Generalized First-Order Kinetic Model for Biosolids Decomposition

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Design of Cyanovinylene-Containing Polymer Acceptors with Large Dipole Moment Change for Efficient Charge Generation in High-Performance All-Polymer Solar Cells Han-Hee Cho, Seonha Kim, Taesu Kim, Vijaya Gopalan Sree, Sung-Ho Jin, Felix Sunjoo Kim, and Bumjoon J. Kim* over fullerene-based PSCs, including easily tunable polymer properties, simultaneous light absorption by both donors and acceptors, and enhanced stability against mechanical and thermal stresses.[1] However, few all-PSCs have been reported to exhibit power conversion efficiencies (PCEs) higher than 7%, as many systems have relatively low short-circuit current densities (JSC) and fill factors (FF).[1d,e,2] The low performance of all-PSCs is mainly attributed to (i) low electron mobility of polymer acceptors within the photoactive layer and (ii) inefficient exciton dissociation at donor/acceptor (D/A) interfaces as a result of the anisotropic packing structure of donor and acceptor polymers.[3] Another hurdle for efficient exciton dissociation is lower dielectric constant of the polymers than that of fullerene derivatives, which increases the binding energy of the excitons in all-PSCs.[4] To develop polymer acceptors with high electron mobility, various n-type polymers have been designed and synthesized, among which naphthalenediimide (NDI)-based copolymers have attracted great attention due to strong π–π interactions between NDI units and facile functionalization through the N-position of NDI moiety.[1b,c,2a,c,5] However, lowest unoccupied molecular orbital (LUMO) of NDI-based polymers is often largely localized on the NDI units due to the high electron affinity of NDI, which hinders efficient intermolecular electron transport.[5n,6] Thus, insertion of strong electron-withdrawing groups into the electron donating moieties of the NDI-based copolymers would be a promising approach to enhance electron transport and intermolecular interactions by delocalizing the LUMO over the polymer backbone and generating stronger orbital overlaps between the adjacent polymer chains.[6a,b] Charge generation at the interfaces of the D/A polymer domains within the photoactive layer depends significantly on the interfacial dipole moment between the donor and acceptor and the internal dipole moment of the polymers.[3a,5l,7] Additionally, for conjugated polymers with a large dipole moment difference between the ground and excited states (Δµge), the electron–hole separation distance within the polymer chain increases as the polarized exciton is formed, which reduces the

Designing polymers that facilitate exciton dissociation and charge transport is critical for the production of highly efficient all-polymer solar cells (allPSCs). Here, the development of a new class of high-performance naphthalenediimide (NDI)-based polymers with large dipole moment change (Δµge) and delocalized lowest unoccupied molecular orbital (LUMO) as electron acceptors for all-PSCs is reported. A series of NDI-based copolymers incorporating electron-withdrawing cyanovinylene groups into the backbone (PNDITCVT-R) is designed and synthesized with 2-hexyldecyl (R = HD) and 2-octyldodecyl (R = OD) side chains. Density functional theory calculations reveal an enhancement in Δµge and delocalization of the LUMO upon the incorporation of cyanovinylene groups. All-PSCs fabricated from these new NDI-based polymer acceptors exhibit outstanding power conversion efficiencies (7.4%) and high fill factors (65%), which is attributed to efficient exciton dissociation, well-balanced charge transport, and suppressed monomolecular recombination. Morphological studies by grazing X-ray scattering and resonant soft X-ray scattering measurements show the blend films containing polymer donor and PNDITCVT-R acceptors to exhibit favorable face-on orientation and well-mixed morphology with small domain spacing (30–40 nm).

1. Introduction All-polymer solar cells (all-PSCs) composed of binary mixtures of conjugated polymer donors and acceptors have attracted significant attention due to their many advantages Dr. H.-H. Cho, S. Kim, T. Kim, Prof. B. J. Kim Department of Chemical and Biomolecular Engineering Korea Advanced Institute of Science and Technology (KAIST) Daejeon 34141, Republic of Korea E-mail: [email protected] V. G. Sree, Prof. S.-H. Jin Department of Chemistry Education Graduate Department of Chemical Materials, and Institute for Plastic Information and Energy Materials Pusan National University Busan 46241, Republic of Korea Prof. F. S. Kim School of Chemical Engineering and Materials Science Chung-Ang University Seoul 06974, Republic of Korea The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/aenm.201701436.

DOI: 10.1002/aenm.201701436

Adv. Energy Mater. 2017, 1701436

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Coulombic attraction and exciton binding energy, promoting exciton dissociation.[4a,7c,d,8] Therefore, polymer acceptors with large Δµge are anticipated to facilitate efficient exciton dissociation at D/A interfaces in all-PSCs.[3a,5l,7,9] However, the influence of the Δµge of polymer acceptors on exciton dissociation processes and photovoltaic performance of all-PSCs has not yet been explored in detail. Herein, we report a new class of polymer acceptors with large Δµge and high electron mobility that provide efficient charge generation and yield high-performance all-PSCs. Density functional theory (DFT) calculations showed that introduction of electronwithdrawing cyanovinylene groups, consisting of a cyano group on a vinylene linkage, into the NDI-based copolymer backbone (PNDITCVT-R) led to the delocalized LUMO over the polymer chain and the enhanced Δµge value. Notably, the cyanovinylene groups achieved the aforementioned effects without disrupting the π-extended structure of the polymer acceptors due to the presence of the conjugated vinylene bond. All-PSCs fabricated from these new polymer acceptors and a poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene-alt-5-octyl4H-thieno[3,4-c]-pyrrole-4,6(5H)-dione]) (PBDTTTPD) donor exhibited high performances. In particular, the device constructed from a PBDTTTPD:PNDITCVT-HD blend film generated an outstanding PCE (7.4%), with high open-circuit voltage (VOC > 0.9 V) and high FF (65%), attributed to the efficient charge dissociation and suppressed germinate and trap-assisted recombination. Grazing X-ray scattering (GIXS) and resonant soft X-ray scattering (RSoXS) measurements showed that blend films of PBDTTTPD and PNDITCVT-R exhibited favorable faceon orientation and bulk-heterojunction (BHJ) morphology with small domain spacings (30–40 nm).

2. Results and Discussion 2.1. Synthesis and Thermal Properties of Polymers A series of n-type copolymers was prepared by Stille poly condensation of 4,9-dibromo-2,7-bis(R)benzo[lmn][3,8] phenanthroline-1,3,6,8(2H,7H)-tetraone and (E)-2,3-bis(5(trimethylstannyl)thiophen-2-yl)acrylonitrile. Polymer acceptors with 2-hexydecyl(HD) and 2-octadecyl (OD) side chains are denoted as PNDITCVT-HD and PNDITCVT-OD, respectively. PBDTTTPD was selected as the polymer donor due to its lowlying highest occupied molecular orbital (HOMO) energy level anticipated to yield high VOC, and was synthesized according to a previously reported procedure.[1b,10] The chemical structures of PBDTTTPD and the polymer acceptors, PNDITCVT-HD and PNDITCVT-OD, are provided in Figure 1a. The number-average molecular weight (Mn) and dispersity (Ð) of PNDITCVT-HD and PNDITCVT-OD were determined to be 35 kg mol−1 (Ð = 2.34) and 25 kg mol−1 (Ð = 1.92), respectively, by size exclusion chromatography (SEC) relative to polystyrene standards in o-dichlorobenzene (Table 1). The effect of molecular weight in this study is assumed to be negligible due to the similar mole cular weights (≈30 kg mol−1) and distributions of PNDITCVT-R. PNDITCVT-HD, and PNDITCVT-OD exhibited high solubility in common organic solvents, including chloroform, chlorobenzene, and o-dichlorobenzene, attributed to the polar cyano


group in the polymer backbone. In addition, PNDITCVT-R displayed distinct crystallization behavior due to the rigid carbon–carbon double bond of the vinylene moiety and low steric hindrance of the cyano groups. Differential scanning calorimetry (DSC) measurements showed that PNDITCVTHD and PNDITCVT-OD exhibited endothermic melting transitions (Tm) at 319 and 272 °C, and exothermic crystallization transitions (Tc) at 244 and 210 °C, respectively (Table 1 and Figure S1, Supporting Information). Additionally, a higher crystallization enthalpy (ΔHc) was measured for PNDITCVT-HD (4.7 J g−1) than for PNDITCVT-OD (4.2 J g−1). The use of shorter alkyl side chains induced stronger crystallization behavior due to a stronger tendency for intermolecular assembly, which is consistent with crystallization behaviors reported for other NDI-based polymers.[5k,m]

2.2. Optical and Electrochemical Properties UV-visible (UV-vis) absorption spectra of thin films of PNDITCVT-HD, PNDITCVT-OD, and PBDTTTPD were measured to evaluate the light absorption ability as active layer components (Figure 1b). Both PNDITCVT-HD and PNDITCVT-OD films produced similar absorption spectra, with an absorption maximum at 637 nm and an optical bandgap of 1.64 eV (Table 1). Notably, PNDITCVT-R exhibited a complementary absorption with the polymer donor, PBDTTTPD, which is particularly beneficial for all-PSCs as it broadens the range of light adsorption.[1b] The HOMO and LUMO energy levels of the polymers were estimated by cyclic voltammetry (CV) (Figure S2, Supporting Information) and the optical bandgap. PNDITCVTHD and PNDITCVT-OD exhibited same HOMO and LUMO energy levels of −5.59 and −3.95 eV, respectively (Figure 1a and Table 1). Both the HOMO and LUMO energy levels of PNDITCVT-R were downshifted due to the electron-withdrawing cyanovinylene groups compared to those (−5.34 and −3.89 eV, respectively) of an analogous copolymer without the cyanovinylene groups, poly[[N,N′-bis(2-alkyl(R))-naphthalene1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)] (PNDI2R-T2).[2b] Since the HOMO energy level of the NDIbased copolymers is mainly affected by the nature of electronrich units, the incorporation of the cyanovinylene group in the electron-rich part of PNDITCVT-R induced a stronger downshift in the HOMO level, resulting in the increased bandgap (1.64 eV) for PNDITCVT-R polymer than that (1.45 eV) of PNDI2R-T2.[11] The HOMO and LUMO energy levels of PBDTTTPD were determined to be −5.49 and −3.64 eV, respectively. The large LUMO‒LUMO offset (0.31 eV) between PBDTTTPD and PNDITCVT-R, attributed to the presence of the electron-withdrawing cyanovinylene groups, is expected to be sufficient to generate free charge carriers at the D/A interface.[10a,12]

2.3. Molecular Simulation To estimate the change in LUMO level and electron density distribution within the polymer chain upon the incorporation of cyanovinylene groups, DFT calculations were conducted using

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Figure 1. a) Chemical structures and energy levels, and b) absorption spectra of thin films of PNDITCVT-R and PBDTTTPD.

the B3LYP/6-31G* basis set with a Spartan 14 package.[13] The equilibrium geometry and frontier molecular orbitals at the HOMO and LUMO levels are shown in Figure S3 (Supporting Information) for two model compounds, NDI-bithiophene-NDI (NDI-T2-NDI) and NDI-thiophene-cyanovinylene-thiopheneNDI (NDI-TCVT-NDI). The alkyl side chains were simplified to methyl groups. In the case of NDI-T2-NDI, the frontier molecular orbital was strongly localized on the two NDI moieties. Interestingly, when the cyanovinylene group was introduced between the two thiophene rings, as in NDI-TCVT-NDI, the left-hand side NDI moiety, which was closer to the cyano group, showed relatively more delocalization of the frontier molecular orbital. In addition, the calculated LUMO energy level of NDIT2-NDI (−3.5 eV) decreased to −3.6 eV in the NDI-TCVT-NDI. Thus, the cyanovinylene-containing PNDITCVT-R is anticipated to show improved charge transport through enhanced intermolecular interaction by the delocalized π-overlap.[6a,14]

2.4. Photovoltaic Performance and Charge Mobility To examine the capability of the cyanovinylene-containing NDI polymers as acceptors in all-PSCs, photovoltaic devices were fabricated with an inverted structure of ITO/ZnO/polymer blend/ MoO3/Ag. For convenience, the PBDTTTPD:PNDITCVT-HD and PBDTTTPD:PNDITCVT-OD blend films are denoted as PNDITCVT-HD blend and PNDITCVT-OD blend, respectively. The donor:acceptor weight ratio in the blend films was optimized at 1.3:1, and 1.5 vol% diphenylether (DPE) was used to optimize the blend morphology (Tables S1 and S2, Supporting Information).[2c,15] The current density‒voltage (J‒V) curves and external quantum efficiency (EQE) characteristics of PNDITCVT-HD and PNDITCVT-OD blend films are shown in Figure 2, and their photovoltaic performances are summarized in Table 2. The VOC values of all-PSCs with PNDITCVT-HD and PNDITCVT-OD blend active layers exceeded 0.9 V, attributed

Table 1. Properties of PBDTTTPD, PNDITCVT-HD, and PNDITCVT-OD.

PBDTTTPD PNDITCVT-HD PNDITCVT-OD a)

Mn/Mwa) [kg mol−1]

Ða)

Tmb) [°C]

Tcb) [°C]

ΔHcb) [J g−1]

Egoptc) [eV]

EHOMO [eV]

ELUMO [eV]

24/59

2.46

–

–

–

1.85

−5.49d)

−3.64e)

1.64

−5.59e)

−3.95d)

1.64

−5.59e)

−3.95d)

35/82 25/48

2.34 1.92

319 272

244 210

4.7 4.2

Determined by SEC eluting in o-DCB relative to polystyrene standards; b)Determined from DSC measurements; c)Measured from UV–vis absorption spectra of thin films; from CV curves; e)Calculated from ELUMO = EHOMO + Egopt.

d)Measured


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PCE of 6.5%. The difference between the performances of PNDITCVT-HD and PNDITCVT-OD blend devices was mainly attributed to the higher JSC of 12.15 mA cm−2 obtained with PNDITCVT-HD blend devices compared to that of PNDITCVTOD blend devices (10.41 mA cm−2). As shown in Figure 2b, the PNDITCVT-HD blend devices produced higher photocurrent than PNDITCVT-OD devices over the entire range of the EQE spectra, which is consistent with the previous finding that NDI-based polymers having shorter alkyl side chains provide greater photocurrent.[5k,m] The higher performance of the PNDITCVT-HD device is further supported by the difference in absorbance of the PNDITCVT-HD and PNDITCVT-OD blends (Figure 2c). In addition, the higher shunt resistance (Rsh) in the PNDITCVT-HD blend device (Rsh = 1.05 kΩ cm2) compared to that measured in the PNDITCVT-OD blend device (0.95 kΩ cm2) was partly responsible for the higher PCE.[1e] To better understand the performances of the all-PSCs, the electron (µe) and the hole (µh) mobilities of the blends were measured using the space charge-limited current (SCLC) method (Figure S4, Supporting Information).[16] As shown in Table 2, the µh/µe values were measured to be 6.11 × 10−5/1.44 × 10−4 cm2 V−1 s−1 for PNDITCVT-HD blend films and 3.48 × 10−5/4.31 × 10−5 cm2 V−1 s−1 for PNDITCVTOD blend films. Notably, the µe measured in the PNDITCVTHD blend films was much higher than those of other NDI-based copolymer blend films, likely due to the more delocalized LUMO and the high electron affinity of polymers with cyano groups.[2c,5k–m,11a] The mobility ratio, defined as the ratio of the slower carrier mobility to the faster carrier mobility, was close to unity for both PNDITCVT-HD and PNDITCVT-OD blends, suggesting that well-balanced mobilities are important for producing the high FF of the corresponding devices.[17]

2.5. Charge Dissociation and Recombination Properties

Figure 2. a) J–V curves, b) EQE characteristics, and c) absorption spectra of the all-PSCs fabricated with PNDITCVT-HD blend and PNDITCVT-OD blend.

to the low-lying HOMO levels of PBDTTTPD.[1b,10] Interestingly, unlike all-PSCs with typical NDI-based polymer acceptors that generally exhibit FF values lower than 0.55, the devices with PNDITCVT-HD and PNDITCVT-OD blend active layers yielded surprisingly high FFs of over 0.65 without the use of an interlayer.[1f,2a,3a,5k,m,10a,11b] As a result, the all-PSCs with PNDITCVT-HD blend films exhibited the outstanding PCE of 7.4%, and those based on PNDITCVT-OD blend afforded the


The charge dissociation efficiencies of the PNDITCVT-R blend films were calculated by measuring the photocurrent density (Jph) as a function of the effective voltage (Veff) (Figure S5, Supporting Information).[5l] The charge dissociation efficiency was estimated from the ratio of Jph at the short-circuit condition to the saturated Jph value at high Veff (≈10 V). PNDITCVT-HD and PNDITCVT-OD blends afforded similar, high charge dissociation efficiencies of 83 and 84%, respectively. In addition, the charge recombination behavior within the photoactive layer was then investigated by measuring the J‒V characteristics as a function of light intensity (P).[18] The VOC and JSC curves as a function of P were plotted on linear-log and log-log scales, respectively (Figure 3). In general, upon reduction of monomolecular recombination under open-circuit conditions, the slope of VOC versus ln(P) decreases from 2kBTq–1, where kB is the Boltzmann constant, T is the temperature, and q is the elementary charge.[19] As shown in Figure 3a, the slopes of VOC versus ln(P) of PNDITCVT-HD and PNDITCVT-OD blends were 0.95 and 0.94kBTq–1, respectively, suggesting that germinate and/or trap-assisted recombination within the active layer was dramatically suppressed.[5l,19] To the best of our knowledge, these values are among the lowest reported for non-fullerene-based PSCs. Slopes smaller than kBTq–1 are due to recombination at the

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Table 2. Photovoltaic performances and SCLC electron and hole mobilities of the PBDTTTPD:PNDITCVT-HD and PBDTTTPD:PNDITCVT-OD blend films. Active layera)

VOC [V]

JSC [mA cm−2]

FF

PCEmax (PCEavg)b) [%]

Rsh [kΩ cm2]

µh [cm2 V−1 s−1]

µe [cm2 V−1 s−1]

PBDTTTPD:PNDITCVT-HD

0.94

12.15

0.65

7.4 (7.2)

1.05

6.11 × 10−5

1.44 × 10−4

0.95

10−5

4.31 × 10−5

PBDTTTPD:PNDITCVT-OD

0.95

10.41

0.66

6.5 (6.3)

3.48 ×

a) Photovoltaic characteristics were measured under AM 1.5 G-simulated solar illumination (100 mW cm−2); b)The average values were determined from measurements of at least ten devices.

interfaces between the active layer and adjacent layers.[20] Meanwhile, the slopes (α) of ln (JSC) versus ln (P) for PNDITCVT-HD and PNDITCVT-OD blend films measured under short-circuit conditions were close to unity, 0.994 and 0.996, respectively (Figure 3b), indicating negligible bimolecular recombination of both blend films at the short-circuit condition. Therefore, the P-dependent VOC and JSC trends of PNDITCVT-R blend films demonstrated the suppressed unfavorable recombination behavior under both open-circuit and short-circuit conditions, which is beneficial for achieving high FFs. 2.6. Dipole Moment Change (Δµge) To gain a deeper understanding of the highly efficient exciton dissociation and high FF observed for all-PSCs with PNDITCVT-R blends, Δµge values for PNDITCVT-R and a family of well-known NDI-based polymer acceptors (Figure S6, Supporting Information), including PNDI2R-T2 and poly [[N,N′-bis(2-alkyl(R))-naphthalene-1,4,5,8-bis(dicarboximide)2,6-diyl]-alt-thiophene] (PNDI2R-T), were calculated with the Gaussian 09 package. The Δµge values were determined according to the following equation: Δµge = [(µgx − µex)2 + (µgy − µey)2 + (µgz − µez)2]1/2, where µgx − µex, µgy − µey, and µgz − µez are the components of the difference between the dipole moments in the ground (g) and excited (e) states along the x, y, and z axes, respectively.[7c,d] The resulting Δµge values for the polymer acceptors are summarized in Table 3 without any distinction for the alkyl side chain length because the Δµge value is irrelevant to the alkyl side chain length.[21] Among the polymer acceptors in this study, PNDITCVT-R showed the highest Δµge of 23.53 D, with large dipole moments in both the ground and excited states of 4.31 and 26.21 D, respectively. In contrast, significantly lower Δµge values were calculated

for PNDI2R-T2 (13.35 D) and PNDI2R-T (12.34 D). The higher Δµge values are attributed mainly to the asymmetric chemical structure of TCVT and the presence of the electronwithdrawing cyano groups.[22] With these large Δµge values of PNDITCVT-R, more polarized excitons can be produced and the electron‒hole separation distance increased, resulting in reduced exciton binding energy.[7c,d] Thus, efficient dissociation of excitons generated from PNDITCVT-R into electrons and holes within the active layer of all-PSCs, taken together with the suppressed charge recombination observed in the P-dependent device characterization, contributed to the high FFs and overall photovoltaic performances of these devices.

2.7. Structural and Morphological Properties We next investigated the structural and morphological properties of the optimized PNDITCVT-HD and PNDITCVT-OD blends (Figure 4a,b and Figure S7, Supporting Information). Since the pristine films of PNDITCVT-R (Figure S8, Supporting Information) and PBDTTTPD exhibited face-on π–π stacking, the face-on/face-on alignment between PBDTTTPD and PNDITCVT-R in the blend is anticipated to facilitate efficient exciton dissociation and reduced charge recombination at D/A interfaces.[1b,23] In particular, the PNDITCVT-HD blend film showed a stronger (010) scattering peak at qz = 1.70 Å−1 with slightly tighter π–π stacking of 3.70 Å, compared to the PNDITCVT-OD blend film with a (010) spacing of 3.76 Å (qz = 1.67 Å−1) (Figure S7, Supporting Information). Next, RSoXS and atomic force microscopy (AFM) measurements were employed to investigate the phase-separated morphology of the blend films. RSoXS data were acquired at a photon energy of 285.4 eV to maximize scattering contrast between PBDTTTPD and PNDITCVT-R.[1b,5m] The maximum

Figure 3. Dependence of a) VOC and b) JSC on illuminated light intensity (P) of all-PSCs with PNDITCVT-HD blend and PNDITCVT-OD blend films.


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www.advancedsciencenews.com Table 3. Calculated dipole moments of the polymer acceptors. µga) [D]

µeb) [D]

Δµgec) [D]

PNDITCVT-R

4.31

26.21

23.53

PNDI2R-T2

2.58

15.85

13.35

PNDI2R-T

1.59

13.73

12.34

Polymer

a)Ground-state dipole moment; b)Excited-state dipole moment; c)Difference between the ground- and excited-state dipole moments (Δµge = [(µgx − µex)2 + (µgy − µey)2 + (µgz − µez)2]1/2).

scattering intensities of PNDITCVT-HD and PNDITCVT-OD blend films were observed at q = 0.0195 and 0.0151 Å−1, respectively, and the corresponding domain sizes were 32 and 42 nm, respectively (Figure 4c). The domains were much smaller than those of blend films formed from other NDI-based polymer acceptors, indicating that PNDITCVT-R blend films possessed

larger interfacial area.[1b,5k,m,11b] The smaller domain spacing likely results from the high solubility of PNDITCVT-R, which could be supported by temperature-dependent UV–vis absorption spectra (Figure S9, Supporting Information). Interestingly, whereas a solution of PNDI2OD-T2 (PNDI2R-T2 where R = OD) in o-dichlorobenzene (0.02 mg mL−1) showed severe aggregation behavior at low temperature (Figure S9a, Supporting Information), PNDITCVT-R were well-dissolved in o-dichlorobenzene at 25 °C (Figure S9b,c, Supporting Information). In addition, the absorption from intramolecular charge transfer (500−800 nm) of PNDITCVT-R was significantly enhanced during the film formation from the well-dissolved solutions. Therefore, the enhanced solubility of PNDITCVT-R by the incorporated cyanovinylene groups is anticipated to suppress the formation of large polymer aggregation and induce the favorable blend morphology during casting and drying of the active layer on the substrate. Moreover, AFM measurements showed that the two

Figure 4. 2D-GIXS images of a) PNDITCVT-HD and b) PNDITCVT-OD blend films. c) RSoXS profiles of PNDITCVT-HD and PNDITCVT-OD blend films measured at 285.4 eV.


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blend films had well-mixed morphology and smooth surface, with similar root-mean-square (RMS) roughness (1.1–1.3 nm, Figure S10, Supporting Information). Consequently, the combined results from the morphological analyses demonstrated that both PNDITCVT-HD and PNDITCVT-OD blends produced well-mixed morphology with large D/A interfacial areas, which makes the pair of PBDTTTPD and PNDITCVT-R promising as the high-performance active layer in all-PSCs.

3. Conclusion In summary, we have demonstrated highly efficient all-PSCs (PCE = 7.4%, FF = 65%) comprised of active layers formed with a new class of PNDITCVT-R acceptors. Introducing polar electron-withdrawing cyanovinylene groups into NDI-based polymer acceptors resulted in the large Δµge and more delocalized LUMO that promoted exciton dissociation and electron transport. These features led to all-PSCs with significantly reduced monomolecular recombination, well-balanced charge transport, and finely separated polymer domains. The experimental and computational efforts reported herein have generated new knowledge and guidelines for further development of high-performance polymer acceptors that efficiently generate and transport charges.

1,3,6,8(2H,7H)- tetraone (0.20 g, 0.20 mmol) and (E)-2,3-bis(5(trimethylstannyl) thiophen-2-yl)but-2-enenitrile (0.11 g, 0.20 mmol) gave PNDITCVT-OD. Yield: 0.16 g, 74%. 1H NMR (400 MHz, CDCl3) (Figure S11b, Supporting Information): δ 8.80 (2H), 7.72 (1H), 7.58 (1H), 7.47 (1H), 7.33 (2H), 4.04‒4.20 (4H), 1.93‒2.05 (2H), 1.16–1.51 (64H), 0.82–0.93 (12H). Elemental analysis—Calculated for (C65H89N3O4S2)n: C, 75.03; H, 8.62; N, 4.04; S, 6.16. Found: C, 74.89; H, 8.60; N, 3.93; S, 6.03. Synthesis of PBDTTTPD: PBDTTTPD was synthesized according to a previously reported procedure, with (4,8-bis(5-(2-ethylhexyl)thiophen-2yl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl)bis(trimethylstannane) (0.20 g, 0.22 mmol), 1,3-dibromo-5-octyl-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione (0.09 g, 0.22 mmol), Pd2(dba)3 (3 mol%), and P(o-tol)3 (12 mol%) in dry chlorobenzene (4 mL).[1b] Yield: 0.17 g, 93%. Synthesis of PNDI2OD-T2: PNDI2OD-T2 was synthesized according to a previously reported procedure, with 4,9-dibromo-2,7-bis(2octyldodecyl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone (0.30 g, 0.30 mmol), 5,5′-bis(trimethylstannyl)-2,2′-bithiophene (0.15 g, 0.20 mmol), Pd2(dba)3 (2 mol%), and P(o-tol)3 (8 mol%) in dry toluene (4 mL) and anhydrous DMF (0.4 mL).[11a] Yield: 0.23 g, 75%. Mn = 48 kg mol−1 and Mw = 99 kg mol−1.

Supporting Information Supporting Information is available from the Wiley Online Library or from the author.

Acknowledgements 4. Experimental Section Materials: Tris(dibenzylideneacetone)dipalladium(0) (Pd2(dba)3, 97%), tri(o-tolyl)phosphine (P(o-tol)3, 97%), and 5,5′-bis(trimethylstannyl)2,2′-bithiophene were purchased from Sigma-Aldrich. (4,8-Bis(5-(2ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl) bis(trimethylstannane) and 1,3-dibromo-5-octyl-4H-thieno[3,4-c]pyrrole4,6(5H)-dione were purchased from Solarmer Energy Inc. 4,9-Dibromo-2,7-bis(2-hexyldecyl)benzo[lmn][3,8]phenanthroline1,3,6,8(2H,7H)-tetraone, 4,9-dibromo-2,7-bis(2-octyldodecyl)benzo[lmn] [3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone, and (E)-2,3-bis(5(trimethylstannyl)thiophen-2-yl)but-2-enenitrile were purchased from Suna Tech. All reagents were purified by recrystallization or flash chromatography on silica gel. General Procedure for Polymerization: Monomers, Pd2(dba)3 (2 mol%), and P(o-tol)3 (8 mol%) were placed in a microwave reactor vial equipped with a magnetic stirrer and sealed with a cap. Dry toluene (4 mL) and anhydrous N,N-dimethylformamide (DMF) (0.3 mL) were added and the mixture was degassed with argon for 30 min. The vial was placed in the microwave reactor and vigorously stirred at 170 °C for 2 h. After cooling to room temperature, the solution was precipitated into methanol (300 mL). The precipitated polymers were purified by successive Soxhlet extraction with methanol, acetone, hexane, ethyl acetate, and chloroform. The chloroform fraction was precipitated into methanol (200 mL), isolated by filtration, and dried under vacuum at 40 °C for 24 h. PNDITCVT-HD: The procedure described above using 4,9-dibromo-2,7bis(2-hexyldecyl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)- tetraone (0.30 g, 0.34 mmol) and (E)-2,3-bis(5-(trimethylstannyl)thiophen-2-yl) but-2-enenitrile (0.19 g, 0.34 mmol) gave PNDITCVT-HD. Yield: 0.26 g, 81%. 1H NMR (400 MHz, CDCl3) (Figure S11a, Supporting Information): δ 8.79 (2H), 7.72 (1H), 7.58 (1H), 7.46 (1H), 7.33 (2H), 4.04‒4.19 (4H), 1.91‒2.06 (2H), 1.17–1.51 (48H), 0.81–0.95 (12H). Elemental analysis— Calculated for (C57H73N3O4S2)n: C, 73.75; H, 7.93; N, 4.53; S, 6.91. Found: C, 73.60; H, 7.90; N, 4.51; S, 6.68. PNDITCVT-OD: The procedure described above using 4,9-dibromo-2,7-bis(2-octyldodecyl)benzo[lmn][3,8]phenanthroline-


This research was supported by the National Research Foundation Grant (NRF-2016R1E1A1A02921128), provided by the Korean Government. The authors thank Dr. Cheng Wang for help with the RSoXS measurements. The authors acknowledge Prof. Biwu Ma and Dr. Rachel Letteri for helpful discussions.

Conflict of Interest The authors declare no conflict of interest.

Keywords all-polymer solar cells, cyanovinylene, naphthalenediimide, polymer acceptors

dipole

moments,

Received: May 24, 2017 Revised: July 17, 2017 Published online:

[1] a) H. Benten, D. Mori, H. Ohkita, S. Ito, J. Mater. Chem. A 2016, 4, 5340; b) T. Kim, J.-H. Kim, T. E. Kang, C. Lee, H. Kang, M. Shin, C. Wang, B. Ma, U. Jeong, T.-S. Kim, B. J. Kim, Nat. Commun. 2015, 6, 8547; c) H. Kang, W. Lee, J. Oh, T. Kim, C. Lee, B. J. Kim, Acc. Chem. Res. 2016, 49, 2424; d) Y. Guo, Y. Li, O. Awartani, J. Zhao, H. Han, H. Ade, D. Zhao, H. Yan, Adv. Mater. 2016, 28, 8483; e) L. Gao, Z.-G. Zhang, L. Xue, J. Min, J. Zhang, Z. Wei, Y. Li, Adv. Mater. 2016, 28, 1884; f) D. Mori, H. Benten, I. Okada, H. Ohkita, S. Ito, Energy Environ. Sci. 2014, 7, 2939. [2] a) Y.-J. Hwang, B. A. E. Courtright, A. S. Ferreira, S. H. Tolbert, S. A. Jenekhe, Adv. Mater. 2015, 27, 4578; b) S. Chen, Y. An, G. K. Dutta, Y. Kim, Z.-G. Zhang, Y. Li, C. Yang, Adv. Funct. Mater.

1701436 (7 of 8)


www.advenergymat.de

www.advancedsciencenews.com 2017, 27, 1603564; c) J. Oh, K. Kranthiraja, C. Lee, K. Gunasekar, S. Kim, B. Ma, B. J. Kim, S.-H. Jin, Adv. Mater. 2016, 28, 10016; d) Z. Li, X. Xu, W. Zhang, X. Meng, W. Ma, A. Yartsev, O. Inganäs, M. R. Andersson, R. A. J. Janssen, E. Wang, J. Am. Chem. Soc. 2016, 138, 10935; e) Y. Guo, Y. Li, O. Awartani, H. Han, J. Zhao, H. Ade, H. Yan, D. Zhao, Adv. Mater. 2017, 29, 1700309; f) J. W. Jo, J. W. Jung, H. Ahn, M. J. Ko, A. K. Y. Jen, H. J. Son, Adv. Energy Mater. 2017, 7, 1601365. [3] a) L. Ye, X. Jiao, M. Zhou, S. Zhang, H. Yao, W. Zhao, A. Xia, H. Ade, J. Hou, Adv. Mater. 2015, 27, 6046; b) M. Schubert, B. A. Collins, H. Mangold, I. A. Howard, W. Schindler, K. Vandewal, S. Roland, J. Behrends, F. Kraffert, R. Steyrleuthner, Z. Chen, K. Fostiropoulos, R. Bittl, A. Salleo, A. Facchetti, F. Laquai, H. W. Ade, D. Neher, Adv. Funct. Mater. 2014, 24, 4068; c) N. Zhou, A. S. Dudnik, T. I. N. G. Li, E. F. Manley, T. J. Aldrich, P. Guo, H.-C. Liao, Z. Chen, L. X. Chen, R. P. H. Chang, A. Facchetti, M. Olvera de la Cruz, T. J. Marks, J. Am. Chem. Soc. 2016, 138, 1240; d) K. Zhou, R. Zhang, J. Liu, M. Li, X. Yu, R. Xing, Y. Han, ACS Appl. Mater. Interfaces 2015, 7, 25352. [4] a) T. M. Clarke, J. R. Durrant, Chem. Rev. 2010, 110, 6736; b) B. A. Gregg, M. C. Hanna, J. Appl. Phys. 2003, 93, 3605. [5] a) X. Long, Z. Ding, C. Dou, J. Zhang, J. Liu, L. Wang, Adv. Mater. 2016, 28, 6504; b) C. Dou, X. Long, Z. Ding, Z. Xie, J. Liu, L. Wang, Angew. Chem. Int. Ed. 2016, 55, 1436; c) Y. Fukutomi, M. Nakano, J.-Y. Hu, I. Osaka, K. Takimiya, J. Am. Chem. Soc. 2013, 135, 11445; d) Z. Ding, X. Long, C. Dou, J. Liu, L. Wang, Chem. Sci. 2016, 7, 6197; e) Y. Guo, Y. Li, O. Awartani, J. Zhao, H. Han, H. Ade, D. Zhao, H. Yan, Adv. Mater. 2016, 28, 8483; f) L. Xue, Y. Yang, Z.-G. Zhang, X. Dong, L. Gao, H. Bin, J. Zhang, Y. Yang, Y. Li, J. Mater. Chem. A 2016, 4, 5810; g) S. Liu, Z. Kan, S. Thomas, F. Cruciani, J.-L. Brédas, P. M. Beaujuge, Angew. Chem. Int. Ed. 2016, 55, 12996; h) M. Sommer, J. Mater. Chem. C 2014, 2, 3088; i) X. Zhan, A. Facchetti, S. Barlow, T. J. Marks, M. A. Ratner, M. R. Wasielewski, S. R. Marder, Adv. Mater. 2011, 23, 268; j) J. W. Jung, J. W. Jo, C.-C. Chueh, F. Liu, W. H. Jo, T. P. Russell, A. K. Y. Jen, Adv. Mater. 2015, 27, 3310; k) W. Lee, C. Lee, H. Yu, D.-J. Kim, C. Wang, H. Y. Woo, J. H. Oh, B. J. Kim, Adv. Funct. Mater. 2016, 26, 1543; l) J. Jung, W. Lee, C. Lee, H. Ahn, B. J. Kim, Adv. Energy Mater. 2016, 6, 1600504; m) C. Lee, H. Kang, W. Lee, T. Kim, K.-H. Kim, H. Y. Woo, C. Wang, B. J. Kim, Adv. Mater. 2015, 27, 2466; n) K. Takimiya, I. Osaka, M. Nakano, Chem. Mater. 2014, 26, 587; o) Y.-J. Hwang, T. Earmme, B. A. E. Courtright, F. N. Eberle, S. A. Jenekhe, J. Am. Chem. Soc. 2015, 137, 4424; p) T. Earmme, Y.-J. Hwang, S. Subramaniyan, S. A. Jenekhe, Adv. Mater. 2014, 26, 6080; q) T. Earmme, Y.-J. Hwang, N. M. Murari, S. Subramaniyan, S. A. Jenekhe, J. Am. Chem. Soc. 2013, 135, 14960; r) P. Deng, C. H. Y. Ho, Y. Lu, H.-W. Li, S.-W. Tsang, S. K. So, B. S. Ong, Chem. Commun. 2017, 53, 3249; s) Z. Fei, Y. Han, J. Martin, F. H. Scholes, M. Al-Hashimi, S. Y. AlQaradawi, N. Stingelin, T. D. Anthopoulos, M. Heeney, Macromolecules 2016, 49, 6384. [6] a) H.-J. Yun, S.-J. Kang, Y. Xu, S. O. Kim, Y.-H. Kim, Y.-Y. Noh, S.-K. Kwon, Adv. Mater. 2014, 26, 7300; b) S. Chai, S.-H. Wen, K.-L. Han, Org. Electron. 2011, 12, 1806; c) S. Cho, J. H. Seo, S. H. Kim, S. Song, Y. Jin, K. Lee, H. Suh, A. J. Heeger, Appl. Phys.


Lett. 2008, 93, 263301; d) S. Cho, J. Lee, M. Tong, J. H. Seo, C. Yang, Adv. Funct. Mater. 2011, 21, 1910; e) T. Yamada, F. Suzuki, A. Goto, T. Sato, K. Tanaka, H. Kaji, Org. Electron. 2011, 12, 169. [7] a) N. Camaioni, R. Po, J. Phys. Chem. Lett. 2013, 4, 1821; b) L. J. A. Koster, S. E. Shaheen, J. C. Hummelen, Adv. Energy Mater. 2012, 2, 1246; c) B. Carsten, J. M. Szarko, L. Lu, H. J. Son, F. He, Y. Y. Botros, L. X. Chen, L. Yu, Macromolecules 2012, 45, 6390; d) B. Carsten, J. M. Szarko, H. J. Son, W. Wang, L. Lu, F. He, B. S. Rolczynski, S. J. Lou, L. X. Chen, L. Yu, J. Am. Chem. Soc. 2011, 133, 20468. [8] L. Lu, L. Yu, Adv. Mater. 2014, 26, 4413. [9] K. Kranthiraja, S. Kim, C. Lee, K. Gunasekar, V. G. Sree, B. Gautam, K. Gundogdu, S.-H. Jin, B. J. Kim, Adv. Funct. Mater. 2017, 27, 1701256. [10] a) M. A. Uddin, Y. Kim, R. Younts, W. Lee, B. Gautam, J. Choi, C. Wang, K. Gundogdu, B. J. Kim, H. Y. Woo, Macromolecules 2016, 49, 6374; b) J. Warnan, A. El Labban, C. Cabanetos, E. T. Hoke, P. K. Shukla, C. Risko, J.-L. Brédas, M. D. McGehee, P. M. Beaujuge, Chem. Mater. 2014, 26, 2299. [11] a) J. Choi, K.-H. Kim, H. Yu, C. Lee, H. Kang, I. Song, Y. Kim, J. H. Oh, B. J. Kim, Chem. Mater. 2015, 27, 5230; b) H.-J. Yun, H. H. Choi, S.-K. Kwon, Y.-H. Kim, K. Cho, ACS Appl. Mater. Interfaces 2015, 7, 5898. [12] T. E. Kang, H.-H. Cho, C.-H. Cho, K.-H. Kim, H. Kang, M. Lee, S. Lee, B. Kim, C. Im, B. J. Kim, ACS Appl. Mater. Interfaces 2013, 5, 861. [13] H.-H. Cho, T. E. Kang, K.-H. Kim, H. Kang, H. J. Kim, B. J. Kim, Macromolecules 2012, 45, 6415. [14] a) A. Casey, Y. Han, Z. Fei, A. J. P. White, T. D. Anthopoulos, M. Heeney, J. Mater. Chem. C 2015, 3, 265; b) W. Li, L. Yan, H. Zhou, W. You, Chem. Mater. 2015, 27, 6470. [15] H. Kang, M. A. Uddin, C. Lee, K.-H. Kim, T. L. Nguyen, W. Lee, Y. Li, C. Wang, H. Y. Woo, B. J. Kim, J. Am. Chem. Soc. 2015, 137, 2359. [16] Z. Chiguvare, V. Dyakonov, Phys. Rev. B 2004, 70, 235207. [17] a) C. M. Proctor, J. A. Love, T.-Q. Nguyen, Adv. Mater. 2014, 26, 5957; b) J. D. Kotlarski, P. W. M. Blom, Appl. Phys. Lett. 2012, 100, 013306. [18] D. Bartesaghi, I. d. C. Pérez, J. Kniepert, S. Roland, M. Turbiez, D. Neher, L. J. A. Koster, Nat. Commun. 2015, 6, 7083. [19] S. R. Cowan, A. Roy, A. J. Heeger, Phys. Rev. B 2010, 82, 245207. [20] V. V. Brus, Org. Electron. 2016, 29, 1. [21] S. Mukherjee, A. Chattopadhyay, A. Samanta, T. Soujanya, J. Phys. Chem. 1994, 98, 2809. [22] J. Wudarczyk, G. Papamokos, V. Margaritis, D. Schollmeyer, F. Hinkel, M. Baumgarten, G. Floudas, K. Müllen, Angew. Chem. Int. Ed. 2016, 55, 3220. [23] a) C. Piliego, T. W. Holcombe, J. D. Douglas, C. H. Woo, P. M. Beaujuge, J. M. J. Fréchet, J. Am. Chem. Soc. 2010, 132, 7595; b) M. R. Hammond, R. J. Kline, A. A. Herzing, L. J. Richter, D. S. Germack, H.-W. Ro, C. L. Soles, D. A. Fischer, T. Xu, L. Yu, M. F. Toney, D. M. DeLongchamp, ACS Nano 2011, 5, 8248; c) T. E. Kang, H.-H. Cho, H. j. Kim, W. Lee, H. Kang, B. J. Kim, Macromolecules 2013, 46, 6806.

1701436 (8 of 8)


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