was added slowly with a syringe at 0 ºC. The mixture 13 ACS Paragon Plus Environment


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was stirred at room temperature for 30 min. Secondly, the mixture, IT-S (1.6 g, 1.09 mmol) and 1,2-dichloroethane (40 mL) were stirred together in a 50 mL round bottom flask at rt under under nitrogen atmosphere. The mixture was stirred for 14 h at 85 ºC. The reaction mixture was cooled to at room temperature, then the reaction mixture was extracted with dichloromethane and water. After solvent evaporate from filtrate, the residue was purified by silica gel (200 – 300 mesh) column chromatography. Using dichloromethane/petroleum ether (1:3) as the eluent, 300 mg (yield 18%) of target product was obtained as orange solid. 1H NMR (400 MHz, CD2Cl2) δ 9.66 (s, 1H), 7.42 (s, 1H), 7.06 – 6.95 (m, 6H), 6.86 (d, 2H), 6.69 (s, 1H), 6.21 (s, 1H), 2.84 (s, 1H), 2.76 (d, 2H), 2.58 (s, 5H), 1.61 (s, 4H), 1.54 – 1.41 (m, 5H), 1.30 (d, , 20H), 0.91 ppm (d, 13H); 13C NMR (100 MHz, CD2Cl2): δ 184.87, 182.30, 164.92, 146.18, 141.89, 141.80, 141.64, 130.60, 130.44, 128.41, 128.37 – 128.24, 128.11, 127.63, 109.86, 108.22, 43.33, 39.08, 35.29, 32.00, 31.72, 31.46, 29.65, 29.07, 28.85, 16.14 – 16.11, 13.84, 10.53 ppm; HRMS (MALDI-TOF) m/z: [M + H]+ calcd for C94H110O2S8 1526.6; found, 1527.0 Synthesis

of

ITIC-S.

IT-S-CHO

(150

mg,

0.094

mmol)

and

1,1-dicyanomethylene-3-indanone (138 mg, 0.69 mmol), chloroform (17 mL) and pyridine (0.5 mL) were stirred together in a 50 mL round bottom flask at rt under the protection of argon. Then, the reaction was placed in an oil bath at 70 °C and stirred for 12 h. The reaction mixture was cooled to room temperature, the mixture was poured into methanol (100 mL) and filtered. The residue was purified by silica gel (200 – 300 mesh) column chromatography. Using dichloromethane/petroleum ether (1:2) as the eluent, 148 mg (yield 80%) of target product was obtained as dark blue solid. 1H NMR (400 MHz, CDCl3) δ 8.69 (s, 1H), 8.62 (d, 1H), 7.85 (d, 1H), 7.69 (s, 2H), 7.39 (s, 1H), 7.10 – 6.95 (m, 6H), 6.79 (s, 2H), 6.70 (s, 1H), 6.23 (s, 1H), 2.84 (s, 3H), 2.57 (s, 4H), 1.60 (s, 4H), 1.53 – 1.43 (m, 3H), 1.32 (s, 16H), 0.92 (d, 12H) ppm; 13C NMR (100MHz, CDCl3) δ 141.98, 141.69 , 141.18, 139.86, 139.49, 66.31, 43.68, 39.18, 35.60, 35.47, 33.01, 32.17, 32.10, 31.79, 31.73, 31.40, 29.21, 28.94, 25.33, 14 ACS Paragon Plus Environment

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23.02, 22.64, 14.25 – 14.20, 14.14, 10.95, 10.86 ppm; HRMS (MALDI-TOF) m/z: [M + H]+ calcd for C118H118N4O2S8 1878.7; found, 1879.2.

Associated Content Supporting Information Experimental details of characterization, solar cell fabrication, TGA, CV, AFM, GIWAXS patterns of pure film, and the hole and electron mobilities for organic photovoltaic.

Author Information Corresponding Author E-mail: [email protected] [email protected] [email protected] [email protected] Author Contributions Y. Z. and Y. W. conceived the idea and designed the experiments. Y. Z. performed all of the measurements, and wrote the paper. X. L. fabricated the organic photovoltaic. T. Y. helped measure electrochemical performance. Y. X. tested the morphologies of organic solar cells. X. L., H. Y., Z. Y, Y. C and Y. L. assisted in revising the paper. All authors reviewed the paper.

Notes The authors declare no competing financial interest.

Acknowledgements This work was supported by the National Natural Science Foundation of China (Nos. 21602150, 51763017, 51425304, 51863012, 21861025, 51833004), and the Science and 15 ACS Paragon Plus Environment


Technology

Commission

of

the

Military

Commission

Page 16 of 23

of

China

(No.

18-H863-00-TS-002-006-01).

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