Organic Heterojunctions Formed by Interfacing Two Single Crystals

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Article Cite This: J. Am. Chem. Soc. 2019, 141, 10007−10015

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Organic Heterojunctions Formed by Interfacing Two Single Crystals from a Mixed Solution Huanbin Li,†,‡ Jiake Wu,†,‡ Kohtaro Takahashi,§ Jie Ren,†,‡ Ruihan Wu,†,‡ Hongyi Cai,† Jieru Wang,‡ Huolin L. Xin,∥,¶ Qian Miao,⊥ Hiroko Yamada,§ Hongzheng Chen,†,‡ and Hanying Li*,†,‡

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MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, China ‡ State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027, China § Division of Materials Science, Graduate School of Science and Technology, Nara Institute of Science and Technology, Ikoma, Nara 630-0192, Japan ∥ Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, United States ⊥ Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China S Supporting Information *

ABSTRACT: Organic heterojunctions are widely used in organic electronics and they are composed of semiconductors interfaced together. Good ordering in the molecular packing inside the heterojunctions is highly desired but it is still challenging to interface organic single crystals to form singlecrystalline heterojunctions. Here, we describe how organic heterojunctions are formed by interfacing two single crystals from a droplet of a mixed solution containing two semiconductors. Based on crystallization of six organic semiconductors from a droplet on a substrate, two distinct crystallization mechanisms have been recognized in the sense that crystals form at either the top interface between the air and solution or the bottom interface between the substrate and solution. The preference for one interface rather than the other depends on the semiconductor−substrate pair and, for a given semiconductor, it can be switched by changing the substrate, suggesting that the preference is associated with the semiconductor−substrate molecular interaction. Furthermore, simultaneous crystallization of two semiconductors at two different interfaces to reduce their mutual disturbance results in the formation of bilayer single crystals interfaced together for organic heterojunctions. These single-crystalline heterojunctions exhibit ambipolar charge transport in field-effect transistors, with the highest electron mobility of 1.90 cm2 V−1 s−1 and the highest hole mobility of 1.02 cm2 V−1 s−1. Hence, by elucidating the interfacial crystallization events, this work should greatly harvest the solution-grown organic single-crystalline heterojunctions.

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growth,28,34 and a solution crystallization method.35−38 Alternatively, one-step crystallization has been recently developed as a facile approach to prepare bilayer crystals from a droplet of a mixed solution containing two semiconductor molecules.27,39 In this method, the key factor is to separate crystallization fronts of two crystals to attenuate mutual disturbance. The separation of growth fronts can be realized when the crystallization rates of the two semiconductors are varied, as shown in the limited reported cases.29,39,40 Expanding the variety of single-crystalline heterojunctions relies on the elucidation of the crystallization mechanism by which two types of crystals grow simultaneously from one droplet. Considering that a droplet on a substrate presents two interfaces (Figure 1a) and crystals tend to

INTRODUCTION Organic heterojunctions are basic elements used in many sophisticated organic optoelectronic devices such as light emitting transistors,1−4 solar cells,5−7 light emitting diodes,8−11 memory devices,12−14 complementary circuits15−18 and sensors.19−21 Similar to the devices based on a singlecomponent semiconductor, heterojunction-based devices also require high charge mobility and long-range ordering in the molecular packing within the semiconductors is desired. Although single-crystalline materials are widely used for organic electronics especially for transistors,22−26 interfacing single crystals together to form single-crystalline heterojunctions is still challenging.27 Various attempts have been made to achieve organic single-crystalline heterojunctions and corresponding electronic devices.27−31 Progress had been made via interfacing two types of single crystals grown in two different steps using a lamination technique,32,33 epitaxial vapor © 2019 American Chemical Society

Received: April 9, 2019 Published: June 4, 2019 10007

DOI: 10.1021/jacs.9b03819 J. Am. Chem. Soc. 2019, 141, 10007−10015

Journal of the American Chemical Society

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Article

RESULTS AND DISCUSSION

Crystallization of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-PEN),42 a typical organic semiconductor, from a droplet is first investigated. As shown in Figure 1a, a droplet on a substrate presents a top interface between the air and solution as well as a bottom interface between the substrate and solution. In order to differentiate the crystallization events at the bottom interface from the top, Ag nanowires were predeposited on the substrate and the subsequent crystallization of TIPS-PEN was imaged to show the mutual interaction between the TIPS-PEN crystal and the nanowires. The thickness of crystals (25 nm in Figure 1f) is comparable to Ag nanowires (20−40 nm) so that the crystallization on the bottom interface would be impeded by obstacles while top interface crystallization would not be dramatically affected. Distinct situations were imaged for the crystallization on two different substrates covered by divinyltetramethyldisiloxanebis(benzocyclobutene) (BCB)43 or cross-linked poly(methyl methacrylate) (c-PMMA).44 In the case of BCB substrates, TIPS-PEN crystal maintains its typical ribbon-like shape45 even as it intersects several Ag nanowires (Figure 1b). As shown in the side view image of scanning electron microscope (SEM), Ag nanowire is buried under a single crystal and there are small cavities between nanowires and crystals (Figure 1c,d). In sharp contrast, crystals grown on the c-PMMA substrate lose their shapes, as shown in Figure 1e, because the crystallization path is obviously impeded by the Ag nanowires. Furthermore, atomic force microscopy (AFM) imaging indicates that the Ag nanowires on the substrate block the crystallization fronts (Figure 1f,g). Based on the observed variations, two single crystal formation mechanisms are proposed to explain the discrepancies between the cases of TIPS-PEN on two substrates. (1) Top interface crystallization: in the case of BCB substrates, TIPS-PEN single crystals first form at the top interface. With solvent evaporating and droplet receding, crystal ribbons begin to fall on top of Ag nanowires and slightly deform due to the flexibility of organic crystals.46−48 Because the crystal growth fronts locate at the top interface, the crystallization is not significantly disturbed by the Ag nanowires that are on the bottom interface. Thus, the crystals exhibit the well-defined ribbon-shape and the nanowires are buried underneath (Figure 1b−d). This mechanism is similar to the previous observations of the TIPS-PEN in the presence of organic fibers.48 (2) Bottom interface crystallization: as for the c-PMMA substrate, TIPS-PEN single crystals grow at the bottom interface. When crystals come across with Ag nanowires, the mass transport for crystal growth would be impeded and thus the growing crystal has to make a detour. As a result, instead of being covered by single crystals, Ag nanowires block the crystallization fronts (Figure 1e−g). The morphology of single crystals does not maintain their typical ribbon shape after coming across with Ag nanowires. In both mechanisms, the location of the nucleation is not clear while that for the crystal growth process is distinctly different. The similar discrepancies between crystallization on the two different substrates also arise for other organic semiconductors like C60. On one hand, the growth of C60 single crystals is impeded by Ag nanowires on the BCB substrate (Figure 2a,b), indicating the bottom interface crystallization. On the other hand, the growing C60 single crystals are not blocked by the Ag nanowires on the c-PMMA substrate (Figure 2c,d), indicative

Figure 1. Schemes and morphologies of TIPS-PEN crystals grown on BCB and c-PMMA substrates with predeposited Ag nanowires, from mixed solvents of m-xylene and CCl4 under 25 °C (0.1 mg/mL). (a) A schematic representation of crystallization from a droplet where crystals form at either the top interface or the bottom one. Two types of coating layers on the crystallization substrate are also shown with their molecular structures presented. (b, c) SEM images of TIPS-PEN crystals (dark ribbons) with Ag nanowires (bright wires) on a BCB substrate, indicating the crystallization occurs at the top interface. (d) A scheme providing a visual guide for panel c. (e, f) SEM and AFM images of TIPS-PEN crystals with Ag nanowires on a c-PMMA substrate, indicating the crystallization occurs at the bottom interface. (g) A scheme providing a visual guide for panel f.

nucleate from an interface,41 we envision that the crystallization mechanism of the bilayer crystals should be associated with the interfacial crystallization events. In this work, we examine the crystallization of six organic semiconductors and provide insights into how to select pairs of semiconductors for the preparation of bilayer crystals for organic single-crystalline heterojunctions. 10008

DOI: 10.1021/jacs.9b03819 J. Am. Chem. Soc. 2019, 141, 10007−10015

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uniquely observed in spite of the changes of solvents (hexane or m-xylene), TIPS-PEN concentrations (0.1 or 0.4 mg/mL) and crystallization temperatures (30 or 80 °C) (Figure S1a−e). Similarly, for C60 crystals grown on BCB substrates, bottom interface crystallization dominates regardless of the change in C60 concentration (Figure S1f). The unchanged crystallization interface suggests that it is dictated by the pair of the crystallizing molecules and the substrates. Second, crystallization on BCB substrates depends on how extended the conjugated structure is. In total, we have examined the crystallization of six molecules on BCB substrates under the presence of Ag nanowires. AFM (Figure 3) and SEM (Table S1) imaging for the obtained crystals clearly shows that top interface crystallization occurs for the four molecules with one-dimensional conjugated structures, while bottom interface crystallization arises for the two molecules with more extended conjugated systems that interact with the BCB substrate more strongly (Table 1). On the basis of the above results, we conclude that crystallization from a droplet may locate at either the top or bottom interface and the location can be changed by using varied substrates. For both the interfaces, the examined six molecules crystallize into ribbon-like single crystals in the absence of the Ag nanowires (Figure S2). The single set of diffraction spots in the selected area electron diffraction (SAED) pattern confirms the single-crystallinity of the ribbons (Figure 4a−f), and the crystallographic structures are consistent with the previous reports (Table S2).42,52−56 Except for C60, the other five crystals are solvate free. The incorporation of the solvent molecules (m-xylene and CCl4)56 inside the C60 crystals improves the crystallization into a long ribbon shape.56,57 The above-mentioned two crystallization locations in one single droplet suggests a strategy to crystallize two different molecules simultaneously. We envision that if the two molecules crystallize from different locations, their crystallization fronts will be spatially separated and their mutual disturbance can be greatly attenuated. With the drying/receding of the droplet, two single crystals will first grow separately at top and bottom interfaces and then automatically laminate together to form single-crystalline heterojunctions. This hypothesis is further verified by the crystallization of two pairs of molecules. We first selected the pair of C60 and 2,8-difluoro-5,11bis(triethylsilylethynyl)anthradithiophene (diF-TES-ADT)54,58 because C60 crystals grow at the bottom interface and diF-TESADT at the top on the BCB substrate (Table 1). They were dissolved together to form a mixed solution, and crystallization from one droplet of this mixed solution was examined by optical microscopy (OM), AFM and SEM imaging, which all indicate the formation of bilayer crystals (Figure 5a−d). The OM image (Figure 5a) shows two ribbon-like crystals overlapping together, with one narrow and the other wide. And the fluorescent microscopy image for the same crystals identifies that the wide ones are diF-TES-ADT as they are fluorescent. Furthermore, the AFM image indicates the wide diF-TES-ADT crystals locate at the top layer. The relative position with a diF-TES-ADT top and C 60 bottom configuration is well consistent with the top and bottom interface crystallization for the diF-TES-ADT and C60, respectively (Table 1). Similarly, the pair of 6,13-bis(triisopropylsilylethynyl)-5,7,12,14-tetraazapentacene (TIPSTAP)59 and 5,15-bis(triisopropylsilylethynyl)tetrabenzoporphyrin (TIPS-BP)55,60 was examined and bilayer

Figure 2. Morphologies of C60 crystals grown on BCB and c-PMMA substrates with predeposited Ag nanowires, from mixed solvents of mxylene and CCl4 under 25 °C (0.1 mg/mL). (a, b) SEM and AFM images of C60 crystals with Ag nanowires on a BCB substrate, indicating the crystallization occurs at the bottom interface. (c, d) SEM and AFM images of C60 crystals with Ag nanowires on a cPMMA substrate, indicating the crystallization occurs at the top interface.

of the top interface crystallization. Interestingly, the correlation between the crystallization mechanisms and the substrates is inverted compared to the case of TIPS-PEN where top interface crystallization happens for BCB and bottom interface crystallization for c-PMMA. When BCB substrates are selected for crystallization, TIPS-PEN always grow at the top interface while C60 at the bottom, and this distinct difference is observed in a large area (Figure S1c,f). The driving force for crystallization originates from the supersaturation induced by solvent evaporation (Figure 1a). And near the top interface where solvent evaporates, the local supersaturation level should be higher than the bottom interface. As a result, top interface crystallization should dominate. Interestingly, in the cases of C60/BCB and TIPSPEN/c-PMMA pairs, bottom interface crystallization emerges. The preferential crystallization from the bottom interface is attributed to the molecular interaction between the crystallizing molecules and the substrates. Specifically, BCB is a polymer with plenty of aromatic rings allowing for strong π−π interaction with C60. Similarly, the cross-linked poly(methyl methacrylate) (PMMA) has lots of methyl groups and may favorably interact with the alkyl groups of the TIPS-PEN molecules. It has been previously reported that interaction between various substrates and organic semiconductors would change orientation and molecular packing in their crystals.49−51 Herein, we speculate that the molecular interaction leads to preferential crystal growth from the bottom interface, which is supported by the two pieces of evidence. First, the crystallization interface does not change with a variety of crystallization conditions. For TIPS-PEN crystals grown on BCB substrates, top interface crystallization was 10009

DOI: 10.1021/jacs.9b03819 J. Am. Chem. Soc. 2019, 141, 10007−10015

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crystals were obtained (Figure 5e). The AFM image shows that the narrow crystal ribbons locate at the bottom layer (Figure 5f) and Raman mapping (Figure S3) identifies that the narrow crystal ribbons are TIPS-BP. Again, the relative position between these two crystals is consistent with the top and bottom interface crystallization for the TIPS-TAP and TIPSBP, respectively (Table 1). Therefore, crystallizing at the two different interfaces will provide bilayer crystals. More importantly, the two crystals maintain their long-range ordering in the molecular packing, suggesting a strategy for single-crystalline heterojunctions. The SAED patterns of the two pairs of bilayer crystals both give two sets of single crystal patterns, indicative of the single-crystallinity (Figure 4g,h). For the bilayer crystals of C60 and diF-TES-ADT, the pattern (Figure 4g) is consistent with those for individual C60 (Figure 4a) and diF-TES-ADT (Figure 4e), as guided by the lines in Figure 4g. And for the bilayer crystals of TIPS-TAP and TIPSBP, the patterns exhibit the similar corresponding relation (Figure 4b,d,h). For comparison, crystallizing at the same interface was studied. According to Table 1, C60 and TIPS-BP both crystallize at the bottom interface. Interestingly, simultaneous crystallization of this pair also led to bilayer crystals (Figure S4). Similarly, 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT)61 and TIPS-TAP both crystallize at the top interface and bilayer crystals of this pair were obtained as well (Figure S5). However, as compared to the well-defined ribbons of the single-component crystals shown in Figure S2, these bilayer crystals exhibit much worse morphologies with zigzag patterns and voids in the crystals (Figure S4, S5). The poor morphology indicates mutual disturbance of the two growing crystals by blocking the mass transport path. The SAED patterns for the bilayer crystals are consistent with their constituent crystals (Figure 4i,j). But spots in addition to the two sets of single crystal patterns are shown for the pair of C8-BTBT and TIPS-TAP (Figure 4j, circles), indicative of the polycrystallinity. The above comparison suggests that simultaneous crystallization of two molecules at two different interfaces is a preferential strategy to prepare bilayer single crystals for organic heterojunctions. Based on Table 1, the six semiconductors include both typical p- and n-type materials. A pair of p- and n-type semiconductors forms heterojunctions and their charge transport properties are examined. Field-effect transistors (FETs) were fabricated based on heterojunctions with Au as the source and drain electrodes and tested in the saturation regime under N2 atmosphere. For the heterojunctions made from the pair of TIPS-TAP and TIPS-BP that crystallize from the different interfaces, FETs exhibit average electron and hole mobilities of 0.79 ± 0.36 and 0.58 ± 0.22 cm2 V−1 s−1 for 52 devices, respectively. The highest electron mobility is 1.90 cm2 V−1 s−1 and the highest hole mobility is 1.02 cm2 V−1 s−1 (Figure 6a−f). As the ribbon crystals have gaps in between and do not cover the whole area of conductive channel, the effective mobility of the material should be slightly higher. The relatively balanced electron and hole mobilities promise the inverting functionality of the complementary inverters fabricated from this heterojunction. For the inverter, a sharp conversion near 30 V and a gain up to 70 were achieved, with the supply voltage of 60 V (Figure 6g,h). In addition to the pair of TIPS-TAP and TIPS-BP, heterojunctions of another pair that crystallize from the different interfaces show similar ambipolar charge transport. For example, C60 and diF-TES-

Figure 3. Morphologies of organic crystals grown on BCB substrates with predeposited Ag nanowires, sorted by top or bottom crystallization mechanism. (a−d) AFM images of organic crystals (TIPS-PEN, C8-BTBT, diF-TES-ADT and TIPS-TAP, respectively) with Ag nanowires on a BCB substrate, indicating that these crystals formed at the top interface. (e, f) AFM images of organic crystals (TIPS-BP and C60) with Ag nanowires on a BCB substrate, showing these crystals formed at the bottom interface. The molecular structures of the crystallizing organic semiconductors are shown as insets.

Table 1. Summary of Crystallization Mechanisms on BCB Substrates for Organic Single-Crystalline Semiconductors Bottom Interface Crystallization Typical ntype Typical ptype

Top Interface Crystallization

C60

TIPS-TAP

TIPS-BP

TIPS-PEN, diF-TES-ADT, C8BTBT

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Figure 4. SAED patterns of single-component crystals and corresponding bilayer crystals. (a−f) SAED patterns of the single-component crystals (C60, TIPS-TAP, TIPS-PEN, TIPS-BP, diF-TES-ADT and C8-BTBT, respectively) showing the single-crystallinity. (g−j) SAED patterns of the bilayer crystals (C60 and diF-TES-ADT, TIPS-TAP and TIPS-BP, C60 and TIPS-BP, TIPS-TAP and C8-BTBT, respectively). The lines provide the visual guide for the two patterns and the white circles in panel j highlight the additional spots.

while C60 and TIPS-BP at the bottom. Interestingly, the crystallization interface of TIPS-PEN and C60 switches as the substrate coating changes to c-PMMA. The preferential crystallization at one interface rather than the other depends on the semiconductor−substrate molecular interaction. According to these two distinct interfacial crystallization mechanisms, we have developed a facile one-step solution method to grow organic single-crystalline heterojunctions. Essentially, the top interface allows for crystallization of one semiconductor, while the bottom interface for the other. The two growing crystals are interfaced together to form singlecrystalline heterojunctions as the droplet recedes. The obtained single-crystalline heterojunctions exhibited ambipolar charge transport with electron mobility up to 1.90 cm2 V−1 s−1 and the highest hole mobility of 1.02 cm2 V−1 s−1. In addition, complementary inverters based on the heterojunctions have been achieved. By showing the two distinct interfacial crystallization events and their relevance to interface single crystals, this work has the potential to lead to design criteria for solution-grown organic single-crystalline heterojunctions.

ADT heterojunctions have the highest electron mobility of 1.55 cm2 V−1 s−1 and the highest hole mobility of 0.60 cm2 V−1 s−1 (Figure S6). As far as we know, these FET mobilities are among the highest values in organic single-crystalline heterojunctions.29,38 We attribute the high mobilities of these heterojunctions to the maintenance of the single crystallinity in both p- and n-type materials. In addition, the electron mobility in heterojunctions is much higher than the solution-grown crystals of C60 and its derivative in the reported cases.57,62,63 One possible reason for the improvement of mobility is the smooth interface64 between single crystals and BCB dielectric, which has been reported to be one of the most suitable dielectric materials for n-channel FETs.43 In comparison, the heterojunctions with crystals grown at the same interfaces exhibit much lower mobilities. For FETs based on the heterojunctions of TIPS-TAP and C8-BTBT that both crystallize from the top interface, we achieved the average electron and hole mobilities of 0.27 ± 0.16 and (1.84 ± 0.99) × 10−2 cm2 V−1 s−1, respectively (Figure S7). The inferior mobilities are consistent with the poor morphology (Figure S5).

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CONCLUSION In summary, we have examined the crystallization of six organic semiconductors from a droplet on a BCB-coated substrate, including C60, TIPS-TAP, TIPS-PEN, TIPS-BP, diFTES-ADT and C8-BTBT. And we have demonstrated that the droplet allows crystallization at either the top interface or the bottom interface, as shown in Figure 1a. TIPS-PEN, diF-TESADT, TIPS-TAP and C8-BTBT crystallize at the top interface,

EXPERIMENTAL SECTION

TIPS-PEN, C60 and diF-TES-ADT were purchased from SigmaAldrich, Alfa Aesar and Lumtec, respectively, and used without further purification. TIPS-BP, TIPS-TAP and C8-BTBT were prepared following the reported procedures.55,59,61 Single crystals were grown using the droplet-pinned crystallization (DPC) method56 on BCB (Dow Chemicals) or c-PMMA covered highly doped silicon substrates with 300 nm SiO2. The BCB layer was spin-coated from a mesitylene (Acros) solution (V BCB:V mesitylene = 1:30) and subsequently thermally cross-linked on a hot plate in a N2 glovebox.43 10011

DOI: 10.1021/jacs.9b03819 J. Am. Chem. Soc. 2019, 141, 10007−10015

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Figure 5. Morphologies of the bilayer crystals for the pair of C60 and diF-TES-ADT (a−d) as well as the pair of TIPS-TAP and TIPS-BP (e, f). (a, b) OM and fluorescent (λex = 532 nm) microscope images of the bilayer C60 and diF-TES-ADT crystals. (c) An AFM image of the bilayer structure. (d) A SEM image (side view) showing the bilayer structure, with a scheme providing a visual guide. (e) An OM image of the bilayer TIPS-TAP and TIPS-BP crystals, showing the bilayer structure with wide ribbons crystals (yellow) and narrow ones (blue). (f) An AFM image of bilayer structure showing the top layer as wide crystals and the bottom layers as narrow crystals.

Figure 6. FET and inverter characteristics of TIPS-TAP and TIPS-BP heterojunctions. (a, b) Typical transfer characteristics of the FETs based on TIPS-TAP and TIPS-BP heterojunctions under n-channel and p-channel operation modes (the gate voltage ranges for calculating the electron and hole mobilities are presented with red lines). (c, d) Typical output characteristics of the FETs based on TIPS-TAP and TIPS-BP heterojunctions under n-channel and pchannel operation modes. Inset: A schematic representation of the FET configuration of heterojunctions, the real channel length and width were measured to calculate the mobility. (e, f) Histograms of the electron and hole mobilities of 52 FETs. (g, h) The switching characteristic and corresponding gain of an inverter. Inset: the inverter configuration.

PMMA (Mw = 120k, Sigma-Aldrich) was spin-coated in n-butyl acetate solution (10 mg/mL, Sigma-Aldrich) at 4000 rpm with 10 μL/mL 1,6-bis(trichlorosilyl)hexane (Sigma-Aldrich) and subsequently thermally cross-linked on a 100 °C hot plate in a N2 glovebox for 1 h.44 If not specified, the substrates used for crystal growth were BCB covered silicon substrates. For single crystals grown with predeposited Ag nanowires (Suzhou Nord), Ag nanowires/ ethanol solution (1 mg/mL, Aladin) was first spin-coated on BCB or c-PMMA covered silicon substrates at 2000 rpm for 30s and then heated at 80 °C for 0.5 h. For crystallization of single crystals, organic semiconductor solution (15 μL, 0.1 mg/mL unless specified) was dropped on BCB or c-PMMA covered silicon substrates (1 cm × 1 cm) with a small piece of silicon wafer (0.4 cm × 0.4 cm, pinner) to pin the solution droplet. The substrate was then placed on a Teflon slide inside a Petri dish (35 mm × 10 mm) sealed with parafilm, which allows solvent to evaporate on a hot plate under selected temperature (25, 30 or 80 °C). TIPS-PEN was grown in hexane (TCI, 25 °C), m-xylene (TCI, 30 or 80 °C) or mixed solvents of mxylene and carbon tetrachloride (CCl4, Aladin) (Vm‑xylene:VCCl4 = 1:1) under 25 °C. C60 and TIPS-BP were crystallized in mixed solvents (Vm‑xylene:VCCl4 = 1:1) under 25 °C. TIPS-TAP and diF-TES-ADT

were crystallized in chloroform (Ourchem, 25 °C). C8-BTBT was crystallized in heptane (TCI, 30 °C). For crystallization of bilayer crystals, two organic semiconductors were first dissolved in one solution and then dropped on BCB-covered silicon substrates (20 μL, 0.2 mg/mL if not specified) using the same DPC method. C60 and diF-TES-ADT (0.4 mg/mL) bilayer crystals as well as C60 and TIPSBP (0.25 mg/mL) bilayer crystals crystallized in mixed solvents (Vm‑xylene:VCCl4 = 1:1) under 25 °C. TIPS-TAP and TIPS-BP bilayer crystals, TIPS-TAP and C8-BTBT bilayer crystals formed in m-xylene under 30 °C. We note that the CCl4 is toxic and harmful. 10012

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Journal of the American Chemical Society The morphologies and single-crystalline structures of the crystals and bilayer crystals were characterized by OM (Nikon LV100 POL), Raman mapping (Renishaw InVia Raman Microscope), SEM (Hitachi S4800 field-emission System), AFM (Veeco 3D) and SAED (JEOL 1400). For devices fabrication, FETs and inverters were constructed in a top contact, bottom gate configuration by depositing 100 nm Au source and drain electrodes using shadow masks (50 μm in channel length and 1 mm in width). The devices were characterized in a N2 glovebox using a Keithley 4200-SCS semiconductor parameter analyzer after being heated and then cooled down naturally to remove the residual solvents. The measured capacitance of the BCBcovered SiO2/Si substrates was 11 nF/cm2, and this value was used for mobility calculation. The mobility was extracted from the saturation regime with a gate voltage range of 15 V. The contact resistance was not excluded when mobilities were extracted from the FET tests.

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(5) Beaujuge, P. M.; Fréchet, J. M. Molecular Design and Ordering Effects in π-Functional Materials for Transistor and Solar Cell Applications. J. Am. Chem. Soc. 2011, 133, 20009−20029. (6) Cui, Y.; Yao, H.; Gao, B.; Qin, Y.; Zhang, S.; Yang, B.; He, C.; Xu, B.; Hou, J. Fine-Tuned Photoactive and Interconnection Layers for Achieving over 13% Efficiency in a Fullerene-Free Tandem Organic Solar Cell. J. Am. Chem. Soc. 2017, 139, 7302−7309. (7) Huang, H.; Yang, L.; Facchetti, A.; Marks, T. J. Organic and Polymeric Semiconductors Enhanced by Noncovalent Conformational Locks. Chem. Rev. 2017, 117, 10291−10318. (8) Pei, Q. B.; Yang, Y.; Yu, G.; Zhang, C.; Heeger, A. J. Polymer Light-Emitting Electrochemical Cells: In Situ Formation of a LightEmitting p-n Junction. J. Am. Chem. Soc. 1996, 118, 3922−3929. (9) Zhang, Q.; Li, J.; Shizu, K.; Huang, S.; Hirata, S.; Miyazaki, H.; Adachi, C. Design of Efficient Thermally Activated Delayed Fluorescence Materials for Pure Blue Organic Light Emitting Diodes. J. Am. Chem. Soc. 2012, 134, 14706−14709. (10) Ostroverkhova, O. Organic Optoelectronic Materials: Mechanisms and Applications. Chem. Rev. 2016, 116, 13279−13412. (11) Thejo Kalyani, N.; Dhoble, S. J. Organic Light Emitting Diodes: Energy Saving Lighting Technology-A Review. Renewable Sustainable Energy Rev. 2012, 16, 2696−2723. (12) Heremans, P.; Gelinck, G. H.; Müller, R.; Baeg, K. J.; Kim, D. Y.; Noh, Y. Y. Polymer and Organic Nonvolatile Memory Devices. Chem. Mater. 2011, 23, 341−358. (13) Xiao, J. C.; Yin, Z. Y.; Li, H.; Zhang, Q.; Boey, F.; Zhang, H.; Zhang, Q. C. Postchemistry of Organic Particles: When TTF Microparticles Meet TCNQ Microstructures in Aqueous Solution. J. Am. Chem. Soc. 2010, 132, 6926−6928. (14) Chang, H. C.; Lu, C.; Liu, C. L.; Chen, W. C. Single-Crystal C60 Needle/CuPc Nanoparticle Double Floating-Gate for LowVoltage Organic Transistors Based Non-Volatile Memory Devices. Adv. Mater. 2015, 27, 27−33. (15) Crone, B.; Dodabalapur, A.; Lin, Y. Y.; Filas, R. W.; Bao, Z.; LaDuca, A.; Sarpeshkar, R.; Katz, H. E.; Li, W. Large-Scale Complementary Integrated Circuits Based on Organic Transistors. Nature 2000, 403, 521−523. (16) Sakamoto, Y.; Suzuki, T.; Kobayashi, M.; Gao, Y.; Fukai, Y.; Inoue, Y.; Sato, F.; Tokito, S. Perfluoropentacene: High-Performance p-n Junctions and Complementary Circuits with Pentacene. J. Am. Chem. Soc. 2004, 126, 8138−8140. (17) Wang, C. L.; Dong, H. L.; Hu, W. P.; Liu, Y. Q.; Zhu, D. B. Semiconducting π-Conjugated Systems in Field-Effect Transistors: A Material Odyssey of Organic Electronics. Chem. Rev. 2012, 112, 2208−2267. (18) Tybrandt, K.; Gabrielsson, E. O.; Berggren, M. Toward Complementary Ionic Circuits: The npn Ion Bipolar Junction Transistor. J. Am. Chem. Soc. 2011, 133, 10141−10145. (19) Li, H.; Shi, W.; Song, J.; Jang, H. J.; Dailey, J.; Yu, J.; Katz, H. E. Chemical and Biomolecule Sensing with Organic Field-Effect Transistors. Chem. Rev. 2019, 119, 3−35. (20) Kang, B.; Jang, M.; Chung, Y.; Kim, H.; Kwak, S. K.; Oh, J. H.; Cho, K. Enhancing 2D Growth of Organic Semiconductor Thin Films with Macroporous Structures via a Small-Molecule Heterointerface. Nat. Commun. 2014, 5, 4752. (21) Huang, J.; Zhang, G.; Zhao, X.; Wu, X.; Liu, D.; Chu, Y.; Katz, H. E. Direct Detection of Dilute Solid Chemicals with Responsive Lateral Organic Diodes. J. Am. Chem. Soc. 2017, 139, 12366−12369. (22) Wang, C.; Dong, H.; Jiang, L.; Hu, W. Organic Semiconductor Crystals. Chem. Soc. Rev. 2018, 47, 422−500. (23) Podzorov, V. Organic Single Crystals: Addressing the Fundamentals of Organic Electronics. MRS Bull. 2013, 38, 15−24. (24) Li, R. J.; Hu, W. P.; Liu, Y. Q.; Zhu, D. B. Micro- and Nanocrystals of Organic Semiconductors. Acc. Chem. Res. 2010, 43, 529−540. (25) Reese, C.; Bao, Z. N. Organic Single-Crystal Field-Effect Transistors. Mater. Today 2007, 10, 20−27. (26) Chu, M.; Fan, J. X.; Yang, S.; Liu, D.; Ng, C. F.; Dong, H.; Ren, A. M.; Miao, Q. Halogenated Tetraazapentacenes with Electron

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/jacs.9b03819.

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Supplementary images of crystals (OM, SEM and AFM), Raman spectrum and FET characteristics (PDF)

AUTHOR INFORMATION

Corresponding Author

*[email protected] ORCID

Huolin L. Xin: 0000-0002-6521-868X Qian Miao: 0000-0001-9933-6548 Hiroko Yamada: 0000-0002-2138-5902 Hongzheng Chen: 0000-0002-5922-9550 Hanying Li: 0000-0002-5841-6805 Present Address ¶

Department of Physics and Astronomy, University of California, Irvine, CA 92697, USA

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (51625304, 51873182). This research used resources of the Center for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility, at Brookhaven National Laboratory under Contract No. DE-SC0012704.

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REFERENCES

(1) Liu, J.; Engquist, I.; Crispin, X.; Berggren, M. Spatial Control of p-n Junction in an Organic Light-Emitting Electrochemical Transistor. J. Am. Chem. Soc. 2012, 134, 901−904. (2) Facchetti, A. π-Conjugated Polymers for Organic Electronics and Photovoltaic Cell Applications. Chem. Mater. 2011, 23, 733−758. (3) Li, J.; Zhou, K.; Liu, J.; Zhen, Y.; Liu, L.; Zhang, J.; Dong, H.; Zhang, X.; Jiang, L.; Hu, W. Aromatic Extension at 2,6-Positions of Anthracene toward an Elegant Strategy for Organic Semiconductors with Efficient Charge Transport and Strong Solid State Emission. J. Am. Chem. Soc. 2017, 139, 17261−17264. (4) Dinelli, F.; Capelli, R.; Loi, M. A.; Murgia, M.; Muccini, M.; Facchetti, A.; Marks, T. J. High-Mobility Ambipolar Transport in Organic Light-Emitting Transistors. Adv. Mater. 2006, 18, 1416− 1420. 10013

DOI: 10.1021/jacs.9b03819 J. Am. Chem. Soc. 2019, 141, 10007−10015

Article

Journal of the American Chemical Society Mobility as High as 27.8 cm2V−1s−1 in Solution-Processed n-Channel Organic Thin-Film Transistors. Adv. Mater. 2018, 30, 1803467. (27) Wu, J. K.; Li, Q. F.; Xue, G. B.; Chen, H. Z.; Li, H. Y. Preparation of Single-Crystalline Heterojunctions for Organic Electronics. Adv. Mater. 2017, 29, 1606101. (28) Zhang, Y. J.; Dong, H. L.; Tang, Q. X.; Ferdous, S.; Liu, F.; Mannsfeld, S. C. B.; Hu, W. P.; Briseno, A. L. Organic SingleCrystalline p-n Junction Nanoribbons. J. Am. Chem. Soc. 2010, 132, 11580−11584. (29) Zhang, X.; Mao, J.; Deng, W.; Xu, X.; Huang, L.; Zhang, X.; Lee, S. T.; Jie, J. Precise Patterning of Laterally Stacked Organic Microbelt Heterojunction Arrays by Surface-Energy-Controlled Stepwise Crystallization for Ambipolar Organic Field-Effect Transistors. Adv. Mater. 2018, 30, 1800187. (30) Chen, Y. Z.; Zhang, C. Y.; Zhang, X. J.; Ou, X. M.; Zhang, X. H. One-Step Growth of Organic Single-Crystal p-n Nano-Heterojunctions with Enhanced Visible-Light Photocatalytic Activity. Chem. Commun. 2013, 49, 9200−9202. (31) Cui, Q. H.; Jiang, L.; Zhang, C.; Zhao, Y. S.; Hu, W. P.; Yao, J. N. Coaxial Organic p-n Heterojunction Nanowire Arrays: One-Step Synthesis and Photoelectric Properties. Adv. Mater. 2012, 24, 2332− 2336. (32) Alves, H.; Pinto, R. M.; Maçôas, E. S. Photoconductive Response in Organic Charge Transfer Interfaces with High Quantum Efficiency. Nat. Commun. 2013, 4, 1842. (33) Alves, H.; Molinari, A. S.; Xie, H. X.; Morpurgo, A. F. Metallic Conduction at Organic Charge-Transfer Interfaces. Nat. Mater. 2008, 7, 574−580. (34) Mitsuta, H.; Miyadera, T.; Ohashi, N.; Zhou, Y.; Taima, T.; Koganezawa, T.; Yoshida, Y.; Tamura, M. Epitaxial Growth of C60 on Rubrene Single Crystals for a Highly Ordered Organic Donor/ Acceptor Interface. Cryst. Growth Des. 2017, 17, 4622−4627. (35) Wu, J. K.; Fan, C. C.; Xue, G. B.; Ye, T.; Liu, S.; Lin, R. Q.; Chen, H. Z.; Xin, H. L. L.; Xiong, R. G.; Li, H. Y. Interfacing SolutionGrown C60 and (3-Pyrrolinium)(CdCl3) Single Crystals for HighMobility Transistor-Based Memory Devices. Adv. Mater. 2015, 27, 4476−4480. (36) Zhao, X. M.; Liu, T. J.; Zhang, Y. T.; Wang, S. R.; Li, X. G.; Xiao, Y.; Hou, X. Y.; Liu, Z. L.; Shi, W. D.; Dennis, T. J. S. Organic Single-Crystalline Donor-Acceptor Heterojunctions with Ambipolar Band-Like Charge Transport for Photovoltaics. Adv. Mater. Interfaces 2018, 5, 1800336. (37) Park, K. S.; Lee, K. S.; Baek, J.; Lee, L.; Son, B. H.; Koo Lee, Y. E.; Ahn, Y. H.; Park, W. I.; Kang, Y.; Sung, M. M. Observation of Charge Separation and Space-Charge Region in Single-Crystal P3HT/C60 Heterojunction Nanowires. Angew. Chem., Int. Ed. 2016, 55, 10273−10277. (38) Zhao, X.; Liu, T.; Liu, H.; Wang, S.; Li, X.; Zhang, Y.; Hou, X.; Liu, Z.; Shi, W.; Dennis, T. J. S. Organic Single-Crystalline p-n Heterojunctions for High-Performance Ambipolar Field-Effect Transistors and Broadband Photodetectors. ACS Appl. Mater. Interfaces 2018, 10, 42715−42722. (39) Fan, C. C.; Zoombelt, A. P.; Jiang, H.; Fu, W. F.; Wu, J. K.; Yuan, W. T.; Wang, Y.; Li, H. Y.; Chen, H. Z.; Bao, Z. N. SolutionGrown Organic Single-Crystalline p-n Junctions with Ambipolar Charge Transport. Adv. Mater. 2013, 25, 5762−5766. (40) Li, H. Y.; Fan, C. C.; Fu, W. F.; Xin, H. L. L.; Chen, H. Z. Solution-Grown Organic Single-Crystalline Donor-Acceptor Heterojunctions for Photovoltaics. Angew. Chem., Int. Ed. 2015, 54, 956−960. (41) Vesselinov, M. I. Crystal Growth for Beginners: Fundamentals of Nucleation, Crystal Growth and Epitaxy; World Scientific, 2016. (42) 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. (43) Chua, L. L.; Zaumseil, J.; Chang, J. F.; Ou, E. C. W.; Ho, P. K. H.; Sirringhaus, H.; Friend, R. H. General Observation of n-Type Field-Effect Behaviour in Organic Semiconductors. Nature 2005, 434, 194−199.

(44) Noh, Y. Y.; Sirringhaus, H. Ultra-Thin Polymer Gate Dielectrics for Top-Gate Polymer Field-Effect Transistors. Org. Electron. 2009, 10, 174−180. (45) Kim, D. H.; Lee, D. Y.; Lee, H. S.; Lee, W. H.; Kim, Y. H.; Han, J. I.; Cho, K. High-Mobility Organic Transistors Based on SingleCrystalline Microribbons of Triisopropylsilylethynyl Pentacene via Solution-Phase Self-Assembly. Adv. Mater. 2007, 19, 678−682. (46) Briseno, A. L.; Tseng, R. J.; Ling, M. M.; Falcao, E. H. L.; Yang, Y.; Wudl, F.; Bao, Z. N. High-Performance Organic Single-Crystal Transistors on Flexible Substrates. Adv. Mater. 2006, 18, 2320−2324. (47) Reyes-Martinez, M. A.; Crosby, A. J.; Briseno, A. L. Rubrene Crystal Field-Effect Mobility Modulation via Conducting Channel Wrinkling. Nat. Commun. 2015, 6, 6948. (48) Li, H. B.; Xue, G. B.; Wu, J. K.; Zhang, W. Q.; Huang, Z. T.; Xie, Z. Q.; Xin, H. L.; Wu, G.; Chen, H. Z.; Li, H. Y. Long-Range Ordering of Composites for Organic Electronics: TIPS-Pentacene Single Crystals with Incorporated Nano-Fibers. Chin. Chem. Lett. 2017, 28, 2121−2124. (49) Don Park, Y.; Lim, J. A.; Lee, H. S.; Cho, K. Interface Engineering in Organic Transistors. Mater. Today 2007, 10, 46−54. (50) Liu, C.; Xu, Y.; Noh, Y. Y. Contact Engineering in Organic Field-Effect Transistors. Mater. Today 2015, 18, 79−96. (51) Briseno, A. L.; Aizenberg, J.; Han, Y. J.; Penkala, R. A.; Moon, H.; Lovinger, A. J.; Kloc, C.; Bao, Z. N. Patterned Growth of Large Oriented Organic Semiconductor Single Crystals on Self-Assembled Monolayer Templates. J. Am. Chem. Soc. 2005, 127, 12164−12165. (52) Izawa, T.; Miyazaki, E.; Takimiya, K. Molecular Ordering of High-Performance Soluble Molecular Semiconductors and Reevaluation of Their Field-Effect Transistor Characteristics. Adv. Mater. 2008, 20, 3388−3392. (53) Liang, Z.; Tang, Q.; Xu, J.; Miao, Q. Soluble and Stable NHeteropentacenes with High Field-Effect Mobility. Adv. Mater. 2011, 23, 1535−1539. (54) Jurchescu, O. D.; Subramanian, S.; Kline, R. J.; Hudson, S. D.; Anthony, J. E.; Jackson, T. N.; Gundlach, D. J. Organic Single-Crystal Field-Effect Transistors of a Soluble Anthradithiophene. Chem. Mater. 2008, 20, 6733−6737. (55) Takahashi, K.; Kuzuhara, D.; Aratani, N.; Yamada, H. Synthesis and Crystal Structures of 5,15-Bis(triisopropylsilylethynyl)-tetrabenzoporphyrins. J. Photopolym. Sci. Technol. 2013, 26, 213−216. (56) Li, H. Y.; Tee, B. C. K.; Cha, J. J.; Cui, Y.; Chung, J. W.; Lee, S. Y.; Bao, Z. N. High-Mobility Field-Effect Transistors from Large-Area Solution-Grown Aligned C60 Single Crystals. J. Am. Chem. Soc. 2012, 134, 2760−2765. (57) Larsen, C.; Barzegar, H. R.; Nitze, F.; Wågberg, T.; Edman, L. On the Fabrication of Crystalline C60 Nanorod Transistors from Solution. Nanotechnology 2012, 23, 344015. (58) Platt, A. D.; Day, J.; Subramanian, S.; Anthony, J. E.; Ostroverkhova, O. Optical, Fluorescent, and (Photo)conductive Properties of High-Performance Functionalized Pentacene and Anthradithiophene Derivatives. J. Phys. Chem. C 2009, 113, 14006− 14014. (59) Liu, D. Q.; Xu, X. M.; Su, Y. R.; He, Z. K.; Xu, J. B.; Miao, Q. Self-Assembled Monolayers of Phosphonic Acids with Enhanced Surface Energy for High-Performance Solution-Processed N-Channel Organic Thin-Film Transistors. Angew. Chem., Int. Ed. 2013, 52, 6222−6227. (60) Takahashi, K.; Shan, B.; Xu, X.; Yang, S.; Koganezawa, T.; Kuzuhara, D.; Aratani, N.; Suzuki, M.; Miao, Q.; Yamada, H. Engineering Thin Films of a Tetrabenzoporphyrin toward Efficient Charge-Carrier Transport: Selective Formation of a Brickwork Motif. ACS Appl. Mater. Interfaces 2017, 9, 8211−8218. (61) Ebata, H.; Izawa, T.; Miyazaki, E.; Takimiya, K.; Ikeda, M.; Kuwabara, H.; Yui, T. Highly Soluble [1]Benzothieno[3,2-b]benzothiophene (BTBT) Derivatives for High-Performance, Solution-Processed Organic Field-Effect Transistors. J. Am. Chem. Soc. 2007, 129, 15732−15733. (62) Barzegar, H. R.; Larsen, C.; Boulanger, N.; Zettl, A.; Edman, L.; Wågberg, T. Self-Assembled PCBM Nanosheets: A Facile Route to 10014

DOI: 10.1021/jacs.9b03819 J. Am. Chem. Soc. 2019, 141, 10007−10015

Article

Journal of the American Chemical Society Electronic Layer-on-Layer Heterostructures. Nano Lett. 2018, 18, 1442−1447. (63) Ochiai, Y.; Ogawa, K.; Aoki, N.; Bird, J. P. Field-EffectTransistor Characteristics of Solvate C60 Fullerene Nanowhiskers. Journal of Physics: Conference Series 2009, 159, 012004. (64) Li, H. Y.; Fan, C. C.; Vosgueritchian, M.; Tee, B. C. K.; Chen, H. Z. Solution-Grown Aligned C60 Single-Crystals for Field-Effect Transistors. J. Mater. Chem. C 2014, 2, 3617−3624.

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DOI: 10.1021/jacs.9b03819 J. Am. Chem. Soc. 2019, 141, 10007−10015