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Bis(naphthothiophene diimide)indacenodithiophenes as Acceptors for Organic Photovoltaics Johan Hamonnet, Masahiro Nakano, Kyohei Nakano, Hiroyoshi Sugino, Kazuo Takimiya, and Keisuke Tajima Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.7b03733 • Publication Date (Web): 07 Nov 2017 Downloaded from http://pubs.acs.org on November 8, 2017

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Bis(naphthothiophene diimide)indacenodithiophenes as Acceptors for Organic Photovoltaics Johan Hamonnet,a Masahiro Nakano,a* Kyohei Nakano,b Hiroyoshi Sugino,a Kazuo Takimiya,a,c* Keisuke Tajimab a

Emergent Molecular Function Research Group, RIKEN Center for Emergent Matter Science (CEMS), 2-1, Hirosawa, Wako, Saitama, 351-0198, Japan b

Emergent Functional Polymers Research Team, RIKEN Center for Emergent Matter Science (CEMS), 2-1, Hirosawa, Wako, Saitama, 351-0198, Japan c

Department of Chemistry, Graduate School of Science, Tohoku University, 6-3, Aoba, Aramaki, Aoba-ku, Sendai, 980-8578, Japan ABSTRACT: Novel naphtho[2,3-b]thiophene diimide (NTI)-based molecules, IDT-NTIs, in which two NTI units are linked to indaceno[1,2-b:5,6-b´]dithiophene (IDT), were developed as acceptors for organic photovoltaics (OPVs). The characteristic features of IDT-NTIs were their absorption spectra with two bands at 400-500 and 600-780 nm covering a wide range of the solar spectrum and tunable LUMO energy levels by the N-alkyl groups in the NTI units, which were easily modified by a new synthetic protocol using the N-unsubstituted NTI intermediate. By combining with a donor polymer, PBDB-T, with the complementary absorption to those of IDT-NTIs, the resulting OPVs yielded promising PCEs as high as 9% with relatively high open-circuit voltages (VOC) of up to 1.02 V. These results indicate that NTI is a promising electron-deficient unit for the development of superior acceptors for OPVs.

Organic photovoltaics (OPVs) have recently received considerable attention because of their unique advantages, such as light-weight, mechanical flexibility, and solutionprocessability.1-3 Fullerene-based acceptors have played an important role in the improvement of power conversion efficiency (PCE) of OPVs; in particular, OPVs based on [6,6]phenyl-C71-butyric acid methyl ester (PC71BM) and appropriate -conjugated donor materials have shown PCEs higher than 11% in single junction solar cells.4,5 However, fullerene derivatives have several drawbacks, such as weak absorption in the visible region, poor chemical stability, and limited tunability of their chemical structures and electronic properties. As a consequence, non-fullerene acceptors (NFAs) is now emerging as an alternative. The performances of OPVs based on NFAs have been rapidly improved in recent years,6-9 and several small-molecular NFAs have been reported to afford OPVs with PCEs comparable to or higher than those of the best OPVs with fullerene derivatives.10-16 In the small-molecular NFAs, rylene diimide (RyDI, Figure 1a),17 e.g., perylene diimide (PDI) and naphthalene diimide (NDI), have been employed as a building unit due to their strong electron affinity and good thermal stability.16-22 In particular, the PCEs of the OPVs with PDI-based small-molecular acceptors have already exceeded 9%.18-20 As a novel RyDI-based electron-deficient unit, we have recently reported the mono-thiophene-fused NDI, naphtho[2,3-b]thiophene diimide (NTI, Figure 1b), for organic semiconducting materials.24,25 The NTI unit can be integrated via its vacant thiophene -position into -extended

Figure 1. Chemical structures of RyDIs (a), NTI (b), IDT-NTIs (c), and PBDB-T (d). systems with planar -structures, which gives red-shifted absorption and - stacking in the solid state. As a model compound for NTI-based acceptors, we combined the NTI unit with indaceno[1,2-b:5,6-b´]dithiophene (IDT), a frequently used core-unit in superior NFAs.8,9,25-31 In this work, we synthesized and characterized NTI-IDT-NTI-triads, namely, IDT-NTI-2EH and IDT-NTI-1HH,32 and utilized them as NFAs (Figure 1c). Compared to a NFA with a similar triad structure, PDI-IDT-PDI triad,33 IDT-NTIs have a planar -conjugated skeleton (Figure S1ab). Owing to the effective -conjugation in the planar structures, IDT-NTIs exhibited red-shifted absorption of up to 780 nm. By combining with PBDB-T10,34,35 (Figure 1d) as a donor material

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Figure 3. Schematic energy-levels diagrams of MoO3, IDT-NTIs, PBDB-T, and ZnO (a). J-V characteristics (b) and EQE spectra (c) of IDT-NTI-2EH:PBDB-T and IDTNTI-1HH:PBDB-T based OPVs.

Scheme 1. Synthetic route to IDT-NTIs. with the complementary absorption, the resulting OPVs yielded promising PCEs as high as 9%, comparable to the best PCEs so far reported for RyDI-based OPVs.19

thermogravimetric (TG) measurements; the decomposition temperatures (5% weight loss) of IDT-NTI -2EH and 1HH were 466 and 411 °C, respectively. (Figure S2).

Scheme 1 shows the synthesis of IDT-NTIs. The NTIunits, 3a and 3b, were prepared from N,N´-unsubstituted NTI (1) (the synthesis is detailed in Supporting Information). The N-substituents, 2-ethylhexyl (2EH) or 1-hexylheptyl (1HH), were introduced on the unsubstituted imide N-positions of 1 by Mitsunobu reaction using readily available corresponding alcohols to afford 2a and 2b. The following bromination at the -position of the fused-thiophene gave 3a and 3b, respectively. The target compounds, IDT-NTI-2EH and IDT-NTI-1HH, were synthesized by Stille coupling reaction of 3a or 3b with 2,7-bis(trimethylstannyl)-4,4,9,9-tetrakis(4-hexylphenyl)-s-indaceno[1,2-b:5,6-b´]dithiophene.36 IDT-NTI-2EH and IDTNTI-1HH were fully characterized by 1H and 13C NMR, IR, and high-resolution mass spectra (see Supporting Information). Note that the present 3-step synthesis of IDTNTIs featuring the alkylation on the NTI core enables facile molecular modifications of NTI-based acceptors. IDT-NTIs were soluble in common organic solvents, such as chloroform, chlorobenzene, and o-dichlorobenzene at room temperature. Their good thermal stability was confirmed by

The HOMO and LUMO energy levels (EHOMO and ELUMO, respectively) of IDT-NTIs were estimated from the onset potentials of oxidation and reduction waves in the cyclic voltammograms (Figure 2a) recorded with their thin films deposited on the working electrode. The estimated ELUMOs of IDT-NTI -2EH and -1HH were −3.9 and −3.8 eV, respectively. The slightly higher ELUMO of IDT-NTI-1HH can be explained by the enhanced electron donating nature of the 1HH group, where the first carbon atom connecting to the imide nitrogen atom has two alkyl branches. A similar effect of the branching position of N-alkyl groups on ELUMOs was observed in related molecules.37 This result indicates that the ELUMOs of NTI-based acceptors can be controlled by modification of substituents on the imide nitrogen atoms. In contrast to the ELUMOs, EHOMOs of both IDT-NTIs were almost the same (EHOMO = −5.4 eV), which is consistent with the relatively small contribution of the NTI moieties to the HOMO (Figure S1c). Figure 2b shows the absorption spectra of IDT-NTIs in the thin-film state. The effective -conjugation gave the red-shifted absorption of up to 780 nm compared with the absorption of NTI (~ 510 nm). Reflecting the higher ELUMO of IDT-NTI-1HH, its absorption edge was slightly blueshifted compared with that of IDT-NTI-2EH (edge ~ 30 nm). The absorption band at 600 – 780 nm has the largest absorption coefficient () (IDT-NTI-2EH: 6.6×104 cm-1, IDT-NTI-1HH: 6.2×104 cm-1) in the spectrum. Additionally, IDT-NTIs have another absorption band at 400 – 500 nm (IDT-NTI-2EH:  = 4.0×104 cm-1, IDT-NTI-1HH:  = 3.4×104 cm-1). The simulated absorption spectrum of the model compound of IDT-NTI reproduced the experimental results with the absorption at 732 nm (oscillator strength: f = 1.61) and at 449 nm (f = 1.12) (see Supporting Information,

Figure 2. Cyclic voltammograms (a) and absorption spectra in the thin-film state (b) of IDT-NTIs.

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Table 1. Photovoltaic parameters of OPVs based on IDTNTI-2EH:PBDB-T and IDT-NTI-1HH:PBDB-T. Acceptor IDTNTI2EHa IDTNTI1HHb

Anneal

w/o 210 °C, 60 min. w/o

VOC

JSC

/V

/ mAcm-2

FF

PCE /%

0.91

11.71

0.58

6.26 c

±0.00

±0.06

±0.01

(6.21±0.05)

0.92

14.43

0.69

9.07 c

±0.00

±0.05

±0.00

(9.01±0.06)

1.01

8.07

0.59

5.05 c

±0.01

±0.22

±0.01

(4.83±0.22)

a)

Optimized D/A weight ratio was 1.3:1.0, b) Optimized D/A weight ratio was 1.0:1.0. c) Maximum value. Figure S4). With these two absorption bands in the spectrum, IDT-NTIs can cover wide range of the solar spectrum. PBDB-T, which exhibits complementary absorption to IDT-NTIs (Figure 2b) and favorable EHOMO/ELUMO, was chosen as a suitable donor material for fabrication of OPVs (Figure 3a). Their photovoltaic parameters with optimized solvent and donor/acceptor (D/A) weight ratio are summarized in Table 1 (the details of the optimization are shown in Table S1). Figure 3b and 3c shows the current densityvoltage (J-V) curves and the EQE spectra, respectively. From Figure 3b, typical photovoltaic responses with relatively high open-circuit voltage (VOC), short-circuit current density (JSC), and fill factor (FF) are confirmed. The spectra in Figure 3c cover a wide range of wavelength ca. 350 – 800 nm, in agreement with the absorption spectra of the active materials, which demonstrates the contribution of both donor and acceptor to the current generation. The maximum PCEs of the OPVs based on as-spun films of IDT-NTI-1HH:PBDB-T and IDT-NTI-2EH:PBDB-T were 5.05% and 6.26%, respectively. The OPVs with IDT-NTI1HH showed higher VOC (1.02 V) than those with IDT-NTI2EH (0.91V) as expected from the higher ELUMO. On the other hand, the IDT-NTI-2EH-based devices showed a higher JSC, reflecting the red-shifted absorption of the acceptor material and the higher EQE (Figure 3c) than that of IDT-NTI-1HH-based devices (vide infra). These results indicate that the N-substituents in IDT-NTIs can influence the OPV properties. Another influence caused by the alkyl substituent was observed upon thermal annealing of the active layers (Table S2): The annealed OPVs with IDT-NTI2EH (210 °C, 60 min.) showed enhanced PCEs of up to 9.07% with a JSC of 14.38 mA cm-2 and a FF of 0.69. In contrast, thermal annealing did not improve the photovoltaic properties of IDT-NTI-1HH-based OPVs (90, 120, 180 °C), and, after thermal annealing at 210 °C, they were drastically diminished (PCE < 1%). The ordering natures of IDT-NTI -2EH and -1HH in the neat thin films and in the bulk-heterojunction layer were investigated by two-dimensional grazing incidence X-ray diffraction (2D-GIXD, Figure 4 and S5). The 2D diffraction image of IDT-NTI-2EH shows peaks assignable to the faceon stacking (Figure 4a, ~qz = 1.75 Å-1 and qxy = 0.33 Å-1); this ordering is beneficial for the carrier transport in OPVs with a vertical device structure. In contrast, IDT-NTI-1HH did

Figure 4. 2D-GIXD diffraction images of the neat films of IDT-NTI-2EH (a) and IDT-NTI-1HH (b), the non-annealed blend films of IDT-NTI-2EH:PBDB-T (c) and IDT-NTI-1HH:PBDB-T (d), and the annealed blend films of IDT-NTI-2EH:PBDB-T (e, 210 °C, 60 min.) and IDT-NTI-1HH:PBDB-T (f, 210 °C, 60 min.). not show any detectable peaks (Figure 4b). The lower ordering nature of IDT-NTI-1HH could be caused by the branching position in the 1HH groups close to the -conjugated skeleton. This likely disturbs - stacking of IDTNTI-1HH in the thin-film state. As observed in Figure 4c and 4d, these ordering natures were maintained in the bulk-heterojunction layers, which could explain the higher JSC of the non-annealed OPVs based on IDT-NTI2EH:PBDB-T. After the thermal annealing (210 °C, 60 min.), the crystallinity in IDT-NTI-2EH:PBDB-T films was improved (Figure 4e): the full widths at half maximum (FWHMs) of the peaks assignable to the face-on stacking (0.31 Å-1 at ~qz = 1.74 Å-1 and 0.066 Å-1 at qxy = 0.31 Å-1) were smaller than those of the non-annealed film (0.42 Å-1 at ~qz = 1.71 Å-1 and 0.127 Å-1 at qxy = 0.30 Å-1). The better crystallinity could explain the higher JSCs and FFs of the annealed devices; as reported by Zusan et al. and Bernardo et al., dissociation of charge-transfer states is improved by the carrier delocalization, which can be correlated with an increased carrier mobility in well-ordered active materials.38,39 To confirm this hypothesis in the present devices, the mobilities of the annealed and the non-annealed films of IDT-NTI2EH:PBDB-T were evaluated by the steady-state spacecharge-limited current (SCLC) technique (Figure S7, Table S3). The electron mobility of the annealed film was 1.4×10-3 cm2 V-1 s-1, which is higher than that of the non-annealed one (2.4×10-4 cm2 V-1 s-1). Moreover, the exciton dissociation

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probability (Pdiss) in the OPV devices were estimated from the plot of photogenerated current density (Jph) versus effective voltage (Veff) (Figure S9).40 The annealed devices gave an improved Pdiss of 84% (non-annealed device: 73%). As a result, it can be confirmed that effective exciton dissociation in the annealed device gives the improved JSCs and FFs.

Supporting Information. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.chemmater.XXXXXXX. Experimental details, additional data, Scheme S1, Tables S1–S5, and Figures S1–S13

Concerning the IDT-NTI-1HH:PBDB-T films, annealing caused a drastic change in crystallinity: from the amorphous-like nature (Figure 4d) to the well-ordered crystalline film, as confirmed by the many peaks both on the qz and qxy axes (Figure 4f). In opposition to the IDT-NTI2EH:PBDB-T films, better ordering decreased the OPV performances. In order to understand this counterintuitive phenomena, the morphological properties of the blend films of both IDT-NTI-2EH:PBDB-T and IDT-NTI1HH:PBDB-T were investigated by transmission electron microscopy (TEM, Figure S10). The TEM images of the annealed film of IDT-NTI-2EH:PBDB-T (210 °C, 60 min.) showed more homogeneous morphology with a uniform nano-structure than that of as-cast film. In contrast, aggregates were observed in the TEM image of the annealed film of IDT-NTI-1HH:PBDB-T while such aggregates could not be observed in the image of the as-cast film. This morphological change of IDT-NTI-1HH:PBDB-T films could be directly correlated to the change of ordering observed in the 2D-GIXD. It can be associated with a 3D-like crystallite formation with a large-scale phase separation, which can disturb the effective charge carrier generation and transport in the OPVs. This explains the diminished photovoltaic properties of the annealed devices of IDT-NTI-1HH. It is worth mentioning that the N-substituents on the NTI unit also affect the ordering nature in the thin-film state, thereby the OPV properties.

Corresponding Author

In summary, IDT-NTIs were synthesized and evaluated as acceptors in OPVs. IDT-NTIs have two absorption bands; one is at 600 – 780 nm, which is red-shifted compared with the absorption of NTI (~ 510 nm) thanks to the planar -conjugated structure, and the other is at 400 – 500 nm. Owing to these two bands, IDT-NTIs can absorb a wide range of the solar spectrum. By combining with a donor polymer, PBDB-T, with complementary absorption the resulting OPVs yielded PCEs as high as 9%. These performances are comparable to those of the best OPVs with PDI-based acceptors, suggesting that NTI is a promising unit for superior NFAs. In addition, the substituents in the imide groups of the NTI unit, 1HH and 2EH, affected the physicochemical properties and the ordering natures in the thin-film state, which gave distinct photovoltaic properties. N-substituted NTIs can be synthesized easily from the N,N´-unsubstituted NTI, which allows us to modify structures and properties of NTI-based materials for further development of efficient NFAs. Molecular design, synthesis, and evaluation of new NTI-based acceptors are now underway in our group.

AUTHOR INFORMATION * M. Nakano E-mail: [email protected] * K. Takimiya E-mail: [email protected]

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This work was financially supported by JSPS KAKENHI Grant Numbers 15H02196, 16K05900, Iketani Science and Technology Foundation, and the Strategic Promotion of Innovative Research and Development from the Japan Science and Technology Agency (JST). HRMSs were measured at the Molecular Structure Characterization Unit, RIKEN Center for Sustainable Resource Science (CSRS). The DFT calculations using Gaussian 09 were carried out by using the RIKEN Integrated Cluster of Clusters (RICC). Elemental analysis and TEM measurement were carried out at the Materials Characterization Support Unit in RIKEN, Advanced Technology Support Division. 2D-GIXD experiments were performed at BL46XU of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI). We thank Dr. T. Koganezawa for supporting the GIXD measurements.

REFERENCES (1) Yu,G,; Gao, J.; Hummelen, J. C.; Wudl, F.; Heeger, A. J. Polymer Photovoltaic Cells: Enhanced Efficiencies via a Network of Internal Donor-Acceptor heterojunctions Science 1995, 270, 1789– 1791. (2) Arias, A. C.; MacKenzie, J. D.; McCulloch, I.; Rivnay, J.;Salleo, A. Materials and Applications for Large Area Electronics: Solution-Based Approaches. Chem. Rev. 2010, 110, 3–24. (3) Dennler, G.; Scharber, M. C.; Brabek, C. J. Polymer-Fullerene Bulk-Heterojunction Solar Cells. Adv. Mater. 2009, 21, 1323–1338. (4) Zhao, J.; Li, Y.; Yang, G.; Jiang, K.; Lin, H.; Ade, H.; Ma, W.; Yan, H. Efficient organic solar cells processed from hydrocarbon solvents. Nat. Energy, 2016, 1, 15027. (5) Deng, D.; Zhang, Y.; Zhang, J.; Wang, Z.; Zhu, L.; Fang, J.; Xia, B.; Wang, Z.; Li, K.; Ma, W.; Wei, Z. Fluorination-enabled optimal morphology leads to over 11% efficiency for inverted small-molecule organic solar cells. Nat. Commun. 2016, 7, 13740. (6) Anthony, J. E. Small-Molecule, Nonfullerene Acceptors for Polymer Bulk Heterojunction Organic Photovoltaics. Chem. Mater. 2011, 23, 583–590. (7) Lin, Y.; Zhan, X. Non-fullerene acceptors for organic photovoltaics: an emerging horizon. Mater. Horiz. 2014, 1, 470–488. (8) Nielsen, C. B.; Holliday, S.; Chen, H.-Y.; Cryer, S. J.; McCulloch, I.; Non-fullerene electron acceptors for use in organic solar cells. Acc. Chem. Res. 2015, 48, 2803–2812. (9) Liang, N.; Jiang, W.; Hou, J.; Wang, Z. New developments in non-fullerene small molecule acceptors for polymer solar cells. Mater. Chem. Front. 2017, 1, 1291–1303. (10) Zhao, W.; Qian, D.; Zhang, S.; Li, S.; Inganäs, O.; Gao, F.; Hou, J. Fullerene-Free Polymer Solar Cells with over 11% Efficiency and Excellent Thermal Stability. Adv. Mater. 2016, 28, 4734–4749.

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(11) Yang, Y.; Zhang, Z.-G.; Bin, H.; Chen, S.; Gao, L.; Xue, L.; Yang, C.; Li, Y. Side-Chain Isomerization on an n-type Organic Semiconductor ITIC Acceptor Makes 11.77% High Efficiency Polymer Solar Cells. J. Am. Chem. Soc. 2016, 138, 15011–15018. (12) Li, S.; Ye, L.; Zhao, W.; Zhang, S.; Mukherjee, S.; Ade, H.; Hou, J. Energy-Level Modulation of Small-Molecule Electron Acceptors to Achieve over 12% Efficiency in Polymer Solar Cells. Adv. Mater. 2016, 28, 9423–9429. (13) Zhao, W.; Li, S.; Yao, H.; Zhang, S.; Zhang, Y.; Yang, B.; Hou, J. Molecular Optimization Enables over 13% Efficiency in Organic Solar Cells. J. Am. Chem. Soc. 2017, 139, 7148–7151. (14) Bin, H.; Gao, L.; Zhang, Z.-G.; Yang, Y.; Zhang, Y.; Zhang, C.; Chen, A.; Xue, L.; Yang, C.; Xiao, M.; Li, Y. 11.4% Efficiency nonfullerene polymer solar cells with trialkylsilyl substituted 2D-conjugated polymer as donor. Nat. Commun. 2016, 7, 13651. (15) Chen, S.; Liu, Y.; Zhang, L.; Chow, P. C. Y.; Wang, Z.; Zhang, G.; Ma, W.; Yan, H. A Wide-Bandgap Donor Polymer for Highly Efficient Non-fullerene Organic Solar Cells with a Small Voltage Loss. J. Am. Chem. Soc. 2017, 139, 6298–6301. (16) Liu, Y.; Zhang, Z.; Feng, S.; Li, M.; Wu, L.; Hou, R.; Xu, X.; Chen, X.; Bo, Z. Exploiting Noncovalently Conformational Locking as a Design Strategy for High Performance Fused-Ring Electron Acceptor Used in Polymer Solar Cells. J. Am. Chem. Soc. 2017, 139, 3356–3339. (17) Zhan, X.; Facchetti, A.; Barlow, S.; Marks, T. J.; Ratner, M. A.; Wasielewski, M. R.; Marder S. R. Rylene and Related Diimides for Organic Electronics. Adv. Mater. 2011, 23, 268–284. (18) Fernández-Lázaro, F.; Zink-Lorre, N.; Sastre-Santos, A. Perylenediimides as non-fullerene acceptors in bulk-heterojunction solar cells (BHJSCs). J. Mater. Chem. A 2016, 4, 9336–9346. (19) Liu, J.; Chen, S.; Qian, D.; Gautam, B.; Yang, G.; Zhao, J.; Bergqvist, J.; Zhang, F.; Ma, W.; Ade, H.; Inganäs, O.; Gundogdu, K.; Gao, F.; Yan, H. Fast charge separation in a non-fullerene organic solar cell with a small driving force. Nat. Energy 2016, 1, 16089. (20) Meng, D.; Fu, H.; Xiao, C.; Meng, X.; Winands, T.; Ma, W.; Wei, W.; Fan, B.; Huo, L.; Doltsinis, N. L.; Li, Y.; Sun, Y.; Wang, Z. Three-Bladed Rylene Propellers with Three-Dimensional Network Assembly for Organic Electronics. J. Am. Chem. Soc. 2016, 138, 10184–10190. (21) Duan, Y.; Xu, X.; Yan, H.; Wu, W.; Li, Z.; Peng, Q. Pronounced Effects of a Triazine Core on Photovoltaic PerformanceEfficient Organic Solar Cells Enabled by a PDI Trimer-Based Small Molecular Acceptor. Adv. Mater. 2017, 29, 1605115. (22) Liu, Y.; Zhang, L.; Lee, H.; Wang, H.-W.; Santala, A,; Liu, F.; Diao, Y.; Briseno, A.-L.; Russell, T. P. NDI-Based Small Molecule as Promising Nonfullerene Acceptor for Solution-Processed Organic Photovoltaics. Adv. Energy Mater. 2015, 5, 1500195. (23) Srivani, D.; Gupta, A.; Bhosale, S. V.; Puyad, A. L.; Xiang, W.; Li, J.; Evans, R. A.; Bhosale, S. V. Non-fullerene acceptors based on central naphthalene diimide flanked by rhodamine or 1,3-indanedione. Chem. Commun. 2017, 53, 7080–7083. (24) Chen, W.; Nakano, M.; Kim, J.-H.; Takimiya, K.; Zhang, Q. Naphtho[2,3-b]thiophene diimide (NTI): a mono-functionalisable core-extended naphthalene diimide for electron-deficient architectures. J. Mater. Chem. C 2016, 4, 8879–8883. (25) Chen, W.; Nakano, M.; Takimiya, K.; Zhang, Q. Selective thionation of naphtho[2,3-b]thiophene diimide:tuning of the optoelectronic properties and packing structure. Org. Chem. Front. 2017, 4, 704-710.

(26) Bai, H.; Wang, Y.; Cheng, P.; Wang, J.; Wu, Y.; Hou, J.; Zhan, X. An electron acceptor based on indacenodithiophene and 1,1-dicyanomethylene-3-indanone for fullerene-free organic solar cells. J. Mater. Chem. A 2015, 3, 1910-1914. (27) Wu, Y.; Bai, H.; Wang, Z.; Cheng, P.; Zhu, S.; Wang.; Ma, W.; Zhan, X. A planar electron acceptor for efficient polymer solar cells. Energy Environ. Sci. 2015, 8, 3215–3221. (28) Li, Y.; Liu, X.; Wu, F.-P.; Zhou, Y.; Jiang, Z.-Q.; Song, B.; Zhang, Z.-G.; Gao, F.; Inganäs, O.; Li, Y.; Liao, L.-S. Non-fullerene acceptor with low energy loss and high external quantum efficiency: towards high performance polymer solar cells. J. Mater. Chem. A 2016, 4, 5890–5897. (29) Lin, Y.; Zhang, Z.-G.; Bai, H.; Wang, J.; Yao, Y.; Li, Y.; Zhu, D.; Zhan, X. High-performance fullerene-free polymer solar cells with 6.31% efficiency. Energy Environ. Sci. 2015, 8, 610–616. (30) Lin, Y.; Li, T.; Zhao, F.; Han, L.; Wang, Z.; Wu, Yang.; He. Q.; Wang, J.; Huo, L.; Sun, Y.; Wang, C.; Ma, W.; Zhan, X. Structure Evolution of Oligomer Fused-Ring Electron Acceptors toward High Efficiency of As-Cast Polymer Solar Cells. Adv. Energy Mater. 2016, 6, 1600854. (31) Wang, J.-L.; Liu, K.-K.; Yan, J.; Wu, Z.; Liu, F.; Xiao, F.; Chang, Z.-F.; Wu, H.-B.; Cao, Y.; Russell, T. P.; Series of Multifluorine Substituted Oligomers for Organic Solar Cells with Efficiency over 9% and Fill Factor of 0.77 by Combination Thermal and Solvent Vapor Annealing. J. Am. Chem. Soc. 2016, 138, 7687–7697. (32) N,N´,N´´,N´´´-Tetrakis(2-ethylhexyl)-2,7-bis(naphtho[2,3b]thiophen-2-yl)-4,4,9,9-tetrakis(4-hexylphenyl)-s-indaceno[1,2b:5,6-b´]dithiophene-4´,4´´,5´,5´´,8´,8´´,9´,9´´-octacarboxytetraimide (IDT-NTI-2EH) and N,N´,N´´,N´´´-tetrakis(1-hexylheptyl)-2,7-bis(naphtho[2,3-b]thiophen-2-yl)-4,4,9,9tetrakis(4-hexylphenyl)-s-indaceno[1,2-b:5,6-b´]dithiophene4´,4´´,5´,5´´,8´,8´´,9´,9´´-octacarboxytetraimide (IDT-NTI-1HH) (33) Lin, Y.; Wang, J.; Dai, S.; Li, Y.; Zhu, D.; Zhan, X. A Twisted Dimeric Perylene Diimide Electron Acceptor for Efficient Organic Solar Cells. Adv. Energy Mater. 2014, 4, 1400420. (34) Poly[(2,6-{4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]benzo[1,2b:4,5-b´]dithiophene})-alt-{5,5-[1´,3´-di(thiophen-2-yl)-5´,7´bis(2-ethylhexyl)benzo[1´,2´-c:4´,5´-c´]dithiophene-4´,8´-dione]}] (PBDB-T) (35) Qian, D.; Ye, L.; Zhang, M.; Liang, Y.; Li, L.; Huang, Y.; Guo, X.; Zhang, S.; Tan, Z.; Hou, J. Design, Application, and Morphology Study of a New Photovoltaic Polymer with Strong Aggregation in Solution State. Macromolecules 2012, 45, 9611–9617. (36)Wen, W.; Ying, L.; Hsu, B. B. Y.; Zhang, Y.; Nguyen, T.-Q.; Bazan, G. C. Regioregular pyridyl[2,1,3]thiadiazole-co-indacenodithiophene conjugated polymers. Chem. Commun. 2013, 49, 7192– 7194. (37) Nakano, M.; Sawamoto, M.; Yuki, M.; Takimiya, K. N,N´-Unsubstituted Naphthodithiophene Diimide: Synthesis and Derivatization via N-Alkylation and -Arylation. Org. Lett. 2016, 18, 37703773. (38) Zusan, A.; Vandewal, K.; Allendorf, B.; Hansen, N. H.; Pflaum, J.; Salleo, A.; Dyakonov, V.; Deibel, C. The Crucial Infuluence of Fullerene Phases on Photogeneration in Organic Bulk Heterojunction Solar Cells. Adv. Energy Mater. 2014, 4, 1400922. (39) Bernardo, B.; Cheyns, D.; Verreet, B.; Schaller, R. D.; Rand, B. P.; Giebink, N. C. Delocalization and dielectric screening of charge transfer states in organic photovoltaic cells. Nat. Commun. 2014, 5, 3245. (40) Wu, J.-L.; Chen, F.-C.; Hsiao, Y.-S.; Chien, F.-C.; Chen, P.; Kuo, C.-H.; Huang, M. H.; Hsu, C.-S. Surface plasmonic effects of metallic nanoparticles on the performance of polymer bulk heterojunction solar cells. ACS Nano 2011, 5, 959–967.

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