Ethanol-Processable, Highly Crystalline Conjugated Polymers for Eco

Article pubs.acs.org/Macromolecules

Ethanol-Processable, Highly Crystalline Conjugated Polymers for Eco-Friendly Fabrication of Organic Transistors and Solar Cells Thanh Luan Nguyen,†,‡ Changyeon Lee,§,‡ Hyoeun Kim,∥ Youngwoong Kim,§ Wonho Lee,§ Joon Hak Oh,*,∥ Bumjoon J. Kim,*,§ and Han Young Woo*,† †

Department of Chemistry, Korea University, Seoul 136-713, South Korea Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, South Korea ∥ Department of Chemical Engineering, Pohang University of Science and Technology (POSTECH), 77 Cheongam-ro, Pohang, Gyeongbuk 37673, South Korea §

S Supporting Information *

ABSTRACT: We report eco- and human-friendly fabrication of organic field-effect transistors (OFETs) and polymer solar cells (PSCs) using only ethanol as a processing solvent at ambient condition, in stark contrast to that involving the use of halogenated and/or aromatic solvents. New ethanol-processable electroactive materials, p-type polymer (PPDT2FBT-A) and n-type bisadduct fullerene acceptor (Bis-C60-A) are designed rationally by incorporation of oligoethylene glycol (OEG) side-chains. By ethanol processing, PPDT2FBT-A shows a broad light absorption in the range of 300−700 nm and highly crystalline interchain ordering with out-of-plane interlamellar scattering up to (400) with strong π−π stacking. As a result, the ethanol-processed PPDT2FBT-A OFETs yield high charge-carrier mobilities up to 1.0 × 10−2 cm2 V−1 s−1, which is the highest value reported to date from alcohol-processed devices. Importantly, the ethanol-processed PPDT2FBT-A OFET outperformed that processed using typical processing solvent, chlorobenzene (CB), with ∼10-fold enhancement in hole mobility, because the highly edge-on oriented packing of PPDT2FBT-A was produced by ethanol-process. Also, for the first time, significant photovoltaic performance was achieved for the ethanol-processed device of PPDT2FBT-A and Bis-C60-A due to the formation of an interpenetrating nanofibrillar morphology of highly crystalline PPDT2FBT-A polymers. The relationships between molecular structure, nanoscale morphology and electronic properties within ethanol-processed OFETs and PSCs were elucidated by comparing to typical CBprocessed devices. These comparisons provide important guidelines for the design of new ethanol/water-soluble active layer materials and their use in the development of green solvent-processed efficient OFETs and PSCs.

■

power conversion efficiency.6−12 A paramount task at this stage is optimizing the technologies developed from laboratory-scale research into industrial-scale mass production for commercialization. One of the serious obstacles to the practical application of this technology is that the film-forming process of the vast majority of the high-performing OFETs and PSCs requires the use of halogenated solvents such as chloroform (CF), chlorobenzene (CB), and dichlorobenzene (DCB),13−16

INTRODUCTION Conjugated organic semiconductors, which feature good solution processability and promising optoelectronic properties, have been investigated over the past decade and widely applied as active materials in various organic electronic devices. Organic field-effect transistors (OFETs) and polymer solar cells (PSCs) are the cases in point that demonstrate the successful use of organic semiconductors. Several high-performance p- or n-type organic semiconductors have been developed through rational molecular design, which has led to the fabrication of OFETs with high charge carrier mobilities competitive with amorphous Si-based transistors1−5 and high-efficiency PSCs, exceeding 10% © 2017 American Chemical Society

Received: February 28, 2017 Revised: April 19, 2017 Published: May 18, 2017 4415

DOI: 10.1021/acs.macromol.7b00452 Macromolecules 2017, 50, 4415−4424

Article

Macromolecules

Figure 1. (a) Chemical structures. (b) Normalized UV−visible absorption spectra in ethanol and in thin film. (c) TGA and DSC thermograms of PPDT2FBT, PPDT2FBT-A, and Bis-C60-A.

including xylene, toluene, and NMP are listed in the Toxics Release Inventory (TRI) program,28 as required by the United States Environmental Protection Agency for the management of toxic chemical waste (Table S2). In recent years, aqueous/ alcohol processing of PSCs based on the water-dispersed polymer nanoparticles has emerged as an alternative ecocompatible processing.29−31 However, the dispersion technique requires additional insulating surfactants to stabilize the water dispersion of hydrophobic photoactive organic materials, and it still involves a large amount of toxic organic solvents such as CF, CB, and THF in the dispersion formulation step. Growing environmental concerns encourage the eco-friendly large-scale mass production of electronic devices, thus it is imperative to develop new electroactive materials that can be processed with real environmentally benign, green solvents. Indisputably, ethanol and water are considered the most ideal eco-friendly solvents. In order to develop ethanol- and/or water-processed OFETs and PSCs, significant challenges must be overcome. First, both new p- and n-type active materials must be designed to have sufficient processability (solubility ≥5−10 mg mL−1) in ethanol and/or water solvent systems. One design strategy is to introduce hydrophilic polar side chains into p- and n-type photoactive materials by replacing the aliphatic alkyl side chains.32,33 However, the selected hydrophilic side chains should not disturb the π-orbital interactions of the active materials or act as charge-trapping sites so as to preserve the efficient light-harvesting and charge-transport characteristics in electronic devices. Because of these particular requirements, there have been very sparse attempts to develop ethanol- and/or water-processed OFETs and PSCs. One main approach involved the incorporation of ionic moieties at the distal end of the alkyl side chains to improve solubility in alcohols and water.34−39 However, such ionic groups have been reported as potential trapping sites, hindering their successful

which are very harmful to human health. Additionally, the toxicity, environmental impact, and high energy cost associated with the treatment of waste solvents make their use unsustainable.17,18 Furthermore, stricter regulations on the mass production of halogenated solvents, with the eventual objective of eliminating the use of these chemicals, compel the removal of the halogenated solvents from OFET and PSC fabrication processes for successful commercialization. In recent years, several approaches have been attempted to replace halogenated solvents with halogen-free solvents such as xylene, 1,2-dimethylnaphthalene, toluene, 1-methyl-2-pyrrolidone (NMP), and anisole.19−23 Selection of appropriate halogen-free solvents that provide good solubility for highperformance conjugated polymers will enable the production of tailored thin-film morphologies for active layers, resulting in good device functions comparable to those of devices fabricated from halogenated solvents. For example, tetrahydrofuran (THF), toluene, xylene, and tetralin were investigated in the fabrication of diketopyrrolopyrrole (DPP)-based OFETs. The devices were found to exhibit excellent charge-carrier mobilities, ca. 5−8 cm2 V−1 s−1, commensurate with those of the OFETs processed from CF.24−27 There have also been several efforts to fabricate PSCs using nonhalogenated solvents of o-xylene, 1,2dimethylnaphthalene, toluene, NMP and anisole, showing similar or comparable PCEs (∼7%) with the devices processed using halogenated solvents.19−23 Although these halogen-free, aromatic solvent systems can provide a milder production condition relative to halogenated solvent systems, they are still inherently toxic (Table S1) and threaten the health of people who work with them. Therefore, most of these nonhalogenated aromatic solvents are also strictly prohibited for use in the semiconductor industry, and the regulations related to the use of these hazardous solvents are strict all around the world. For example, a large number of nonhalogenated/aromatic solvents 4416


Article

Macromolecules application as active materials.34−36,40 In addition, the counterions on ionic conjugated polymers could migrate, and thus degrade the long-term stability of the devices. To circumvent the adverse effects of ionic conjugated polymers, hydrophilic, nonionic functional groups (e.g., polar amines) have been included in conjugated polymers.41 However, the performance of OFETs and PSCs having either ionic or nonionic active materials still remains very poor, as charge-carrier mobilities of ∼10−4 cm2 V−1 s−142,43 and PCEs as low as 0.01−0.04%34,41 were obtained. The polarity, surface tension and viscosity of water and ethanol are very different from those of halogenated and/or aromatic solvents, and thus significantly affect the film fabrication and the resulting morphology. Thus, the systematic study on the molecular design, morphology control, charge transport and device properties is a significant and urgent challenge. Herein, we report the synthesis of a novel nonionic, ethanolsoluble conjugated polymer, poly[(2,5-bis(1,3-bis(2-(2-(2methoxyethoxy)ethoxy)ethoxy)propan-2-yloxy)phenylene)-alt(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole)] (PPDT2FBT-A), and a fullerene bis-adduct electron acceptor (Bis-C60-A) (Figure 1a) and investigate their electronic properties in OFET and PSC devices fabricated using only ethanol as the solvent. Oligoethylene glycol (OEG)-based polar nonionic side chains were selected to impart solubility of photoactive materials in ethanol without forming chargetrapping sites in the active layer. The OEG solubilizing groups were introduced, not only onto the p-type polymer, but also onto the n-type C60 fullerene to form a bis-C60 adduct to provide sufficient processability in ethanol to both active layer components. We note that all of the solution processing involved in the OFET and PSC device fabrication described herein was conducted at ambient conditions in ethanol, promoting a worker-friendly environment, in stark contrast to that involving the use of halogenated and/or aromatic solvents. The ethanol-processed PPDT2FBT-A OFETs exhibited high hole mobilities, up to 1.0 × 10−2 cm2 V−1 s−1, which, to the best of our knowledge, is the highest mobility value reported to date for alcohol-processed devices. The high OFET performance was attributed to the highly edge-on oriented crystalline nature of PPDT2FBT-A. Importantly, it is noteworthy to mention that the ethanol-processed PPDT2FBT-A OFET outperformed that processed using CB, with ∼10-fold enhancement in hole mobility. The PSC device fabricated with a blend of PPDT2FBT-A and Bis-C60-A yielded a PCE of 0.75% with a short-circuit current density (JSC), an open-circuit voltage (VOC), and a fill factor of 2.36 mA cm−2, 0.81 V, and 0.39, respectively. To our knowledge, this is the highest PCE value reported for ethanol/water-processed PSCs to date. The optical, structural, and electrical properties of PPDT2FBT-A and Bis-C60-A films were compared using two different solvents of ethanol and CB to discuss important guidelines for the design of new ethanol-soluble active layer materials and their use in the development of green solvent-processed OFETs and PSCs.

the range 350−750 nm, high chain planarity, and pronounced intermolecular ordering via intra- and interchain noncovalent Coulombic interactions, which yielded excellent electrical and photovoltaic properties (PCE ∼ 9%). Therefore, in this study, the same polymer backbone was selected for the design of an ethanol-soluble p-type polymer. In order to render the polymer soluble in ethanol without sacrificing its optical and electrical properties, the hydrophobic aliphatic side chains were replaced with highly polar side chains. Hydrophilic OEG group is one good candidate to provide high solubility of the resulting polymer in polar solvents such as ethanol. Furthermore, its nonionic structure avoids the adverse effect (i.e., charge trapping) associated with ionic side chains. The length of the OEG groups was carefully designed to be similar to the length of the hexyldecyl side chain in PPDT2FBT, allowing the comparison between PPDT2FBT-A and PPDT2FBT. Detailed procedures for the preparation of the monomers, ethanolsoluble polymer, and Bis-C 60 -A are provided in the Experimental Section and Supporting Information (Scheme S1). Briefly, 1,3-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)propan-2-yl-toluenesulfonate (2) was prepared according to a literature procedure,45 and then coupled to 2,5-dibromohydroquinone via the Williamson etherification reaction, affording 1,4-dibromo-2,5-bis(1,3-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)propan-2-yloxy)benzene (M1). PPDT2FBT-A was synthesized in ∼90% yield via Stille-coupling of M1 and 4,7bis(5-trimethylstannylthiophen-2-yl)-5,6-difluoro-2,1,3-benzothiadiazole (M2)44 in toluene using tris(dibenzylideneacetone)dipalladium(0) as the catalyst. The number-average molecular weight (Mn) and dispersity (Đ) of PPDT2FBT-A were 16 kDa and 2.2, respectively, as measured relative to polystyrene (PS) standards by size exclusion chromatography (SEC) eluting in DCB at 80 °C. PPDT2FBT-A possessed good solubility, in not only halogenated and aromatic solvents such as CF, CB, and DCB, but also in nonhalogenated and nonaromatic solvents such as N,N-dimethylformamide, THF, dimethyl sulfoxide, and acetone. Notably, PPDT2FBT-A exhibited good solubility (>10 mg mL−1) in polar alcohol solvents, such as ethanol and methanol. The OEG-based polar solubilizing group was also used for the development of an ethanol-soluble fullerene derivative, BisC60-A (Figure 1a). Recently, Yamamura et al. synthesized a C60 derivative with a branched OEG side chain,46 however the resulting monoadduct C60 was insoluble in polar solvents. Therefore, we attempted to synthesize the OEG bis-adduct fullerene derivative to improve solubility in ethanol. In addition, the higher lowest unoccupied molecular orbital (LUMO) energy level of the bis-adduct compared to that of monoadduct will be beneficial in obtaining a high VOC value in PSCs.47−50 Scheme S1 describes the synthetic routes to Bis-C60-A, wherein the OEG-based solubilizing group, 3,4,5-(2-(2-(2methoxyethoxy)ethoxy)ethoxy)benzaldehyde (4)51 was attached to fullerene C60 by the Prato reaction52,53 using sarcosinic acid in CB. Both mono- and bis-adduct C60 were produced following this reaction, and the bis-adduct isolated by column chromatography in 25% yield. Indeed, Bis-C60-A showed high solubility (>120 mg mL−1) in ethanol, whereas the monoadduct was insoluble. Figure 1b shows the normalized UV−vis absorption spectra of PPDT2FBT-A in ethanol and in film. The absorption spectrum of a PPDT2FBT film is also provided for comparison. The PPDT2FBT-A polymer exhibited light absorption over a wide wavelength range, 350−750 nm and showed two main

■

RESULTS AND DISCUSSION Molecular Design, Synthesis, and Characterization. Recently, we reported the synthesis and electronic properties of a highly efficient, semicrystalline photovoltaic polymer donor, poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole)] (PPDT2FBT, Figure 1a).44 PPDT2FBT exhibited broad light absorption in 4417


Article

Macromolecules absorption bands at high and low energy ranges, attributed to the π−π* transition and intramolecular charge transfer interaction, respectively. The maximum molar absorption coefficient of PPDT2FBT-A was measured to be εmax = 5.8 × 10 4 M −1 cm−1 (Figure S1), comparable with that of PPDT2FBT in chloroform (εmax = 6.9 × 104 M−1 cm−1).54 In addition, the absorption spectrum of the PPDT2FBT-A film showed a strong vibronic shoulder peak at ∼650 nm, suggesting that PPDT2FBT-A polymers had strong interchain interactions in thin film. The optical band gap of PPDT2FBT-A was determined to be 1.76 eV, identical to that of PPDT2FBT. The highest occupied molecular orbital (HOMO) and LUMO energy levels of PPDT2FBT-A and Bis-C60-A were investigated by cyclic voltammetry (CV) by comparison with those of PPDT2FBT and PC60BM (Figure S2). The HOMO/ LUMO energy levels of PPDT2FBT-A and Bis-C60-A were measured to be −4.95 eV/−3.19 eV and −5.45 eV/−3.80 eV, respectively. The replacement of the alkyl substituents on the conjugated backbone with OEG significantly affected the electronic structure. The electron-donating OEG side chains raised both the HOMO and LUMO energy levels of the PPDT2FBT-A and Bis-C 60 -A, compared to those of PPDT2FBT (HOMO/LUMO: − 5.45 eV/−3.69 eV)44 and PC60BM (HOMO/LUMO: − 5.90 eV/−3.90 eV).55 However, a pair of PPDT2FBT-A and Bis-C60-A showed sufficient LUMO offset and HOMO offset required for efficient exciton dissociation at the interface. The thermal properties of PPDT2FBT-A, PPDT2FBT, and Bis-C60-A were assessed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). TGA showed PPDT2FBT-A to exhibit good thermal stability, with a high decomposition temperature (Td) of ∼380 °C (5% weight loss) (Figure 1c), which is comparable to that of PPDT2FBT (Td = 400 °C). The Td of Bis-C60-A was found to be 336 °C, which is lower than that of PC60BM (>400 °C).56 DSC revealed distinct crystalline melting and recrystallization transitions at 177 and 162 °C, respectively, for PPDT2FBT-A (Figure 1c). The melting (ΔHm) and crystallization (ΔHc) enthalpies of PPDT2FBT-A were determined to be 34.8 and 32.1 J g−1, respectively. Notably, the ΔHm and ΔHc values exceeded those of highly crystalline PPDT2FBT polymers (ΔHm= 28.7 J g−1, ΔHc= 17.4 J g−1), suggesting that PPDT2FBT-A polymers possessed very strong crystalline feature and the introduction of the OEG groups promoted the intermolecular packing of the polymers. Interestingly, the Tm and Tc of PPDT2FBT-A were significantly lower than those of PPDT2FBT (Tm= 317 and Tc= 308 °C, respectively), likely due to the enhanced chain flexibility associated with the OEG groups, indicating that a facile self-organization of the polymer in thin films can be achieved with much lower processing temperatures. We anticipate that the excellent processability of PPDT2FBT-A into crystalline thin films will be very important to fabricate the large-area solar cells by the low-temperature roll-to-roll processing in eco-friendly solvents, which typically have lower boiling points than common processing solvents (i.e., CB and DCB).57 Grazing incidence X-ray scattering (GIXS) was employed to evaluate polymer packing and structural orientation of pristine PPDT2FBT-A films processed from ethanol or CB. The GIXS patterns presented in Figure 2a showed the highly crystalline nature of ethanol-processed PPDT2FBT-A film, with distinct Bragg reflection peaks up to the fourth order (400) in the outof-plane direction (Figure 2a,b). From the first order (100)

Figure 2. (a) 2D-GIXS pattern and (b, c) in-plane and out-of-plane line-cut profiles of pristine PPDT2FBT-A films processed from ethanol and CB, respectively.

reflection peak, the lamellar d spacing was calculated to be 22.85 Å, which was larger than that of PPDT2FBT (20.7 Å).44 In addition, a strong (010) reflection peak corresponding to the π−π stacking appeared in the in-plane direction. The π−π stacking distance was measured to be 3.65 Å, which was even smaller than that of PPDT2FBT (3.72 Å).44 This feature suggested that the introduction of the OEG side chains did not interrupt the interchain organization of PPDT2FBT-A polymers, and rather promoted very tight π−π interchain stacking, which is highly important for producing efficient charge transport.54,58 Next, we investigated the effects of the processing solvent on the crystalline structure and orientation of PPDT2FBT-A in films. Ethanol and a representative halogenated solvent, CB, were selected for this comparative study. Interestingly, the 2D GIXS pattern of PPDT2FBT-A films differed dramatically between the two processing solvents. The (010) reflection peak of the CB-processed PPDT2FBT-A film was apparent in the out-of-plane direction, and the high-order (h00) lamellar peaks observed in ethanol-processed PPDT2FBT-A film disappeared (Figure 2b,c), indicating that the CB-processed PPDT2FBT-A film contained polymer predominantly oriented in a face-on fashion with a rather disordered crystalline packing structure relative to that in the ethanol-processed film. We speculated that these intriguing features may arise from polymer aggregation induced by the relatively low solubility of PPDT2FBT-A in ethanol. Additionally, the hydrophilic character of ethanol along with its lower boiling point may alter the kinetics of morphological evolution of PPDT2FBT-A in thin films. The different structural properties observed in the ethanol- and CB-processed PPDT2FBT-A thin films were expected to strongly influence their electrical properties. OFET and Charge Carrier Transport Characterization. The charge transport and electrical properties of PPDT2FBT-A were first examined in bottom-gate top-contact OFET devices, consisting of a highly n-doped (100) Si wafer (105 >104

−22.3 −15.4

μh,

SCLC

(max)b (cm2 V−1 s−1) 2.9 × 10−4 2.3 × 10−3

μh,

SCLC

(avg)b (cm2 V−1 s−1)

2.0 × 10−4 (±8.6 × 10−5)c 1.6 × 10−3 (±7.5 × 10−4)

The maximum and average mobilities obtained from at least 20 OFET devices (L = 50 μm and W/L = 17.5). bThe maximum and average mobilities obtained from at least 5 SCLC devices. cStandard deviation.

a

4419


Article

Macromolecules

Figure 4. (a) J−V characteristics and (b) EQE responses of ethanol-processed PPDT2FBT-A:Bis-C60-A devices with various D:A ratios.

experiment (Figure S6). Clear interlamellar peaks were observed, up to (300) (from the PPDT2FBT-A polymer donor in the blend) in the out-of-plane direction, identical to the edge-on oriented GIXS pattern measured from the pristine PPDT2FBT-A film (Figure 2). However, the scattering intensity of the PPDT2FBT-A polymers in the blend film decreased, which may be attributed to disruption of the polymer packing structure by Bis-C60-A having two bulky OEG side chains. We note that this edge-on orientation of PPDT2FBT-A in the blend could be one reason for the low PCE value of the ethanol-processed PSC devices, since the faceon orientation is an important factor contributing to charge carrier transport in the vertical direction of the PSC device.64−67 The hole (μh, SCLC) and electron (μe, SCLC) mobilities of the pristine PPDT2FBT-A and Bis-C60-A acceptor, and their blend films were evaluated by the SCLC method (Figure S7 and Table S4). The μh, SCLC value of PPDT2FBT-A was measured to be 7.5 × 10−5 cm2 V−1 s−1. However, Bis-C60-A was found to have a much smaller μe, SCLC value of 8.8 × 10−7 cm2 V−1 s−1, likely due to the presence of the two bulky insulating OEG side chains attached to the fullerene core. This feature gives rise not only significant disorder in the fullerene domains, but also poor interconnectivity between the fullerene phases. In addition, the presence of multiple isomers of Bis-C60-A may significantly reduce the electron mobility by disruption of molecular packing within the fullerene domains.68−74 The two bulky OEG side chains in Bis-C60-A perturbed the formation of crystalline PPDT2FBT-A structures in the active layer, as evidenced by the GIXS experiments (Figure S6). Accordingly, the PPDT2FBTA:Bis-C60-A blend film showed decrease in both hole (2.6 × 10−5 cm2 V−1 s−1) and electron (2.3 × 10−8 cm2 V−1 s−1) mobilities compared to those of the pristine films. Significantly reduced electron transport in the blend film resulted in poor μh/μe balance. Thus, the hole/electron accumulation was expected to occur in the device and photocurrent became space-charge limited, resulting in a low FF value.75 Taking all of the characterizations into account, developing a new ethanol-soluble, monoadduct type fullerene acceptor with high electron mobility will be of prime importance to enhance the ethanol-processed photovoltaic devices.76,77 It will be challenging, however, to design side chains that solubilize the fullerene monoadduct in ethanol and/or water while retaining the high intermolecular packing of fullerene units. In addition, based on the TEM, RSoXS, and PL quenching experiments, an interconnected fibrillar network in the PPDT2FBT-A:Bis-C60-A active layer was clearly observed with finely phase-separated domain spacing of ∼30 nm, producing efficient exciton dissociation. Despite this beneficial length scale of the bulk heterojunction (BHJ) domains of the PPDT2FBT-A:Bis-C60-A blend, the dominant edge-on oriented microstructure of

Table 2. Photovoltaic Characteristics of Ethanol-Processed Devices with Changing the PPDT2FBT-A:Bis-C60-A Blend Ratios D:A weight ratio

VOC

Jsc (mA cm−2)

FF

PCE (%)

1:1 1:1.5 1:2

0.80 0.81 0.81

1.77 2.36 1.78

0.32 0.39 0.38

0.45 0.75 0.55

Figure 5. AFM (a) height and (b) phase images of PPDT2FBT-A:BisC60-A blend films. (c) TEM image and (d) RSoXS profile of PPDT2FBT-A:Bis-C60-A films, which were prepared under same condition for optimized ethanol-processed PSC device.

PPDT2FBT-A:Bis-C60-A thin films.62,63 Figure 5d displays the scattering profile of the PPDT2FBT-A:Bis-C60-A blend as a function of scattering vector q. For this ethanol-processed blend film, an obvious reflection was measured at q = 0.0188 Å−1, corresponding to an average domain spacing (d-spacing) of 33.4 nm between PPDT2FBT-A and Bis-C60-A phases. This dspacing obtained from the RSoXS agrees well with the value estimated from the TEM image. In addition, the efficient exciton dissociation in the blend film was evidenced by photoluminescence quenching experiments (Figure S5). The PPDT2FBT-A pristine and PPDT2FBT-A:Bis-C60-A blend films were excited at 650 nm, corresponding to the dominant absorption of the polymer donor. The films yielded remarkable PL quenching with ∼90% efficiency, indicating that the interpenetrating fibrillar nanomorphology in the PPDT2FBTA:Bis-C60-A active layer provides efficient exciton dissociation. The packing structure of the PPDT2FBT-A:Bis-C60-A blend in ethanol-processed film was also observed by GIXS 4420


Article

Macromolecules

fraction containing the bis-adduct was collected with a solvent mixture of CH2CH2/MeOH (95/5 v/v) as an eluent (yield: 340 mg, 25%). 1H NMR (400 MHz, CDCl3): δ (ppm) 2.70 (s, 6H), 3.36 (s, 18H), 3.54− 3.88 (m, 60H), 4.07−4.29 (m, 12H), 4.88 (br, 6H), 6.80 (br, 4H). MALDI−TOF (C120H106N2O24): 1959.39 (M+). Characterizations. A microwave reactor (Biotage Initiator) was used to synthesize the polymers. 1H and 13C NMR spectra were recorded on a Bruker 400 MHz spectrometer. The Mn and Đ values of a polymer were determined relative to a polystyrene standard by SEC eluting with DCB at 80 °C on an Agilent GPC 1200 series. CV experiments were performed with a Versa STAT 3 analyzer. All CV measurements were carried out in 0.1 M Bu4NBF4 in acetonitrile with a conventional three-electrode configuration, employing a platinum wire as the counter electrode, a platinum electrode coated with a thin polymer film as the working electrode, and Ag/Ag+ electrode as the reference electrode (scan rate: 50 mV·s−1). TGA (2050 TGA V5.4A, Universal V4.2E TA Instruments) and DSC (DSC Q200 V24.4 Build 116, Universal V4.5A TA Instruments) measurements were performed at a heating and cooling rate of 10 °C·min−1 under nitrogen (purity, 99.999%). UV−vis absorption spectra were acquired on a UV-1800 spectrophotometer (Shimadzu Scientific Instruments). PL spectra were obtained using a Horiba Jobin Yvon NanoLog spectrophotometer with a 650 nm excitation wavelength. Surface morphology of the ethanol-processed blend film was measured by AFM (Veeco Dimension 3100 instrument) in tapping mode. Thin film morphologies were investigated by TEM (JEOL 2000FX). GIXS experiments were performed at a beamline 3C in the Pohang Accelerator Laboratory (South Korea). GIXS samples were prepared with optimized active layer condition and spin-coated onto a ZnO/Si substrate. For these measurements, an X-ray wavelength of 1.1179 Å was used. RSoXS measurements were performed at beamline, BL 11.0.1.2 in the Advanced Light Source (USA). PPDT2FBT-A:Bis-C60A active layers were prepared for RSoXS on a PEDOT:PSS/Si substrate. Then, the films were floated on water and transferred to a 1.0 mm ×1.0 mm, 100 nm thick Si3N4 membrane supported by a 5 mm × 5 mm, 200 μm thick Si frame (Norcada Inc.).

PPDT2FBT-A in the active layer remains a concern. Face-on orientation of the polymer donor is crucial for facilitating vertical charge transport in the BHJ film devices.78−81 Thus, engineering the intermolecular orientation of the polymer donor to achieve highly efficient ethanol-processed PSCs is currently underway in our laboratory.

■

CONCLUSIONS In conclusion, we designed and synthesized a novel semicrystalline conjugated polymer (PPDT2FBT-A) and a fullerene derivative (Bis-C60-A) capable of being processed from ethanol, a nontoxic and environment-friendly solvent. The ethanolprocessable active materials were prepared by replacing the solubilizing alkyl groups connected to the conjugated backbone with OEG chains. The polar OEG substituents did not show any significant effects on the optical properties of polymer, whereas the electrochemical properties, thermal properties, and especially the interchain crystalline orientation were influenced significantly. The ethanol-processed PPDT2FBT-A OFETs yielded high charge-carrier mobilities up to 1.0 × 10−2 cm2 V−1 s−1. The high OFET performance correlated with the primarily edge-on oriented crystalline nature of PPDT2FBT-A. More importantly, the PPDT2FBT-A device outperformed the device fabricated using CB as the solvent, with the 10-fold enhancement in the charge-carrier mobility. This result highlights the significant potential of ethanol-processed PPDT2FBT-A OFETs as a green and human-friendly technology. Furthermore, the PSC device based on the binary blend of PPDT2FBT-A and Bis-C60-A yielded the best PCE of 0.75% in the inverted device configuration, demonstrating significant photovoltaic performance of ethanol-processed devices for the first time. To enhance the PCE of ethanolprocessed devices, it is strongly suggested to develop a new alcohol-soluble monoadduct fullerene acceptor with an electron mobility similar to the hole mobility of the donor. The results generated in this work provide important guidelines for the design of eco-friendly, alcohol-processable active materials and devices.

■

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge via the Internet at The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/ acs.macromol.7b00452. Methods, detail experimental procedures, and additional data (PDF)

EXPERIMENTAL SECTION

Synthesis of PPDT2FBT-A. The detailed synthetic routes to monomers and PPDT2FBT-A polymer are described in Scheme S1. In a glovebox, M1 (300 mg, 0.30 mmol), M2 (199.5 mg, 0.30 mmol), tris(dibenzylideneacetone)dipalladium(0) (4 mol %), tri(o-tolyl)phosphine (8 mol %), and 3 mL of toluene were added into a 5 mL microwave vial. The reaction mixture was heated at 80 °C (10 min), at 100 °C (10 min) and at 140 °C (40 min) in a microwave reactor. The polymer was end-capped by addition of 2-tributylstannylthiophene (0.05 g, 0.14 mmol) and the mixture was further reacted at 140 °C for 20 min. The solution was cooled down and 2bromothiophene (0.09 g, 0.53 mmol) was added by syringe. The reaction solution was heated 140 °C for another 20 min. After the reaction was finished, the crude polymer was precipitated into hexane and further purified by Soxhlet extraction with hexane and chloroform. The extracted PPDT2FBT-A in chloroform was precipitated into hexane, filtered and dried under vacuum. Yield: 85%. Number-average molecular weight (Mn) = 16 kDa, dispersity (Đ) = 2.2. 1H NMR (400 MHz, CDCl3): δ (ppm) 8.37 (br, 2H), 7.80 (br, 2H), 7.68 (br, 2H), 4.80 (br, 2H), 3.92 (m, 8H), 3.80−3.40 (m, 48H), 3.34 (s, 12H). Synthesis of Bis-C60-A. The detailed synthetic routes to the monomers and Bis-C60-A are described in Scheme S1. A solution of fullerene (C60) (500 mg, 0.7 mmol), 4 (822 mg, 1.4 mmol) and sarcosinic acid (187 mg, 2.1 mmol) in chlorobenzene (30 mL) was refluxed under N2 for 4 h. After evaporation of the solvent, the residue was subjected to silica gel column chromatography purification. A

■

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (H.Y.W.). *E-mail: [email protected] (B.J.K.). *E-mail: [email protected] (J.H.O.). ORCID

Joon Hak Oh: 0000-0003-0481-6069 Bumjoon J. Kim: 0000-0001-7783-9689 Author Contributions ‡

T.L.N. and C.L. contributed equally to this work.

Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported by the National Research Foundation (NRF) of Korea (2016M1A2A2940911, 2015M1A2A2057509, 2012M3A6A7055540, 20100020209). We thank Dr. Cheng Wang for the RSoXS measurement 4421


Article

Macromolecules

■

A. K. Y. Non-halogenated solvents for environmentally friendly processing of high-performance bulk-heterojunction polymer solar cells. Energy Environ. Sci. 2013, 6, 3241−3248. (20) Chang, J.-H.; Wang, H.-F.; Lin, W.-C.; Chiang, K.-M.; Chen, K.C.; Huang, W.-C.; Huang, Z.-Y.; Meng, H.-F.; Ho, R.-M.; Lin, H.-W. Efficient inverted quasi-bilayer organic solar cells fabricated by using non-halogenated solvent processes. J. Mater. Chem. A 2014, 2, 13398− 13406. (21) Chen, Y.; Cui, Y.; Zhang, S.; Hou, J. Molecular design toward efficient polymer solar cells processed by green solvents. Polym. Chem. 2015, 6, 4089−4095. (22) Guo, X.; Zhang, M.; Cui, C.; Hou, J.; Li, Y. Efficient Polymer Solar Cells Based on Poly(3-hexylthiophene) and Indene−C60 Bisadduct Fabricated with Non-halogenated Solvents. ACS Appl. Mater. Interfaces 2014, 6, 8190−8198. (23) Yuan, J.; McDowell, C.; Mai, C.-K.; Bazan, G. C.; Ma, W. Ternary D1−D2−A−D2 Structured Conjugated Polymer: Efficient “Green” Solvent-Processed Polymer/Neat-C70 Solar Cells. Chem. Mater. 2016, 28, 7479−7486. (24) Matthews, J. R.; Niu, W.; Tandia, A.; Wallace, A. L.; Hu, J.; Lee, W.-Y.; Giri, G.; Mannsfeld, S. C. B.; Xie, Y.; Cai, S.; Fong, H. H.; Bao, Z.; He, M. Scalable Synthesis of Fused Thiophene-Diketopyrrolopyrrole Semiconducting Polymers Processed from Nonchlorinated Solvents into High Performance Thin Film Transistors. Chem. Mater. 2013, 25, 782−789. (25) Lee, W.-Y.; Giri, G.; Diao, Y.; Tassone, C. J.; Matthews, J. R.; Sorensen, M. L.; Mannsfeld, S. C. B.; Chen, W.-C.; Fong, H. H.; Tok, J. B. H.; Toney, M. F.; He, M.; Bao, Z. Effect of Non-Chlorinated Mixed Solvents on Charge Transport and Morphology of SolutionProcessed Polymer Field-Effect Transistors. Adv. Funct. Mater. 2014, 24, 3524−3534. (26) Yun, H.-J.; Lee, G. B.; Chung, D. S.; Kim, Y.-H.; Kwon, S.-K. Novel Diketopyrroloppyrrole Random Copolymers: High ChargeCarrier Mobility From Environmentally Benign Processing. Adv. Mater. 2014, 26, 6612−6616. (27) Choi, H. H.; Baek, J. Y.; Song, E.; Kang, B.; Cho, K.; Kwon, S.K.; Kim, Y.-H. A Pseudo-Regular Alternating Conjugated Copolymer Using an Asymmetric Monomer: A High-Mobility Organic Transistor in Nonchlorinated Solvents. Adv. Mater. 2015, 27, 3626−3631. (28) U. S. Environmental Protection Agency. http://www.epa.gov/ toxics-release-inventory-tri-program/tri-listed-chemicals; U. S. Environmental Protection Agency. (29) Andersen, T. R.; Larsen-Olsen, T. T.; Andreasen, B.; Böttiger, A. P. L.; Carlé, J. E.; Helgesen, M.; Bundgaard, E.; Norrman, K.; Andreasen, J. W.; Jørgensen, M.; Krebs, F. C. Aqueous Processing of Low-Band-Gap Polymer Solar Cells Using Roll-to-Roll Methods. ACS Nano 2011, 5, 4188−4196. (30) Gärtner, S.; Christmann, M.; Sankaran, S.; Röhm, H.; Prinz, E.M.; Penth, F.; Pütz, A.; Türeli, A. E.; Penth, B.; Baumstümmler, B.; Colsmann, A. Eco-Friendly Fabrication of 4% Efficient Organic Solar Cells from Surfactant-Free P3HT:ICBA Nanoparticle Dispersions. Adv. Mater. 2014, 26, 6653−6657. (31) Pedersen, E. B. L.; Pedersen, M. C.; Simonsen, S. B.; Brandt, R. G.; Bottiger, A. P. L.; Andersen, T. R.; Jiang, W.; Xie, Z. Y.; Krebs, F. C.; Arleth, L.; Andreasen, J. W. Structure and crystallinity of water dispersible photoactive nanoparticles for organic solar cells. J. Mater. Chem. A 2015, 3, 17022−17031. (32) Mei, J.; Bao, Z. Side Chain Engineering in Solution-Processable Conjugated Polymers. Chem. Mater. 2014, 26, 604−615. (33) Huang, F.; Wu, H.; Cao, Y. Water/alcohol soluble conjugated polymers as highly efficient electron transporting/injection layer in optoelectronic devices. Chem. Soc. Rev. 2010, 39, 2500−2521. (34) Mwaura, J. K.; Pinto, M. R.; Witker, D.; Ananthakrishnan, N.; Schanze, K. S.; Reynolds, J. R. Photovoltaic Cells Based on Sequentially Adsorbed Multilayers of Conjugated Poly(p-phenylene ethynylene)s and a Water-Soluble Fullerene Derivative. Langmuir 2005, 21, 10119−10126. (35) Qiao, Q.; McLeskey, J. T., Jr. Water-soluble polythiophene/ nanocrystalline TiO2 solar cells. Appl. Phys. Lett. 2005, 86, 153501.

REFERENCES

(1) Tseng, H.-R.; Phan, H.; Luo, C.; Wang, M.; Perez, L. A.; Patel, S. N.; Ying, L.; Kramer, E. J.; Nguyen, T.-Q.; Bazan, G. C.; Heeger, A. J. High-Mobility Field-Effect Transistors Fabricated with Macroscopic Aligned Semiconducting Polymers. Adv. Mater. 2014, 26, 2993−2998. (2) Luo, C.; Kyaw, A. K. K.; Perez, L. A.; Patel, S.; Wang, M.; Grimm, B.; Bazan, G. C.; Kramer, E. J.; Heeger, A. J. General Strategy for SelfAssembly of Highly Oriented Nanocrystalline Semiconducting Polymers with High Mobility. Nano Lett. 2014, 14, 2764−2771. (3) Diao, Y.; Tee, B. C. K.; Giri, G.; Xu, J.; Kim, D. H.; Becerril, H. A.; Stoltenberg, R. M.; Lee, T. H.; Xue, G.; Mannsfeld, S. C. B.; Bao, Z. Solution coating of large-area organic semiconductor thin films with aligned single-crystalline domains. Nat. Mater. 2013, 12, 665−671. (4) Minemawari, H.; Yamada, T.; Matsui, H.; Tsutsumi, J. y.; Haas, S.; Chiba, R.; Kumai, R.; Hasegawa, T. Inkjet printing of single-crystal films. Nature 2011, 475, 364−367. (5) Li, J.; Zhao, Y.; Tan, H. S.; Guo, Y.; Di, C.-A.; Yu, G.; Liu, Y.; Lin, M.; Lim, S. H.; Zhou, Y.; Su, H.; Ong, B. S. A stable solutionprocessed polymer semiconductor with record high-mobility for printed transistors. Sci. Rep. 2012, 2, 754. (6) Liu, Y.; Zhao, J.; Li, Z.; Mu, C.; Ma, W.; Hu, H.; Jiang, K.; Lin, H.; Ade, H.; Yan, H. Aggregation and morphology control enables multiple cases of high-efficiency polymer solar cells. Nat. Commun. 2014, 5, 5293. (7) Vohra, V.; Kawashima, K.; Kakara, T.; Koganezawa, T.; Osaka, I.; Takimiya, K.; Murata, H. Efficient inverted polymer solar cells employing favourable molecular orientation. Nat. Photonics 2015, 9, 403−408. (8) 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, 4734−4739. (9) 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. (10) 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. (11) Kang, H.; Lee, W.; Oh, J.; Kim, T.; Lee, C.; Kim, B. J. From Fullerene−Polymer to All-Polymer Solar Cells: The Importance of Molecular Packing, Orientation, and Morphology Control. Acc. Chem. Res. 2016, 49, 2424−2434. (12) Kang, T. E.; Kim, K.-H.; Kim, B. J. Design of terpolymers as electron donors for highly efficient polymer solar cells. J. Mater. Chem. A 2014, 2, 15252−15267. (13) Ye, L.; Zhang, S.; Zhao, W.; Yao, H.; Hou, J. Highly Efficient 2D-Conjugated Benzodithiophene-Based Photovoltaic Polymer with Linear Alkylthio Side Chain. Chem. Mater. 2014, 26, 3603−3605. (14) Huo, L.; Liu, T.; Sun, X.; Cai, Y.; Heeger, A. J.; Sun, Y. SingleJunction Organic Solar Cells Based on a Novel Wide-Bandgap Polymer with Efficiency of 9.7%. Adv. Mater. 2015, 27, 2938−2944. (15) He, Z.; Zhong, C.; Su, S.; Xu, M.; Wu, H.; Cao, Y. Enhanced power-conversion efficiency in polymer solar cells using an inverted device structure. Nat. Photonics 2012, 6, 591−595. (16) Choi, H.; Ko, S.-J.; Kim, T.; Morin, P.-O.; Walker, B.; Lee, B. H.; Leclerc, M.; Kim, J. Y.; Heeger, A. J. Small-Bandgap Polymer Solar Cells with Unprecedented Short-Circuit Current Density and High Fill Factor. Adv. Mater. 2015, 27, 3318−3324. (17) Chen, X.; Liu, X.; Burgers, M. A.; Huang, Y.; Bazan, G. C. Green-Solvent-Processed Molecular Solar Cells. Angew. Chem., Int. Ed. 2014, 53, 14378−14381. (18) Burgués-Ceballos, I.; Machui, F.; Min, J.; Ameri, T.; Voigt, M. M.; Luponosov, Y. N.; Ponomarenko, S. A.; Lacharmoise, P. D.; Campoy-Quiles, M.; Brabec, C. J. Solubility Based Identification of Green Solvents for Small Molecule Organic Solar Cells. Adv. Funct. Mater. 2014, 24, 1449−1457. (19) Chueh, C.-C.; Yao, K.; Yip, H.-L.; Chang, C.-Y.; Xu, Y.-X.; Chen, K.-S.; Li, C.-Z.; Liu, P.; Huang, F.; Chen, Y.; Chen, W.-C.; Jen, 4422


Article

Macromolecules (36) Yang, J.; Garcia, A.; Nguyen, T.-Q. Organic solar cells from water-soluble poly(thiophene)/fullerene heterojunction. Appl. Phys. Lett. 2007, 90, 103514. (37) He, Z.; Zhong, C.; Huang, X.; Wong, W.-Y.; Wu, H.; Chen, L.; Su, S.; Cao, Y. Simultaneous Enhancement of Open-Circuit Voltage, Short-Circuit Current Density, and Fill Factor in Polymer Solar Cells. Adv. Mater. 2011, 23, 4636−4643. (38) Yao, K.; Chen, L.; Chen, Y.; Li, F.; Wang, P. Influence of watersoluble polythiophene as an interfacial layer on the P3HT/PCBM bulk heterojunction organic photovoltaics. J. Mater. Chem. 2011, 21, 13780−13784. (39) Mai, C.-K.; Schlitz, R. A.; Su, G. M.; Spitzer, D.; Wang, X.; Fronk, S. L.; Cahill, D. G.; Chabinyc, M. L.; Bazan, G. C. Side-Chain Effects on the Conductivity, Morphology, and Thermoelectric Properties of Self-Doped Narrow-Band-Gap Conjugated Polyelectrolytes. J. Am. Chem. Soc. 2014, 136, 13478−13481. (40) Liu, Z.; Liu, L.; Li, H.; Dong, Q.; Yao, S.; Kidd, A. B., IV; Zhang, X.; Li, J.; Tian, W. Green” polymer solar cell based on water-soluble poly [3-(potassium-6-hexanoate) thiophene-2, 5-diyl] and aqueousdispersible noncovalent functionalized graphene sheets. Sol. Energy Mater. Sol. Cells 2012, 97, 28−33. (41) Duan, C.; Cai, W.; Hsu, B. B. Y.; Zhong, C.; Zhang, K.; Liu, C.; Hu, Z.; Huang, F.; Bazan, G. C.; Heeger, A. J.; Cao, Y. Toward green solvent processable photovoltaic materials for polymer solar cells: the role of highly polar pendant groups in charge carrier transport and photovoltaic behavior. Energy Environ. Sci. 2013, 6, 3022−3034. (42) Shao, M.; He, Y.; Hong, K.; Rouleau, C. M.; Geohegan, D. B.; Xiao, K. A water-soluble polythiophene for organic field-effect transistors. Polym. Chem. 2013, 4, 5270−5274. (43) Wei, H.; Zhang, H.; Jin, G.; Na, T.; Zhang, G.; Zhang, X.; Wang, Y.; Sun, H.; Tian, W.; Yang, B. Coordinatable and High ChargeCarrier-Mobility Water-Soluble Conjugated Copolymers for Effective Aqueous-Processed Polymer−Nanocrystal Hybrid Solar Cells and OFET Applications. Adv. Funct. Mater. 2013, 23, 4035−4042. (44) Nguyen, T. L.; Choi, H.; Ko, S. J.; Uddin, M. A.; Walker, B.; Yum, S.; Jeong, J. E.; Yun, M. H.; Shin, T. J.; Hwang, S.; Kim, J. Y.; Woo, H. Y. Semi-crystalline photovoltaic polymers with efficiency exceeding 9% in a 300 nm thick conventional single-cell device. Energy Environ. Sci. 2014, 7, 3040−3051. (45) Vandenbergh, J.; Dergent, J.; Conings, B.; Gopala Krishna, T. V. V.; Maes, W.; Cleij, T. J.; Lutsen, L.; Manca, J.; Vanderzande, D. J. M. Synthesis and characterization of water-soluble poly(p-phenylene vinylene) derivatives via the dithiocarbamate precursor route. Eur. Polym. J. 2011, 47, 1827−1835. (46) Yamamura, M.; Saito, T.; Nabeshima, T. PhosphorusContaining Chiral Molecule for Fullerene Recognition Based on Concave/Convex Interaction. J. Am. Chem. Soc. 2014, 136, 14299− 14306. (47) He, Y.; Chen, H.-Y.; Hou, J.; Li, Y. Indene−C60 Bisadduct: A New Acceptor for High-Performance Polymer Solar Cells. J. Am. Chem. Soc. 2010, 132, 1377−1382. (48) Lenes, M.; Wetzelaer, G.-J. A. H.; Kooistra, F. B.; Veenstra, S. C.; Hummelen, J. C.; Blom, P. W. M. Fullerene Bisadducts for Enhanced Open-Circuit Voltages and Efficiencies in Polymer Solar Cells. Adv. Mater. 2008, 20, 2116−2119. (49) Kim, K.-H.; Kang, H.; Nam, S. Y.; Jung, J.; Kim, P. S.; Cho, C.H.; Lee, C.; Yoon, S. C.; Kim, B. J. Facile Synthesis of o-Xylenyl Fullerene Multiadducts for High Open Circuit Voltage and Efficient Polymer Solar Cells. Chem. Mater. 2011, 23, 5090−5095. (50) Kim, K.-H.; Kang, H.; Kim, H. J.; Kim, P. S.; Yoon, S. C.; Kim, B. J. Effects of Solubilizing Group Modification in Fullerene BisAdducts on Normal and Inverted Type Polymer Solar Cells. Chem. Mater. 2012, 24, 2373−2381. (51) Xie, Y.; Akada, M.; Hill, J. P.; Ji, Q.; Charvet, R.; Ariga, K. Real time self-assembly and reassembly of molecular nanowires of trigeminal amphiphile porphyrins. Chem. Commun. 2011, 47, 2285− 2287. (52) Prato, M.; Maggini, M. Fulleropyrrolidines: A Family of FullFledged Fullerene Derivatives. Acc. Chem. Res. 1998, 31, 519−526.

(53) Hummelen, J. C.; Knight, B. W.; LePeq, F.; Wudl, F.; Yao, J.; Wilkins, C. L. Preparation and Characterization of Fulleroid and Methanofullerene Derivatives. J. Org. Chem. 1995, 60, 532−538. (54) Kang, H.; Uddin, M. A.; Lee, C.; Kim, K.-H.; Nguyen, T. L.; Lee, W.; Li, Y.; Wang, C.; Woo, H. Y.; Kim, B. J. Determining the Role of Polymer Molecular Weight for High-Performance All-Polymer Solar Cells: Its Effect on Polymer Aggregation and Phase Separation. J. Am. Chem. Soc. 2015, 137, 2359−2365. (55) Tan, Z. A.; Li, S.; Wang, F.; Qian, D.; Lin, J.; Hou, J.; Li, Y. High performance polymer solar cells with as-prepared zirconium acetylacetonate film as cathode buffer layer. Sci. Rep. 2015, 4, 4691. (56) Warman, J. M.; de Haas, M. P.; Anthopoulos, T. D.; de Leeuw, D. M. The Negative Effect of High-Temperature Annealing on Charge-Carrier Lifetimes in Microcrystalline PCBM. Adv. Mater. 2006, 18, 2294−2298. (57) Søndergaard, R.; Hösel, M.; Angmo, D.; Larsen-Olsen, T. T.; Krebs, F. C. Roll-to-roll fabrication of polymer solar cells. Mater. Today 2012, 15, 36−49. (58) Choi, J.; Kim, K.-H.; Yu, H.; Lee, C.; Kang, H.; Song, I.; Kim, Y.; Oh, J. H.; Kim, B. J. Importance of Electron Transport Ability in Naphthalene Diimide-Based Polymer Acceptors for High-Performance, Additive-Free, All-Polymer Solar Cells. Chem. Mater. 2015, 27, 5230−5237. (59) Ford, M. J.; Wang, M.; Patel, S. N.; Phan, H.; Segalman, R. A.; Nguyen, T.-Q.; Bazan, G. C. High Mobility Organic Field-Effect Transistors from Majority Insulator Blends. Chem. Mater. 2016, 28, 1256−1260. (60) Lee, B. H.; Hsu, B. B. Y.; Patel, S. N.; Labram, J.; Luo, C.; Bazan, G. C.; Heeger, A. J. Flexible Organic Transistors with Controlled Nanomorphology. Nano Lett. 2016, 16, 314−319. (61) Liu, Y.; Dong, H.; Jiang, S.; Zhao, G.; Shi, Q.; Tan, J.; Jiang, L.; Hu, W.; Zhan, X. High Performance Nanocrystals of a Donor− Acceptor Conjugated Polymer. Chem. Mater. 2013, 25, 2649−2655. (62) Ma, W.; Tumbleston, J. R.; Ye, L.; Wang, C.; Hou, J.; Ade, H. Quantification of Nano- and Mesoscale Phase Separation and Relation to Donor and Acceptor Quantum Efficiency, Jsc, and FF in Polymer:Fullerene Solar Cells. Adv. Mater. 2014, 26, 4234−4241. (63) Kesava, S. V.; Fei, Z.; Rimshaw, A. D.; Wang, C.; Hexemer, A.; Asbury, J. B.; Heeney, M.; Gomez, E. D. Domain Compositions and Fullerene Aggregation Govern Charge Photogeneration in Polymer/ Fullerene Solar Cells. Adv. Energy Mater. 2014, 4, 1400116. (64) Tumbleston, J. R.; Collins, B. A.; Yang, L.; Stuart, A. C.; Gann, E.; Ma, W.; You, W.; Ade, H. The influence of molecular orientation on organic bulk heterojunction solar cells. Nat. Photonics 2014, 8, 385−391. (65) Rand, B. P.; Cheyns, D.; Vasseur, K.; Giebink, N. C.; Mothy, S.; Yi, Y.; Coropceanu, V.; Beljonne, D.; Cornil, J.; Brédas, J.-L.; Genoe, J. The Impact of Molecular Orientation on the Photovoltaic Properties of a Phthalocyanine/Fullerene Heterojunction. Adv. Funct. Mater. 2012, 22, 2987−2995. (66) Verlaak, S.; Beljonne, D.; Cheyns, D.; Rolin, C.; Linares, M.; Castet, F.; Cornil, J.; Heremans, P. Electronic Structure and Geminate Pair Energetics at Organic−Organic Interfaces: The Case of Pentacene/C60 Heterojunctions. Adv. Funct. Mater. 2009, 19, 3809− 3814. (67) Li, Y.; Ko, S.-J.; Park, S. Y.; Choi, H.; Nguyen, T. L.; Uddin, M. A.; Kim, T.; Hwang, S.; Kim, J. Y.; Woo, H. Y. Quinoxaline-thiophene based thick photovoltaic devices with an efficiency of 8%. J. Mater. Chem. A 2016, 4, 9967−9976. (68) Azimi, H.; Senes, A.; Scharber, M. C.; Hingerl, K.; Brabec, C. J. Charge Transport and Recombination in Low-Bandgap Bulk Heterojunction Solar Cell using Bis-adduct Fullerene. Adv. Energy Mater. 2011, 1, 1162−1168. (69) Meng, X.; Zhao, G.; Xu, Q.; Tan, Z. a.; Zhang, Z.; Jiang, L.; Shu, C.; Wang, C.; Li, Y. Effects of Fullerene Bisadduct Regioisomers on Photovoltaic Performance. Adv. Funct. Mater. 2014, 24, 158−163. (70) Nardes, A. M.; Ferguson, A. J.; Whitaker, J. B.; Larson, B. W.; Larsen, R. E.; Maturová, K.; Graf, P. A.; Boltalina, O. V.; Strauss, S. H.; Kopidakis, N. Beyond PCBM: Understanding the Photovoltaic 4423


Article

Macromolecules Performance of Blends of Indene-C60 Multiadducts with Poly(3hexylthiophene). Adv. Funct. Mater. 2012, 22, 4115−4127. (71) Lenes, M.; Shelton, S. W.; Sieval, A. B.; Kronholm, D. F.; Hummelen, J. C.; Blom, P. W. M. Electron Trapping in Higher Adduct Fullerene-Based Solar Cells. Adv. Funct. Mater. 2009, 19, 3002−3007. (72) Kang, H.; Cho, C.-H.; Cho, H.-H.; Kang, T. E.; Kim, H. J.; Kim, K.-H.; Yoon, S. C.; Kim, B. J. Controlling Number of Indene Solubilizing Groups in Multiadduct Fullerenes for Tuning Optoelectronic Properties and Open-Circuit Voltage in Organic Solar Cells. ACS Appl. Mater. Interfaces 2012, 4, 110−116. (73) Kang, T. E.; Cho, H.-H.; Cho, C.-H.; Kim, K.-H.; Kang, H.; Lee, M.; Lee, S.; Kim, B.; Im, C.; Kim, B. J. Photoinduced Charge Transfer in Donor−Acceptor (DA) Copolymer: Fullerene Bis-adduct Polymer Solar Cells. ACS Appl. Mater. Interfaces 2013, 5, 861−868. (74) Kang, H.; Kim, K.-H.; Kang, T. E.; Cho, C.-H.; Park, S.; Yoon, S. C.; Kim, B. J. Effect of Fullerene Tris-adducts on the Photovoltaic Performance of P3HT:Fullerene Ternary Blends. ACS Appl. Mater. Interfaces 2013, 5, 4401−4408. (75) Melzer, C.; Koop, E. J.; Mihailetchi, V. D.; Blom, P. W. M. Hole Transport in Poly(phenylene vinylene)/Methanofullerene BulkHeterojunction Solar Cells. Adv. Funct. Mater. 2004, 14, 865−870. (76) Page, Z. A.; Liu, Y.; Duzhko, V. V.; Russell, T. P.; Emrick, T. Fulleropyrrolidine interlayers: Tailoring electrodes to raise organic solar cell efficiency. Science 2014, 346, 441−444. (77) Liu, Y.; Duzhko, V. V.; Page, Z. A.; Emrick, T.; Russell, T. P. Conjugated Polymer Zwitterions: Efficient Interlayer Materials in Organic Electronics. Acc. Chem. Res. 2016, 49, 2478−2488. (78) Piliego, C.; Holcombe, T. W.; Douglas, J. D.; Woo, C. H.; Beaujuge, P. M.; Fréchet, J. M. J. Synthetic Control of Structural Order in N-Alkylthieno[3,4-c]pyrrole-4,6-dione-Based Polymers for Efficient Solar Cells. J. Am. Chem. Soc. 2010, 132, 7595−7597. (79) Schubert, M.; Collins, B. A.; Mangold, H.; Howard, I. A.; Schindler, W.; Vandewal, K.; Roland, S.; Behrends, J.; Kraffert, F.; Steyrleuthner, R.; Chen, Z.; Fostiropoulos, K.; Bittl, R.; Salleo, A.; Facchetti, A.; Laquai, F.; Ade, H. W.; Neher, D. Correlated Donor/ Acceptor Crystal Orientation Controls Photocurrent Generation in All-Polymer Solar Cells. Adv. Funct. Mater. 2014, 24, 4068−4081. (80) Lee, C.; Kang, H.; Lee, W.; Kim, T.; Kim, K.-H.; Woo, H. Y.; Wang, C.; Kim, B. J. High-Performance All-Polymer Solar Cells Via Side-Chain Engineering of the Polymer Acceptor: The Importance of the Polymer Packing Structure and the Nanoscale Blend Morphology. Adv. Mater. 2015, 27, 2466−2471. (81) Jung, J.; Lee, W.; Lee, C.; Ahn, H.; Kim, B. J. Controlling Molecular Orientation of Naphthalenediimide-Based Polymer Acceptors for High Performance All-Polymer Solar Cells. Adv. Energy Mater. 2016, 6, 1600504.

4424


Ethanol-Processable, Highly Crystalline Conjugated Polymers for Eco

Recommend Documents