Modulating PCBM-Acceptor Crystallinity and Organic Solar Cell

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Modulating PCBM-Acceptor Crystallinity and Organic Solar Cell Performance by Judiciously Designing Small-Molecule Mainchain End-Capping Units Bo Jiang, Jiannian Yao, and Chuanlang Zhan* Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P.R. China S Supporting Information *

ABSTRACT: In this article, we report that the bulk-size and electron-donating/ electron-accepting nature of moieties, which are end-capping onto small-molecule donor mainchain, not only modulate the donor’s absorption, molecular frontier orbitals, and phase ordering, but also effectively tune the PC71BM-acceptor phase crystallinity. Compared to the electron-deficient trifluoromethyl (SM-CF3) units on the diketopyrrolopyrrole (DPP) small molecule mainchain ends, the electron-rich methoxyl (SM-OCH3) units ending on the same mainchain help improve the PC71BM-acceptor phase short-range ordering. As a result, the −OCH3 capping small-molecule displays larger short-circuit current density (Jsc) when blended with PC71BM (10.72 ± 0.22 vs. 16.15 ± 0.53 mA/cm2). However, the electron-donating nature of −OCH3 raises the donor HOMO level, which leads to a quite small opencircuit voltage (Voc) (0.624 vs. 0.881 V). Replacement of the −OCH3 with the large and weak electron-donating aromatic carbazolyl (SM-Cz) ones affords the small molecule of SM-Cz. The SM-Cz:PC71BM system affords a high Voc of 0.846 V and a large Jsc of 13.33 ± 0.34 mA/cm2 after thermal annealing, and hence gives a larger power conversion efficiency (PCE) of 6.26 ± 0.13%, which is among the top values achieved so far from the DPP molecules. Taken together, these results demonstrate that engineering the end-capping units on small-molecule donor mainchain can effectively modulate the organic solar cell performance. KEYWORDS: end-capping, bulk-size, electron-donating/electron-accepting, small-molecule, PCBM crystallinity

1. INTRODUCTION A solution-processable organic solar cell (OSC) utilizes an electron donor-material (D) and electron acceptor-material (A) blended film as the photoactive layer to absorb solar photons. The excitons created by both the blended D and A nanophases are separated into mobile electrons and holes at the D−A interfaces.1,2 The D−A interactions, such as D−A arrangement and separation distance, affect the charge dissociation efficiency and hence OSC performance.3−8 Recently, it was reported that the charge separation barrier can be effectively decreased when a greater D−A separated distance was achieved via introducing twisted octylphenyl substituent onto the polymer backbones. As a result, a higher power conversion efficiency (PCE) was achieved.9 It was revealed that a molecular shape-complementarity between the small molecule donor and C60 could lead to a faster electron transfer from the donor to the C60.10 For polymer PBDTTPD derivatives, introduction of bulky 2-ethylhexyl on the electrondonating units can hinder the electron donating units to interact with the fullerene, while involving the fullerene docking with the electron-accepting moieties, which leads to an improving PCE (8% vs 2%), compared to those with the 2ethylhexyl on the electron-accepting moieties.11 © XXXX American Chemical Society

Otherwise, it has been demonstrated that the conjugation ends onto the conjugation backbone impact on the solar cell performance. For example, introduction of aromatic, instead of alkyl capping units onto small molecule (SM) mainchain helps to improve the D−A compatibility through the π−π interactions between the end-capping aromatic units and PC71BM ([6,6]-phenyl-C71-butyric acid methyl ester), leading to nanoscale domain formation. As a result, the aromatic caps give a much higher short-circuit current-density (Jsc) than the alkyl chain ones.12 Herein, we show that the small molecule mainchain flanks (Figure 1) can not only tune the donor’s absorption spectrum, the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels and the donor phase ordering, but it can also effectively modulate the PCBM-acceptor phase crystallinity.

2. RESULTS AND DISCUSSION Synthesis and Characterizations. Scheme 1 is the synthetic procedure toward the three donor molecules. They Received: July 10, 2016 Accepted: September 13, 2016

A

DOI: 10.1021/acsami.6b08407 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces

Figure 1. (a) Molecular structures, (b) optimized configurations, and (c) orbital surfaces of the molecular frontier orbitals for the three SMs. In (b) the box represents the conjugation backbone, and the circle represents the end-capping units, respectively.

Scheme 1. Synthetic Routes for SM-CF3, SM-OCH3, and SM-Cz

Figure 2. UV−vis absorption spectra of the three SMs obtained from dilute chloroform solutions (a) and neat thin films (b).

110 °C and the yield was 74, 81, and 71% for SM-CF3, SMOCH3, and SM-Cz, respectively. They are characterized by using 1H NMR and 13C NMR spectroscopy, TOF-MS (timeof-flight mass spectrometry), and elemental analysis. The synthetic details are given in the Experimental Section. Thermogravimetric analyses (TGA) showed that the decomposition temperature at 5% weight-loss is 411.4, 390.7, and 381.1 °C, respectively, indicating that all of the three molecules

share the same backbone, DPP-BDT-DPP (DPP: diketopyrrolopyrrole, BDT: benzo[1,2-b:4,5-b′]dithiophene), but differ only in the end-capping groups, namely SM-CF3, SM-OCH3, and SM-Cz, respectively. DPP and BDT are very often used building blocks for OPV materials.13,14 Three benzene boronic acids with different functional units in the para-position were selected as starting materials, respectively. The terminal products were synthesized by using Pd(PPh3)4 as the catalyst and the Stille coupling reaction was performed in toluene at B


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ACS Applied Materials & Interfaces Table 1. Optoelectronic Properties of the Three SMs λmax (nm)a

λedge (nm)b

Egopt

SM

solution

film

film

(eV)

SM-CF3 SM-OCH3 SM-Cz

653 656 655

650, 710 650, 714 648, 704

772 771 772

1.61 1.61 1.61

c

HOMO (eV)

d

−5.06 −4.75 −4.89

LUMO (eV)

d

−3.20 −2.87 −3.02

Egcal

HOMO

HOMO

(eV)d

(eV)e

(eV)f

1.86 1.88 1.87

−5.26 −5.06 −5.13

−5.21 −5.04 −5.16

Absorption peak wavelength. bOnset of absorption. cOptical band gap, estimated from the λedge of films, Egopt = 1240/λedge. dResults from DFT calculations. eResults from CV tests. fResults from UPS measurements. a

Figure 3. (a) Cyclic voltammogram of three SM film samples which were directly drop-casted on the glassy carbon electrode. The solid green lines are indicative of the determinations of the HOMOs. (b) Energy level diagram of the three molecules, PC71BM, the electron and hole interlayer, and the electrodes used for fabrications of OSCs in this article.

−5.21, −5.04, and −5.16 eV, respectively. These results agree well with those values estimated from the CV tests. The HOMO energy level of the parent DPP-BDT-DPP is −5.15 eV.15 Introduction of electron-deficient −CF3 onto the backbone ends lowers the HOMO level moderately down to −5.26 eV. When the strong electron-donating unit,−OCH3, was capped onto the backbone ends, the HOMO energy is obviously raised to −5.06 eV, and as weak electron-donating unit,−Cz, is introduced, the HOMO energy is kept without obvious changes (−5.13 eV). These results clearly imply that the HOMO energy level can be judiciously tuned via the endcapping unit (Figure 3b), which makes it possible to control the solar cell open-circuit voltage, Voc. The DFT calculated Eg value for SM-CF3, SM-OCH3, and SM-Cz is 1.86, 1.88, and 1.87 eV, respectively, which are of no obvious differences. In consideration of the same optical Eg value (1.61 eV) for the three molecules, as obtained from the film absorption spectra, one can find that the end-capping units change both the HOMO and LUMO energy levels. The LUMO values shown in Figure 3b are calculated by using the equation of ELUMO = EHOMO + Egopt, where the EHOMO is obtained from CV tests. Phase Crystallinity in Solid Films. Grazing-incidence wide-angle X-ray scattering (GIWAXS) is a useful tool to probe the underlining structures of the solar cell blended film. In principle, the shape and intensity distribution of the diffraction bands in the qxy − qz space are both associated with the distributions of the orientations of the diffracting crystallites, and the width of the diffraction peak involves the information on the coherence length (size) of the crystalline grains.17,18 Two-dimensional (2D) and one-dimensional (1D) GIWAXS were therefore applied to get structure information on the three donors in the pure and blended films and of the PC71BMacceptor in the blended films. Figure S3 shows the 2D GIWAXS images of the three SMs’ pristine films. The corresponding 1D plots for in-plane and out-of-plane trances are shown in Figures 4 and S3, respectively. The (100) and (010) diffractions are clearly observed in both in-plane and out-

exhibit excellent thermal stability (Figure S1, Supporting Information). Optoelectronic Properties. Optimized configurations and the HOMO and LUMO orbital surfaces of the three SMs are calculated with density function theory (DFT) and shown in Figure 1. UV−vis absorption spectra of the three SMs in dilute CF solution and in thin films are displayed in Figure 2. The corresponding optical data, including the absorption peak wavelength (λmax), edge wavelength (λedge), and optical band gap (Eg), are summarized in Table 1. Benefiting from the intrinsic intramolecular charge transfer of the A-D-A backbone, all the three SMs show an absorption band at 500−700 nm wavelength region in CF solution. Relative to the solution spectra, the λmax as well as λedge for thin films are obviously redshifted. Meanwhile, a shoulder peak emerges at about 710 nm, indicating intermolecular interactions in the film state. The strength of this shoulder peak obeys the sequence of SM-OCH3 > SM-CF3 ≈ SM-Cz, implying stronger π−π stacking for SMOCH3 than the other two donors.15,16 The optical Eg values, obtained from the λedge of films, are nearly identical for three SMs (1.61 eV). We performed cyclic voltammetry (CV) to estimate the electrochemical properties of the three molecules. The CV experiments were conducted by using the SM film samples which were prepared directly atop the working electrode (Figure 3a). Table 1 is the estimated data. The onsets of oxidation potential of SM-CF3, SM-OCH3, and SM-Cz are estimated to be 0.86, 0.66, and 0.73 V, respectively. Based on the empirical equation: EHOMO = −e(Eox,onset + 4.4), the calculated HOMO energy levels of SM-CF3, SM-OCH3, and SM-Cz are −5.26, −5.06, and −5.13 eV, respectively. The DFT calculations displayed a same trend of HOMO values, as shown in Table 1, which is −5.06, −4.75, and −4.89 eV for SM-CF3, SM-OCH3, and SM-Cz, respectively. Ultraviolet photoelectron spectroscopy (UPS) measurements were further applied to estimate the three molecules’ HOMO energies (Figure S2). The HOMO energy value calculated from the UPS data is C


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Figure 4. 1D plots represent in-plane traces for pristine films.

Figure 6. 1D DIWAXS represents out-of-plane traces for blend films.

of-plane directions, while the π−π stacking (010) peak, appearing at 2θ ≈ 24° (q = 1.70 Å−1), is stronger along the in-plane direction than out-of-plane, indicating a favorable edge-on orientation for three SMs. Notably, the (010) diffraction strength obeys the sequence of SM-OCH3 > SMCF3 > SM-Cz. The small units of −OCH3 and −CF3 enhance small molecule packing and lead to greater crystallinity than that of the large −Cz units. The π−π stacking distance is calculated to be 3.65, 3.72, and 3.78 Å for SM-OCH3, SM-CF3, and SM-Cz, respectively, which indicates that (1) the electrondonating −OCH3 caps lead to a smaller π−π stacking distance than the electron-deficient −CF3 ones, and (2) the smaller electron-donating −OCH3 caps result in more compact packing than the larger electron-donating −Cz ones. The decreasing trend of the π−π stacking distance is in agreement with the absorption characteristics of the solid film (Figure 2). Figure 5 shows the 2D GIWAXS images of the PC71BMblended films of the three SMs, the corresponding 1D plots for in-plane and out-of-plane trances are shown in Figures S4 and 6, respectively. After being blended with PC71BM, though the (010) diffraction for three SMs becomes inconspicuous, it is clear that the (100) and (200) diffractions are stronger along the out-of-plane direction than along the in-plane direction, implying that the small molecule conducts similar edge-on stacking in the blended film to that in the pristine films. The peak at 2θ ≈ 19.6° (q = 1.42 Å−1) is assigned to the diffraction originated from the clusters of the isotropic fullerene.19−22 This diffraction peak at 1.42 Å−1 is also indicative of the short-range ordering of PC71BM-acceptor.23 In OSCs, the effective charge carriers transport perpendicular to the substrate, so the molecular stacking along the out-of-plane direction is more concerned. As shown in Figures 5 and 6, the PC71BM diffractions for three blended films exhibit different band widths The bandwidth is 0.25, 0.13, and 0.27 Å−1 for the SMCF3:PC71BM, SM-OCH3:PC71BM, and SM-Cz:PC71BM sys-

tem, respectively. Smaller bandwidth means greater crystallinity and also means greater coherence length (short-range ordering).18 The changing tendency of the bandwidth of the PC71BM diffraction band indicates (1) replacement of the electron-deficient −CF3 with the electron-rich −OCH3 endcapping units helps to improve the PC71BM-acceptor phase crystallinity and coherence length. This might be due to that the electron-rich −OCH3 units help enhance the small molecule-PC71BM interaction, and (2) replacement of the small electron-rich −OCH3 end-capping units with the weak and large electron-donating Cz ones again reduce the shortrange ordering of the PC71BM-acceptor phase domains. This might be related to two facts. One is that the large aromatic −Cz units can introduce bulky steric effects between the DPP and PC71BM, which weakens the small molecule-PC71BM interactions. The other is that the large −Cz units may be randomly oriented in different directions as the small molecule forms slipped aggregates. Such random orientations of the large −Cz units reduce the packing ordering of the PC71BM-acceptor phases. Otherwise, the greatest crystallinity of the PC71BMacceptor phase might be due to the intercalations of the small molecule of SM-OCH3 into the PC71BM aggregates, as observed in the polymer:PCBM systems.23 Similar to the Czcaps, introduction of the large diphenylamine (SM-DPA) endcaps also leads to small PC71BM-acceptor phase crystallinity.12 Film Morphology. Transmission electron microscopy (TEM) is a powerful tool to probe the blend film nanoscale film-morphologies. As shown in Figure 7, the bright phases are assigned to the domains involving the SM donors and the dark phases are mainly formed from the PC71BM acceptor because the fullerene has relatively higher electron-scattering density than the small molecule.24 The SM-CF3 based blended film (Figure 7a) exhibits some large-scale and heterogeneous dark domains, ca. 50 nm in size. In the SM-OCH3 based blended film, the dark phases are coherent to form fiber-like domains,

Figure 5. 2D GIWAXS images of the PC71BM-blended films of SM-CF3 (a), SM-OCH3 (b), and SM-Cz (c), respectively. D


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Figure 7. TEM images of the optimal solar cells based on SM-CF3 (a), SM-OCH3 (b), and SM-Cz (c), respectively.

Figure 8. (a) J−V characteristics and (b) EQE curves of optimal devices based on SMs:PC71BM.

Table 2. Photovoltaic Parameters of the Optimal Solar Cell Devices.a

a

donor

thermal annealing

Jsc (mA cm−2)

Voc (V)

FF

PCEb (%)

SM-CF3 SM-OCH3 SM-Cz

110 °C 90 °C 110 °C

10.72 ± 0.22 16.15 ± 0.53 13.33 ± 0.34

0.881 ± 0.004 0.624 ± 0.010 0.846 ± 0.008

0.568 ± 0.012 0.563 ± 0.016 0.548 ± 0.013

5.31 ± 0.13 (5.54) 5.89 ± 0.16 (6.05) 6.26 ± 0.13 (6.44)

Average value from 10 devices. bThe values in brackets represent the highest performance.

affording rather homogeneous and even continuous nanoscale interpenetrating networks. Obviously, the coherence length of the dark phase is larger than that in the SM-CF3 based blended film, which agrees well with the GIWAXS data: the PC71BMacceptor phase in the SM-OCH3:PC71BM system shows greater coherence length than that in the SM-CF3:PC71BM system. The dark phase diameter is of 16 nm. This size is similar to the exciton diffusion length, which is about 5−20 nm.25 The SMCz:PC71BM blended film is homogeneous, compared to the SM-CF3:PC71BM blended film. Otherwise, most dark phases are less coherent in the SM-Cz:PC71BM blended film than in the SM-OCH3:PC71BM blended film. Again, the bright phase diameter is larger in the SM-Cz:PC71BM blended film than in the SM-OCH3:PC71BM blended film. The more homogeneous interpenetrating morphology, larger coherence length of the PC71BM-acceptor phases, and smaller donor phase size, as observed from the SM-OCH3 based blended film may generate a larger volume density of the D−A interfaces, which can enhance the exciton dissociation and the mobile carrier generation, affording a larger short-circuit current-density.26−30 Photovoltaic Performances. The photovoltaic properties of the three molecules were investigated with a conventional solar cell device structure: indium tin oxide (ITO)/poly(3,4ethylene-dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/active layer/Ca/Al. The small molecule is blended

with PC71BM to form the active layer. The device fabrications are showed in details in the Experimental Section. We optimized the D/A weight ratio and the 1,8-diiodooctane (DIO) to host solvent volume ratio. The photovoltaic results are given in Table S1. Thermal annealing the solar cell blend improves the short-circuit current-density (Jsc) for all three small molecules. Again, thermal annealing increases the opencircuit voltage (Voc) from 0.65 to 0.85 V for SM-Cz (Figure S5), but impacts less effects for other two molecules. Figure 8a and b are the current density−voltage (J−V) curves and the external quantum efficiency (EQE) responses of three optimal solar cells in which the three small molecules were used as the blended donor material, respectively, Table 2 shows the average values of the three small molecules based solar cells. Under the optimal thermal annealing condition, the Voc values are 0.890, 0.630, and 0.850 V, respectively, for SM-CF3, SM-OCH3, and SM-Cz. The changing tendency of the Voc agrees well with the HOMO energy levels of these three molecules, which are −5.26, −5.06, and −5.13 eV, respectively. The measured Jsc values of the devices based on SM-CF3, SM-OCH3, and SM-Cz are 10.91, 16.69, and 13.62 mA cm−2, respectively. Both the electron-donating −OCH3 and the aromatic Cz ones gives a much higher Jsc than the electron-deficient −CF3 ones. Because the Cz-caps yield a much higher Voc (0.85 vs. 0.65 V), SM-Cz gives a higher PCE value than SM-OCH3 (6.05% vs. 6.44%). E


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Figure 9. Plots of ln(J) vs ln(V) for the three SMs, (a) hole-only and (b) electron-only.

Figure 10. Illumination-dependent Jsc (a) and Voc (b) of the SMs based devices.

described approximately using equation Jsc ∝ Pα (Figure 10a).32,33 At open-circuit, the photogenerated free electrons and holes all recombine, and the loss mechanism can be reflected by the equation Voc ∝ nkT/qln(P) (Figure 10b), where k, T, and q are the Boltzmann constant, the temperature in Kelvin, and the elementary charge, respectively.34 The fitting α values (Figure 10a) obey the sequence of SM-OCH3 > SMCz > SM-CF3, and the fitting n values (Figure 10b) obey the sequence of SM-OCH3 < SM-Cz < SM-CF3, which is in line with the sequence of Jsc values. The results suggest that electron-rich small units −OCH3 are helpful to reduce both monomolecular and bimolecular recombination loss, resulting from the better crystallinity for both donor and acceptor phase and better nanomorphology in blend film.

Previously, we have reported a DPA capping small molecule (SM-DPA). When blended with PC71BM, SM-DPA has a Voc of 0.62 V obtained without usage of thermal annealing, the optimal average Jsc is 15.43 mA/cm2,12 which is comparable to the Jsc value obtained from SM-Cz and SM-OCH3. These comparisons again demonstrate that incorporation of electrondonating caps onto the DPP ends helps improve the solar cell short-circuit current. Charge Carrier Mobility. The hole and electron mobilities were estimated with the space-charge-limited current (SCLC) method. For this purpose, the hole-only device structure is ITO/PEDOT:PSS/active layer/Au. The electron-only device configuration is ITO/TIPD/active layer/Al, in which TIPD31 is used as the buried interlayer. We performed the optimal conditions, as obtained for fabrications of the optimal photovoltaic devices, to fabricate the active layer of the holeonly and electron-only device both. Figure 9 shows the corresponding plots of ln(J) vs ln(V). The hole/electron mobility of the SM-CF3, SM-OCH3, and SM-Cz based films is estimated to be 2.02 × 10−4/6.39 × 10−4, 5.96 × 10−4/9.53 × 10−4, and 1.01 × 10−4/8.04 × 10−4 cm2 V−1 s−1, respectively. The scale of the electron mobility agrees with the coherence length of the blended film dark phases, as revealed from the TEM images. The scale of the hole mobility is again consistent with the trend of the phase cystallinity of the three small molecules in their pristine films. Charge Recombination. Light-power dependent J−V characteristics were performed to investigate the recombination losses. Figure 10 displays the plots of Jsc and Voc at various light intensities (P) from 3 to 100 mW cm−2. The good linear relationship for both Jsc and Voc indicates good quality of the devices. Both geminate and nongeminate mechanisms contributes the recombination losses in the three optimal OSCs. At short-circuit, the large internal voltage can effectively sweep out the photogenerated electrons and holes to the right electrodes before they recombined. The recombination mechanism can be

3. CONCLUSIONS In summary, we reported herein that the PC71BM-acceptor phase crystallinity is effectively modulated by judiciously selecting the small molecule mainchain end-caps. Introduction of small electron-rich −OCH3 units leads to great PC71BMacceptor phase short-range ordering, compared to the small electron-deficient −CF3 units. As a result, the −OCH3 endcapping small-molecule displays the larger Jsc when blended with PC71BM. As the small electron-rich −OCH3 caps are replaced by the large and weak electron-donating −Cz moieties, the resulting SM-Cz shows a higher Voc value upon thermal annealing and a comparable Jsc value as well as a comparable FF value, and hence a higher PCE. These results demonstrate that engineering the end-capping units on small-molecule donor mainchain is an effective approach to modulate the PCBM phase morphology and thus OSC performance. 4. EXPERIMENTAL SECTION Synthesis. Synthetic procedures of the products are shown in Scheme 1. F


ACS Applied Materials & Interfaces Synthesis of Compounds 2a, 2b, and 2c. These three products were synthesized by following our previously reported procedure.12 The yield is 82, 76, and 74%, respectively for 2a, 3b, and 2c. The characterization data are as follows. For 2a: 1H NMR (400 MHz, CDCl3, δ), 8.93−8.91 (m, 2H), 7.79− 7.76 (m, 2H), 7.69−7.53 (m, 4H), 4.08−4.02 (m, 4H), 1.89 (m, 2H), 1.36−0.88 (m, 28H). For 2b: 1H NMR (400 MHz, CD2Cl2, δ), 8.90−8.88 (m, 1H), 8.50−8.48 (m, 1H), 7.58−7.55 (m, 2H), 7.33−7.32 (m, 1H), 7.18− 7.16 (m, 1H), 6.91−6.88 (m, 2H), 3.97−3.84 (m, 4H), 3.77 (s, 3H), 1.83−1.74 (m, 2H), 1.26−0.79 (m, 28H). For 2c: 1H NMR (400 MHz, CDCl3, δ), 8.93 (m, 1H), 8.58 (m, 1H), 8.19 (m, 1H), 8.04−8.02 (m, 1H), 7.83 (m, 2H), 7.56−7.28 (m, 10H), 4.02−3.90 (m, 4H), 1.89−1.80 (m, 2H), 1.31−0.81 (m, 28H). Synthesis of Products 3a (SM-CF3), 3b (SM-OCH3), and 3c (SMCz). These three products were synthesized by following our previously reported procedure.12 The yield is 74, 81, and 71, respectively. The characterization data are as follows. For 3a (SM-CF3): 1H NMR (400 MHz, CD2Cl2, δ), 8.93−8.87 (m, 4H), 7.52−7.32 (m, 14H), 7.05 (m, 4H), 3.82−3.64 (m, 8H), 3.02 (m, 4H), 1.86−1.72 (m, 6H), 1.32 (m, 48H), 1.07−0.91 (m, 36H). 13C NMR (100 MHz, CDCl3, δ), 161.79, 161.68, 146.56, 144.58, 142.44, 140.19, 139.61, 139.34, 137.63, 137.06, 136.79, 136.47, 135.50, 133.50, 131.92, 130.68, 130.02, 129.49, 128.62, 128.25, 127.38, 126.35, 125.78, 124.02, 123.24, 120.87, 108.58, 108.31, 46.01, 41.63, 39.49, 39.30, 34.53, 32.73, 30.54, 30.38, 29.11, 28.70, 28.50, 25.93, 23.87, 23.71, 23.24, 23.22, 14.37, 14.24, 14.19, 11.09, 10.76, 10.67. MS (MALDITOF): m/z 1913.7 [M]+. 1912.7; Anal. Calcd for C108H124F6N4O4S8: C, 67.82; H, 6.53; N, 2.93; found: C, 67.62; H, 6.49; N, 2.91. For 3b (SM-OCH3): 1H NMR (400 MHz, CDCl3, δ), 8.93 (m, 4H), 7.43−7.31 (m, 10H), 6.92−6.79 (m, 8H), 3.89−3.68 (m, 14H), 2.90−2.82 (m, 4H), 1.83−1.73 (m, 6H), 1.33−1.19 (m, 48H), 0.90− 0.81 (m, 36H). 13C NMR (100 MHz, CDCl3, δ), 161.75, 161.65, 146.57, 144.13, 142.47, 140.21, 139.63, 139.37, 137.65, 137.08, 136.81, 136.49, 135.52, 134.05, 131.89, 130.63, 129.96, 129.44, 128.59, 128.22, 127.48, 126.35, 125.78, 124.02, 120.87, 108.58, 108.31, 46.07, 43.87, 41.61, 39.47, 39.28, 34.54, 32.80, 32.73, 30.51, 30.36, 29.09, 28.68, 28.48, 25.93, 23.87, 23.71, 23.25, 23.22, 14.37, 14.24, 14.19, 11.13, 10.80, 10.71, 10.67. MS (MALDI-TOF): m/z 1837.7 [M]+. 1836.7; Anal. Calcd for C108H130N4O6S8: C, 70.62; H, 7.13; N, 3.05; found: C, 70.43; H, 7.01; N, 2.98. For 3c (SM-Cz): 1H NMR (400 MHz, CDCl3, δ), 8.95 (m, 4H), 8.19−7.96 (m, 6H), 7.45−7.19 (m, 24H), 6.95 (m, 4H), 3.92 (m, 8H), 2.91 (m, 4H), 1.86−1.76 (m, 6H), 1.36−1.18 (m, 48H), 0.92−0.81 (m, 36H). 13C NMR (100 MHz, CDCl3, δ), 161.77, 161.67, 147.17, 146.57, 142.47, 140.21, 139.63, 139.36, 137.65, 137.08, 136.81, 136.49, 135.52, 130.65, 130.35, 129.99, 129.77, 129.46, 128.59, 128.22, 127.72, 127.26, 126.35, 125.78, 124.02, 123.27, 122.89, 122.12, 121.95, 120.87, 116.32, 108.58, 108.31, 46.01, 45.92, 41.52, 39.37, 39.18, 34.45, 32.64, 30.59, 30.43, 29.16, 28.75, 28.55, 25.98, 23.92, 23.76, 23.30, 23.27, 14.42, 14.29, 14.24, 11.14, 10.81, 10.72. MS (MALDI-TOF): m/z 1837.7 [M]+. 1836.7; Anal. Calcd for C130H140N6O4S8: C, 74.10; H, 6.70; N, 3.99; found: C, 73.91; H, 6.53; N, 3.93.

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ACKNOWLEDGMENTS

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REFERENCES

The authors gratefully acknowledge the financial support of the National Natural Science Foundation of China (NSFC, Nos. 91433202, 21327805, 91227112, and 21221002), Chinese Academy of Sciences (CAS, XDB12010200), and Ministry of Science and Technology of the People’s Republic of China (MOST, 2013CB933503 and 2012YQ120060). Beijing Synchrotron Radiation Facility (BSRF) is acknowledged for supports of GIWAXS measurements.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.6b08407. Experimental details, TGA curves, 1H NMR spectra, 13C NMR spectra, and GIWAXS and their in-plane and outof-plane profiles (PDF)

■

Research Article

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest. G


Research Article

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Modulating PCBM-Acceptor Crystallinity and Organic Solar Cell

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