Simple Solvent-Engineering for High-Mobility and Thermally Robust

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Organic Electronic Devices

Simple Solvent-Engineering for High-Mobility and Thermally Robust Conjugated Polymer Nanowire Field-Effect Transistors Gyeong G. Jeon, Myeongjae Lee, Jinwoo Nam, Wongi Park, Minyong Yang, Jong-Ho Choi, Dong Ki Yoon, Eunji Lee, BongSoo Kim, and Jong Hyun Kim ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b07643 • Publication Date (Web): 08 Aug 2018 Downloaded from http://pubs.acs.org on August 8, 2018

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ACS Applied Materials & Interfaces

Simple Solvent-Engineering for High-Mobility and Thermally Robust Conjugated Polymer Nanowire Field-Effect Transistors Gyeong G. Jeon,†‡ Myeongjae Lee,∇‡ Jinwoo Nam□◀, Wongi Park,◇ Minyong Yang,◇

Jong-Ho Choi,∇ Dong Ki Yoon,◇▼ Eunji Lee,*◀ BongSoo Kim,*◎ and Jong H. Kim*†

†

Department of Molecular Science and Technology, Ajou University, Suwon 16419, Republic of Korea. ∇

Department of Chemistry, Korea University, Seoul 02841, Republic of Korea.

□Graduate

School of Analytical Science and Technology, Chungnam National University, Daejeon 34134, Republic of Korea.

◇Graduate

School of Nanoscience and Technology, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea.

ACS Paragon Plus Environment

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ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

▼Department

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of Chemistry and KINC, Korea Advanced Institute of Science and Technology (KAIST), Daejoen 34141, Republic of Korea.

◀School

of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju 61005, Republic of Korea.

◎Department

of Science Education, EwhaWomans University, Seoul 03760, Republic of Korea.

Email: [email protected] (E. L.), [email protected] (B. K.), and [email protected] (J. H. K.) KEYWORDS: Organic field-effect transistors, conjugated polymers, nanowires, Hansen solubility parameters, high-mobility, stability


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Abstract

Electron donor (D)-acceptor (A)-type conjugated polymers (CPs) have emerged as promising semiconductor candidatesfor organic field-effect transistors (OFETs). Despite their high charge carrier mobilities, optimization of electrical properties of D-A-type CPs generally suffers from complicated post-deposition treatments such as high-temperature thermal annealing or solventvapor annealing. In this work, we report a high-mobility diketopyrrolopyrrole (DPP)-based D-Atype CP nanowires,self-assembled by a simple but very effective solvent engineering method that requires no additional processes after film deposition. In-situ grown uniform nanowires at room temperature were shown to possess distinct edge-on chain orientation that is beneficial for lateral charge transport between source and drain electrodes in FETs. FETs based on the polymer nanowire networks exhibit impressive hole mobility of up to 4.0 cm2V-1s-1. Moreover, nanowire FETs showed excellent operational stability in high temperature up to 200 oC due to the strong interchain interaction and alignment.


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1. Introduction Organic field-effect transistors (OFETs) have attracted great interest from both academic and industrial researchersdue to their appealing merits including solution-processability, lightness, flexibility, and high charge carrier mobility.1-7 Of the various OFET types, those based on conjugated polymers (CPs) have received particular attention in recent years due to their facile thin-film formation capability and excellent electrical performance.8-14 Significant effort has been made, from molecular design of optimized CPs’ backbone to device engineering, which has resulted in the successful realization of promising-mobility CP-based FETs, whose mobility exceeds the benchmark value of 1.0 cm2 V-1s-1 set by amorphous silicon (a-Si) transistors.15-17 Despite such efforts, mobilities achieved from CPs are still relatively lower compared to those from highly crystalline conjugated small molecules, because of amorphous regions along with crystalline domains in polymer thin-films.18-21 It is widely known that the charge carrier mobility of CPs strongly depends on thin-film morphology. It is governed by the solidification process and can be dramatically improved by the application of several post-deposition treatments, providing CPs with a higher degree of crystallinity.22-25 However, these additional processes, such as thermal or solvent-vapor annealing and use of additives, may not be ultimately desirable solutions for real applications because they are frequently complicated to proceed and would eventually increase the device fabrication cost. Moreover, high-temperature post-thermal annealing over the glass transition temperature (Tg) of plastic substrates limits the use of CPs in flexible electronics.26 In the preparation of CP thin-films, choosing the solvent or solvent additive is one of the most critical steps in the creation of the charge transport pathway, because it significantly influences polymer chain alignment and related crystalline structure growth.27-30 This implies that the charge


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carrier mobility of CPs can be controlled by selection of appropriate solvents or solvent additives, even without post-deposition treatments. In this context, many studies have been conducted on poly(3-hexylthiophene) (P3HT) nanowire webs grown by solvent manipulation which show one order of magnitude higher hole mobility (µh=6.4 ⅹ 10-2 cm2 V-1s-1) than thermally annealed P3HT thin-films (4.0ⅹ10-3cm2 V-1s-1).31In addition to nanowire webs, highly ordered polymer (cyclopentadithiophene-benzothiadiazole copolymer (CDT-BTZ)) single nanowire also exhibited dramaticµhincrease up to 5.5 cm2 V-1s-1 compared to that of thin-film (1.4 cm2V-1s-1).32 The choice of solvents or solvent additives is very important not only for crystalline structure control of pristine polymer films but also for microstructure improvement of polymer/fullerene bulk heterojunction films since it significantly enhances photovoltaic performances.33-35 Characterizations revealed that the remarkable mobility enhancement was the result of enhanced self-assembly of the polymers into crystalline nanostructures, which facilitates intra-/interchain π-orbital overlap and efficient charge transport.31,36-38 The formation of the resultant nanostructure was found to be driven by a synergistic effect between the highly crystalline nature of the used polymer and the particular physical properties, such as polarity, of the selected solvents.38 However, even with excellent charge carrier mobilities, less progress has been made toward efficient fabrication of crystalline nanostructures using state-of-the-art semiconducting CPs such as diketopyrrolopyrrole (DPP)-based electron donor-acceptor (D-A)type co-polymers.39,40 Thus, the mobility optimization of these types of CPs still primarily depends on additional post-treatments mentioned above. In this article, we report on high-mobility and thermally stable DPP polymer nanowire networks by adopting a simple but highly effective in-situ co-solvent engineering approach.


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Rather than trial-and-error empirical post-treatments, the method used herein is based on preparation of pre-crystallized polymer nanostructures using a rational combination of solvents, considering the Hansen solubility parameters (HSPs) of the solvents. A-few-layer polymer nanowire-based field-effect transistors (PN-FETs) fabricated by this method exhibit high µh up to 4.0 cm2 V-1s-1 at room temperature without any conventional post-treatments and demonstrate excellent thermal stability.

2. Results and Discussion The chemical structures of the DPP polymer (PDPP2DT-T2) and solvents used in this work are shown in Figure 1a.41 Detailed information on the used polymers and synthesis is described in the supporting information. For the in-situ production of pre-crystallized polymer aggregates, we used a binary solvent system consisting of good and marginal ones. Since crystallization is very sensitively influenced by miscibility between the polymer and solvents, we attempted to predict polymer-solvent interactions based on the HSPs. The HSPs of PDPP2DT-T2 and the chosen solvents were first calculated followingthe group contribution theory.42 Next, the HSP space (Ra) was obtained using equation (1),43 Ra2 = 4(δd1-δd2)2 + (δp1-δp2)2 + (δh1-δh2)2

(1)

where δd, δp, and δh are the dispersion force solubility parameter, dipolar intermolecular force solubility parameter, and hydrogen bonding solubility parameter, respectively. Figure 1b demonstrates a three-dimensional (3D) representation of each of the solubility parameters (δd, δp, and δh) for PDPP2DT-T2 and solvents, and Table 1 summarizes correspondingδd, δp, and δh, and Ra values.


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Based on Hansen’s theory that lower Ra valuesimply a higher degree of molecular interactions (good miscibility) between the polymer and solvents, we selected chloroform (CF, Ra=2.8 MPa1/2) as a good solvent and anisole (Ani, Ra=3.7 MPa1/2) as a marginal solvent.42,43 In addition, the lower evaporation rate of Ani due to its sufficiently high boiling point (bp), 153.8oC was considered to enable efficient polymer chain alignment and crystallization.44 To control the polymer crystallization using these two solvents, we prepared a series of 1.0 mg/ml polymer solutions with different volume percentages of Ani (20, 40, 60, and 80 vol.%) to CF. Figure 1c displays a 3D representation of the solubility parameters for the prepared cosolvent systems and the corresponding solution states with photographs. With increasing percentage of the marginal solvent (Ani), PDPP2DT-T2 polymer was observed to form a gel-like, viscous solution. Each solution was spin-coated on the octadecyltrichlorosilane (ODTS)-treated SiO2/Si substrates, and microstructures of the polymer nanostructures in coated film were examined by atomic force microscopy (AFM). Detailed information on the solution and film preparation is described in the Experimental section. Discontinuous wires were found when the amount of Ani was low (20%, Ra: 2.9 MPa1/2) (Figure 2a) due to the low tendency to form aggregates in the presences of high amounts of good solvent (CF (80%)). With a slightly increased level of Ani (40%, Ra: 3.1 MPa1/2), a balance between aggregation and disaggregation of the polymer chains existed to form continuous nanowire networks. Notably, AFM image revealed the formation of a-few-layer thick yet very uniform nanowire networks in the film cast using CF/Ani(40%) solution as shown in Figure 2b. These ultra-thin nanowires have dimensions of ~100 nm width and ~2.6 nm height with an average coverage of 57.6% (Figure S7).46 As the amount of Ani increased, heavily aggregated particle-like structures were spontaneously developed. CF/Ani(60%) solution (Ra: 3.3 MPa1/2)


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formed a mixed state of nanowires and nanoparticles (Figure 2c) and CF/Ani(80%) solution (Ra: 3.5 MPa1/2) promoted the formation of only particle-like large aggregates (Figure 2d) due to the strong influence of the marginal solvent. The aggregates are induced to avoid unfavorable contact between the polymer and marginal solvent. These observations indicate that there is an optimized ratio between good and marginal solvents that results in Ra appropriate for the desirable formation of the nanowire network morphology for efficient charge transport. Structural analysis of the PDPP2DT-T2 nanowires was conducted by two-dimensional grazing-incidence X-ray diffraction (2D-GIXD) measurements at the 9A U-SAXS and 6D C&S UNIST-PAL beamlines of Pohang Accelerator Laboratory (PAL). Figure 3a shows the 2DGIXD pattern of the PDPP2DT-T2 nanowires cast from CF/Ani(40%) solution on the ODTStreated SiO2/Si substrates. Even with very thin polymer nanowire layers, we observed strong lamellar peaks (d = 22.0 Å) up to (400) in the out-of-plane direction and 1.5 and 1.66 Å-1 (d = 3.78 Å) peaks in the in-plane direction corresponding to the ordered alkyl chains and π-π stacking between polymer chains, respectively, as shown in Figure 3a and b. Compared to the 2D-GIXD pattern of the PDPP2DT-T2 thin-film cast using pristine CF (Figure S8), both the very narrow (100) peak (Figure 3c) and the absence of (010) peak in the out-of-plane direction (Figure3a and b) indicate that all the polymer nanowires can be assumed to possess edge-on chain orientation relative to the substrate. These peak patterns reflect that the electronic channel of the polymer nanowire layer is well-ordered and densely-packed to endow efficient charge transport in the lateral direction between the source and drain electrodes of the FETs. We note that the absence of (010) peak and the presence of edge-on orientation of the PDPP2DT-T2 chains in the PDPP2DT-T2nanowire films is a result of thermodynamically favorable process upon drying.47,48 During spin-coating of pristine PDPP2DT-T2 CF solution, single PDPP2DT-T2


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chains would interact with the substrate with thermodynamically favorable face-on orientation and aggregated PDPP2DT-T2 chains that are formed by the reduction of remaining CF solvent would make an edge-on oriented film. As a result, the pristine CF solution produced a mixed face PDPP2DT-T2 film. For the pre-crystallized PDPP2DT-T2 nanowire solution, the stacking of PDPP2DT-T2 nanowire occurs with edge-on orientation throughout the drying process because there is no chance for a single chain to interact with the substrate and the nanowire bundles would like to interact each other rather than with the substrate. In order to investigate the underlying mechanism of nanowire growth, we modified the composition of the solvent mixture by replacing Ani (40%) with ethylbenzene (EB, 40%). EB was carefully selected to reveal the effect of the marginal solvent’s polar interaction or hydrogen bonding strengths with PDPP2DT-T2. EB has the same δd and Ra but much lower δp and δh than Ani, as presented in Table 1. Interestingly, no discernible long nanowire structures were found in the spin-cast film from the CF/EB(40%) solution as shown in Figure S9a. For further investigation of the effect of δp and δh, on PDPP2DT-T2 nanowire formation, we also employed toluene (Tol) and p-xylene (p-Xyl) as marginal solvents which have similar structure to Ani but lower δp and δh values (δp is 1.4 and 3.1, and δh is 2.0 and 3.1 for Tol and p-Xyl, respectively). In sharp contrast to the films coated using CF/Ani(40%) solution showing long nanowire structures with web-like interconnection, short aggregates and densely packed short nanowires were found from the films spin-coated using CF/Tol(40%) and CF/p-Xyl solution (see Figure S10a and b). Considering the importance of δp and δh values for long nanowire formation, we introduced Nmethyl aniline (MA) as a marginal solvent which has high δp (6.0) and δh (11.5) values and can endow hydrogen bonding interaction by electronegative nitrogen atom. Interestingly, we obtained long nanowire structures from the spin-coated films using CF/MA(40%) solution, as


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shown in Figure S10c.From these observations, we speculate that the primary driving force behind nanowire formation is polar interactivity and/or the hydrogen bonding capability of Ani, which contains a highly electronegative oxygen atom. The charge transport properties of the nanowires were studied by the fabrication of FET devices with top contact (TC)/bottom gate (BG) configuration. Detailed information on the device fabrication is described in the Experimental section. The PDPP2DT-T2 PN-FETs using a CF/Ani(40%) solution showed clear p-type FET characteristics as presented in Figure 4. The devices exhibit an average µh of 3.28±0.43 cm2 V-1s-1 (maximum µh = 4.00 cm2 V-1s-1 (Figure 4)). We note that this high carrier mobility was achieved without any post-treatments like thermal or solvent-vapor annealing. For comparison, we also fabricated reference transistors using spin-cast PDPP2DT-T2 thin-films from pristine CF solution with a post-annealing process. The constructed devices exhibited µh of 0.88±0.20 cm2 V-1s-1 (maximum µh,max= 0.94 cm2 V-1s-1) without thermal annealing, which increased significantly to 1.27±0.32 (maximum µh,max= 1.60 cm2 V-1s-1) and 1.81±0.40 cm2 V-1s-1 (maximum µh,max= 2.50 cm2 V-1s-1) after annealing the thinfilms at 150 and 200 oC, respectively (see Figure S11 for thin-film FET transfer curves). This result indicates that the PDPP2DT-T2 nanowire networks can transport holes almost four times better than the thin-film. Furthermore, it is noted from UV/visible absorption spectra in Figure S12 that the absorption intensity of the 0-1 intramolecular charge transfer (ICT) transition in nanowire networks is even stronger than the increased intensity of thin-film after thermal annealing. This implies that the polymer nanowires can possess stronger interchain interactions than post-treated thin-films.


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In addition, we compared the performance of FET devices fabricated from a CF/EB(40%) solution. An average µh of devices was extracted to be 0.31 ± 0.12 cm2 V-1s-1 (maximum

µh,max=0.58 cm2 V-1s-1, as presented in Figure 3b (Table 2 summarizes FET parameters). These comparisons clearly demonstrate the key advantage of our in-situ nanowire growth method. Based on the film characterization data, we conclude that the higher mobility of the PN-FETs is a result of the enhanced crystalline network formation of the polymer chains in self-assembled nanostructures. Furthermore, electrical measurements on the thermal stability of PDPP2DT-T2 PNFETs were carried out after applying different temperatures (150, 200, and 250 oC) to the nanowires for 30 min. The device exhibited thermally stable electrical property, maintaining its initial mobility without noticeable change even up to 200 oC, as shown in Figure5a. Significant degradation was observed after 250 oC. The origin of the performance degradation was investigated by transmission electron microscopy (TEM) measurements performed on the polymer nanowires after applying different temperatures. Figure 5b-d display the well-preserved polymer nanowires at the elevated temperature (room temperature to 200 oC). By contrast, Figure 5e shows the partially disassembled and disrupted morphology of polymer nanowires for the sample annealed at 250 oC, which are shown in the darker regions. Thus, it is revealed that the mobility decrease is caused by the randomly reoriented polymer chains upon annealing at 250 oC, hampering charge carrier transport. These results indicate that the observed thermalstability of the nanowire networks is due to the excellent resistance to the temperature, which originated from the preserved crystalline chain alignment of the PDPP2DT-T2 nanowires. Lastly, we have applied our solvent engineering method to two other CPs (PDPP2DT-F2T2 and PDPP2DT-TVT).49,50 Solubility parameters for PDPP2DT-F2T2 (δd:18.2, δp:3.0 and δh:3.5)


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and PDPP2DT-TVT (δd:18.7, δp:3.0 and δh:3.6) are very close to those of PDPP2DT-T2. As shown in Figure S13, in-situ grown nanowires with coverage of 70.7 and 61.0% for PDPP2DTF2T2 and PDPP2DT-TVT were clearly observed from the spin-coated films using both polymer solutions in CF/Ani(40%). FETs based on PDPP2DT-F2T2 and PDPP2DT-TVT nanowires exhibited good µh values of 2.38 and 2.67 cm2 V-1s-1(see Figure S14), which are higher than those achieved from FETs fabricated using CF solutions (0.53 and 0.83 cm2 V-1s-1 for PDPP2DTF2T2 and PDPP2DT-TVT, respectively, see Figure S15). This result demonstrates that solvent engineering process can be utilized as a versatile method for the fabrication of high-mobility nanowire FETs using DPP-based CPs. 3. Conclusions In conclusion, we demonstrated high-mobility and thermally robust DPP polymer nanowire (PN)-FETs by utilizing a simple but very effective in-situ co-solvent engineering method. The co-solvent system, designed by considering the HSPs and boiling points of the solvents, promoted crystalline polymer nanowire growth with strong interchain interactions. PN-FETs based on this process exhibited high hole mobility up to 4.0 cm2 V-1s-1 with high operational stability under temperatures up to 200 oC. This encouraging result demonstrates that solubility parameters-considered rationally designing of solvent system would be a beneficial route for the fabrication of annealing-free, high-mobility flexible polymer transistors at low-cost.

4. Experimental Section Solution preparation and FET fabrication To investigate the effect of the proportion of the marginal solvent on microstructure growth, 1.0 mg/mL PDPP2DT-T2 solutions in co-solvent, consisting of different volume percentages of


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anisole (20, 40, 60, and 80 %) to chloroform, were prepared. After the solutions were kept overnight

at

room

temperature

to

allow

gelation,

they

were

spin-cast

on

the

octadecyltrichlorosilane (ODTS)-modified SiO2/Si substrates. Before the device fabrication SiO2 (gate dielectric)/p-doped Si (gate electrode, G)substrates were cleaned with acetone and isopropyl alcohol in an ultrasonicator. After drying under vacuum at 100 oC for 1 h, the substrates were exposed to UV (360 nm) for 10 min and were treated with ODTS in toluene. PDPP2DT-T2 thin-films and nanowires were deposited on the ODTSmodified substrates by spin-coating using 5.0 mg/mL polymer solution in chloroform and 1.0 mg/mL polymer nanowire solution in co-solvent, respectively. The polymer thin-films were thermally annealed at 100, 150, and 200 oC for 10 min, while the polymer nanowire films were kept at room temperature without annealing. After then, source (S) and drain (D) electrodes (50 nm-thick Au) were thermally evaporated through the shadow mask under 3.0ⅹ10-6 Torr vacuum on top of the spin-coated PDPP2DT-T2 layers. The channel lengths (L) were 100 and 150 µm and the width (W) was 1 mm.Charge carrier mobilities were calculated in the saturation regime using the equation (2): IDS=(W/2L)µC0(VG-VTH)2 (2) where L is the channel length, W is the channel width, C0 is the capacitance per unit area of the gate dielectric layer, VTH is the threshold voltage, and µ is the charge carrier’s field effect mobility. Substrate coverage of the nanowires was taken into account in the calculation of the mobility (coverage calculation is presented in Figure S1).46 Characterization The morphology and structural analyses of the PDPP2DT-T2 thin-film and nanowires were performed by atomic force microscopy (AFM, XE-100, park system), transmission electron microscopy (TEM, JEM-1400, JEOK Ltd), and two-dimensional grazing-incidence X-ray


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diffraction (2D-GIXD) measurements. TEM experiments were conducted at an operating voltage of 120 kV, and the images were acquired with a SC 1000 CCD camera (Gatan, Warrendale, PA, USA). The samples for TEM analyses are prepared by drop casting the in-situ grown PDPP2DTT2 polymer nanowire solution onto a carbon-coated Cu grid. 2D-GIXD was conducted at the Pohang Accelerator Laboratory, Republic of Korea. X-ray (0.1115 nm) was incident on the PDPP2DT-T2 polymer nanowire film and the polymer thin film with an angle of 0.12o. Diffraction patterns were recorded using a Rayonix 2D SX165 detector. UV/Vis spectra were measured for the PDPP2DT-T2 thin-film and nanowires using a UV-Vis spectrophotometer (V670, JASCO).


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FIGURES

Figure 1. (a) Chemical structures of PDPP2DT-T2 and solvents (chloroform (CF), anisole (Ani), and ethylbenzene (EB)). Solubility parameter diagram for (b) PDPP2DT-T2 and each solvent and for (c) CF/Ani co-solvents.


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Figure 2. Tapping-mode AFM images (5µmX5µm) of PDPP2DT-T2 films cast from chloroform mixed with (a) 20, (b) 40, (c) 60, and (d) 80 vol.% anisole.


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Figure 3. (a) 2D-GIXD patterns of the PDPP2DT-T2nanowires, (b) corresponding line-cut profiles of out-of-plane (red line) and in-plane (black line) directions, and (c) comparison of pole figures for PDPP2DT-T2 thin-film (red line) and nanowires (black line).


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Figure 4.(a) Transfer and (b) output characteristics of the PDPP2DT-T2 nanowire field-effect transistor.


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Figure 5.(a) Transfer characteristics of the PDPP2DT-T2 nanowire transistor after annealing at different temperatures (inset: normalized mobility changes with annealing temperature) and TEM images of (b) as-cast, (c) 150oC, (d) 200oC, and (e) 250oC annealed PDPP2DT-T2 nanowires (scale bar: 200 nm).


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TABLES Table 1.Hansen solubility parameters (δd, δp, δh, and δt) for PDPP2DT-T2, chloroform (CF), anisole (Ani), etylbenzene (EB), and co-solvents; Hansen solubility parameter spaces (Ra) of PDPP2DT-T2 in each solvent; and boiling points (bp) of each solvent42,45

Solvents

δda(MPa1/2)

δpb(MPa1/2)

δhc(MPa1/2)

Rad(MPa1/2)

bp(oC)

PDPP2DT-T2

18.7

3.0

3.6

-

-

CF

17.8

3.1

5.7

2.8

61.1

Ani

17.8

4.1

6.7

3.7

153.8

EB

17.8

0.6

1.4

3.7

136.1

CF/Ani(40%)

17.8

3.5

6.1

3.1

-

CF/EB(40%)

17.8

2.1

4.0

2.1

-

a

Dispersion force solubility. bDipolar intermolecular force solubility. cHydrogen bonding solubility. dHansen solubility parameter space between PDPP2DT-T2 and solvents, calculated by equation (1).


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Table 2.Hole mobility (µh), threshold voltage (VTH) and on/off current ratio (Ion/off) of the PDPP2DT-T2 FETs. Solvents

µha (cm2V-1s-1)

VTH (V)

Ion/off

CF/Ani(40%)

4.00 (3.28)

-26.1

105-106

CF/EB(40%)

0.58 (0.31)

-26.0

105-106

CF (non-annealed)

0.94 (0.88)

-14.6

105-106

CF (150oC annealed)

1.60 (1.27)

-15.8

105-106

CF (200oC annealed)

2.50 (1.81)

-15.7

105-106

All device characteristics were averaged from 10 devices without any post-treatment. aMaximum values and average values in parentheses.


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ASSOCIATED CONTENT Supporting Information. Additional results, including synthesis, AFM images, current-voltage characteristics, and UVVis spectrum data. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author *Email: [email protected](E. L.) *Email: [email protected] (B. K) *Email: [email protected] (J. H. K.) Author Contributions ‡These authors contributed equally. ACKNOWLEDGMENT This work was supported by the National Research Foundation (NRF) grant funded by the Korea government

(MSIP:

Ministry

of

Science,

ICT

and

Future

Planning)

(No.

2015R1C1A1A01053241), and supported by Basic Science Research Program through the NRF


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funded by the Ministry of Education (No. 2018R1D1A1B07047645 and No. 2009-0093826). This work was also supported by a grant (NRF-2015M1A2A2056218) from the Technology Development Program to Solve Climate Changes of the NRF funded by MSIP. Experiments at the PLS-II were supported in part by MSIP and Pohang University of Science and Technology. REFERENCES (1) Yan, H.; Chen, Z.; Zheng Y.; Newman, C.; Quinn, J. R.;Dötz, F.; KastlerM.;Facchetti,A. A High-Mobility Electron-Transporting Polymer for Printed Transistors. Nature 2009, 457, 679686. (2) Sekitani, T.; Zschieschang, U.; Klauk, H.; Someya, T. Flexible Organic Transistors and Circuits with Extreme Bending Stability. Nat. Mater. 2010, 9, 1015-1022. (3) Wang, Z.; Kim, C.; Facchetti, A.; Marks, T. J. Anthracenedicarboximides as Air-Stable nChannel Semiconductors for Thin-Film Transistors with Remarkable Current On-Off Ratios. J. Am. Chem. Soc. 2007, 129, 13362-13363. (4) Kimura, Y.; Nagase, T.; Kobayashi, T.; Hamaguchi, A.; Ikeda, Y.; Shiro, T.; Takimiya, K.; Naito, H. Soluble Organic Semiconductor Precursor with Specific Phase Separation for HighPerformance Printed Organic Transistors. Adv. Mater. 2015, 27, 727-732. (5) Shin, E.-S.; Ha, Y. H.; Gann, E.; Lee, Y.-J.; Kwon, S.-K.; McNeil, C. R.; Noh, Y.-Y; Kim, Y.-H. Design of New Isoindigo-Based Copolymer for Ambipolar Organic Field-Effect Transistors. ACS Appl. Mater. Interfaces 2018, 10, 13774-13782. (6) Moon, H.; Zeis, R.; Borkent, E.-J.; Besnard, C.; Lovinger, A. J.; Siegrist, T.; Kloc, C.; Bao, Z. Synthesis, Crystal Structure, and Transistor Performance of Tetracene Derivatives. J. Am. Chem. Soc. 2004, 126, 15322-15323. (7) Katz, H. E.; Bao, Z.; Gilat, S. L. Synthetic Chemistry for Ultrapure, Processable, and HighMobility organic transistor semiconductors. Acc. Chem. Res. 2001, 34, 359-369.


23


Page 24 of 29

(8) Nikolka, M.; Nasrallah, I.; Rose, B.; Ravva, M. K.; Broch, K.; Sadhanala, A.; Harkin, D.; Charmet, J.; Hurhangee, M.; Brown, A.; Illig, S.; Too, P.; Jongman, J; McCulloch, I.; Bredas, J.L.; Sirringhaus, H. High Operational and Environmental Stability of High-Mobility Conjugated Polymer Field-Effect Transistors Through the Use of Molecular Additives. Nat. Mater.2017, 16, 356-362. (9) Sung, M. J.; Luzio, A.; Park, W.-T.; Kim, R.; Gann, E.; Maddalena, F.; Pace, G.; Xu, Y.; Natali, D.; de Falco, C.; Dang, L.; McNeil, C. R.; Caironi, M.; Noh, Y.-Y.; Kim, Y.-H. HighMobility Naphthalene Diimide and Selenophene-vinylene-selenophene-Based Conjugated Polymer: n-Channel Organic Field-Effect Transistors and Structure-Property Relationship. Adv. Funct. Mater. 2016, 26, 4984-4997. (10) Yang, J.; Zhao, Z.; Geng, H.; Cheng, C.; Chen, J.; Sun, Y.; Shi, L.; Yi, Y.; Shuai, Z.; Guo, Y.; Wang, S.; Liu, Y. Isoindigo-Based Polymers with Small Effective Masses for High-Mobility Ambipolar Field-Effect Transistors. Adv. Mater. 2017, 29, 1702115. (11) Kim, J. Y.; Yang, D. S.; Shin, J.; Bilby, D.; Chung, K.; Um, H. A.; Chun, J.; Pyo, S.; Cho, M. J.; Kim, J.; Choi, D. H. High-Performing Thin-Film Transistors in Large Spherulites of Conjugated Polymer Formed by Epitaxial Growth on Removable Organic Crystalline Templates. ACS Appl. Mater. Interfaces 2015, 7, 13431-13439. (12) Wang, M.; Ford, M. J.; Zhou, C.; Seifrid, M.; Nguyen, T.-Q.; Bazan G. C. Linear Conjugated Polymer Backbones Improve Alignment in Nanogroove-Assisted Organic FieldEffect Transistors. J. Am. Chem. Soc. 2017, 139, 17624-17631. (13) Kim, D. H.; Lee, B.-L.; Moon, H.; Kang, H. M.; Jeong, E. J.; Park, J.-I.; Han K.-M.; Lee, S.; Yoo, B. W.; Koo, B. W.; Kim, J. Y.; Lee, W. H.; Cho, K.; Becerril, H. A.; Bao, Z. LiquidCrystalline Semiconducting Copolymers with Intramolecular Donor-Acceptor Building Blocks for High-Stability Polymer Transistors. J. Am. Chem. Soc. 2009, 131, 6124-6132. (14) Son, S.; K, Y.; Lee, J.; Lee, G.-Y.; Park, W.-T.; Noh, Y.-Y.; Park, C. E.; Park, T. HighField-Effect Mobility of Low-Crystallinity Conjugated Polymers with Localized Aggregates. J. Am. Chem. Soc. 2016, 138, 8096-8103.


24

Page 25 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(15) Chen, H.; Hurhangee, M.; Nikolka, M.; Zhang, W.; Kirkus, M.; Neophytou, M.; Cryer, S. J.; Harkin, D.; Hayoz, P.; Abdi-Jalebi, M.; McNeil, C. R.; Sirringhaus, H.; McCulloch, I. Dithiopheneindenofluorene (TIF) Semiconducting Polymers with Very High Mobility in FieldEffect Transistors. Adv. Mater. 2017, 29, 1702523. (16) Panidi, J.; Paterson, A. F.; Khim, D.; Fei, Z.; Han, Y.; Tsetseris, L.; Vourlias, G.; Patsalas, P. A.; Heeney, M.; Anthopoulos, T. D. Remarkable Enhancement of the Hole Mobility in Several Organic Small-Molecules, Polymers, and Small-Molecule:Polymer Blend Transistors by Simple Admixing of the Lewis Acid p-Dopant B(C6F5)3. Adv. Sci. 2018, 5, 1700290. (17) Liang, X.; Gu, S.; Cai, Z.; Sun, W.; Tan, L.; Dong, L.; Wang, L.; Liu, Z.; Chen, W.; Li, J. Multi-Vinyl Linked Benzothiadiazole Conjugated Polymers: High Performance, Low Crystalline Material for Transistors. Chem. Comm. 2017, 53, 8176-8179. (18) Abe, M.; Mori, T.; Osaka, I.; Sugimoto, K.; Takimiya K. Thermally, Operationally, and Environmentally Stable Organic Thin-Film Transistors Based on Bis[1]benzothieno[2,3-d:2′,3′d′]naphtho[2,3-b:6,7-b′]dithiophene Derivatives: Effective Synthesis, Electronic Structures, and Structure-Property Relationship. Chem. Mater. 2015, 27, 5049-5057. (19) Xie,W.;McGarry,K. A.; Liu, F.;Wu, Y.; Ruden, P. P.; Douglas,C. J.;Frisbie,C. D. HighMobility Transistors Based on Single Crystals of Isotopically Substituted Rubrene-d28. J. Phys. Chem. C 2013, 117, 11522-11529. (20) Takeya, J.; Yamagishi, M.; Tominari, T.; Hirahara, R.; Nakazawa, Y. Very High-Mobility Organic Single-Crystal Transistors with In-Crystal Conduction Channels. Appl. Phys. Lett. 2007, 90, 102120. (21) Lu, G.; KongX.; Sun, J.; Zhang, L., Chen, Y.; Jiang,J. Solution-Processed Single Crystal Microsheets of a Novel Dimeric Phthalocyanine-Involved Triple-Decker for High-Performance Ambipolar Organic Field Effect Transistors. Chem. Comm. 2017, 53, 12754-12757. (22) Fei, Z.; Han, Y.; Gann, E.; Hodsden, T.; Chesman, A. S. R.; McNeill, C. R.; Anthopoulos, T. D.; Heeney, M. Alkylated Selenophene-Based Ladder-Type Monomers via a Facile Route for High-Performance Thin-Film Transistor Applications. J. Am. Chem. Soc. 2017, 139, 8552-8561.


25


Page 26 of 29

(23) Wang, Y.; Guo, H.; Harbuzaru, A.; Uddin, M. A.; Arrechea-Marcos, I.; Ling, S.; Yu, J.; Tang, Y.; Sung, H.; Navarrete, J. T. L.; Ortiz, R. P.; Woo, H. Y.; Guo, X. (Semi)ladder-Type Bithiophene

Imide-Based

All-Acceptor

Semiconductors:

Synthesis,

Structure–Property

Correlations, and Unipolar N-Type Transistor Performance. J. Am. Chem. Soc. 2018, 140, 60956108. (24) Li, Y.; Singh, S. P.; Sonar,P. A High Mobility P-Type DPP-thieno[3,2-b]thiophene copolymer for Organic Thin-Film Transistors. Adv. Mater. 2010, 22, 4862-4866. (25) Yang,H.; Zhang,G.; Zhu,J.; He,W.;Lan,S.; Liao,L.; Chen,H.;Guo,T. Improving Charge Mobility of Polymer Transistors by Judicious Choice of the Molecular Weight of Insulating Polymer Additive. J. Phys. Chem. C 2016, 120, 17282-17289. (26) MacDonald,W. A. Engineered Films for Display Technologies. J. Mater. Chem. 2004, 14, 4-10. (27) Schulz, G. L.; Ludwigs, S. Controlled Crystallization of Conjugated Polymer Films from Solution and Solvent Vapor for Polymer Electronics. Adv. Funct. Mater. 2017, 27, 1603083. (28) Lee,E.; Hammer,B.; Kim,J. -K.; Page, Z.; Emrick,T.; Hayward,R. C. Hierachical Helical Assembly of Conjugated Poly(3-hexylthiophene)-block-poly(3-triethylene glycol thiophene) Diblock Copolymers. J. Am. Chem. Soc., 2011, 133, 10390-10393. (29) Xiao,M.; Zhang,X.;Bryan,Z. J.;Jasensky,J.; McNeil,A. J.; Chen,Z. Effect of Solvent on Surface Ordering of Poly(3-hexylthiophene) Thin Films. Langmuir, 2015, 31, 5050-5056. (30) Ji, Y.; Xiao, C.; Wang, Q.; Zhang, J.; Li, C.; Wu, Y.; Wei, Z.; Zhan, X.; Hu, W.; Wang, Z.; Janssen, R. A. J.; Si, W. Asymmetric Diketopyrrolopyrrole Conjugated Polymers for FieldEffect Transistors and Polymer Solar Cells Processed from a Nonchlorinated Solvent. Adv. Mater. 2016, 28, 943-950. (31) Kim,B.-G.; Kwon,U.; Park,D. H.; Park,H. J. Nano-Geometry Dependent Electrical Property of Organic Semiconductor. Electron. Mater. Lett. 2015, 11, 435-439.


26

Page 27 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(32) Wang, S.; Kappl, M.; Liebewirth, I.; Muller, M.; Kirchhoff, K.; Pisula, W.; Müllen, K. Organic Field-Effect Transistors Based on Highly Ordered Single Polymer Fibers. Adv. Mater. 2012, 24, 417-420. (33) Xie, Y.; Hu, X.; Yin, J.; Zhang, L.; Meng, X.; Xu, G.; Ai, Q.; Zhou, W.; Chen, Y. Butanedithiol Solvent Additive Extracting Fullerenes from Donor Phase to Improve Performance and Photostability in Polymer Solar Cells. ACS Appl. Mater. Interfaces 2017, 9, 9918-9925. (34) Buss, F.; Schmidt-Hansberg, B.; Sanyal, M.; Munuera, C.; Scharfer, P.; Schabel, W.; Barrena, E. Gaining Further Insight into the Solvent Additive-Driven Crystallization of BulkHeterojunction Solar Cells by In situ X-Ray Scattering and Optical Reflectometry. Macromolecules 2016, 49, 4867-4874. (35)Lee, J. K.; Ma, W. L.; Brabec, C. J.; Yuen, J.; Moon, J. S.; Kim, J. Y.; Lee, K.; Bazan, G. C.; Heeger, A. J. Processing Additives for Improved Efficiency from Bulk Heterojunction Solar Cells. J. Am. Chem. Soc. 2008, 130, 3619-3623. (36) Merlo,J. A.;Frisbie,C. D. Field effect Transport and Trapping in Regioregular Polythiophene Nanofibers. J. Phys. Chem. B 2004, 108, 19169-19179. (37) Kiriy,N.;Jahne,E.; Adler,H.-J.; Schneider,M.;Kiriy,A.; Gorodyska,G.; Minko,S.; Jehnichen, D.; Simon,P.; Fokin, A. A.; Stamm, M. One-Dimensional Aggregation of Regioregular Polyalkylthiophenes. Nano. Lett. 2003, 3, 707-712. (38) Kim, B.-G.; Kim, M.-S.;Kim, J. Ultrasonic-Assisted Nanodimensional Self-Assembly of Poly-3-Hexylthiophene for Organic Photovoltaic Cells. ACS Nano 2010, 4, 2160-2166. (39) Um, H. A.; Lee,D. H.; Heo,D. U.; Yang, D. S.; Shin, J.; Baik, H.; Cho, M. J.; Choi, D. H. High Aspect Ratio Conjugated Polymer Nanowires for High Performance Field-Effect Transistors and Phototransistors. ACS Nano 2015, 9, 5264-5274. (40) Ji, Y.; Xiao, C.; Heintges, G. H. L.; Wu, Y.; Janssen, R. A. J.; Zhang, D.; Hu, W.; Wang, Z.; Li, W. Conjugated Polymer with Ternary Electron-Deficient Units for Ambipolar Nanowire Field-Effect Transistors. J. Polym. Sci.:Part A Polymer Chemistry 2016, 54, 34-38.


27


Page 28 of 29

(41) Lee,M.; Kim, M. J.; Ro, S.; Choi, S.; Jin, S. M.; Nguyen, H. D.; Yang, J.; Lee, K. K.; Lim, D. U.; Lee, E.; Kang, M. S.; Choi, J. H.; Cho, J. H.; Kim, B. A Nonchlorinated SolventProcessable Fluorinated Planar Conjugated Polymer for Flexible Field-Effect Transistors. ACS Appl. Mater. Interfaces 2017, 9, 28817-28827. (42) Barton, A. F. M. CRC Handbook of Solubility Parameters and Other Cohesion Parameters, CRC Press, Boca Raton, FL, USA, 1991. (43) Hansen, C. M. Hansen Solubility Parameters: A User’s Handbook, CRC Press, Boca Raton, FL, USA, 2007. (44) Chang, J.-F.; Sun, B.; Breiby, D. W.; Nielsen, M. M.; Sölling, T. I.; Giles, M.; McCulloch, I.; Sirringhaus, H. Enhanced Mobility of Poly(3-hexylthiophene) Transistors by Spin-Coating from High-Boiling-Point Solvents. Chem. Mater. 2004, 16, 4772-4776. (45) Marcus, Y. The Properties of Solvents, Wiley, Chichester, NY, USA, 1998. (46) Khim, D.; Ryu, G. S.; Park, W. T.; Kim, H.; Lee, M.; Noh, Y. Y. Precisely Controlled Ultrathin Conjugated Polymer Films for Large Area Transparent Transistors and Highly Sensitive Chemical Sensors. Adv. Mater. 2016, 28, 2752-2759. (47) Xu, L.; Yang, L.; Lei, S. Self-Assembly of Conjugated Oligomers and Polymers at the Interface: Structure and Properties. Nanoscale 2012, 4, 4399-4415. (48) Jung, M.; Yoon, Y.; Park, J. H.; Cha, W.; Kim, A.; Kang, J.; Gautam, S.; Seo, D.; Cho, J. H.; Kim H.; Choi, J. Y.; Chae, K. H.; Choi, K.; Kim, B. Nanoscopic Management of Molecular Packing and Orientation of Small Molecules by Combination of Linear and Branched Alkyl Side Chains. ACS Nano, 2014, 8, 5988-6003. (49) Lee, M.; Kim, M. J.; Ro, S.; Choi, S.; Jin, S.-M.; Nguyen, H. D.; Yang J.; Lee, K.-K.; Lim, D. U.; Lee, E.; Kang, M. S.; Choi, J.-H.; Cho, J. H.; Kim, B. A Nonchlorinated Solvent-


28

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Processable Fluorinated Planar Conjugated Polymer for Flexible Field-Effect Transistors. ACS Appl. Mater. Interfaces 2017,9, 28817-28827. (50) Lee, J. H.; Lee, Y. H.; Ha, Y. H.; Kwon, J.; Pyo, S.; Kim, Y.-H.; Lee, W. H. Semiconducting/Insulating Polymer Blends with Dual Phase Separation for Organic Field-Effect Transistors. RSC Adv. 2017, 7, 7526-7530.

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Simple Solvent-Engineering for High-Mobility and Thermally Robust

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