Buta-1,3-diyne-Based π-Conjugated Polymers for ... - ACS Publications

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Buta-1,3-diyne-Based π‑Conjugated Polymers for Organic Transistors and Solar Cells Brian J. Eckstein,† Ferdinand S. Melkonyan,† Nanjia Zhou,‡ Eric F. Manley,†,§ Jeremy Smith,† Amod Timalsina,† Robert P. H. Chang,‡ Lin X. Chen,†,§ Antonio Facchetti,*,†,∥ and Tobin J. Marks*,†,‡ †

Department of Chemistry and the Materials Research Center and the Argonne-Northwestern Solar Energy Research Center and Department of Materials Science and Engineering and the Materials Research Center and the Argonne-Northwestern Solar Energy Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States § Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 South Cass Avenue, Lemont, Illinois 60439, United States ∥ Polyera Corporation, 8045 Lamon Avenue, Skokie, Illinois 60077, United States ‡

S Supporting Information *

ABSTRACT: We report the synthesis and characterization of new alkyl-substituted 1,4-di(thiophen-2-yl)buta-1,3-diyne (R-DTB) donor building blocks, based on the −CC−CC− conjugative pathway, and their incorporation with thienyl-diketopyrrolopyrrole (R′-TDPP) acceptor units into π-conjugated PTDPP-DTB polymers (P1−P4). The solubility of the new polymers strongly depends on the DTB and DPP solubilizing (R and R′, respectively) substituents. Thus, solution processable and high molecular weight PDPP-DTB polymers are achieved for P3 (R = n-C12H25, R′ = 2butyloctyl) and P4 (R = 2-ethylhexyl, R′ = 2-butyloctyl). Systematic studies of P3 and P4 physicochemical properties are carried using optical spectroscopy, cyclic voltammetry, and thermal analysis, revealing characteristic features of the dialkynyl motif. For the first time, optoelectronic devices (OFETs, OPVs) are fabricated with 1,3-butadiyne containing organic semiconductors. OFET hole mobilities and record OPV power conversion efficiencies for acetylenic organic materials approach 0.1 cm2/(V s) and 4%, respectively, which can be understood from detailed thin-film morphology and microstructural characterization using AFM, TEM, XRD, and GIWAXS methodologies. Importantly, DTB-based polymers (P3 and P4) exhibit, in addition to stabilization of frontier molecular orbitals and to −CC−CC− relief of steric torsions, discrete morphological pliability through thermal annealing and processing additives. The advantageous materials properties and preliminary device performance reported here demonstrate the promise of 1,3-butadiyne-based semiconducting polymers.

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structural modifications, which have propelled the field.18−32 Molecular design and synthetic exploration can be used to establish the effect of polymer structural variations on electronic properties, i.e., the frontier MO energies and band gap, and the solid state morphological properties, such as film crystallinity and preferred chain orientation.33−42 Furthermore, structural explorations are necessary for optimizing performance in commercially relevant devices such as charge mobilities (μ) in organic field-effect transistors (OFETs) and power conversion efficiencies (PCEs) in organic photovoltaic cells (OPVs), combined with robust environmental stability. Investigations centered on ethynylene/acetylene moieties for creating new optoelectronic materials have been carried out for more than two decades.43,44 When installed in a semiconductor core, the compact, electron-withdrawing, and rigid −CC−

INTRODUCTION

Organic semiconducting polymers are a growing materials class employed to investigate the fundamental charge transport properties of soft matter solids and for developing unconventional organic optoelectronic technologies.1−4 These polymers offer the attractions of solution processability, mechanical resilience, and modular structural tunability, combined with the functionality of charge transport.5−12 In particular, solution processing of organic semiconductors permits the implementation of scalable thin-film deposition methodologies, including roll-to-roll and high-throughput printing on large areas of electronic circuits, solar panels, and light-emitting elements, to cite a few examples.13−17 Printing is usually carried out at room temperature or slightly above, rendering semiconducting polymer deposition compatible with inexpensive and flexible plastic substrates, thereby enabling the exploration and prototyping of novel mechanically flexible devices. Fueled by these benefits, the design of new semiconducting polymers by bottom-up synthetic approaches enables molecular level © XXXX American Chemical Society

Received: December 14, 2016 Revised: January 24, 2017

A

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Figure 1. (A) Alkynyl moiety incorporated organic semiconductors. (B) 1,3-Butadiynyl-based polymers (this work).

high charge carrier mobility and ambipolarity of PTDPP-TAT is the alkyne moiety of the TAT building block. The sphybridized carbons of the ethynylene group afford efficient overlap of the electron wave functions, providing effective and conformation-insensitive conjugation along the polymer chain. Very recently, Russell et al. reported the ethynylene-linked benzo[1,2-b:4,5-b]dithiophene-alt-diketopyrrolopyrrole alternating copolymer, EDPP (Figure 1A).59 The unit was designed to increase the low open-circuit voltage (Voc = 0.68 V) of the polymer (poly(BDT-TPD)) reported in early studies. In fact, the ethynylene-incorporated EDPP has a significantly deeper HOMO (−5.68 eV), and the corresponding EDPP:PC71BM BHJ OPVs exhibit a high Voc of 0.88 V. In contrast to ethynylene (alkyne) containing moieties, the 1,3-butadiynyl (diacetylene) group has been barely studied. Only a handful of π-conjugated semiconductors containing a diacetylene linker have been reported to date,60−64 and none implemented in OFET or OPV devices. Considering the limited understanding of the properties of 1,3-butadiynecontaining organic semiconductors, studies addressing the synthesis and optoelectronic characterization of diacetylenecontaining materials should be of great interest from both chemistry and materials science standpoints. For example, the unique reactivity of diacetylene moieties toward volatile nucleophiles like ammonia, hydrazine, hydrogen sulfide, and carbonyl compounds could render diacetylene-based semiconductors suitable active layer materials for next-generation OFET-based gas sensors.65−67 Additionally, the synthesis and study of diacetylene-containing polymers is a valuable step toward a new materials family with a potentially rich postfabrication functionalization chemistry. Postfilm deposition topochemical polymerization, in particular, could yield new platforms for two-dimensional (2D) π-conjugated organic semiconductors.63,68 Here we report the synthesis of several alkyl-substituted 1,4di(thiophen-2-yl)buta-1,3-diyne (R-DTB) electron-rich build-

triple bond can impart a number of desired properties including stabilization of the frontier molecular orbitals (HOMO and LUMO) and planarization of the conjugated backbone, reducing unfavorable steric interactions between in-chain πblocks.45−52 For example, in 2006, Janssen et al. reported an acetylenic analogue of P3HT, PEBT (Figure 1A).53 The polymer was found to have a 0.3 eV lower-lying HOMO than that of P3HT and exhibited a very high open circuit voltage (Voc = 1.01 V) in PEBT:PCBM bulk heterojunction(BHJ) solar cells. In 2011, Baumgarten et al. reported thiadiazoloquinoxaline-(TQ)-based PXTQT polymers.54 The use of the ethynylene π-spacer between TQ and thiophene building blocks favored planarity of the conjugated macromolecular chain and enabled ambipolar transport with well-balanced hole and electron mobilities (μh/μe) in OFETs. Furthermore, insertion of a −CC− moiety between pyromellitic diimide building blocks also enabled n-channel performance in semiconducting polymers such as PC8EPyDI (Figure 1A), affording a moderate μe of 2 × 10−4 cm2/(V s).55 In the alkynebased semiconductors discussed above, good intrachain πdelocalization and strong interchain interactions are promoted by the low steric demands of the alkyne bridges. In 2010, Silvestri et al. reported a series of extended arylacetylene small molecule semiconductors, which demonstrated good OFET hole mobilities (up to 0.07 cm2/(V s)) and promising OPV performance (up to 1.3% PCE).56 This laboratory recently reported soluble semiconductors (TDPP)2-EBT, Figure 1A) containing the 2,2′-ethyne-1,2-diylbis(3-(alk-1-yn-1-yl)thiophene) (EBT) unit with a −CC− triple bond as part of the solubilizing chains.57 (TDPP)2-EBT is a p-channel semiconductor for OFETs as well as a good donor for BHJ OPV cells. Another remarkable example utilizing an ethynylene linker was reported by Cho et al. in 2013 (Figure 1A). The PDPP-TAT polymer exhibits impressive hole and electron mobilities as high as 2.19 and 0.38 cm2/(V s), respectively.58 A detailed analysis showed that a key component enabling the B

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Macromolecules Scheme 1. Synthesis of DTB Monomersa,b

Reagents/conditions: (i) Ni(dppp)Cl2, RMgBr, THF, 0 °C, then 50 °C; (ii) NBS, CHCl3, AcOH, 0 °C, then rt; (iii) Pd(PPh3)2Cl2, piperidine, toluene, TMS−acetylene, rt, then 70 °C; (iv) K2CO3, MeOH, CH2Cl2, rt; (v) Cu(OAc)2, O2, CH2Cl2, rt; (vi) n-BuLi, THF, −78 °C, then rt; Me3SnCl, −78 °C, then rt. b4a was synthesized starting from commercially available 2-bromothiophene. a

Table 1. Summary of Polymers P3 and P4 Optical, Electrochemical, and Electronic Characterization Dataa

MWb polymer

optical absorptionc

Mn (kDa)

PDI

11.3

3.32

53.8

1.65

P3

P4

cyclic voltammetryd

condition

λmax (nm)

EgOPT (eV)

solution as cast 180 °C solution as cast 180 °C

661 729 678 667 726 683

1.61 1.51 1.51 1.63 1.54 1.53

EIP (eV)

EEA (eV)

EgCV (eV)

5.16

3.46

5.25

3.59

OFET performancee anneal

μhole (10−2 × cm2/(V s))

Vth (V)

log Ion/Ioff

1.70

as cast 180 °C

1.7 (1.8) 6.2 (6.3)

−8.3 −8.3

5.6 6.3

1.66

as cast 180 °C

4.9 (6.3) 7.7 (8.0)

−27.9 −15.2

5.7 6.1

a

2-OD = 2-octyldodecyl, 2-BO = 2-butyloctyl, 2-EH = 2-ethylhexyl. Polymers P1 and P2 are not solution processable. bMolecular weights were determined with high temperature GPC. cEgOPTs determined as the onset of optical absorption. dOxidation and reduction potentials Eox/red determined vs Fc/Fc+, EIP/EA = Eox/red + 4.80; EgCV = EIP − EEA. eFilms annealed for 10 min in an inert atmosphere; μhole measured for devices operating in saturation regime; maximum μhole given in parentheses; logarithms of on/off current ratios given.

ing blocks, functionalized with diverse solubilizing alkyl chains at the thiophene 4-position, and their incorporation into new copolymers P1−P4 with the electron-deficient thienyldiketopyrrolopyrrole (TDPP) unit (Figure 1B). TDPP was selected because it has become a ubiquitous acceptor-type monomer in organic semiconductors for several types of optoelectronic devices.69−72 The planar and polar TDPP core is thought to enhance both intramolecular and intermole to enhance both intramolecular and intermolecular charge transport in polymer semiconductors.73 Importantly, according to density functional theory calculations (DFT), the DTB building block is very planar and possesses appropriate frontier molecular orbital (FMO) energies to act as an effective donor unit (Figure S11). All of the new DTB units were characterized by 1H NMR, 13C NMR, and high-resolution mass spectrometry (HRMS). Because of severe aggregation, polymers P1 and P2 are insoluble, even in hot halogenated and high boiling point solvents such as 1,1,2,2-tetrachloroethane and 1,2-dichlorobenzene, whereas the polymers P3 and P4 with longer solubilizing chains are solution-processable. The soluble polymers were characterized by high-temperature 1H NMR, gel permeation chromatography (GPC), CHN elemental analysis (EA), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). Films of P3 and P4 were also characterized by UV−vis absorption spectroscopy (UV−vis), cyclic voltammetry (CV), grazing-incidence wideangle X-ray scattering (GIWAXS), atomic force microscopy (AFM), and transmission electron microscopy (TEM). It will

be seen that the OFET and OPV performance of P3 and P4 can be effected with preliminary morphological tuning to exhibit hole mobilities of 0.063−0.080 cm2/(V s) and power conversion efficiency up to 3.8%, respectively.

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RESULTS AND DISCUSSION Synthesis of DTB-Based Monomers and Polymers. The synthetic route to the DTB monomers 6a−d is depicted in Scheme 1. First, 3-alkylthiophenes 1b−d were obtained by Nicatalyzed Kumada coupling of 3-bromothiophene with the respective alkylmagnesium bromides. Bromination of thiophenes 1b−d with N-bromosuccinimide (NBS) delivered 2b− d. Next, the bromothiophenes 2 were subjected to Pd-catalyzed Sonogashira coupling with ethynyltrimethylsilane to afford intermediates 3. Subsequent removal of protecting trimethylsilyl (TMS) group under basic conditions in dichloromethane (DCM) affords 4b−d. The terminal alkynes 4b−d and 2ethynylthiophene were next homocoupled via Cu-catalyzed Glazer−Hay reaction, affording the key 1,3-butadiynes 5a−d in overall 67−81% yields. The polymerization-ready monomers 6a−d were synthesized via stannylation of the corresponding compounds 5 (Scheme 1). The respective polymers P1−P4 were then synthesized via Stille condensation polymerization of the corresponding stannylated DTB monomers 6 with 3,6bis(5-bromothiophen-2-yl)-2,5-bis(alkyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (TDPP-Br2) monomers (Table 1). For the monomers 6a,b the corresponding polymerizations did not yield any processable materials. High-temperature gel permeC

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solution to film and upon annealing demonstrate that the DTBbased polymers offer interchain morphological malleability that can be utilized in the device fabrication process, especially for photovoltaic devices (vide inf ra). The film optical band gaps of P3 and P4 are larger than those reported for PDPP-4T polymers (∼1.4 eV), but not much greater than the 1.50 eV optical band gap of acetylene-incorporated DPP-TAT (see Figure 1A for structure), indicating that the attenuation of band gap compression by diacetylene moieties does not extend much beyond that of single acetylene spacers in polymer films. However, the solution λmax values of P3 and P4 (661 and 667 nm, respectively) are considerably blue-shifted compared to that of DPP-TAT (761 nm), suggesting that a continuing absorption band widening effect indeed exists.58 Electrochemistry was used to characterize the HOMO and LUMO energies, which can be taken as the ionization potential (EIP) and electron affinity (EEA) energies of these polymers (compiled in Table 1) below vacuum level.77 Cyclic voltammetry of drop-cast films (from 3 mg/mL in CF) yielded first oxidation onset potentials of 0.805 V (P3) and 0.891 V (P4) vs Ag/AgCl, and the first reduction onset potentials of P3 and P4 were estimated as −0.896 and −0.765 V vs Ag/AgCl, respectively. The EIPs and EEAs were estimated by referencing the respective first oxidation and reduction onset potentials vs Ag/AgCl to the ferrocene/ferrocenium (Fc/Fc+) redox couple potential (measured as 0.445 V vs Ag/AgCl) and then referencing to the commonly reported Fc/Fc+ ionization potential of 4.8 eV.78 Thus, the P3 and P4 HOMO energies can be considered to be −5.16 and −5.25 eV, respectively, which are deeper than that of known DT-PdPP4T (−5.09 eV).79 Similar to acetylene bridges, the diacetylene moiety has a strong electronic effect, stabilizing the HOMO. Lower HOMO levels can prevent adverse OFET off currents (Ioff) and device instability in ambient as well as afford higher OPV open circuit voltages.21,80 Field-Effect Transistor Performance and Polymer Film Morphology. The charge transport properties of the TDPPDTB polymers were investigated by fabricating bottom-gate/ top-contact (BGTC) OFETs. For the BGTC devices, the semiconducting layer was deposited by spin-coating a 10 mg/ mL polymer solution in chloroform under a nitrogen atmosphere on octadecyltrichlorosilane (OTS)-treated pdoped Si (100) wafers having a 300 nm thermally grown SiO2 dielectric layer. After spin-coating the polymer solutions, the semiconducting films were dried at 80 °C and either thermally annealed under an N2 atmosphere at 180 °C or left unannealed, then followed by thermal evaporation of Au source and drain contacts (W/L = 1000/50 μm). Both the P3- and P4-based transistors exhibit a distinct p-type response, and representative FET transfer plots are given in Figures 2C and 2D. Table 1 collects all relevant FET performance parameters. The hole transport in these devices significantly depend on the film thermal history. Thus, the carrier mobilities of the unannealed/annealed devices are 0.017/0.062 and 0.049/ 0.077 cm2/(V s) for P3 and P4, respectively. Current modulations (Ion/Ioff) for all of the devices exceed 105, displaying, as expected from the electrochemical characterization, desirable switching behavior. To better understand the charge transport properties of the polymers, the film microstructure and morphology were next investigated with GIWAXS and AFM. Note that DSC measurements on P3 and P4 (Figure S13) do not reveal any obvious thermal transitions, indicating largely amorphous states

ation chromatography (GPC) was used to determine the P3 and P4 molecular weights and dispersities. The molecular weight and dispersity difference between P3 and P4 (Table 1) could be due to variations in the polymerization media viscosity and aggregation of the polymers with different side chains, which will effect end-group reactivity during the later stages of polymerization.74 Additionally, the branched 2-ethylhexyl side chains on the DTB core in P4 may sterically prevent π-philic Pd nanoparticles from cross-linking the diacetylene moieties, a process observed in alkyne-containing polymers synthesized with relatively high Pd loadings.75 Optical and Electrochemical Properties of Polymers. The optical absorption spectra of DTB-based polymers P3 and P4 in dilute chloroform (CF) solutions and as thin-films (spincoated from 3 mg/mL CF solutions) are shown in Figures 2A

Figure 2. Solution and thin-film UV−vis absorption spectra of P3 (A) and P4 (B). OFET transfer curves of devices for P3 (C) and P4 (D).

and 2B, respectively, and relevant data are collected in Table 1. Notably, the Gaussian line shapes in the solution absorption spectra of P3 and P4 indicate negligible intrachain aggregation, which is rare for TDPP polymers, including the acetylenecontaining PTDPP-TAT. This suggests that the 1,3-butadiyne moiety may be imparting unique rigid-rod character that inhibits polymer chain self-folding in solution. The peaks corresponding to λmax in solution are red-shifted by 30 nm (P3) and 7 nm (P4) in the as-cast films. Furthermore, the optical profiles of P3 and P4 reveal the appearance of shoulders at 729 and 726 nm, respectively, indicating formation of intermolecular interactions and ordering.76 The solid-state optical bandgaps (Egopts), estimated from the absorption onsets of the as-cast/annealed films, are 1.51/1.51 eV and 1.54/1.53 eV for P3 and P4, respectively. Bulkier side chains, such as the 2ethylhexyl groups on P4, usually result in slightly enlarged polymer bandgaps versus linear substituent groups due to the increased intermolecular π−π stacking spacing and decreased πorbital overlap. Interestingly, the relative intensities of the vibronic peaks reverse upon short time annealing at 180 °C. The prominent shifts in spectral line shapes going from D

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Organic Photovoltaic Performance and BHJ Blend Film Morphology. Based on the favorable molecular structures, electronic properties, and respectable OFET performance, it was of interest to next investigate P3 and P4 OPV performance. Thus, inverted OPV architectures (ITO/ ZnO/polymer:PC71BM/MoO3/Ag) were due to the high performance and environmental stability of such devices.84,85 For the inverted OPVs, the active layer (polymer:PC71BM = 1:2 by weight) was deposited by spin-coating 10 mg/mL polymer solutions onto indium tin oxide (ITO) substrates with a ZnO as a hole-blocking layer. Then, an electron-blocking MoO3 layer followed by Ag contacts was deposited on top of the active layer by thermal evaporation. Interestingly, devices fabricated using both P3 and P4 blended with PC71BM in CF demonstrated very low OPV performance (Table 2). For P3-

for these polymers in the bulk. Figure 3 shows GIWAXS profiles of the unannealed and annealed P3 and P4 films on

Table 2. OPV Metrics for P3- and P4-Based Devices Using CF or CF:CN = 95:5 (v/v) as Processing Solventa donor

solvent

Voc (V)

Jsc (mA/cm2)

FF (%)

P3

CF CF/CN CF CF/CN

0.725 0.674 0.716 0.697

1.20 7.06 1.22 8.37

38.0 57.3 51.0 64.3

P4

Figure 3. (A) Out-of-plane and (B) in-plane GIWAXS diffractograms.

a b

OTS-treated Si/SiO2 substrates (see Figure S16 for the corresponding 2D images). Lamellar d-spacings can be estimated from the diffraction peaks using the Bragg condition q = 2π/d. Additionally, to assess film order, crystalline correlation lengths can be estimated using the fwhm of the peaks via a modified Scherrer equation adjusting for the distortions of a 2D detector.81 Both polymers show both “edge-on” and “face-on” crystalline interactions as evidenced by the existence of lamellar interactions in both the out-of-plane (qz) and in-plane (qxy) directions. In the out-of-plane direction, the “edge-on” lamellar side-chain diffraction peaks indicate d-spacings of 18.5 Å for P3 and 16.2 Å for P4 (Figure 3A). Upon annealing, these peaks sharpen for both polymers, indicating formation of larger ordered domains. A similar effect is seen with the in-plane, “face-on,” lamellar interactions as the peaks sharpen with annealing in both P3 and P4. Additionally, there is a noticeable expansion in “face-on” lamellar spacing of P4 from 16.6 to 17.1 Å, indicating that along with increasing the domain size of the crystalline interactions there is also a shift in the polymer chain interactions. Similarly to the lamellar domains, the π−π stacking domains appear to be growing with thermal annealing as well. There is not any obvious “face-on” out-of-plane πstacking reflection for the unannealed P3 film, whereas unannealed P4 shows a clearer broad peak around, thus indicating that despite the coexistence of both orientations, the “face-on” orientation is preferred. For both P3 and P4, the general trend of increased domain size and order upon thermal annealing correlates well with the increase in the field-effect mobility of the corresponding FETs. AFM images of P3 and P4 films (Figure S15) reveal that the film surfaces are all quite smooth and do not change significantly with annealing. The average film roughnesses (Ra) of the polymer films before and after annealing remains in a narrow range (∼0.2−0.5 nm). Such smooth surface topologies are generally desirable for OFET fabrication, especially for solution-processed top-gate FETs used in more complicated circuits.82,83

PCEb (%) 0.31 2.69 0.41 3.70

(0.33) (2.73) (0.45) (3.75)

OPV cell architecture: ITO/ZnO/polymer:PC71BM/MoO3/Ag. The highest PCEs are given in parentheses.

based cells a PCE of 0.33% was obtained along with a Voc = 0.725 V, Jsc = 1.20 mA/cm2, and FF = 38.0%. Similarly, P4based cells show a PCE of 0.45% with Voc = 0.716 V, Jsc = 1.22 mA/cm2, and FF = 51.0% (Figure 4A and Table 2).

Figure 4. BHJ OPV cell characterization for the ITO/ZnO/ polymer:PC71BM/MoO3/Ag architecture. (A) Illuminated J−V photoresponse and (B) EQE spectra.

It is well-known that using a solvent mixture to process BHJ photoactive blends, especially with small amounts of a high boiling point solvent such as 1-chloronaphthalene (CN), is an effective approach to optimize the blend film morphology and increase film crystallinity.86,87 Therefore, a solvent combination comprising a CF:CN = 95:5 volume ratio was chosen to optimize the OPV performance (Table 2). When using this solvent mixture, P3-based OPVs show PCEs up to 2.73%, with a Voc = 0.674 V, Jsc = 7.06 mA/cm2, and FF = 57.3%, while P4based devices show a PCE up to 3.75%, with a Voc = 0.697 V, Jsc = 8.37 mA/cm2, and FF = 64.3% (Table 2). Importantly, these PCE values are the highest reported to date for acetylene-based organic semiconductors and the first for diacetylene-based OPVs, including both small molecules and polymers.43,53,56,57,59 The significant PCE enhancement is mainly a result of the greatly increased Jsc. This is also in excellent agreement with the external quantum efficiency (EQE) spectra showing maximum E

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without CN, both the neat polymers and the blends with PC71BM exhibit a “face-on” preferred orientation characterized by greater out-of-plane π−π stacking (010) interactions and sharper in-plane lamellar (100) interactions similar to the previously examined OFET films. Conversely, when the films were spun with CN, an “edge-on” orientation is preferred, as indicated by prominence of the out-of-plane lamellar peaks and in-plane π−π stacking peaks. The in-plane diffractogram profiles of P3 (Figure 6C) most notably reveal π−π stacking peaks around 1.7 Å−1 when both the neat and PC71BM blends are processed with CN. For P4, the out-of-plane diffraction patterns (Figure 6B) similarly evidence a general growth and sharpening of the neat and blended film lamellar peaks at ∼0.3 Å−1 and disappearance of the neat film π−π stacking peak, observed at ∼1.7 Å−1 without CN, when the films are processed with CN. Compared to films processed without CN, the inplane diffractogram profiles of P4 processed with CN (Figure 6D) most notably display a broadening in the lamellar peaks at ∼0.3 Å−1 for both the neat and the blend films as well as appearance of a distinct π−π stacking peak at ∼1.7 Å−1 for the blend film. Table 3 summarizes all respective d-spacings and correlation lengths (CL) extracted from the P3 and P4 diffraction data in their preferred orientations (e.g., lamellar (100)/π−π (010) d-spacing measured from in-plane/out-ofplane diffractogram profile for “face-on” orientation). While a change in d-spacing is observed when switching from “face-on” to “edge-on” domains, no significant change is detected when blending with PC71BM, indicating that the ordered polymer domains do not experience significant cocrystalline intermixing with PC71BM.90 When processed with CN, the CLs of lamellar ordered domains increase in both the neat and blends for P3 but decrease slightly for P4. This is likely due to the linear P3 n-dodecyl chains which are more likely to promote side-chain ordering than the branched P4 2-ethylhexyl chains. The CL analysis shows an increase in π−π stacking domain size when processed with CN, especially for P4. Note that the morphological changes caused by solvent additives in the present OPV blends are distinct from thermally induced morphological evolution in the OFET films. This indicates a level of morphological malleability in these materials in response to specific optimization conditions. However, while the switch in orientations with CN addition is interesting, it is more likely that general increases in overall ordering are responsible for increases in performance. In particular, increased π−π correlation lengths likely contribute to the dramatically improved charge transport characteristics observed in CN processed OPVs as indicated by higher FFs and JSCs.

values exceeding 45% and 30% and for P3 at 485 nm and P4 at 555 nm, respectively (Figure 4B). The greatly enhanced Jsc and FF suggest an improved blend film morphology for both exciton charge separation and percolation pathways for collecting charges.88 In contrast, compared to the OPVs processed without CN, the slight reduction of Voc for the devices processed with the addition of CN is likely a result of increased polymer−PC71BM charge transfer states accompanying the morphological evolution.89 To investigate the film morphology evolution in these systems upon CN addition, AFM, TEM, and GIWAXS characterization was performed for P3 and P4 pristine and blend films. In all three measurements we observe a marked difference between films processed with and without CN. TEM and AFM images show that when the P3:PC71BM (Figure 5A)

Figure 5. Thin-film TEM and tapping-mode AFM (inset) images of (A) P3:PC71BM = 1:2 (w/w) blend using CF as the processing solvent, (B) P4:PC71BM = 1:2 using CF as the processing solvent, (C) P3:PC71BM = 1:2 using CF:CN = 95:5 (v/v) as the processing solvent, and (D) P4:PC71BM = 1:2 using CF:CN 95:5 (v/v) as the processing solvent.

and P4:PC71BM (Figure 5B) blends are processed from CF without CN, large-scale phase segregation (domain sizes on the order of 100 nm) occurs. This microstructure reduces the donor−acceptor interfaces necessary for exciton separation, thus significantly limiting Jsc. In contrast, the P3:PC71BM (Figure 5C) and P4:PC71BM (Figure 5D) blend films processed with CN show clear interpenetrating networks of the polymer and fullerene phases with domain sizes shifted closer to 10−20 nm, which is a more optimal morphology for OPV device efficiency. GIWAXS of neat and polymer:PC71BM blend films processed from CF and CF:CN solutions provides a clearer picture of how PC71BM and CN affect P3 and P4 aggregation. Out-of-plane (qz) and in-plane (qxy) diffractogram profiles of the neat and PC71BM + P3 and P4 blend films that were processed with and without CN are shown in Figure 6 (for 2D images see Figures S17 and S18). The out-of-plane diffraction of P3 (Figure 6A) shows that upon processing with CN there is a marked increase in the prominence of the lamellar peak around 0.3 Å−1 for both the neat and PC71BM blend films, while the broad π−π stacking peak, observed at around 1.7 Å−1 in the neat film, disappears. When processed

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CONCLUSIONS For the first time organic semiconducting materials based on the 1,3-butadiyne unit were realized. A new key DTB building block was designed and synthesized for implementation of 1,3butadiyne motif into semiconductors π-conjugated backbone. Copolymers of TDPP and DTB functionalized with various side chains were synthesized to examine their molecular, electronic, and morphological properties. The soluble polymers P3 and P4 were evaluated as p-type active layer materials in OFETs and BHJ OPVs, which, notably, represents first investigation of device properties for diacetylene-containing polymer semiconductors. As evidenced by the OFET and BHJ OPV devices fabricated in this study, thermal annealing and use of solvent additives can be used to modify the morphology and microstructure of the PTDPP-DTB device films. GIWAXS and F

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Figure 6. GIWAXS diffractograms of neat and polymer:PC71BM (1:2 w/w) blend films processed using CF and CF:CN = 95:5 (v/v) showing P3 (A) out-of-plane and (C) in-plane scattering and P4 (B) out-of-plane and (D) in-plane scattering, respectively.

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Table 3. Summary of d-Spacings and Correlation Lengths (CL) for Pristine and Blend Films Processed Using CF and CF:CN = 95:5 (v/v) d-spacing (Å) (1−0−0)

(0−1−0)

(1−0−0)

(0−1−0)

P3, CFa P3, CF:CNb P3:PCBM, CFa P3:PCBM, CF:CNb P4, CFa P4, CF:CNb P4:PCBM, CFa P4:PCBM, CF:CNb

21.2 18.8 20.9 19.2 16.8 16.6 16.8 16.1

3.68 3.73 3.71 3.66 3.76 3.78

5.1 8.6 5.2 5.5 6.2 5.4 7.5 6.8

2.8 4.4 2.7 5.2 3.1 8.3

3.76

Materials Synthesis. The reagents 3,6-bis(5-bromothiophen-2yl)-2,5-bis(2-butyloctyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione and 3,6-bis(5-bromothiophen-2-yl)-2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione were synthesized according to literature procedures.3,30 The syntheses of compounds 1b−d through 4b−d are given in the Supporting Information. The reagent 2-ethynylthiophene (4a) was purchased from Sigma-Aldrich and was used without further purification. All other commercially available reagents were used without further purification unless otherwise stated. Anhydrous THF was distilled from Na/benzophenone. Anhydrous toluene was obtained from a Grubbs column purification system. Reactions were carried out under N2 atmospheres using standard Schlenk technique unless otherwise noted. General Procedure for the Glazer−Hay Homocoupling of 4a−d. Terminal alkynes 4a−d were loaded into a one-neck roundbottom flasks having stir bars in ambient atmosphere. Piperidine (1.1 equiv), Cu(OAc)2 (0.1 equiv), and dichloromethane (0.5 M) were added. The atmosphere above the reaction was then purged with 250 mL of UHP O2 at 1 atm, and the reaction was stirred under 1 atm of UHP O2 for 2 h at room temperature. The reaction was then concentrated under reduced pressure and purified by silica gel column chromatography with hexanes as the eluent. 1,4-Di(thiophen-2-yl)buta-1,3-diyne (5a). Yield = 0.365 g (1.70 mmol; 73.6%) of the title compound as white needles. 1H NMR (400 MHz, CDCl3) δ: 7.35 (dd, J = 3.7, 1.2 Hz, 2H), 7.33 (dd, J = 5.2, 1.2 Hz, 2H), 7.00 (dd, J = 5.1, 3.7 Hz, 2H). 13C NMR (101 MHz, CDCl3) δ: 134.54, 129.06, 127.36, 122.07, 77.91, 76.78. HRMS (ESI-TOFMS): m/z calcd for C12H7S2 [M + H]+ 214.9984; found 214.9994. 1,4-Di(3-hexylthiophen-2-yl)buta-1,3-diyne (5b). Yield = 0.716 g (1.87 mmol; 81.1%) of the title compound as a yellow oil. 1H NMR (400 MHz, CDCl3) δ: 7.20 (d, J = 5.1 Hz, 2H), 6.87 (d, J = 5.2 Hz, 2H), 2.74 (t, J = 7.5 Hz, 4H), 1.63 (p, J = 7.5 Hz, 4H), 1.33 (m, 12H), 0.90 (t, J = 7.1 Hz, 6H). 13C NMR (101 MHz, CDCl3) δ: 151.12, 128.42, 127.75, 117.42, 80.10, 76.81, 31.75, 30.42, 29.81, 29.03, 22.75, 14.26. HRMS (ESI-TOF-MS): m/z calcd for C24H31S2 [M + H]+ 383.1862; found 383.1870. 1,4-Di(3-dodecylthiophen-2-yl)buta-1,3-diyne (5c). Yield = 0.730 g (1.33 mmol; 66.9%) of the title compound as a yellow solid. 1H NMR (400 MHz, CDCl3) δ: 7.20 (d, J = 5.1 Hz, 2H), 6.87 (d, J = 5.1

CL (nm)

films

9.7

Corresponds to “face-on” preferred orientation. Corresponds to “edge-on” preferred orientation. PCBM = PC71BM.

a

EXPERIMENTAL SECTION

b

TEM show that thermal annealing and solvent additive improve neat and photoactive blend film morphology for the respective devices in different manners. Additionally, the solution and film optical absorption spectra of P3 and P4 indicate that film formation and morphological evolution are dominated by interchain packing. The demonstrated hole mobility approaching 0.1 cm2/(V s) and PCE approaching 4%, a record for alkyne-containing organic materials, demonstrate the potential of this new family of diacetylene-based semiconductors. Importantly, respectable performance and good stability of transistors fabricated with these diacetylene polymers opens the road for the materials’ implementation and study in OFETbased gas sensors. Further investigations of solution processing techniques and conditions for the optimization of DTB-based polymer chain packing and alignment is in progress. Additionally, postdeposition chemical transformations of DTB polymer diacetylene moieties will be explored en route to 2-D conjugated materials and modular film modification. G

DOI: 10.1021/acs.macromol.6b02702 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules Hz, 2H), 2.73 (t, J = 7.5 Hz, 4H), 1.63 (p, J = 7.5 Hz, 4H), 1.28 (m, 36H), 0.88 (t, J = 7.1 Hz, 6H). 13C NMR (101 MHz, CDCl3) δ: 151.12, 128.43, 127.74, 117.43, 80.12, 76.82, 32.09, 30.46, 29.85, 29.84, 29.82, 29.75, 29.58, 29.52, 29.38, 22.85, 14.28 (aliphatic signals may overlap). HRMS (ESI-TOF-MS): m/z calcd for C36H55S2 [M + H]+ 551.3740; found 551.3750. 1,4-Di(3-(2-ethylhexyl)thiophen-2-yl)buta-1,3-diyne (5d). Yield = 0.763 g (1.74 mmol; 78.4%) of the title compound as a yellow oil. 1H NMR (400 MHz, CDCl3) δ: 7.20 (d, J = 5.1 Hz, 2H), 6.85 (d, J = 5.2 Hz, 2H), 2.67 (d, J = 7.1 Hz, 4H), 1.64 (m, 2H), 1.30 (m, 16H), 0.90 (m, 12H). 13C NMR (101 MHz, CDCl3) δ: 150.33, 129.00, 127.49, 118.06, 80.13, 76.96, 40.81, 34.00, 32.72, 28.97, 25.97, 23.20, 14.31, 11.06. HRMS (ESI-TOF-MS): m/z calcd for C28H39S2 [M + H]+ 439.2488; found 439.2507. General Procedure for the Bis(trimethyl-stannylation) of 1,4-Di(thiophen-2-yl)buta-1,3-diynes 5a−d. Compounds 5a−d were loaded into respective oven-dried Schlenk flasks having stir bars. Anhydrous THF (0.025 M) was added, and the solution was cooled to −78 °C using an acetone and dry ice bath. Then, 2.5 M n-butyllithium in hexanes (2.2 equiv) was added dropwise over 10 min, and the reaction was stirred at −78 °C for 1 h. Then 1.0 M Me3SnCl chloride in THF (2.5 equiv) was added, and the reaction was stirred and slowly warmed to room temperature overnight. The organic phase was washed with brine, dried over MgSO4, and filtered, and the filtrate was concentrated under reduced pressure. Unless otherwise noted, the crude products were redissolved in minimal THF and then precipitated into 150 mL of MeOH. After chilling in a freezer overnight, the precipitated products were collected by filtration, washed with cold methanol, and dried. 1,4-Bis(5-(trimethylstannyl)thiophen-2-yl)buta-1,3-diyne (6a). Yield = 0.243 g (0.45 mmol; 96.3%) of the title compound as a white powder. 1H NMR (499 MHz, C6D6) δ: 7.27 (d, J = 3.4 Hz, 2H), 6.74 (d, J = 3.4 Hz, 2H), 0.12 (s, 18H). 13C NMR (101 MHz, C6D6) δ: 143.98, 135.50, 135.34, 127.98, 80.25, 78.07, −8.55. HRMS (ESITOF-MS): m/z calcd. for C18H23S2Sn2 [M + H]+ 540.9278; found 540.9297. 1,4-Bis(3-hexyl-5-(trimethylstannyl)thiophen-2-yl)buta-1,3-diyne (6b). Yield = 0.580 g (0.82 mmol; 94.7%) of the title compound as a yellow powder. 1H NMR (499 MHz, C6D6) δ: 6.89 (s, 2H), 2.77 (t, J = 7.7 Hz, 4H), 1.60 (p, J = 7.4 Hz, 4H), 1.24 (m, 12H), 0.87 (t, J = 7.1 Hz, 6H), 0.17 (s, 18H). 13C NMR (101 MHz, C6D6) δ: 152.06, 142.81, 136.54, 123.74, 82.29, 78.22, 31.99, 30.98, 29.85, 29.37, 23.00, 14.38, −8.50. HRMS (ESI-TOF-MS): m/z calcd for C30H47S2Sn2 [M + H]+ 709.1160; found 709.1156. 1,4-Bis(3-dodecyl-5-(trimethylstannyl)thiophen-2-yl)buta-1,3diyne (6c). Yield = 0.455 g (0.52 mmol; 98.1%) of the title compound as a yellow powder. 1H NMR (499 MHz, C6D6) δ: 6.90 (s, 2H), 2.81 (t, J = 7.7 Hz, 4H), 1.65 (p, J = 7.4 Hz, 4H), 1.29 (m, 36H), 0.92 (t, J = 6.8 Hz, 6H), 0.17 (s, 18H). 13C NMR (101 MHz, C6D6) δ 152.06, 142.81, 136.54, 123.79, 82.31, 78.23, 32.41, 31.03, 30.22, 30.20, 30.18, 30.08, 29.89, 29.86, 29.71, 23.18, 14.44, −8.51 (aliphatic signals may overlap). HRMS (ESI-TOF-MS): m/z calcd for C42H71S2Sn2 [M + H]+ 877.3035; found 877.3041. 1,4-Bis(3-(2-ethylhexyl)-5-(trimethylstannyl)thiophen-2-yl)buta1,3-diyne (6d). Yield = 0.766 g (1.00 mmol; 94.9%) of the title compound as a yellow oil. Precipitation was not performed for this compound, and the crude compound was used for the next step. 1H NMR (499 MHz, C6D6) δ: 6.94 (s, 2H), 2.77 (d, J = 7.1 Hz, 4H), 1.76 (m, 2H), 1.32 (m, 16H), 0.91 (m, 12H), 0.16 (s, 18H). 13C NMR (101 MHz, C6D6) δ: 151.25, 142.59, 137.10, 124.41, 82.29, 78.33, 41.24, 34.06, 33.02, 29.20, 26.33, 23.50, 14.47, 11.19, −8.49. HRMS (ESI-TOF-MS): m/z calcd for C34H55S2Sn2 [M + H]+ 765.1788; found 765.1795. General Procedure for the Stille Polymerization of DTB Monomers 6a−d with Respective TDPP-Br2 Monomers. DTB monomers 6a−d (0.1 mmol) were loaded with their respective TDPPBr2 monomers (0.1 mmol) and Pd(PPh3)4) (4.0 mol %) into ovendried heavy-walled Schlenk flasks with pressure-sealing Teflon plug valves. Degassed and anhydrous toluene (2.0 mL) was added under N2. The reaction vessel was then sealed, heated to 85 °C, and let stir

for 3 days. Capping was performed by the addition of 0.050 mL of 2(tributylstannyl)thiophene, stirring for 8 h, then adding 0.10 mL of 2bromothiophene, and stirring overnight. The polymerization mixture was then precipitated in a solution of 135 mL of MeOH and 15 mL of 10% HCl(aq), stirred for 2 h, and filtered into a cellulose Soxhlet thimble. Purification was performed by sequential Soxhlet extraction with methanol, acetone, hexanes, and finally chloroform. The chloroform fraction was concentrated under reduced pressure, redissolved in a minimal amount of chloroform, and precipitated in methanol. The solid polymer was collected by filtration and dried under vacuum at 60 °C for 24 h. Poly(1,4-di(3-dodecylthiophen-2-yl)buta-1,3-diyne-alt-2,5-bis(2butyloctyl)-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)dione) (P3). Yield = 0.124 g (87.1%) of the title compound as a green solid. Mn = 11.3 kDa, Mw = 37.5 kDa, PDI = 3.32. 1H NMR (500 MHz, 1,1,2,2-tetrachloroethane-d2, 373 K) δ: 8.65 (br, 2H), 7.23 (br, 2H), 7.00 (br, 2H), 3.92 (br, 4H), 2.65 (br, 4H), 1.87 (br, 2H), 1.62 (br, 4H), 1.27 (m, 68H), 0.78 (m, 18H). CHN elemental analysis calcd for (C74H106N2O2S4)n C: 75.07, H: 9.02, N: 2.37; found C: 74.67, H: 8.87, N: 2.36. Poly(1,4-di(3-(2-ethylhexyl)thiophen-2-yl)buta-1,3-diyne-alt-2,5bis(2-butyloctyl)-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione) (P4). Yield = 0.0979 g (60.4%) of the title compound as a green solid. Mn = 53.8 kDa, Mw = 88.8 kDa, PDI = 1.65. 1H NMR (500 MHz, 1,1,2,2-tetrachloroethane-d2, 373 K) δ: 8.64 (br, 2H), 7.23 (br, 2H), 6.98 (br, 2H), 3.93 (br, 4H), 2.60 (br, 4H), 1.87 (br, 2H), 1.64 (br, 2H), 1.24 (m, 48H), 0.78 (m, 24H). CHN elemental analysis calcd for (C66H90N2O2S4)n C: 73.97, H: 8.46, N: 2.61; found C: 73.62, H: 8.09, N: 2.49. Materials Characterization. NMR spectra were recorded on Varian Inova 500, Agilent DD MR-400, and Agilent DD 500 (high temperature) spectrometers. High-resolution mass spectra were recorded on an Agilent 6210 LC-TOF multimode ionization (MMI) mass spectrometer. UV−vis spectroscopy was performed on a Varian Cary 5000 UV−vis−NIR spectrophotometer. Films for UV−vis were prepared by spin-coating 3 mg/mL solutions of polymer in chloroform onto VWR glass slides at 1000 rpm. Annealing was carried out for 10 min at 180 °C under N2. For solution UV−vis spectroscopy, 30 μL of the 3 mg/mL solutions was diluted to 9 μg/mL with 10 mL of chloroform. Electrochemistry was performed on a C3 Cell Stand electrochemical station equipped with BAS Epsilon software (Bioanalytical Systems, Inc., Lafayette, IN). The voltammograms were acquired in acetonitrile solutions using 0.1 M Bu4NPF6 as the electrolyte. The polymer films were drop-casted from 3 mg/mL solutions onto a glassy carbon (3 mm diameter) working electrode and pseudoblade-coated with a pipet tip for more regular film coverage. The electrochemical cell was also equipped with a Pt-wire counter electrode and Ag/AgCl reference electrode. All scans were performed at 100 mV/s. Prior to the operation, the solutions were stirred and purged with N2. A ferrocene/ferrocenium redox couple was used as an external standard after each film measurement (with the standard approximation that the Fc/Fc+ ionization potential is −4.8 eV vs vacuum level), and the potential values obtained in reference to the Ag/AgCl electrode were converted to the vacuum scale. Polymer molecular weights were determined with a Polymer Laboratories PLGPC 220 using trichlorobenzene as eluent at 170 °C vs polystyrene standards. Elemental analyses were performed by Midwest Microlab (Indianapolis, IN). Differential scanning calorimetry was performed on a TA model DSC 2920 with a heating ramp of 10 °C/min, and data are reported for the second heating−cooling cycle. Thermogravimetric analysis was performed on TGA/SDTA-851 instrument with a heating ramp of 10 °C/min. OFET Fabrication. Top contact/bottom gate transistors were fabricated and tested using the following procedure. Solutions of 10 mg/mL polymer in anhydrous chloroform were prepared in a nitrogen atmosphere glovebox and were stirred at 70 °C for 1 h. Films were deposited under inert conditions by spin-coating the solutions on Si2+/ SiO2 (300 nm thermal oxide; WRS Materials) treated with octadecyltrichlorosilane (OTS) at 5000 rpm (5000 rpm/s acceleration) for 50 s. The films were dried at 80 °C for 2 min and then H

DOI: 10.1021/acs.macromol.6b02702 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules either left unannealed or annealed at 180 °C for 10 min in inert atmosphere. Top contacts (L = 50 μm, W = 1000 μm) were deposited by thermal evaporation of 40 nm of Au under high vacuum (0.1−0.5 A/s at ∼10−6 Torr). Devices (at least five per substrate) were tested in ambient atmosphere using a probestation with an Agilent B1500 parameter analyzer. The capacitance of the OTS-coated 300 nm SiO2 gate dielectric is taken to be 11 nF/cm2. OPV Fabrication. PC71BM was provided by American Dye Source Inc. For OPV device fabrication, prepatterned indium tin oxide (ITO)coated glass wafers (Thin Film Devices, Inc.) with a thickness ∼150 nm and series resistance ∼10 Ω/cm were used as substrates. ITO electrodes were cleaned by sequential sonication in hexane, deionized (DI) water, methanol, isopropanol, and acetone and finally UV/ozone treated (Jelight Co.) for 30 min. The cathode interfacial layer, ZnO, was deposited from a precursor solution according to reported procedures, which involve spin-casting at 5000 rpm for 30 s and annealing at 170 °C. For optimal devices performance, active layers were prepared in weight ratios 1:2 (P3/P4:PC71BM) in CF:CN at a concentration of polymer 10 mg/mL. Thin layers of 7.5 nm MoO3 and 120 nm of Ag were then thermally evaporated through a shadow mask at ∼10−6 Torr. Device I−V characteristics were measured under AM 1.5G light (100 mW/cm2) using the Xe arc lamp of a Spectra-Nova Class A solar simulator. The light intensity was calibrated using an NREL-certified monocrystalline Si diode coupled to a KG3 filter to bring the spectral mismatch to unity. Four-point contact measurements were performed, and electrical characterizations were measured with a Keithley 2400 unit. The area of all devices was 6 mm2. EQEs were characterized using an Oriel model QE-PV-SI instrument equipped with a NIST-certified Si diode. Monochromatic light was generated from an Oriel 300 W lamp source. AFM and TEM. Film topological and morphological characterizations were carried out by an AFM measurements performed using a Dimension Icon scanning probe microscope (Veeco) in tapping mode, and TEM measurements were performed using a JEOL JEM-2100F instrument. Thin-films fabricated for those measurements were prepared using conditions to exactly reproduce films for corresponding OFET/OPV devices. GIWAXS. Grazing incidence wide-angle X-ray scattering measurements were performed at Beamline 8-ID-E of the Advanced Photon Source at Argonne National Laboratory. The photon energy is 7.35 keV (λ = 1.6868 Å), and data were collected on a Pilatus 1M pixel array detector at a sample−detector distance of 204 mm. Spectra were collected at an incidence angle of 0.18°; the films were exposure for 25 s in air (Figure 3 and Figure S14) or in a vacuum (Figure 6 and Figures S15, S16). To account for the gaps in the detector array, two images were taken per sampleone with the detector in the standard position and the other translated 23 mm down to fill the gap; the two images are then merged. 1D line cuts were taken of the 2D scattering spectra in the in-plane and out-of-plane direction using the Gixsgui software package developed by the beamline scientists. To normalize for the differing exposure times and air scatter, the line cuts were background subtracted utilizing an exponential fit. The backgroundsubtracted peaks were fit using the multipeak fit function in Igor Pro. Scherrer analysis was performed utilizing the previously mentioned method by Smiglies to account for instrumental broadening and detection limits.81 The values presented represent a lower limit for correlation length, as the Scherrer analysis does not account for broadening due to defects in the crystallites.

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measurements and AFM images, GIWAXS measurements (PDF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail [email protected] (A.F.). *E-mail [email protected] (T.J.M.). ORCID

Ferdinand S. Melkonyan: 0000-0001-8228-9247 Tobin J. Marks: 0000-0001-8771-0141 Funding

This research was supported in part by Argonne-Northwestern Solar Energy Research (ANSER) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Award DE-SC0001059, and by AFOSR Grant FA9550-15-1-0044. F.S.M. was supported by Award 70NANB14H012 from U.S. Department of Commerce. This work was performed under the following financial assistance award 70NANB14H012 from U.S. Department of Commerce, National Institute of Standards and Technology as part of the Center for Hierarchical Materials Design (CHiMaD). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS For characterization facilities we thank the Northwestern University Materials Research Science and Engineering Center under NSF Grant DMR-1121262 and the Integrated Molecular Structure Education and Research Center (IMSERC) supported by Northwestern University, NSF, under Grants CHE0923236 and CHE-9871268, Pfizer, and the State of Illinois. Use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract DE-AC0206CH11357. The microscopy work was performed in the EPIC facility of the NUANCE Center at Northwestern University, which is supported by NSF-NSEC, NSF-MRSEC, the Keck Foundation, the State of Illinois, and Northwestern University.

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REFERENCES

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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/acs.macromol.6b02702. Synthesis and characterization of intermediate compounds; NMR spectra of monomers and polymers, DFT calculations, CV, TGA, and DSC spectra, OFET I

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