Direct Writing and Aligning of Small-Molecule Organic Semiconductor

Letter pubs.acs.org/JPCL

Cite This: J. Phys. Chem. Lett. 2017, 8, 5492-5500

Direct Writing and Aligning of Small-Molecule Organic Semiconductor Crystals via “Dragging Mode” Electrohydrodynamic Jet Printing for Flexible Organic Field-Effect Transistor Arrays Kyunghun Kim,†,⊥ Jae Hyun Bae,‡,⊥ Sung Hoon Noh,§ Jaeyoung Jang,*,§ Se Hyun Kim,*,‡ and Chan Eon Park*,† †

Department of Chemical Engineering, Pohang University of Science and Technology, Pohang 790-784, Korea School of Chemical Engineering, Yeungnam University, Gyeongsan 712-749, Korea § Department of Energy Engineering, Hanyang University, Seoul 133-791, Korea ‡

S Supporting Information *

ABSTRACT: Patterning and aligning of organic small-molecule semiconductor crystals over large areas is an important issue for their commercialization and practical device applications. This Letter reports “dragging mode” electrohydrodynamic jet printing that can simultaneously achieve direct writing and aligning of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-PEN) crystals. Dragging mode provides favorable conditions for crystal growth with efficient controls over supply voltages and nozzle-to-substrate distances. Optimal printing speed produces millimeter-long TIPS-PEN crystals with unidirectional alignment along the printing direction. These crystals are highly crystalline with a uniform packing structure that favors lateral charge transport. Organic field-effect transistors (OFETs) based on the optimally printed TIPS-PEN crystals exhibit high field-effect mobilities up to 1.65 cm2/(V·s). We also demonstrate the feasibility of controlling pattern shapes of the crystals as well as the fabrication of printed flexible OFET arrays.

rganic field-effect transistors (OFETs) based on solutionprocessable organic semiconductors have emerged as promising components in future electronics applications such as smart wearable and rollable displays due to their flexibility and facile processability in large areas.1−3 Electrical characteristics of OFETs have been dramatically improved by the efforts of synthesizing high-performance organic semiconductors and developing various solution-processing techniques to optimize the crystallinity and molecular packing structures.4−8 For commercialization of OFETs, the development of patterning techniques that enable one to locate highly crystalline organic semiconductors at desired positions has been an essential prerequisite.9−12 Otherwise, severe crosstalk among neighboring devices may take place when applied in practical electronic devices such as multicomponent integrated circuits. In general, patterning methods developed so far can be divided into two major categories: top-down and bottom-up approaches. As top-down methods, photo- or e-beam lithography has been widely used in both academic and industrial fields due to highly matured lithography technologies covering from micro- to nanoscale patterns. Nevertheless, these methods also entail some drawbacks in terms of cost and instrumental/processing complexity, such as elaborate and time-consuming procedures and expensive systems. Moreover, the involved wet chemical etching processes may induce delamination and/or degradation of organic semiconductor layers, which triggered the needs for the development of lowcost and simple patterning methods compatible with organic

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© XXXX American Chemical Society

materials.13,14 In accordance with above-mentioned requirements, microcontact printing and nanoimprinting techniques using geometrically featured elastomeric stamps have been introduced. Organic semiconductors could be successfully patterned by one-step stripping-out processes via high-temperature and high-pressure imprinting or stamping.15−17 However, these methods still require lithographic procedures to fabricate the stamps and include subsidiary problems (e.g., scaling up, residues at the patterned region, deformation of stamps due to thermal damage, and solvent swelling).18−20 Toward overcoming these issues, alternative bottom-up approaches have been extensively studied, such as electrohydrodynamic jet (E-jet) printing, inkjet printing, and aerosol jet printing.21−23 These methods have several advantages: (i) they are noncontact printing methods that can avoid damage of printed semiconductor layers and substrates; (ii) they offer precise printing in designated directions and positions over large areas; and (iii) they are cost-effective approaches that can minimize the waste of materials. Among the bottom-up printing techniques, E-jet printing has received a great deal of attention due to its unique advantages such as high resolutions from the micro- to nanoscale, broad ink selectivity, and fine pattern accuracy compared to Received: September 30, 2017 Accepted: October 30, 2017 Published: October 30, 2017 5492

DOI: 10.1021/acs.jpclett.7b02590 J. Phys. Chem. Lett. 2017, 8, 5492−5500

Letter

The Journal of Physical Chemistry Letters

Figure 1. (a) Schematic illustration of dragging mode E-jet printing. Magnified schematic of TIPS-PEN crystal growth along the printing direction. (b) pOM image and (c) photograph of TIPS-PEN crystals printed in conventional mode; (d) pOM image and (e) photograph of the crystals printed in dragging mode. P and A indicate the axes of the polarizer and analyzer in the microscope, respectively.

conventional inkjet printing.24,25 It is a kind of electrospinning technique that use an electric field to eject various types of inks through a fine nozzle. While the conventional electrospinning techniques suffer from whipping instability and jet splitting problems at the Taylor cone due to a long nozzle-to-substrate distance (DS) of ∼10 cm, E-jet printing can overcome those issues owing to the much shorter DS by about hundreds of micrometers.26 Studies on E-jet printing of various materials (e.g., colloidal nanoparticles, polymers, and small molecules) has been reported for accurate positioning of the materials to fabricate electronic components and devices such as transparent metal mesh electrodes, light-emitting diode pixels, and OFET arrays.27−30 However, most previous studies have focused on printing noncrystalline materials of which nanoscale molecular ordering may not significantly affect their electrical properties. Printing organic small molecular crystalline materials may involve different kinds of issues because it should consider not only fine printing but also optimal molecular packing and selfassembly. Here, we report the “dragging mode” E-jet printing technique (Figure 1a), which is a powerful way to directly write and align small-molecule organic semiconductor crystals. In contrast to the conventional mode, the dragging mode provides a favorable environment for crystal growth of a wellknown organic small molecular semiconductor, 6,13-bis-

(triisopropylsilylethynyl) pentacene (TIPS-PEN). TIPS-PEN crystallizes during printing to yield millimeter-long microcrystals aligned along the printing direction. The crystals printed at an optimal speed were highly crystalline with molecular orientation that favors efficient charge transport. OFETs that used the crystals displayed a high average fieldeffect mobility (μFET) of 1.47 cm2/(V·s) with a maximum μFET of 1.65 cm2/(V·s). To expand the utility of the technique, we demonstrated various shapes of drawings by printed crystals and also demonstrated the feasibility of controlling the line widths. Printing of TIPS-PEN crystal patterns on large (5 cm × 5 cm) polyethylene sulfone (PES) substrates enabled fabrication of flexible OFET arrays. In the conventional E-jet printing mode, a high supply voltage (VS) greater than several kilovolts is applied between the nozzle and the substrate while they are separated by hundreds of micrometers.31−33 The large difference in electric potential between the nozzle and the substrate induces strong tangential electrical stresses that stretch the solution; therefore, it can be ejected at the substrate with high resolution. At first, we emplolyed the conventional mode to print TIPS-PEN solutions and tried to obtain continuous crystals. However, the conventional printing mode was found to be not suitable for growing large and continuous TIPS-PEN crystals, as shown in the polarized optical microscopy (pOM) image in Figure 1b. 5493


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Figure 2. Top: pOM images of E-jet printed TIPS-PEN crystals printed at various SP (noted in each image). Bottom: magnified views of the upper images. White dotted squares: flaws in the crystal structure.

For the next step, we tried to find the optimum VS range for successful printing with the dragging mode. At VS < 10 V, we observed a sudden stop of jetting due to lack of electrostatic attractions for ejecting the solution from the nozzle. As a result, crystal growth stopped even though the nozzle kept moving in the printing direction (see Figure S1a, Supporting Information). At 10 ≤ VS ≤ 50 V, the solution was stably ejected without interruption and continuous crystals were obtained (Figure 1d). However, at VS > 50 V, electrical breakdown occurred between the nozzle and the substrate; therefore, the solution overflowed, and the flow rate could not be controlled (Figure S1b, Supporting Information). These results suggest that 10 ≤ VS ≤ 50 V is the optimal VS range. To obtain high-quality TIPS-PEN crystals, the printing speed (SP) and solvent evaporation rate must be carefully controlled, as demonstrated in previous studies using dip-coating, zonecasting, slot-die coating, and solution shearing methods.40−43 To find the optimal printing condition for our system, SP was systematically varied from 0.1 to 1.0 mm/s while keeping the substrate temperature at 50 °C and solution concentration at 0.2 wt % in chlorobenzene. Figure 2 shows pOM images of resulting TIPS-PEN crystals grown at various SP values. We found that the morphologies of the crystals sensitively changed with respect to the SP. At SP = 0.1 and 0.2 mm/s, TIPS-PEN crystals grew along the printing direction in the form of millimeter-long microwires. As SP increased, however, the crystals gradually became featureless and isotropic; the change might be explained by the crystal growth mechanism during printing. For large crystals to grow in the printing direction, the rate of crystallization along the printing direction should be balanced with SP. During the early stage of printing, the solution ejected to the substrate is pinned at the divinyltetramethyldisiloxanebis(benzocyclobutene) (BCB)-treated substrate that has a moderately high surface energy of 42.04 mJ/m2 (Table S1, Supporting Information). As the nozzle moves in the printing direction, solvent evaporation at the solution−air−substrate contact line induces a concentration gradient in the dropped solution. Therefore, the concentration at the contact line reaches the critical concentration for crystallization, and crystals can grow along the printing direction. Intuitively, in this situation, the optimal condition for continuous crystal growth occurs when the crystallization speed along the printing direction matches SP. The rate of solvent evaporation was consistent in this series of experiments because the substrate temperature was maintained at 50 °C; therefore, the number of

The printed TIPS-PEN displayed discrete texture and large color variation in the pOM image, indicating the failure of continuous crystal growth. This might result from an unfavorable environment for TIPS-PEN molecules to be selfassembled into continuous and large crystals on the substrate owing to discontinuous jets in the form of microdroplets (see Figure 1c and Movie S1 in the Supporting Information). According to previous reports, solutions should have moderate electrical conductivity for continuous jetting during E-jet printing.34,35 However, in this experiment, we used a 0.2 wt % TIPS-PEN solution that has very low electrical conductivity; these factors might be the reason why the solution was ejected in the form of microdroplets rather than a continuous line. At this condition, continuous crystals are difficult to grow because an already-droped microdroplet completely dries before the next droplet is dropped. This fast solvent evaporation leads to a discontinuous meniscus on the substrate as well as insufficient time for molecular self-assembly into ordered structures, leading to poor crystallinity. In addition, a high tangential electrical stress induced by a high VS (1.1 kV) might also impede continuous crystal growth along the lateral direction. It has been reported that organic crystals could be aligned by applying an electric field during crystallization because crystals would be oriented in the direction of the electric field.36−39 However, in our case, because the electric field applied during E-jet printing was perpendicular to the substrate, it could disturb continuous crystal growth in the lateral direction. To grow continuous TIPS-PEN crystals with E-jet printing, we developed dragging mode operation (Figure 1d). In this mode, DS was adjusted to 50 μm, which is much shorter than that of the conventional mode (hundreds of micrometers). This DS is comparable to or even smaller than the diameter of a droplet; therefore, the droplet connects the nozzle to the substrate. This approach offers many advantages that can solve the problems of conventional mode E-jet printing. First of all, because the solution is supplied to the substrate before the already-dropped droplet dries, the solution on the substrate does not form separated droplets but remains connected during the entire printing process (Figure 1e, Movie S2). In addition, VS and therefore tangential electrical stresses during printing can be dramatically reduced. As a result, continuous TIPS-PEN crystals have been successfully obtained along with the printing direction, as shown in Figure 1e, suggesting that dragging mode E-jet printing can be a promising way to grow organic semiconductor crystals by overcoming the drawbacks of conventional mode E-jet printing. 5494


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Figure 3. GIWAXS patterns of E-jet printed TIPS-PEN crystals produced at various SP values (noted in each pattern).

incidence wide-angle X-ray scattering (GIWAXS) experiments (Figure 3). The TIPS-PEN crystals were aligned so that the printing direction was perpendicular to an incident X-ray beam with a grazing incidence angle of 0.12°. All samples showed (00l) diffractions along the qz (out-of-plane) axis with qz = 0.378 regardless of SP (Figure 3 and Table S2); the d-spacing values from these diffractions correspond to a c-axis value (16.6 Å) in a TIPS-PEN unit cell.44 It suggests that TIPS-PEN molecules formed an edge-on orientation with respect to the substrate. The edge-on orientation could be further confirmed by comparing their diffraction patterns with the spin-coated one (Figure S3). This is a favorable orientation for lateral charge transport because π−π conjugations between neighboring molecules are located parallel to the substrate. However, the degree of crystallinity depended on SP. Samples printed at SP = 0.1 mm/s showed arc-shaped diffractions along the qz (out-of-plane) and qxy (in-plane) axes; these diffractions indicate that edge-on orientation is imperfect due to the presence of tilted crystallites with respect to the substrate. Samples printed at SP = 0.2 mm/s showed similar intensity at qz = 0.378, but sharp (00l), (0kl) diffractions along the qz and qxy axes implied improved edge-on orientation as well as a high degree of crystallinity. Samples printed at SP > 0.2 mm/s showed progressively weaker peak intensities and broader arcshaped diffractions. These trends may be the result of reduced film thickness and crystallinity (i.e., mixture of crystallites with different orientations). To get more insight into the crystallinity of our E-jet printed TIPS-PEN crystals, we extracted coherence lengths from (001) diffractions in out-of-plane profiles of the samples, which are determined as 2π/fwhm (fwhm: full width at half-maximum of the peak). As summarized in Table S2, the (001) peak for 0.2 mm/s samples showed the smallest fwhm value, yielding the largest coherence length of 1418.3 Å. This coherence value is certainly larger than that of 0.1 mm/s samples, providing additional evidence for the higher crystallinity of TIPS-PEN crystals printed at SP = 0.2 mm/s than those at SP = 0.1 mm/s. For SP > 0.2 mm/s, coherence lengths decreased as the SP increased. In addition, we also analyzed pole figure plots

TIPS-PEN molecules that could participate in crystallization per unit time would be similar regardless of SP. At the optimal SP, most of the TIPS-PEN molecules may be used for crystallization along the printing direction, but at SP slower than optimal, there should be some remainder molecules that do not participate in crystallization along the printing direction. This is because the SP (i.e., crystallization speed along the printing direction) is slower despite the same rate of production of crystallizable TIPS-PEN molecules. These excess TIPS-PEN molecules result in high nuclei density; therefore, impingements between neighboring crystals can possibly occur, leading to unfavorable crystalline morphology. This speculation is supported by the pOM image at SP = 0.1 mm/s, which shows discernible color variation in a single wire (Figure 2, white squares). By contrast, SP > 0.4 mm/s is faster than the crystallization speed along the printing direction; as a result, residual solvents cannot completely evaporate and therefore remain in the printed solution even after the nozzle has moved away. This situation is analogous to “drop-casting” of solution; therefirem discontinuous, randomly oriented crystals are obtained (Figure 2). To further study the morphologies of the printed crystals, we performed atomic force microscopy (AFM) analyses. Crystals grown at SP = 0.2 mm/s showed uniform color variation in a single wire and clear stepped-layer spacing of approximately 17 Å, which coincided with the c-axis value in a TIPS-PEN unit cell (Figure S2a).44 On the other hand, crystals grown at SP = 0.1 mm/s showed some aggregates of TIPS-PEN molecules that could not participate in crystallization during printing (Figure S2a, white squares). These results agreed well with the results of pOM analyses (Figure 2) and suggest again that SP = 0.2 mm/s is the optimal printing speed for preferential growth of crystals in this study.42 The film thickness gradually decreased with as SP increased (Figure S2b,c); this trend occurred because the solution feed rate from the nozzle was constant regardless of SP; therefore, an increase in SP reduced the amount of TIPSPEN molecules that accumulate in a unit area. Crystallinity and molecular orientation of the printed TIPSPEN crystals were analyzed by synchrotron-based grazing 5495


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Figure 4. (a) Schematic structure of E-jet printed TIPS-PEN OFET. (b) Typical transfer characteristics (inset: pOM images of TIPS-PEN crystals with Au dots). (c) Corresponding average μFET and amount of hysteresis values of OFETs with TIPS-PEN crystals grown at various SP values (listed above each transfer curve).

Table 1. Electrical Characteristics of E-Jet Printed TIPS-PEN OFETs with Various VS Values Obtained from 15-20 OFETs for Each VS Printing Speed (mm/s) average μFET (cm /(V·s)) maximum μFET (cm2/(V·s)) Vth (V) SS (V/dec) Ion/Ioff 2

0.1

0.2

0.4

0.6

0.8

1.0

1.15 1.42 −47.4 10.07 8.0 × 106

1.47 1.65 −40.1 6.86 1.2 × 106

0.25 0.38 −41.6 7.00 2.2 × 106

0.09 0.16 −40.5 8.62 6.7 × 104

0.009 0.018 −44.8 10.95 2.1 × 104

0.0010 0.0014 −47.7 11.87 2.4 × 104

thermally evaporated Au source/drain (S/D) electrodes (channel length L = 26 μm, width W = 55 μm) (Figure 4a). The capacitance of the BCB/SiO2 dielectric film was 10.0 nF/ cm2. Devices fabricated using TIPS-PEN crystals grown at SP = 0.2 mm/s had the smallest hysteresis in transfer curves (Figure 4b) and the highest output characteristics (Figure S7) and had an average μFET = 1.47 cm2/(V·s) and maximum μFET = 1.65 cm2/(V·s) (Table 1). Other samples showed considerable hysteresis in transfer curves (Figure 4b) and much lower μFET (Figure 4c, Table 1). For other properties such as the threshold voltage (Vth) and subthreshold swing (SS), the 0.2 mm/s sample exhibited superior properties compared to other samples (Table 1). In general, hysteresis in transfer curves and low μFET are caused by significant charge trapping in the semiconductor, in the dielectric, at the interface between them, or at some combination of these locations.45−49 Polar moieties such as hydroxyl groups on the dielectric surface and grain boundaries in semiconductor films are known as representative trap sites. In this study, all SiO2 dielectric surfaces were covered by BCB

obtained from the (001) peaks (Figure S5). To compare the crystallinity in more detail, fwhm values were also calculated along the azimuthal angles (Table S3). We found that the results of pole figure plots and fwhm values are also in line with the results of GIWAXS and coherence length analyses. In other words, the fwhm value of 0.2 mm/s samples was found to be the smallest among all printed crystal samples, suggesting again that TIPS-PEN crystals printed at SP = 0.2 mm/s exhibited the highest crystallinity. From these GIWAXS analyses, we concluded that TIPS-PEN crystals printed at SP = 0.2 mm/s grew optimally and were therefore expected to exhibit superior charge-transport characteristics. Additionally, with the 0.2 mm/s sample, we could examine the growth direction of TIPS-PEN crystals in detail by comparing the GIWAXS patterns when the printing direction was aligned parallel or perpendicular to the incident X-ray beam directions (Figure S6). Electrical properties of printed TIPS-PEN crystals were investigated by measuring bottom-gate/top-contact OFETs based on BCB-treated (30 nm) SiO2 (300 nm) dielectrics and 5496


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Figure 5. (a) pOM images and (b) corresponding transfer characteristics of E-jet printed TIPS-PEN crystals with various line widths (noted above each pOM image). Crystals were printed at 0.2 mm/s. μFET values are shown below the pOM images.

thin films, which are free of hydroxyl groups and are widely used to suppress charge trapping. Therefore, the differences in electrical characteristics of the OFETs result from the different quality of TIPS-PEN crystals depending on SP. pOM, AFM, and GIWAXS analyses confirmed that TIPS-PEN films printed at SP = 0.2 mm/s showed the most favorable morphology and highest crystallinity for lateral charge transport and that the other samples were less favorable or unfavorable (i.e., color variation in pOM images, crystal aggregates or randomly grown grains in AFM images, low crystallinity in GIWAXS experiments). These results indicate that the highest μFET and almost hysteresis-free transfer curves of the 0.2 mm/s OFETs were attributed for the preferentially grown, high-quality TIPS-PEN crystals obtained by the optimized E-jet printing. The highest μFET obtained in this study is comparable to or higher than those reported in previous studies using dipcoating, zone-casting, and slot-die coating.40−42 Although these methods are considered as promising ways to form organic semiconductor films, previous researchers have focused only on growing high-quality crystals. However, the dragging mode Ejet printing method enables simultaneous growth and bottomup patterning of high-quality crystals. We believe that these advantages can open up new avenues for facile fabrication of high-performance organic devices without the need for additional patterning steps. Although direct patterning of TIPS-PEN crystals has been achieved using capillary pen lithography or inkjet printing, the devices produced had unsatisfactory μFET probably because crystallinity and morphology were not fully optimized and printed crystals were relatively small.50−53 The controllability of pattern line widths and feasibility of direct writing for desired shapes are important factors for broad applications and good processability of printing techniques. At fitst, we tried to control the width of printed TIPS-PEN line patterns by adjusting the solution flow rate from the syringe pump while keeping other conditions optimal. The line width increased from 150 to 400 μm as the flow rate increased from 0.02 to 0.10 μL/min (Figure 5a). All patterns printed at the optimal SP showed similarly good crystalline morphologies inside of each line, and all OFETs that used the printed crystals had similar transfer characteristics and μFET values (Figure 5b); this result confirms that the optimal printing speed does not vary with the solution flow rate and that the crystallinity of each pattern might be independent of line width. We believe that the

line width can be further narrowed (or widened) by using appropriate nozzles. Next, we demonstrated the broad utility of our E-jet printing technique by writing various shapes of TIPS-PEN crystals beyond line patterns. For this experiment, automated E-jet printing was introduced with a TIPS-PEN solution. Curved and perpendicularly bent patterns could be clearly printed; therefore, alphabetic characters and continuous but successively bent line patterns could be produced (Figure 6). All patterns contained well-grown crystals even at sharp corners, and crystal orientations followed the printing directions.

Figure 6. pOM images of E-jet printed TIPS-PEN crystal patterns with various shapes and feature sizes on a Si substrate.

In addition, we demonstrate that dragging mode E-jet printing can be used to fabricate flexible OFET arrays on flexible polymer substrates. To fabricate bottom-gate topcontact OFETs (Figure 7a), 100 nm thick Al gate electrodes were deposited by thermal evaporation on 5 cm × 5 cm PES substrates. Subsequently, a solution of poly(4-vinylphenol) (PVP) was spin-coated on the substrates and thermally annealed to form 135 nm thick cross-linked PVP (cPVP) gate dielectric films (135 nm). We performed dragging mode Ejet printing using a TIPS-PEN solution on the cPVP-covered PES substrates at the optimal SP = 0.2 mm/s. Finally, to finish the OFET fabrication, 100 nm thick Au S/D electrodes were 5497


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Figure 7. (a) Left: Photograph of a flexible OFET array fabricated by E-jet printing TIPS-PEN crystals (inset: pOM image of TIPS-PEN crystals with Au dots); right: schematic device structure. (b) Output and (c) transfer characteristic of flexible OFETs. (d) Histograms of μFETs obtained from 17 OFETs.

variously shaped crystal patterns and fabricating large-area flexible OFET arrays. Therefore, we believe that our work would be an importnat basis for realizing future flexible electronics by providing a cost-effective and convenient route to form and align high-quality organic semiconductor crystals without the need for any additional patterning step.

deposited on the printed TIPS-PEN crystals by thermally evaporating Au through a shadow mask. cPVP films have higher capacitance (25.2 nF/cm2) than BCB/SiO2 films (10.0 nF/ cm2); therefore, the flexible OFETs exhibited a relatively lower operation voltage; the OFETs showed clear transitions from linear to saturation within −15 V in the output curve (Figure 7b) and off-to-on and on-to-off switchings in the transfer curve (Figure 7c), respectively. μFET obtained from 17 devices was as high as 1.37 cm2/(V·s), with an average value of 0.88 cm2/(V·s) (Figure 7d). The slightly lower average μFET compared to that obtained in BCB-treated SiO2-based OFETs might be attributed to more charge trapping at the polar dielectric surface of cPVP, which contains a small number of unreacted hydroxyl groups.48 Nevertheless, the μFET values are thought to be decent, and the OFETs showed negligible hysteresis in transfer curves, a high on/off ratio (>106), a low Vth (−2.3 V), and a low SS (0.471 V/decade). In conclusion, we demonstrated that the novel dragging mode E-jet printing technique is a powerful means to grow high-quality organic semiconductor crystals and, at the same time, to align them at desired positions. Unlike a conventional mode, the dragging mode enables continuous solution ejection from the nozzle and uses a much smaller VS, minimizing tangential electrical stresses during crystallization. TIPS-PEN crystals printed at 0.2 mm/s showed most favorable crystal morphology along the printing direction. This SP may be optimal because it matches the crystallization speed of TIPSPEN molecules along the printing direction. Optimally grown crystals showed a clear edge-on orientation with high crystallinity. Due to this good crystal morphology and favorable molecular orientation for lateral charge transport, OFETs based on the TIPS-PEN crystals had high average μFET = 1.47 cm2/ (V·s) and negligible operational hysteresis. Finally, dragging mode E-jet printing was successfully utilized in drawing

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpclett.7b02590. Experimental details, crystal information on E-jet printed crystals, pOM images, AFM topographies, GIWAXS patterns, extracted parameters from the patterns, and output characteristics in OFETs (PDF) Recorded movie during E-jet printing with the conventional mode (AVI) Recorded movie during E-jet printing with the dragging mode (AVI)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (C.E.P.). *E-mail: [email protected] (S.H.K.). *E-mail: [email protected] (J.J.). ORCID

Jaeyoung Jang: 0000-0002-5548-8563 Se Hyun Kim: 0000-0001-7818-1903 Chan Eon Park: 0000-0002-3100-0623 Author Contributions ⊥

5498

K.K. and J.H.B. contributed equally to this work. DOI: 10.1021/acs.jpclett.7b02590 J. Phys. Chem. Lett. 2017, 8, 5492−5500

Letter

The Journal of Physical Chemistry Letters Notes

(14) Nakayama, K.; Uno, M.; Uemura, T.; Namba, N.; Kanaoka, Y.; Kato, T.; Katayama, M.; Mitsui, C.; Okamoto, T.; Takeya, J. HighMobility Organic Transistors with Wet-Etch-Patterned Top Electrodes: A Novel Patterning Method for Fine-Pitch Integration of Organic Devices. Adv. Mater. Interfaces 2014, 1, 1300124. (15) Kim, A.; Jang, K. S.; Kim, J.; Won, J. C.; Yi, M. H.; Kim, H.; Yoon, D. K.; Shin, T. J.; Lee, M. H.; Ka, J. W.; et al. Solvent-Free Directed Patterning of a Highly Ordered Liquid Crystalline Organic Semiconductor via Template-Assisted Self-Assembly ofr Organic Transistors. Adv. Mater. 2013, 25, 6219−6225. (16) Bae, I.; Kang, S. J.; Shin, Y. J.; Park, Y. J.; Kim, R. H.; Mathevet, F.; Park, C. Tailored Single Crystals of Triisopropylsilylethynyl Pentacene by Selective Contact Evaporation Printing. Adv. Mater. 2011, 23, 3398−3402. (17) Kim, K.; Jang, M.; Lee, M.; An, T. K.; Anthony, J. E.; Kim, S. H.; Yang, H.; Park, C. E. Unified Film Patterning and Annealing of an Organic Semiconductor with Micro-Grooved Wet Stamps. J. Mater. Chem. C 2016, 4, 6996−7003. (18) Dangla, R.; Gallaire, F.; Baroud, C. N. Microchannel Deformations due to Solvent-Induced PDMS Swelling. Lab Chip 2010, 10, 2972−2978. (19) Lee, J. N.; Park, C.; Whitesides, G. M. Solvent Compatibility of Poly(dimethylsiloxane)-Based Microfluidic Devices. Anal. Chem. 2003, 75, 6544−6554. (20) Guo, L. J. Nanoimprint Lithography: Methods and Material Requirements. Adv. Mater. 2007, 19, 495−513. (21) Park, J. U.; Hardy, M.; Kang, S. J.; Barton, K.; Adair, K.; Mukhopadhyay, D. K.; Lee, C. Y.; Strano, M. S.; Alleyne, A. G.; Georgiadis, J. G.; et al. High-Resolution Electrohydrodynamic Jet Printing. Nat. Mater. 2007, 6, 782−789. (22) Minemawari, H.; Yamada, T.; Matsui, H.; Tsutsumi, J.; Haas, S.; Chiba, R.; Kumai, R.; Hasegawa, T. Inkjet Printing of Single-Crystal Films. Nature 2011, 475, 364−367. (23) Kim, S. H.; Hong, K.; Lee, K. H.; Frisbie, C. D. Performance and Stability of Aerosol-Jet-Printed Electrolyte-Gated Transistors Based on Poly(3-hexylthiophene). ACS Appl. Mater. Interfaces 2013, 5, 6580. (24) Lee, H.; Seong, B.; Kim, J.; Jang, Y.; Byun, D. Direct Alignment and Patterning of Silver Nanowires by Electrohydrodynamic Jet Printing. Small 2014, 10, 3918−3922. (25) Jang, Y.; Hartarto Tambunan, I.; Tak, H.; Dat Nguyen, V.; Kang, T.; Byun, D. Non-Contact Printing of High Aspect Ratio Ag Electrodes for Polycrystalline Silicone Solar Cell with Electrohydrodynamic Jet Printing. Appl. Phys. Lett. 2013, 102, 123901. ́ , Á . G.; Loscertales, I. G.; Barrero, A. (26) Riboux, G.; MarIN Whipping Instability Characterization of an Electrified Visco-Capillary Jet. J. Fluid Mech. 2011, 671, 226−253. (27) Kim, B. H.; Onses, M. S.; Lim, J. B.; Nam, S.; Oh, N.; Kim, H.; Yu, K. J.; Lee, J. W.; Kim, J. H.; Kang, S. K.; et al. High-Resolution Patterns of Quantum Dots Formed by Electrohydrodynamic Jet Printing for Light-Emitting Diodes. Nano Lett. 2015, 15, 969−973. (28) Song, C.; Rogers, J. A.; Kim, J.-M.; Ahn, H. Patterned Polydiacetylene-Embedded Polystyrene Nanofibers Based on Electrohydrodynamic Jet Printing. Macromol. Res. 2015, 23, 118−123. (29) Kim, K.; Kim, G.; Lee, B. R.; Ji, S.; Kim, S. Y.; An, B. W.; Song, M. H.; Park, J. U. High-Resolution Electrohydrodynamic Jet Printing of Small-Molecule Organic Light-Emitting Diodes. Nanoscale 2015, 7, 13410−13415. (30) Seong, B.; Yoo, H.; Nguyen, V. D.; Jang, Y.; Ryu, C.; Byun, D. Metal-Mesh Based Transparent Electrode on a 3-D Curved Surface by Electrohydrodynamic Jet Printing. J. Micromech. Microeng. 2014, 24, 097002. (31) Min, S.-Y.; Kim, T.-S.; Kim, B. J.; Cho, H.; Noh, Y.-Y.; Yang, H.; Cho, J. H.; Lee, T.-W. Large-Scale Organic Nanowire Lithography and Electronics. Nat. Commun. 2013, 4, 1773−1781. (32) Jang, Y.; Hartarto Tambunan, I.; Tak, H.; Dat Nguyen, V.; Kang, T.; Byun, D. Non-Contact Printing of High Aspect Ratio Ag Electrodes for Polycrystalline Silicone Solar Cell with Electrohydrodynamic Jet Printing. Appl. Phys. Lett. 2013, 102, 123901.

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Center for Advanced Soft Electronics under the Global Frontier Research Program (Grant No. 2013M3A6A5073175), Young Researchers Program (NRF-2017R1A1A1A05001233), and Basic Science Research Program (2015R1D1A1A02062369) through the National Research Foundation of Korea (NRF) funded by the Ministry of Education.

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REFERENCES

(1) Kim, R. H.; Kim, H. J.; Bae, I.; Hwang, S. K.; Velusamy, D. B.; Cho, S. M.; Takaishi, K.; Muto, T.; Hashizume, D.; Uchiyama, M.; et al. Non-Volatile Organic Memory with Sub-Millimetre Bending Raduis. Nat. Commun. 2014, 5, 3583−3594. (2) Yi, H. T.; Payne, M. M.; Anthony, J. E.; Podzorov, V. UltraFlexible Solution-Processed Organic Field-Effect Transistors. Nat. Commun. 2012, 3, 1259−1265. (3) Sekitani, T.; Yokota, T.; Kuribara, K.; Kaltenbrunner, M.; Fukushima, T.; Inoue, Y.; Sekino, M.; Isoyama, T.; Abe, Y.; Onodera, H.; et al. Ultraflexible Organic Amplifier with Biocompatible Gel Electrodes. Nat. Commun. 2016, 7, 11425−11435. (4) Zheng, Y. Q.; Lei, T.; Dou, J. H.; Xia, X.; Wang, J. Y.; Liu, C. J.; Pei, J. Strong Electron-Devicient Polymers Lead to High Electron Mobility in Air and Their Morphology-Dependent Transport Behaviors. Adv. Mater. 2016, 28, 7213−7219. (5) An, T. K.; Kang, I.; Yun, H. J.; Cha, H.; Hwang, J.; Park, S.; Kim, J.; Kim, Y. J.; Chung, D. S.; Kwon, S. K.; et al. Solvent Additive to Achieve Highly Ordered Nanostructural Semicrystalline DPP Copolymers: Toward a High Charge Carrier Mobility. Adv. Mater. 2013, 25, 7003−7009. (6) Yuan, Y.; Giri, G.; Ayzner, A. L.; Zoombelt, A. P.; Mannsfeld, S. C.; Chen, J.; Nordlund, D.; Toney, M. F.; Huang, J.; Bao, Z. UltraHigh Mobility Transparent Organic Thin Film Transistors Grown by an Off-Centre Spin-Coating Method. Nat. Commun. 2014, 5, 3005− 3013. (7) Diao, Y.; Tee, B. C.; Giri, G.; Xu, J.; Kim, D. H.; Becerril, H. A.; Stoltenberg, R. M.; Lee, T. H.; Xue, G.; Mannsfeld, S. C.; Bao, Z. Solution Coating of Large-Area Organic Semiconductor Thin Films with Aligned Single-Crystalline Domains. Nat. Mater. 2013, 12, 665− 671. (8) Niazi, M. R.; Li, R.; Qiang Li, E.; Kirmani, A. R.; Abdelsamie, M.; Wang, Q.; Pan, W.; Payne, M. M.; Anthony, J. E.; Smilgies, D. M.; et al. Solution-Printed Organic Semiconductor Blends Exhibiting Transport Properties on par with Single Crystals. Nat. Commun. 2015, 6, 8598−8607. (9) Deng, W.; Zhang, X.; Wang, L.; Wang, J.; Shang, Q.; Zhang, X.; Huang, L.; Jie, J. Wafer-Scale Precise Patterning of Organic SingleCrystal Nanowire Arrays via a Photolithography-Assisted Spin-Coating Method. Adv. Mater. 2015, 27, 7305−7312. (10) Feng, J.; Jiang, X.; Yan, X.; Wu, Y.; Su, B.; Fu, H.; Yao, J.; Jiang, L. Capillary-Bridge Lithography” for Patterning Organic Crystals toward Mode-Tunable Microlaser Arrays. Adv. Mater. 2017, 29, 1603652. (11) Park, K. S.; Baek, J.; Park, Y.; Lee, L.; Lee, Y.-E. K.; Kang, Y.; Sung, M. M. Inkjet-Assisted Nanotransfer Printing for Large-Scale Integrated Nanopatterns of Various Single-Crystal Organic Materials. Adv. Mater. 2016, 28, 2874−2880. (12) Park, K. S.; Cho, B.; Baek, J.; Hwang, J. K.; Lee, H.; Sung, M. M. Single-Crystal Organic Nanowire Electronics by Direct Printing from Molecular Solutions. Adv. Funct. Mater. 2013, 23, 4758−4758. (13) Ji, D.; Jiang, L.; Jiang, L.; Fu, X.; Dong, H.; Yu, J.; Hu, W. A Novel Method for Photolithographic Polymer Shadow Masking: Toward High-Resolution High-Performance Top-Contact Organic Field Effect Transistors. Chem. Commun. 2014, 50, 8328−8330. 5499


Letter

The Journal of Physical Chemistry Letters (33) Lee, Y. G.; Choi, W. S. Electrohydrodynamic Jet-Printed ZincTin Oxide TFTs and Their Bias Stability. ACS Appl. Mater. Interfaces 2014, 6, 11167−11172. (34) Onses, M. S.; Sutanto, E.; Ferreira, P. M.; Alleyne, A. G.; Rogers, J. A. Mechanisms, Capabilities, and Applications of High-Resolution Electrohydrodynamic Jet Printing. Small 2015, 11, 4237−4266. (35) Kamyshny, A.; Magdassi, S. Conductive Nanomaterials for Printed Electronics. Small 2014, 10, 3515−3535. (36) Komino, T.; Kuwabara, H.; Ikeda, M.; Yahiro, M.; Takimiya, K.; Adachi, C. Droplet Manipulation by an External Electric Field for Crystalline Film Growth. Langmuir 2013, 29, 9592−9597. (37) Fischer, F. S.; Tremel, K.; Sommer, M.; Crossland, E. J.; Ludwigs, S. Directed Crystallization of Poly(3-hexylthiphene) in Micrometre Channels under Confinement and in Electric Fields. Nanoscale 2012, 4, 2138−2144. (38) Kotsuki, K.; Obata, S.; Saiki, K. Self-Aligned Growth of Organic Semiconductor Single Crystals by Electric Field. Langmuir 2016, 32, 644−649. (39) Mandal, T.; Garg, A.; Deepak. Thin Film Transistors Fabricated by Evaporating Pentacene under Electric Field. J. Appl. Phys. 2013, 114, 154517. (40) Jang, J.; Nam, S.; Im, K.; Hur, J.; Cha, S. N.; Kim, J.; Son, H. B.; Suh, H.; Loth, M. A.; Anthony, J. E.; et al. Highly Crystalline Soluble Acene Crystal Arrays for Organic Transistors: Mechanism of Crystal Growth During Dip-Coating. Adv. Funct. Mater. 2012, 22, 1005−1014. (41) Sele, C. W.; Kjellander, B. K.; Niesen, B.; Thornton, M. J.; van der Putten, J. B.; Myny, K.; Wondergem, H. J.; Moser, A.; Resel, R.; van Breemen, A. J.; et al. Controlled Deposition of Highly Ordered Soluble Acene Thin Films: Effect of Morphology and Crystal Orientation on Transistor Performance. Adv. Mater. 2009, 21, 4926−4931. (42) Su, Y.; Gao, X.; Liu, J.; Xing, R.; Han, Y. Uniaxial Alignment of Triisopropylsilylethynyl pentacene via Zone-Casting Technique. Phys. Chem. Chem. Phys. 2013, 15, 14396−14404. (43) Giri, G.; Verploegen, E.; Mannsfeld, S. C.; Atahan-Evrenk, S.; Kim, D. H.; Lee, S. Y.; Becerril, H. A.; Aspuru-Guzik, A.; Toney, M. F.; Bao, Z. Tuning Charge Transport in Solution-Sheared Organic Semiconductor Using Lattice Strain. Nature 2011, 480, 504−508. (44) Anthony, J. E.; Brooks, J. S.; Eaton, D. L.; Parkin, S. R. Functionalized Pentacene: Improved Electronic Properties from Control of Solid-State Order. J. Am. Chem. Soc. 2001, 123, 9482−9483. (45) Miyadera, T.; Wang, S. D.; Minari, T.; Tsukagoshi, K.; Aoyagi, Y. Charge Trapping Induced Current Instability in Pentacene Thin Film Transistors: Trapping Barrier and Effect of Surface Treatment. Appl. Phys. Lett. 2008, 93, 033304. (46) Gu, G.; Kane, M. G.; Doty, J. E.; Firester, A. H. Electron Traps and Hysteresis in Pentacene-Based Organic Thin-Film Transistors. Appl. Phys. Lett. 2005, 87, 243512. (47) Hwang, D. K.; Oh, M. S.; Hwang, J. M.; Kim, J. H.; Im, S. Hysteresis Mechanisms of Pentacene Thin-Film Transistors with Polymer/Oxide Bilayer Gate Dielectrics. Appl. Phys. Lett. 2008, 92, 013304. (48) Kim, S. H.; Nam, S.; Jang, J.; Hong, K.; Yang, C.; Chung, D. S.; Park, C. E.; Choi, W.-S. Effect of the Hydrophobic and Thickness of Polymer Gate Dielectrics on the Hysteresis Behavior of PentaceneBased Field-Effect Transistors. J. Appl. Phys. 2009, 105, 104509. (49) Lee, S. S.; Mativetsky, J. M.; Loth, M. A.; Anthony, J. E.; Loo, Y. L. Quantifying Resistances across Nanoscale Low- and High-Angle Interspherulite Boundaries in Solution-Processed Organic Semiconductor Thin Films. ACS Nano 2012, 6, 9879−9886. (50) Lee, W. H.; Min, H.; Park, N.; Lee, J.; Seo, E.; Kang, B.; Cho, K.; Lee, H. S. Microstructural Control over Soluble Pentacene Deposited by Capillary Pen Printing for Organic Electronics. ACS Appl. Mater. Interfaces 2013, 5, 7838−7644. (51) Kang, B.; Park, N.; Min, H.; Lee, J.; Jeong, H.; Baek, S.; Cho, K.; Lee, H. S. Fully Drawn All-Organic Flexible Transistors Prepared by Capillary Pen Printing on Flexible Planar and Curvilinear Substrates. Adv. Electron. Mater. 2015, 1, 1500301.

(52) Cho, S. Y.; Ko, J. M.; Lim, J.; Lee, J. Y.; Lee, C. Inkjet-Printed Orgaic Thin Film Transistors based on TIPS Pentacene with Insulating Polymers. J. Mater. Chem. C 2013, 1, 914−923. (53) Lee, M. W.; Ryu, G. S.; Lee, Y. U.; Pearson, C.; Petty, M. C.; Song, C. K. Control of Droplet Morphology for Inkjet-Printed TIPSpentacene transistors. Microelectron. Eng. 2012, 95, 1−4.

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Direct Writing and Aligning of Small-Molecule Organic Semiconductor

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