Precise Positioning of Organic Semiconductor Single Crystals with

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Surfaces, Interfaces, and Applications

Precise Positioning of Organic Semiconductor Single Crystals with Two-component Aligned Structure Through 3D Wettability-Induced Sequential Assembly Wei Deng, Bei Lu, Jian Mao, Zhengjun Lu, Xiujuan Zhang, and Jiansheng Jie ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b10089 • Publication Date (Web): 30 Aug 2019 Downloaded from pubs.acs.org on August 30, 2019

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ACS Applied Materials & Interfaces

Precise Positioning of Organic Semiconductor Single Crystals with Two-component Aligned Structure Through

3D

Wettability-Induced

Sequential

Assembly Wei Deng,# Bei Lu,# Jian Mao, Zhengjun Lu, Xiujuan Zhang, Jiansheng Jie* Institute of Functional Nano & Soft Materials (FUNSOM), Jiangsu Key Laboratory for CarbonBased Functional Materials & Devices, Soochow University

KEYWORDS: organic semiconductor · 3D wettability-induced sequential assembly · organic pn heterojunction · two-component single crystal array · organic field-effect transistors

ABSTRACT: Highly ordered organic semiconductor single crystal (OSSC) arrays are ideal building blocks for functional organic devices. However, most of the current methods are only applicable to fabricate OSSC arrays of a single component, which significantly hinders the application of OSSC arrays in integrated organic circuits. Here, we present a universal approach, termed three-dimensional (3D) wettability-induced sequential assembly (3DWSA) that can programmatically and progressively manipulate the crystallization locations of different organic semiconductors at the same spatial position by using a 3D microchannel template, for the

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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

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fabrication of the two-component OSSC arrays. As an example, we successfully prepare twocomponent, bilayer structured OSSC arrays consisting of n-type N,N’-bis(2-phenylethyl)perylene-3,4:9,10-tetracarboxylic

diimide

(BPE-PTCDI)

and

p-type

6,13-

bis(triisopropylsilylethynyl) pentacene (TIPS-PEN) microbelts (MBs). The bi-component OSSCs show ambipolar carrier transport properties with hole and electron mobilities of 0.342 and 0.526 cm2 V-1 s-1, respectively. Construction of complementary inverters is further demonstrated based on the two-component OSSCs. The capability of integration of multi-component OSSC arrays opens up unique opportunities for future high-performance organic complementary circuits.

1. INTRODUCTION Organic semiconductor single crystals (OSSCs) with highly ordered molecular packing show great potential for organic electronics and optoelectronics, owing to the higher carrier mobility and longer exciton diffusion length of OSSCs compared to those of the corresponding amorphous or polycrystalline thin films.1-7 Large-area, highly-ordered assembly of OSSC arrays is a prerequisite to achieve practical applications of OSSCs in integrated devices.8 Up to now, many different methodologies have been developed to fabricate OSSC arrays, including evaporation-induced selfassembly, solution-processed coating method, confinement self-assembly, and template-guided self-assembly, etc.9-12 However, most current methods can only generate single-component OSSC arrays on a substrate, because of the difficulty in simultaneously controlling the growth positions, orientations, and morphologies of different types of organic semiconductor crystals. Monolithic integration of different types of organic semiconductors is vital to develop functional organic circuits.13-18 For instance, as a basic circuit element, complementary metal-oxidesemiconductor (CMOS) device is composed of two types of organic semiconducting materials, i.e. n- and p-type semiconductors.19-22 Thus, the capability of assembling bi-component OSSC arrays


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with n- and p-type organic semiconductors will offer the possibility of constructing highperformance organic circuits.23 Recently, a droplet-pinned crystallization technique was reported for the growth of bilayer 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) (p-type) and C60 (n-type) crystal arrays,13 which provides an important avenue to fabricate bi-component p-n OSSC arrays for organic circuits. However, the use of the pinners, which are manually placed on the substrate with millimeter-scale resolution, is difficult to obtain high-resolution crystal patterns that can satisfy the requirement of modern electronic circuits. Inkjet-assisted nanotransfer printing methods are capable of precisely controlling the alignment and positions of the crystals,14 yet a complex after-transfer process and a mold with nanoscale channels (≈100 nm) are needed in the fabrication process. Herein, we demonstrate for the first time a universal method, termed three-dimensional (3D) wettability-induced sequential assembly (3DWSA), for the fabrication of bi-component OSSC arrays with n- and p-type organic semiconductors. In this method, crystallization location of the two organic semiconductors can be precisely controlled by using a 3D microchannel template. The 3D microchannels can offer wettable area on the side walls for the nucleation and growth of different organic semiconductors at the same horizontal position. Simultaneously, an external force applied on the template can induce solution to flow unidirectionally in the microchannels, ensuring continuous growth of the crystals to form uniaxially aligned arrays. Using this approach, we successfully fabricate two-component bilayer OSSC arrays, composed of n-type N,N’-bis(2phenylethyl)-perylene-3,4:9,10-tetracarboxylic diimide (BPE-PTCDI) microbelts (MBs) and ptype 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-PEN) MBs. The two-component, bilayer OSSC arrays possess ambipolar carrier transport properties with balanced hole and electron mobilities of 0.342 and 0.526 cm2 V-1 s-1, respectively, enabling the fabrication of complementary


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inverters based on the OSSC array. Our method provides a new pathway for the growth of bicomponent OSSC arrays for high-integration organic circuits.

2. RESULTS AND DISCUSSION

Figure 1. (a) Optical microscope image and (b) cross-sectional SEM image of 3D microchannel template (patterned SU-8 stripes on SiO2/Si substrate). (c) Water contact-angle measurements on the SiO2 surface and ODPA-treated SiO2 surface, respectively. (d) Optical microscope image of the meniscus in the channel. In-situ optical microscopy investigation of the growth process of (e) BPE-PTCDI and (f) TIPS-PEN crystals beside the lateral walls of SU-8 stripes. (g) Optical microscope image of the resultant bilayer BPE-PTCDI and TIPS-PEN crystals.

Figures 1a, b show the 3D microchannel template (patterned photoresist (SU-8) stripes on SiO2/Si substrate) with a width of 5 μm and a depth of ~1.2 μm fabricated by UV photolithography.


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Octadecylphosphonic acid (ODPA) was employed to tailor the surface polarity of the channels, as shown in Figure 1c. Surface energies of the channel regions were significantly reduced upon the ODPA modification, leading to a large surface-energy difference between SU-8 stripes and SiO2 channels. Table S1 in Supporting Information summarizes the test results of surface energies for both ODPA-modified SiO2 and SU-8 surface. The details of the measurements can be seen in Figure S1, Supporting Information. It is noted that the surface energy of ODPA-modified SiO2 (18.73 mN m-1) is much lower than that of SU-8 photoresist (55.25 mN m-1). As a result, when the BPE-PTCDI solution (1.33 mg mL-1) was dropped onto the heated 3D microchannel template (175 °C), a concave meniscus would be formed in the microchannels. Figure 1d displays a representative optical microscope image of the meniscus, whose front is always close to the lateral walls of the SU-8 stripes due to a large surface energy difference between the SU-8 stripes and the ODPA-modified SiO2 channels. Work of adhesion (W) measurement indicates the large W between BPE-PTCDI molecules and SU-8 photoresist(96.36 mN m-1, Figure S2, Supporting Information). Therefore, BPE-PTCDI molecules would be preferentially adsorbed at the lateral walls of SU-8 stripes, promoting the nucleation and crystallization of BPE-PTCDI molecules at these regions (Figure 1e). After full evaporation of solvent, BPE-PTCDI MBs would be formed clinging to the SU-8 stripes. When TIPS-PEN solution (4 mg mL-1) was dropped onto the 3D microchannel template, where BPE-PDCTI crystals had already been formed besides the SU-8 stripes, concave meniscus was also observed within the 3D channels (Figure 1f). Note that the surface energy of the pre-formed BPE-PTCDI crystals (43.27 mN m-1) is lower than that of the SU-8 stripes, and the W between TIPS-PEN and SU-8 (81.44 mN m-1) is larger than that between TIPS-PEN and BPEPTCDI (75.32 mN m-1). Therefore, the TIPS-PEN molecules would still nucleate and grow next to the lateral walls of the SU-8 stripes, forming two-component composite structure of bilayer


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BPE-PTCDI/TIPS-PEN crystal arrays (Figure 1g). Therefore, by taking advantage of the lateral walls of SU-8 stripes with definite thickness in the 3D microchannels, wettable regions at the vertical side of SU-8 stripes can be utilized to achieve nucleation and growth of different organic semiconductors at the same horizontal position.

Figure 2. (a) Schematic illustration of the fabrication process for n-type BPE-PTCDI MB array. (b) Optical microscope image of the obtained BPE-PTCDI MB array. (c) Magnified SEM image and (d) corresponding cross-sectional SEM image of the BPE-PTCDI MB. (e) Optical microscope image of p-n bilayer MB arrays. (f) Magnified SEM image and (g) corresponding cross-sectional


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SEM image of the p-n bilayer MB. (h) Topography and surface potential image of p-n bilayer MB measured by KPFM.

By using this 3D microchannel template, we further implement two-step dip-coating process to obtain two-component OSSC arrays via the 3DWSA method. The dip-coating method offers a stable and directional external force during coating process, which can guide unidirectional transport of solution in the microchannels, ensuring aligned growth of the OSSCs. First, n-type BPE-PTCDI MB array was fabricated via the dip-coating process with a pulling speed of 100 μm/s at 175 °C (Figure 2a,b). Highly aligned MB array with nearly zero misalignment angle is observed throughout the substrate. The magnified scanning electron microscope (SEM) image, Figure 2c, indicates that the BPE-PTCDI MB has a smooth upper surface and a width of ~1.5 μm. The crosssectional SEM image also clearly manifests that the BPE-PTCDI MB is clinging to the lateral wall of SU-8 stripe (Figure 2d). Statistical analysis on the BPE-PTCDI MBs at different positions discloses a size variation of less than 20% for the MBs with a width of 1.5 ± 0.3 μm and a thickness of 200 ± 40 nm (Figure S3, Supporting Information). To achieve two-component integration of pand n-type OSSC arrays on a single substrate, the 3D microchannel template, along with the predeposited BPE-PTCDI MB array, was subsequently immersed into the p-type TIPS-PEN solution at room temperature, and then pulled out at a controlled speed of 20 μm/s. Owing to the high surface energy feature of the lateral walls of SU-8 stripes, TIPS-PEN molecules would also preferentially nucleate and grow along the lateral walls of SU-8 stripes (on the top of n-type MBs), eventually forming large-area p-n bilayer MB array. Figure 2e is a bright-field microscope image of the resulting p-n bilayer MB array, showing the growth direction of the MBs is parallel to the SU-8 stripes. The p-n MB possesses smooth surface and well-defined structure, revealing the high


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crystallinity nature of two types of semiconductors (Figure 2f). In addition, the cross-sectional SEM image, Figure 2g, clearly reveals that the two types of MBs partly overlap each other with TIPS-PEN MB on the top of BPE-PTCDI MB. However, it is noteworthy that both TIPS-PEN and BPE-PTCDI MBs are located next to the lateral wall of SU-8 stripe. The TIPS-PEN and BPEPTCDI MBs have a width of ≈1.0 and 1.5 μm, respectively, while the p-n MBs possess a continuous length up to hundreds of micrometers (Figure S4, Supporting Information). The AFM topography image in Figure 2h shows that the total thickness of the p-n bilayer MB arrays was ≈500 nm, consisting of ≈350 nm of TIPS-PEN MB and ≈150 nm of BPE-PTCDI MB. In addition, Kelvin probe force microscope (KPFM) measurements yielded the work functions of the BPEPTCDI and TIPS-PEN MBs to be 4.89 and 4.66 eV, respectively, which are consistent with the previous reports.21,22 The surface potential difference (SPD) between the TIPS-PEN MB and BPEPTCDI MB is deduced to be ≈230 mV. Crystal structures of the two-component bilayer MB arrays were systematically investigated. Figure 3a show the typical cross-polarized microscope images of the p-n bilayer MB array under different polarization angles. When the p-n bilayer MB array is at 45° rotation angle with respect to the axis of cross polarizers, both p- and n-type crystals exhibit a bright light emission simultaneously (Figure 3a, left). However, when the p-n bilayer MB array is parallel to the axis of cross-polarizers, light emission of both p- and n-type MBs is completely vanished (Figure 3a, right). The angle-dependent emission intensity shows a fourfold symmetry under different rotation angles (Figure 3b), indicating the ordered crystallographic alignment of both p- and n-type MBs. 2D grazing incidence X-ray diffraction (2D-GIXRD) was used to further evaluate the crystal structures of TIPS-PEN and BPE-PTCDI MBs in the two-component composite structures, as shown in Figure 3c. The bilayer TIPS-PEN/BPE-PTCDI MBs array produce a series of diffraction


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spots at out-of-plane (qz), which can be indexed as (001), (002), and (003) plane diffractions for TIPS-PEN crystals, and (002) and (003) plane diffractions for BPE-PTCDI crystals (Figure 3d). These results are consistent with the X-ray diffraction (XRD) detections (Figure S5, Supporting

Figure 3. (a) Cross-polarized microscope images of the bilayer p-n MB array acquired under different polarization angles of 45° and 0°, respectively. (b) Angle-dependent polarized intensity of the bilayer p-n MB array. (c) 2D-GIXRD pattern and (d) One-dimensional out-of-plane profile of the bilayer p-n MB array. (e) Low-resolution TEM image. (f) Cross-sectional TEM image of the p-n junction MB array. (g) SAED pattern from the p-n overlap region. (h) High-resolution AFM image of the p-type TIPS-PEN MB at upper layer.


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Information). Moreover, clear (01L) and (02L) diffraction families of TIPS-PEN crystals and (11L) diffraction families of BPE-PTCDI crystals could be observed along qz for a given qxy (Figure 3c), and no additional diffraction spots appear, demonstrating the presence of both p- and n-type organic crystals without any mixed phase. The distinct high-order diffraction spots also suggest that both the TIPS-PEN and BPE-PTCDI MBs have high crystallinity as well as highly ordered molecule orientation. Further structural analysis was implemented by using transmission electron microscopy (TEM). The TIPS-PEN/BPE-PTCDI p-n MB with smooth boundary and uniform size can be clearly observed in the TEM image (Figure 3e). From the cross-sectional TEM image (Figure 3f), we also found that the p-type and n-type MB form vertically stacked structure with a very flat and clear interface. Selected-area electron diffraction (SAED) pattern collected from the overlap region shows two sets of diffraction spots (Figure 3g, white circles for TIPS-PEN and red circles for BPE-PTCDI), indicating the single-crystal nature of the p-n MB. In contrast, SAED pattern obtained from other region displays a single set of diffraction pattern, which is consistent with the previously reported BPE-PTCDI single crystals (Figure S6, Supporting information). According to the SAED pattern and TEM image, zone axes [100] and [010] can be determined to be parallel to the long axises of TIPS-PEN MB and BPE-PTCDI MB, respectively. Further structural information of the upper TIPS-PEN MB was gained by high-resolution AFM. A typical herringbone stacking of TIPS-PEN molecules is observed in the MB (Figure 3h), which can give the large intermolecular overlaps and strong transfer integrals with efficient charge transport.24 We note that three key conditions have to be satisfied in order to generate the p-n bilayer MB arrays. Frist, the 3D microchannel template plays an important role in achieving the growth of pn bilayer MB array. Without the 3D microchannel template, only disordered organic crystals can


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be grown on the substrate, and the TIPS-PEN cannot selectively crystallize on the pre-formed BPE-PTCDI crystals (Figure S7, Supporting Information). Second, an appropriate SU-8 thickness is needed to control the crystal growth. When the thickness of SU-8 stripes is reduced to be ≈450 nm, solution would overflow from the microchannels. As a result, many crystals will be formed on the top surface of SU-8 stripes, instead of growing besides the stripes (Figure S8, Supporting Information). Thirdly, the large surface energy difference also plays the dominating role in obtaining the p-n bilayer MB array. When a low surface energy Cytop (10.15 mN m-1) was used to fabricate the stripes (Table S1, Supporting Information), the W between the Cytop and BPEPTCDI or TIPS-PEN would be remarkably reduced. The growth of organic crystals was no longer restricted at the lateral walls of the stripes, but extended to the middle of the channel regions (Figure S9, Supporting Information). Therefore, no bilayer structured organic crystals can be observed. This is due to the fact that the meniscus front is hard to be pinned by the lateral walls of Cytop stripes with lower surface energy. On the other hand, if the SiO2 substrate was not modified with ODPA, the W between BPE-PTCDI and SiO2 (88.35 mN m-1) was close to that between BPEPTCDI and SU-8 (96.36 mN m-1). BPE-PTCDI molecules could also be adsorbed on the SiO2 surface, thus there would exist a gap between the resulting BPE-PTCDI MB and SU-8 stripe (Figure S10, Supporting Information). Then, the TIPS-PEN crystals tended to preferentially occupy the gaps, forming a faulty bilayer structure. Notably, the present 3DWSA method can be readily extended to grow other small-molecule organic p-n bilayer systems (Figure S11, Supporting Information), such as 2,8-difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene (dif-TES-ADT)/N,N’-ditridecyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-C8) and TIPSPEN/N,N’-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C13) p-n bilayer MB arrays. In addition, sizes of TIPS-PEN MBs on the top of BPE-PTCDI MBs could be tuned by


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varying the concentration of TIPS-PEN solution. In control experiments, TIPS-PEN solution with different concentrations from 2 to 6 mg mL-1 was used. As the TIPS-PEN solution concentration increase, the average width of TIPS-PEN MB increases accordingly from 0.33 to 1.3 μm (Figure S12, Supporting Information).

Figure 4. (a) CFD simulation result of the formation of meniscus in the ODPA-treated channel. (b) Mass distribution of DCB vapor around the meniscus edge. (c) Streamline representation of simulated fluid flow in the meniscus. The arrows indicate the flow directions. (d) Schematic illustration of the BPE-PTCDI MB growth at the lateral side of SU-8 stripe. (e) CFD simulation result of the solution trailing on the top of pre-deposited BPE-PTCDI MB array. (f) Schematic illustration of the growth of TIPS-PEN MB on the top of the pre-deposited BPE-PTCDI MB.

To gain insight into the formation mechanism of p-n bilayer MB structure, we performed computational fluid dynamics (CFD) simulations on the system. When the 3D microchannel


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template was immersed into the BPE-PTCDI/dichlorobenzene (DCB) solution, the solution would move up due to surface tension effect and capillary force. However, it would soon split due to the large surface energy difference between SU-8 stripes and ODPA-treated SiO2 channels, yielding a meniscus between two adjacent SU-8 stripes (Figure 4a). Because a little solution would rise and the SU-8 stripes have a certain height, the meniscus front would only partially cover the lateral walls of the SU-8 stripes (Figure S13, Supporting Information). Since crystal nucleation and growth preferentially take place at the meniscus front during solvent evaporation,7 we further simulate the evaporation of the meniscus. Simulation shows that mass fraction of DCB vapor near the liquid-air interface at meniscus is greater than that at the remaining parts (Figure 4b), suggesting that solvent evaporation is faster at the interface. The faster solvent evaporation would trigger the outward convective flow toward the meniscus front to replenish the evaporative loss of solvent. The simulated fluid flow during the evaporation process, Figure 4c, further validates this point. The solution near the edge of meniscus always flows from the liquid bulk to the meniscus front. Meanwhile, the unidirectional flow would transport organic molecules toward the meniscus front. This would yield a supersaturated phase containing continuous aggregated solutes, and thus finally caused the nucleation and growth of organic crystals at the meniscus front. Because the meniscus was always pinned at the lateral sides of the SU-8 stripes, OSSCs thus deposited along the lateral sides of the SU-8 stripes (Figure 4d). When the 3D microchannel template, along with the pre-deposited BPE-PTCDI MB array, was immersed into the TIPS-PEN/toluene solution, surface tension could also drive upward movement of the solution along the SU-8 stripes. Owing to the lyophobic nature of pre-deposited BPE-PTCDI MBs, the TIPS-PEN solution around them would be drained away. But the solution on the top of the BPE-PTCDI MBs would still be pinned by the lateral sides of the SU-8 stripes, forming a narrow solution trailing (Figure 4e). Since the


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width of the solution trailing was much smaller than that of the solution bulk, a higher evaporation velocity was produced at the trailing. Therefore, the solution trailing decided the crystallization position of TIPS-PEN MB (Figure 4f), leading to the generation of p-n bilayer MBs eventually.

Figure 5. (a) Schematic illustration of the ambipolar OFET based on the bilayer p-n MB array. (b, c) Optical microscope and magnified SEM image of an individual OFET based on the bilayer p-n MB array. (d, e) Typical transfer and output characteristics of the OFET in p-channel operation mode under negative drain bias of -50 V. (f) Histogram of hole mobilities obtained from the analysis of 40 devices measured in air at room temperature. (g, h) Typical transfer and output characteristics of the OFET in n-channel operation mode under positive drain bias of 30 V. (i)


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Histogram of electron mobilities obtained from the analysis of 40 devices measured in air at room temperature.

To assess the charge transport properties of the p-n bilayer OSSC arrays, bottom-gate and topcontact organic field-effect transistors (OFETs) were fabricated (Figure 5a-c). The effective channel width (W) for p-channel and n-channel was determined to be 28 and 33.6 µm, respectively, by summing the width of the p- and n-type MBs in the device channel. Figure 5d,g depict the typical transfer characteristics of the devices in p-channel and n-channel operation modes, respectively, which exhibit classic V-shaped curves, confirming the ambipolar behavior of the transistors. Notably, the ambipolar OFETs possess a hole mobility (μh) of 0.526 cm2 V-1 s-1 with an on-off current ratio of ~103 and an electron mobility (μe) of 0.342 cm2 V-1 s-1 with on-off current ratio of ~102. These mobility values represent the highest reported mobilities among organic crystal-based ambipolar OFETs (Table S2, Supporting Information).13,23,25-30 Figure 5e, h also display the output characteristics of the ambipolar OFET in p-channel and n-channel operation modes, respectively. In p-channel operation mode, the output characteristics exhibit a superlinear increase of current at high positive gate voltage due to the injection of charge in a channel dominated by electrons. Similarly, in n-channel operation mode the superlinear regime occurs at low gate voltages, because of the injection of holes. It is noted that the transfer and output curves are not very smooth in the n-channel operation mode. This is possibly attributed to the fact that ntype organic semiconductors generally are ambient instable.23,31 Histograms of hole and electron mobilities analyzed from 40 devices based on the bilayer p-n MB arrays are shown in Figure 5f and 5i, respectively, revealing an average μh of 0.45 ± 0.2 cm2 V-1 s-1 and an average μe of 0.24 ± 0.1 cm2 V-1 s-1. For comparison, we also studied the charge transport properties of pure TIPS-PEN


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and BPE-PTCDI MB arrays (Figures S14-18, Supporting Information). OFETs based on TIPSPEN and BPE-PTCDI MB arrays exhibit an average μh and μe of 0.56 ± 0.09 and 0.38 ± 0.14 cm2 V-1 s-1, respectively. The mobility values of the p-n MB arrays are comparable to but slightly lower than the pure organic crystals, possibly due to the interfacial issues of TIPS-PEN/BPE-PTCDI pn MBs.32 Besides individual OFETs, we also exploited the potential application of bilayer p-n MB arrays in complementary inverter (Figure S19, Supporting Information). It is noted the inverter exhibits a sharp switching of Vout, both in the first and third quadrants, with nearly the same voltage gains of 17. This result unambiguously demonstrates the potential of the p-n OSSC arrays for highperformance organic circuit.

3. CONCLUSIONS In conclusion, two-component OSSCs with a bilayer composite structure, composed of p-type TIPS-PEN and n-type BPE-PTCDI MB arrays, have been successfully fabricated via a 3DWSA method. In this approach, the 3D microchannels offer wettable regions on the lateral walls of photoresist stripes in the vertical direction, which allows the nucleation and growth of both p- and n-type organic crystals at the same horizontal position. Meanwhile, the dip-coating process provides a directional external force to guide orientated growth of p- and n-type organic crystals, achieving the two-component, bilayer p-n OSSC arrays eventually. The two-component OSSC arrays possess bipolar carrier transport properties with balanced hole and electron mobilities of 0.342 and 0.526 cm2 V-1 s-1, respectively, which are among the highest values for OSSC-based ambipolar OFETs. Complementary inverters constructed from the two-component OSSC arrays also exhibit a high gain value of 17. The simple yet efficient solution-processing approach for


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large-area fabrication of multi-component composite OSSC arrays paves the way toward highperformance integrated organic circuits.

4. METHODS Materials. TIPS-PEN, dif-TES-ADT, BPE-PTCDI, PTCDI-C13, PTCDI-C8 and ODPA were purchased from Sigma-Aldrich and used without further purification. Negative photoresist (SU-8, Gersteltec Sarl, 1040) was used in photolithography patterning process. Preparation of solutions. Fixed volume of DCB (2 mL) was firstly heated to 175 °C. Then, 2.66 mg BPE-PTCDI was added in the heated DCB solvent, followed by stirring. After that, the solution was heated for 15 min in order to guarantee complete dissolution of BPE-PTCDI in the DCB. Because BPE-PTCDI has a very limited solubility in DCB at room temperature, a higher temperature of 175 °C was applied to dissolve more BPE-PTCDI molecules. DCB was used as the solvent for BPE-PTCDI due to its high boiling point (~181 °C). The TIPS-PEN solution was prepared by dissolving 8 mg TIPS-PEN in 2 mL toluene at room temperature. Toluene was used as a solvent for TIPS-PEN because it was an orthogonal solvent for the BPE-PTCDI. Fabrication of photoresist stripes on SiO2/Si substrates. SiO2 (300 nm)/Si substrates were first immersed into piranha solution (H2SO4:H2O2 = 3:1) for 12 h and cleaned by sonication in acetone and ethanol, respectively, for 10 min right before use. Then the SiO2/Si substrates were treated with oxygen plasma for 10 min at 300 W. Afterwards, UV Photolithography was performed to generate periodic photoresist stripes on the substrates by using negative photoresist (SU-8) on a UV aligner (SUSS-MJB4). ODPA was used to treat the substrates with the following procedure: The substrate was immersed in a 200 µL solution of ODPA in 20 mL toluene at 90 °C for 12 h. Then the substrates were rinsed with toluene, acetone, alcohol, and dried with a steam of nitrogen.


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Fabrication of bilayer p-n MB arrays. Firstly, 3D microchannel template was immersed vertically into the hot BPE-PTCDI solution (175 °C) and then was pulled out at an optimized speed of 100 μm s-1. Because the temperature of the BPE-PTCDI solution was close to the boiling point of DCB solvent, the DCB would quickly evaporate and BPE-PTCDI molecules would precipitate out, forming BPE-PTCDI MB array along the lateral walls of SU-8 stripes. Subsequently, the 3D microchannel template, along with the pre-deposited BPE-PTCDI MB array, was immersed into the TIPS-PEN solution at room temperature, and then pulled out at a controlled speed of 20 μm s-1, resulting in the formation of bilayer TIPS-PEN and BPE-PTCDI p-n MB array. Characterizations of bilayer p-n MB arrays. Morphologies and structures of the product were characterized by cross-polarized optical microscope (Olympus, BX51) SEM (FEI Quanta 200FEG), and TEM (FEI Tecnai G2 F20). AFM images were taken by a Multi-Mode V AFM (Veeco). XRD profiles were collected by a PANalytical X’Pert PRO X-ray diffractometer using Cu Ka1 radiation (1.541 Å) operating at 40 kV and 40 mA. The 2D-GIXRD measurements were performed on the BL14B1 beam line (energy = 10 keV) at the Shanghai Synchrotron Radiation Facility. The sample-to-detector distance (SDD) was 323 mm, and the diffraction patterns were mostly acquired for 10 s with a two-dimensional charge-coupled device (2DCCD) detector. The data were distortion-corrected (theta-dependent image distortion introduced by planar detector surface) before performing quantitative analysis on the images. Numerical integration of the diffraction peak areas was performed with the software Fit2D. Fluid dynamics simulations. Commercial software package ANSYS DesignModeler was used for the geometry construction, and Meshing was used for mesh generation, while Fluent was used for calculation and CFD-Post for data visualization. The surface tensions of DCB and toluene were set as 35.7 mN m-1 and 28.8 mN m-1, respectively. The contact angles were 20° and 5° for the


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ODPA-modified SiO2 and SU-8 walls, respectively. The heat and mass transfer were simulated by using user-defined functions (UDFs). Device construction and characterizations. OFETs based on the bilayer p-n MB arrays were directly constructed on the 3D microchannel template with the assistance of a shadow mask that consisted of aluminum wires with 25 μm diameter. The ODPA-modified SiO2 (300 nm) was used as gate dielectric layer in the OFETs and its capacitance per unit area was measured to be 10.5 nF cm-2 (Figure S19, Supporting Information). Single-layer electrode of Au (70 nm) was evaporated via a high-vacuum thermal evaporation system (Kurt J. Lesker, PVD 75). All the electrical measurements were conducted under ambient conditions at room temperature with a semiconductor characterization system (Keithley, 4200-SCS) on a probe station (M150, Cascade). The mobility was extracted from the saturation region by using the equation of 2 2𝐿 ∂ 𝐼ds 𝜇sat = ( ) 𝑊𝐶i ∂𝑉g

where μsat is the saturation mobility and Ci is the dielectric capacitance per unit area.

ASSOCIATED CONTENT Supporting Information. Contact angles, surface energies, performance comparison, statistical data, SEM, XRD, TEM characterization, control experiment, universality of this method, and device dates. The following files are available free of charge.

AUTHOR INFORMATION Corresponding Author *Email: [email protected]


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Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. #These authors contributed equally.

ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China (Grant Nos. 51672180, 51622306, 51821002, 91833303, and 21673151), Natural Science Foundation of Jiangsu Province of China (BK20180845), Qing Lan Project, 111 project, Collaborative Innovation Center of Suzhou Nano Science and Technology (Nano-CIC), and the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD). The authors thank Beamline BL14B1 (Shanghai Synchrotron Radiation Facility) for providing the beam time. REFERENCES (1)

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Precise Positioning of Organic Semiconductor Single Crystals with

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