Angular-shaped 4,9-dialkyl Naphthodithiophene-based Octacyclic

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Angular-shaped 4,9-dialkyl Naphthodithiophene-based Octacyclic Ladder-Type Non-fullerene Acceptors for High Efficiency Ternary-blend Organic Photovoltaics Fong-Yi Cao, Wen-Chia Huang, Shao-Ling Chang, and Yen-Ju Cheng Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.8b01089 • Publication Date (Web): 29 Jun 2018 Downloaded from http://pubs.acs.org on June 30, 2018

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Chemistry of Materials

Angular-shaped

4,9-dialkyl

Naphthodithiophene-based

Octacyclic Ladder-Type Non-fullerene Acceptors for High Efficiency Ternary-blend Organic Photovoltaics Fong-Yi Cao, Wen-Chia Huang, Shao-Ling Chang, and Yen-Ju Cheng* Department of Applied Chemistry, National Chiao Tung University, 1001 University Road, Hsinchu, Taiwan 30010. E-mail: [email protected] ABSTRACT: An angular-shaped 4,9-didodecyl naphthodithiophene-based octacyclic ladder-type structure was developed. This new ladder-type donor (LD) was coupled with electron-withdrawing IC and FIC units to form two A-LD-A type non-fullerene acceptor materials, NCIC and NCFIC. NCIC and NCFIC as the n-type acceptors are blended with a p-type donor PBDB-T to form the complementary absorption and suitable energy level alignments. The binary-blend PBDBT:NCIC and PBDB-T:NCFIC devices achieved an efficiency of 7.3% and 7.5%, respectively. PC71BM was incorporated to form D1:A1:A2 ternary blends which further strengthen the absorption at shorter wavelengths. Introduction of PC71BM not only efficiently improves the absorption but also provides multiple channels for exciton dissociation and electron transport to dramatically improve Jsc. It is interesting to find that the Voc of the ternary-blend devices is reversely in proportional to the added amount of PC71BM. The device using the PBDB-

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T:NCIC:PC71BM (1:1:1 in wt%) showed an improved PCE of 8.32%. Moreover, the optimized device using the PBDB-T:NCFIC:PC71BM (1:1:1.5 in wt%) blend achieved the highest efficiency of 9.18%. Introduction Organic photovoltaic solar cells (OPVs) are promising for producing large-area modules and flexible electronics.1-13 For long periods of time, n-type acceptor materials in OPVs are exclusively dominated by fullerene derivatives such as [6,6]-phenyl-C61(or C71)-butyric acid methyl ester (PC61BM or PC71BM)) due to their high electron affinity, high electron mobility and isotropic electron transport.14-25 Consequently, the p-type polymers used in fullerene-based solar cells need to be specifically designed in order to match the properties of n-type fullerene acceptors. However, fullerene derivatives also have several intrinsic drawbacks such as insufficient absorption, untunable energy levels and unstable morphology. To circumvent the deficiencies, recent research efforts have been centered on the development of organic-based non-fullerene acceptors (NFAs).26-29 We have been focused on the development of electron-rich ladder-type donors (denoted as LD) to construct various donor-acceptor copolymers.30-39 The rigidification and planarization of the LDs restrict rotational motions, extend effective conjugated length and promote intermolecular interactions, which is beneficial to broaden light absorption and improve hole mobility.40 In view of these advantageous features, there has been a renewal of interest in employing LD units to construct new NFAs. For example, indacenodithiophene (IDT)41-46 and indacenodithieno[3,2,b]thiophene (IDTT)47-52 have been utilized as the central cores to couple with two electron-deficient 1,1-dicyanomethylene-3indanone (IC) acceptor to form A-LD-A NFAs which have successfully achieved superior efficiencies.53-57 Through the electron push-pull interactions, the organic-based A-LD-A-type


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NFA can possess strong absorption covering UV-visible and near infrared regions to improve the short-circuit current density (Jsc). By varying the combination of LD and A units, the energy levels of NFAs can be adjusted to reduce the energy loss of the exciton dissociation and improve the open-circuit voltage (Voc).58-60 Based on this design principle, a number of high-performance A-LD-A-type NFAs using different LD units have been developed.43-60 We recently reported a non-fullerene

acceptor

BDCPDT-IC

using

a

heptacyclic

ladder-type

benzodi(cyclopentadithiophene) (BDCPDT) where the central benzodithiophene (BDT) subunit is fused with two outer cyclopentathiophene moieties.56 It is of great interest to further design an extended octacyclic ladder-type structure by replacing the central tricyclic benzodithiophene unit in BDCPDT with a tetracyclic naphthodithiophene (NDT) unit. Angular-shaped 5,10dialkylnaphthodithiophene unit has been incorporated into various donor-acceptor conjugated materials showing good molecular packing, high crystallinity, charge transportation properties and thus high efficiencies in solar cell applications.61-70 However, another isomeric angularshaped 4,9-dialkyl naphthodithiophene (4,9-NDT) derivatives have not been well explored due to the lack of useful synthetic method. 71,72 We recently successfully designed a useful synthetic strategy to regiospecifically prepare angular-shaped 4,9-dialkylated naphthodithiophene derivatives, which allows us to systematically investigate the side-chain substitution isomeric effects.31,34,39 Compared to the 5,10-dialkylnaphthodithiophene-based counterparts, the 4,9dialkylnaphthodithiophene-incorporated polymers with aliphatic chains at inner 4,9-positions might reduce steric hindrance to maintain the backbone coplanarity. Additionally, the synthesis of 4,9-dialkyl naphthodithiophene is much easier than that of 5,10-dialkyl naphthodithiophene.73 The 4,9-NDT-based donor-acceptor copolymers have exhibited promising photovoltaic properties. In this research, we design and synthesize an octacyclic ladder-type 4,9-


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didodecylnaphthodithiophenyldi(cyclopentathiophene) structure (denoted as NC) embedding a central 4,9-didodecyl naphthodithiophene unit fused with two outer cyclopentathiophene moieties. The octacyclic NC was formylated to condense with IC or fluorinated IC (FIC, 1,1dicyanamethylene-5,6-difluoro-3-indanone74,75) units, forming two materials called NCIC and NCFIC, respectively (Figure 1). PBDB-T (poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b’]dithiophene))-alt-(5,5-(1’,3’-di-2-thienyl-5’,7’-bis(2-ethylhexyl)benzo[1’,2’c:4’,5’-c’]dithiophene-4,8-dione))]) was selected as the p-type polymer to blend with NCIC and NCFIC. NCFIC displays more red-shifted absorption and higher extinction coefficient. Moreover, the introduction of the fluorine atom can enhance inter/intramolecular interactions and facilitate charge transport.57 The OPV devices using the binary-blend PBDB-T:NCIC and PBDBT:NCFIC blend have achieved an efficiency of 7.3% and 7.5%, respectively. PC71BM, used as the second acceptor, was added into the PBDB-T:NCIC and PBDB-T:NCFIC system to form ternary blends. The introduction of PC71BM efficiently strengthens the absorption around 350500 nm and facilitates electron transport.76-83 The ternary-blend device with the PBDBT:NCIC:PC71BM (1:1:1 in wt%) showed an improved PCE of 8.32%, with a Voc of 0.88 V, a higher Jsc of 16.78 mA cm−2, and an FF of 56.4%, while the optimized ternary-blend device with the PBDB-T:NCFIC:PC71BM (1:1:1.5 in wt%) yielded the highest PCE of 9.18% with a Voc of 0.84 V, a higher Jsc of 17.79 mA cm−2, and an FF of 61.41%.


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Figure 1. Chemical structures of PBDB-T, PC71BM, NCIC and NCFIC. 1. Results and discussion Molecular Design, Synthesis and Characterization. The synthesis of NCIC and NCFIC are described in Scheme 1. The synthesis of compound 1 has been reported previously.30 Stille coupling of compound 1 with ethyl 2-bromothiophene-3-carboxylate afforded compound 2 in 86% yield. Compound 2 was reacted with 4-hexylphenylmagnesium bromide to yield compound 3, which underwent acid-catalyzed cyclization to form the NC (4) in 50% yield. The formylation of compound 4 generated compound 5 in 92% yield. Reaction of compound 5 with 1,1dicyanomethylene-3-indanone (IC) and 1,1-dicyanamethylene-5,6-difluoro-3-indanone (FIC) afforded the final products of NCIC and NCFIC, respectively. Both NCIC and NCFIC can be dissolved in chloroform, chlorobenzene, or o-dichlorobenzene. The detailed synthetic procedure, mass spectrometry, 1H NMR, 13C NMR of new compounds are shown in the experiment section and supporting information. From the thermogravimetric analysis (TGA) measurement shown in Figure S1, the decomposition temperature (Td) of NCIC and NCFIC is 356 °C and 376 °C, respectively. From the differential scanning calorimetry (DSC) measurement as shown in Figure


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S2, NCIC displayed two melting points (Tm) at 89 °C and 173 °C during heating and two crystallization points at 38 °C and 165 °C during cooling, indicating that NCIC has high crystallinity. However, NCFIC did not show melting point and crystallization transition. This discrepancy might be associated with the electron-withdrawing fluoro atom in NCFIC.

Scheme 1. Synthesis of NCIC and NCFIC. Optical and Electrochemical Properties. The normalized absorption spectra of PBDB-T, PC71BM, NCIC and NCFIC in thin film and solution state are shown in Figure 2a. The optical and electrochemical properties are listed in Table 1. In solution state, NCIC displays strong absorption in 600-700 nm region with an extinction coefficient of 2.09 × 105 M−1 cm−1 at the λmax of 675 nm, while NCFIC exhibits more bathochromic absorption with λmax at 690 nm (2.24 × 105 M−1 cm−1) as a result of the two additional electron-withdrawing fluorine atoms. The extinction


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coefficients of NCIC and NCFIC in solution are showed in Figure S3. Compared to the solution state, the λmax of NCIC and NCFIC in thin film is red-shifted by 25 nm and 65 nm, respectively. The greater red-shifted λmax of NCFIC suggests that the fluorinated FIC in NCFIC might induce stronger intermolecular interactions. In addition, the optical bandgaps of NCIC and NCFIC are estimated to be 1.58 eV and 1.51 eV, respectively. The cyclic voltammetry (CV) of NCIC and NCFIC was shown in Figure S4. The ionization potential (IP) and electron affinity (EA) of NCIC and NCFIC were estimated to be −5.37/−3.73 eV and −5.43/−3.94 eV, respectively. The lowerlying IP/EA levels of NCFIC are attributed to the stronger electron-accepting ability of the FIC moiety. The electrochemical bandgaps of NCIC and NCFIC are 1.64 eV and 1.49 eV, respectively.

Figure 2. (a) UV-vis absorption spectra of PBDB-T, NCIC and NCFIC in solution and thin film, (b) Energy levels of PBDB-T, NCIC, NCFIC and PC71BM estimated by cyclic voltammetry. Table1. Summary of the intrinsic properties of NCIC and NCFIC λmax (nm) Film

λonset (nm)a

Egopt (eV)b

IP (eV)c

EA (eV)c

Egele (eV)c

675

700

785

1.58

-5.37

-3.73

1.64

690

755

821

1.51

-5.43

-3.94

1.49

NFA

Extinction coefficient (×105 cm-1M-1)

o-DCB

NCIC

2.09

NCFIC

2.24 a

o-DCB = ortho-dichorobenzene, calculated in the solid state,

b

Egopt

c

= 1240/λonset, determined by cyclic

voltammetry. (IP = ionization potential, EA= electron affinity)


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Photovoltaic Characteristics. The inverted devices with ITO/ZnO/PBDB-T:NFAs/MoO3/Ag configuration were prepared. The J-V curves and the external quantum efficiency (EQE) spectra are shown in Figure 3 (Table 2). The PBDB-T:NCIC (1:1 in wt%) device with 0.5 vol% 1,8diiodooctane (DIO) exhibited a PCE of 7.31% with a high Voc of 1.00 V, a Jsc of 12.69 mA cm−2, and an FF of 57.6%. The high-lying electron affinity of NCIC to reduce the energy loss of the charge separation between donor and acceptor results in the high Voc. In addition, the PBDBT:NCFIC (1:1 in wt%) device with 0.5 vol% DIO led to a PCE of 7.52% with a Voc of 0.88 V, a higher Jsc of 15.19 mA cm−2, and an FF of 56.2%. The Jsc values obtained from the J−V measurements are rather consistent with the values calculated from the EQE spectra. The binary systems display relatively weak photocurrent response at 350 nm to 500 nm in the EQE spectra. In order to strengthen the absorption at the shorter wavelength region, we introduced PC71BM as the second acceptor to form ternary blending systems. As shown in Figure 3a and 3b, the ternary devices using the PBDB-T:NCIC:PC71BM blend showed significant improvement in Jsc and much higher PCE compared to these of the binary system. The EQE of the ternary devices reveal dramatic enhancement at 350 nm to 500 nm. The optimized PBDB-T:NCIC:PC71BM (1:1:1 in wt%) ternary device showed the PCE of 8.32% with a Voc of 0.88 V, a higher Jsc of 16.78 mAcm−2, and an FF of 56.4%. Similarly, the ternaryblend PBDB-T:NCFIC:PC71BM device with the optimized ratio of 1:1:1.5 in wt% delivered the highest PCE of 9.18% with a Voc of 0.84 V, an FF of 61.41% and the highest Jsc of 17.79 mAcm−2. Table 2. Characteristics of the devices with the blending system of PBDB-T:NCIC:PC71BM, PBDB-T:NCFIC:PC71BM.


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Blending system

Blending ratio in wt%a

Voc (V)

Jsc (mA cm-2)

FF (%)

PCE (%)

Eloss b (eV)

µhole (cm2V-1s-1)

µele (cm2V-1s-1)

PBDB-T: PC71BM

1:1

0.82 (0.81 ± 0.01)

13.44 (13.56 ± 0.12)

62.0 (60.9 ± 1.1)

6.84 (6.69 ± 0.15)

1

-

-

1:1:0

1.00 (1 ± 0)

12.69 (12.82 ± 0.24)

57.6 (56.2 ± 0.9)

7.31 (7.21 ± 0.1)

0.61

1.08×10-6

5.98×10-7

1:1:0.5

0.90 (0.91 ± 0.01)

15.55 (15.28 ± 0.2)

52.7 (50.8 ± 1.4)

7.38 (7.04 ± 0.24)

-

2.23×10-5

3.99×10-6

1:1:1

0.88 (0.87 ± 0.01)

16.78 (17.25 ± 0.47)

56.4 (54.8 ± 1.6)

8.32 (8.22 ± 0.1)

-

9.08×10-6

9.52×10-6

1:1:1.5

0.84 (0.84 ± 0)

17.03 (16.48 ± 0.56)

56.4 (58.5 ± 0.6)

8.29 (8.09 ± 0.19)

-

1.77×10-5

2.64×10-6

1:1:0

0.88 (0.88 ± 0)

15.19 (15.09 ± 0.07)

56.3 (56.0 ± 0.7)

7.52 (7.44 ± 0.1)

0.67

1.00×10-6

6.97×10-7

1:1:0.5

0.86 (0.85 ± 0.01)

16.97 (17.6 ± 0.63)

61.8 (60.2 ± 1.6)

9.01 (8.99 ± 0.02)

-

1.98×10-5

7.18×10-6

1:1:1

0.84 (0.83 ± 0.01)

16.98 (16.79 ± 0.77)

61.9 (61.3 ± 2.0)

8.83 (8.57 ± 0.17)

-

2.49×10-5

8.14×10-6

1:1:1.5

0.84 (0.84 ± 0.01)

17.79 (17.81 ± 0.2)

61.4 (59.8 ± 1.1)

9.18 (8.89 ± 0.29)

-

2.60×10-5

1.73×10-5

PBDB-T :NCIC :PC71BM

PBDB-T :NCFIC :PC71BM

a

with 0.5 vol % DIO as the additive. The average values with standard deviation over 10 cells are shown

in parenthesis. bEloss=Egopt–eVoc. The molecular weight of PBDB-T is around 30 kDa with PDI of 1.5.


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Figure 3. J-V curves and EQE spectra of the devices with the binary and ternary blends of PBDB-T:NCIC:PC71BM (a, b); PBDB-T:NCFIC:PC71BM (c, d). We found that the Voc of the NCIC-based devices gradually decreases as the amount of the introduced PC71BM increases (Figure 4a and 4c). Considering the fact that Voc is correlated to the photon energy loss (Eloss) which is defined as the potential energy difference between the absorbed photon and the released electron, we calculated the Eloss of devices based on the equation of Eloss = Egopt –eVoc.84-86 The binary PBDB-T:PC71BM reference device was also fabricated for comparison. The Eloss of the binary PBDB-T:NCIC device is 0.61 eV. The PBDBT:NCFIC device shows a larger Eloss of 0.67 eV, which is associated with the larger ionization potential energy difference between the PBDB-T and NCFIC. Nevertheless, the PBDBT:PC71BM-based binary device shows a much higher Eloss of 1 eV. Although the Jsc is effectively improved as the amount of PC71BM increases in the ternary blend, the proportion of higher Eloss


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(exciton dissociation between PBDB-T and PC71BM) also increases, thereby resulting in lower Voc. Furthermore, the composition dependent Voc of the ternary devices also reveals the good miscibility among PBDB-T, NC-based NFAs and PC71BM.87,88

Figure 4. (a) Voc and (b) Jsc versus different ternary blending ratio of PBDB-T:NCIC:PC71BM; (c) Voc and (d) Jsc versus different ternary blending ratio of PBDB-T:NCFIC:PC71BM. As shown in Figure 4b and 4d, the Jsc gradually enhances as the amount of PC71BM increases in the PBDB-T:NCIC:PC71BM and PBDB-T:NCFIC:PC71BM ternary blends. To gain deeper insight into exciton dissociation and charge transport between NC-based NFAs and PC71BM in the ternary blend, we intentionally fabricated the binary NCIC:PC71BM and NCFIC:PC71BM devices (Table 3). The EQE spectrum and the corresponding absorption spectrum are shown in Figure 5.


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The NCIC:PC71BM device presented a PCE of 2.45% with a Voc of 0.98 V, a Jsc of 5.85 mAcm−2, and an FF of 42.8%. Furthermore, the device displayed EQEs of 20%, 33% and 38% at the wavelength of 400 nm, 663 nm and 728 nm, respectively. The EQE profile is essentially consistent with the UV-visible absorption of NCIC:PC71BM blend (Figure 5a), suggesting that exciton dissociation can also efficiently take place from NCIC to PC71BM. As shown in Figure 5c (1, 2, and 3 electron transfer channels), due to the extra exciton dissociation pathway between NCIC and PC71BM (channel 3), the Jsc of the ternary PBDB-T:NCIC:PC71BM devices was enhanced by 23% (1:1:0.5 in wt%), 32% (1:1:1 in wt%) and 34% (1:1:1.5 in wt%), respectively, compared to the binary device (PBDB-T:NCIC). In contrast, the NCFIC:PC71BM device displayed a much lower PCE of 0.05% with only a weak EQE of 3% at 390 nm (Figure 5b) which corresponds to the absorption of PC71BM, indicating that the slightly higher-lying electron affinity energy of PC71BM prohibits exciton dissociation from NCFIC to PC71BM. As shown in Figure 5d, the exciton dissociation in the PBDB-T:NCFIC:PC71BM blend can only efficiently occur at the PBDB-T:NCFIC or PBDBT:PC71BM (channel 1 and 2) interface. Therefore, compared to the PBDB-T:NCIC:PC71BM ternary system, the Jsc of the ternary PBDB-T:NCFIC:PC71BM devices shows smaller enhancement of 12% (1:1:0.5 in wt), 12% (1:1:1 in wt) and 17% (1:1:1.5 in wt) relative to the binary device (PBDB-T:NCFIC). Furthermore, the EQE enhancement in the short wavelength region of the PBDB-T:NCFIC:PC71BM device should mainly come from the additional PBDBT:PC71BM interface.

Table 3. Characteristics of the devices with the blending system of NCIC:PC71BM and NCFIC:PC71BM.


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Blending system

Blending ratio in wt%a

Voc (V)

Jsc (mAcm-2)

FF (%)

PCE (%)

NCIC: PC71BM

1:1

0.98 (1 ± 0.02)

5.85 (5.56 ± 0.29)

42.8 (42.2 ± 0.6)

2.45 (2.35 ± 0.11)

NCFIC:PC71BM

1:1

0.76 (0.78 ± 0.02)

0.17 (0.18 ± 0.01)

36.8 (33.1 ± 2.7)

0.05 (0.046 ± 0.005 )

The average values with standard deviation over 5 cells are shown in parenthesis.

Figure 5. EQE spectra of the devices and the corresponding UV-vis absorption spectra with the blend of (a) NCIC:PC71BM and (b)NCIC:PC71BM. The energy diagram and the charge transport pathways of the devices with the blend of (c) PBDB-T:NCIC:PC71BM and (d)PBDBT:NCIC:PC71BM. We also fabricated the hole-only ITO/PEDOT:PSS/active layer/Au and electron-only Al/active layer/Al devices to evaluate the hole and electron mobility by space-charge limit


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current (SCLC) model (Figure S5). The hole and electron mobilities were estimated to be 1.08×10-6 /5.98×10-7 and 1.00×10-6/6.97×10-7 cm2V-1s-1 for PBDB-T:NCIC and PBDBT:NCFIC,

respectively.

The

ternary-blend

PBDB-T:NCIC:PC71BM

and

PBDB-

T:NCFIC:PC71BM devices show increased hole/electron mobility. The optimized ternary-blend of PBDB-T:NCIC:PC71BM (1:1:1 in wt%) displays the highest electron mobility of 9.52×10-6 cm2V-1s-1 and the most balanced hole/electron mobility ratio of 0.95. Moreover, the ternary blend of PBDB-T:NCFIC:PC71BM (1:1:1.5 in wt%) with the best device performance also showed the highest electron mobility of 1.73×10-5 cm2V-1s-1 and the most balanced hole/electron mobility ratio of 1.5. The increased hole/electron mobility results in the more efficient charge transport/collection and thus higher current density. We used two-dimensional grazing-incidence wide-angle X-ray diffraction (GIWAXS) to investigate the molecular orientation. In the Figure S6, the neat PBDB-T thin film exhibited a strong (010) diffraction in the out-of-plane direction at qz = 1.76 Å-1 corresponding to the periodic π–π stacking with a distance (dπ) of ca. 3.57 Å. The result suggests that the polymer crystallites adopt a face-on orientation. Furthermore, neat NCIC and NCFIC films displayed edge-on orientations with obvious diffraction in-plane direction at qxy = 1.75 Å-1 and 1.87 Å-1 corresponding to the periodic dπ of ca. 3.59 Å and 3.36 Å, respectively. The shorter dπ of NCFIC indicates the fluorinated NCFIC might produce stronger intermolecular interaction than NCIC. The result is consistent with the larger red-shifted λmax absorption of NCFIC from solution to solid state. As shown in Figure 6, the diffractions of the PBDB-T:NCIC and PBDB-T:NCFIC blending films present π–π stacking signals in both in-plane and out-of-plane directions, indicating that the thin films possess both face-on and edge-on crystalline orientations. However, after the


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incorporation of PC71BM, the π–π stacking signal of the ternary blend in the out-of-plane direction becomes more pronounced. The predominant face-on orientation is beneficial for the vertical charge transport. Furthermore, the 1-dimensional in-plane and out-of-plane GIWAXS patterns of the films are shown in Figure S7.

π-

Figure 6. 2-Dimensional GIWAXS images of the films with PBDB-T:NCIC:PC71BM (1:1:0, 1:1:0.5, 1:1:1 and1:1:1.5 in wt%) and PBDB-T:NCFIC:PC71BM (1:1:0, 1:1:0.5, 1:1:1 and1:1:1.5 in wt%). In order to investigate the surface morphology of the blend films, we measured the AFM images of the binary and ternary blend films with different blending ratios. As shown in the Figure S8, we found the surface roughness of PBDB-T:NCFIC is rougher than that of PBDBT:NCIC attributed to the high crystallinity of flourinated NCFIC. The ternary-blend films show


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similar surface morphology with the binary-blend films, indicating that the three components have good miscibility without altering the surface morphology. 3. Conclusions In summary, an angular-shaped 4,9-didodecyl naphthodithiophene-based octacyclic laddertype structure was developed. This coplanar LD building block was further coupled with electron-withdrawing IC and FIC units to form two A-LD-A type acceptor materials NCIC and NCFIC. NCIC and NCFIC as the n-type acceptors are combined with a p-type donor PBDB-T to form the complementary absorption and suitable energy level alignments. The PBDB-T: NCIC device achieved an efficiency of 7.3%. The device with PBDB-T:NCFIC blend showed a higher efficiency of 7.5% due to the better light-harvesting ability of NCFIC. To further broaden the absorption at shorter wavelengths, the second acceptor A2, PC71BM, was incorporated to form D1:A1:A2 ternary blends. Introduction of PC71BM not only efficiently improves the absorption but also provides multiple channels for exciton dissociation and electron transport in the ternaryblend bulk heterojunction, leading to the dramatic improvement of Jsc. The devices using the PBDB-T:NCIC:PC71BM (1:1:1 in wt%) and PBDB-T:NCFIC:PC71BM (1:1:1.5 in wt%) showed the improved PCE of 8.32% and 9.18%, respectively.

Supporting Information DSC/TGA measurements, cyclic voltammogram, SCLC measurements, 1-D and 2-D GIWAXS images, AFM images, device fabrication and characterization, synthetic procedures, 1H and

13

C

NMR spectra.

ACKNOWLEDGMENT


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This work is supported by Ministry of Science and Technology, Taiwan (grant No. MOST107-3017-F009-003) and Ministry of Education, Taiwan (SPROUT Project-Center for Emergent Functional Matter Science of National Chiao Tung University). We thank the National Synchrotron Radiation Research Center (NSRRC), and Dr. U-Ser Jeng and Dr. Chun-Jen Su at BL23A1 station.

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Tunable Open-Circuit Voltage in Ternary-Blend Organic Solar Cells. Adv. Funct. Mater. 2015, 25, 5557–5563.

Graphical abstract Angular-shaped 4,9-dialkyl Naphthodithiophene-based Octacyclic LadderType Non-fullerene Acceptors for High Efficiency Ternary-blend Organic Photovoltaics A 4,9-didodecyl naphthodithiophene-based ladder-type structure was utilized to synthesize two non-fullerene acceptor materials NCIC and NCFIC which were blended with a p-type donor PBDB-T and PC71BM to form the complementary absorption and suitable energy level alignments. The ternary-blend PBDB-T:NCFIC:PC71BM device achieved a highest efficiency of 9.18%.


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Angular-shaped 4,9-dialkyl Naphthodithiophene-based Octacyclic

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