A Nonchlorinated Solvent-Processable Fluorinated Planar Conjugated

Subscriber access provided by University of Pennsylvania Libraries

Article

A Non-Chlorinated-Solvent-Processable Fluorinated Planar Conjugated Polymer for Flexible Field-Effect Transistors Myeongjae Lee, Min Je Kim, Suhee Ro, Shinyoung Choi, Seon-Mi Jin, Hieu Dinh Nguyen, Jee Hye Yang, Kyung-Koo Lee, Dong Un Lim, Eunji Lee, Moon Sung Kang, Jong-Ho Choi, Jeong Ho Cho, and BongSoo Kim ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b08071 • Publication Date (Web): 07 Aug 2017 Downloaded from http://pubs.acs.org on August 11, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 28

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

ACS Applied Materials & Interfaces

A Non-Chlorinated-Solvent-Processable Fluorinated Planar Conjugated Polymer for Flexible Field-Effect Transistors Myeongjae Lee,1,† Min Je Kim,2,† Suhee Ro,3 Shinyoung Choi,3 Seon-Mi Jin,4 Hieu Dinh Nguyen,5 Jeehye Yang,6 Kyung-Koo Lee, 5 Dong Un Lim,2 Eunji Lee,4 Moon Sung Kang,6 Jong-Ho Choi,1 Jeong Ho Cho,2,* and BongSoo Kim,3,* 1

Department of Chemistry, Korea University, Seoul 02841, Republic of Korea SKKU Advanced Institute of Nanotechnology (SAINT), School of Chemical Engineering, Sungkyunkwan University, Suwon 16419, Republic of Korea 3 Department of Science Education, Ewha Womans University, Seoul 03760, Republic of Korea 4 Graduate School of Analytical Science and Technology, Chungnam National University, Daejeon, 34134, Republic of Korea 5 Department of Chemistry, Kunsan National University, Kunsan-si 54150, Republic of Korea 6 Department of Chemical Engineering, Soongsil University, Seoul 06978, Republic of Korea 2

†

M. Lee and M. J. Kim contributed equally.

*Corresponding authors: Prof. BongSoo Kim: [email protected] Prof. Jeong Ho Cho: [email protected]

1

ACS Paragon Plus Environment


Page 2 of 28

Abstract 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

High carrier mobilities have recently been achieved in polymer field effect transistors (FETs). However, many of these polymer FET devices require the use of chlorinated solvents such as chloroform (CF), chlorobenzene (CB), and o-dichlorobenzene (DCB) during fabrication. The use of these solvents is highly restricted in industry because of health and environmental issues. Here, we report the synthesis of a low band gap (1.43 eV, 870 nm) semiconducting polymer (PDPP2DT-F2T2) having a planar geometry, which can be readily processable with non-chlorinated solvents such as toluene (TOL), o-xylene (XY), and 1,2,4trimethylbenzene (TMB). We performed structural characterization of PDPP2DT-F2T2 films prepared from different solvents, and the electrical properties of the films were measured in the context of FETs. The devices exhibited an ambipolar behavior with hole dominant transport. Hole mobilities increased with increasing boiling point (bp) of the non-chlorinated solvents: 0.03, 0.05, and 0.10 cm2V-1s-1 for devices processed using TOL, XY, and TMB, respectively. Thermal annealing further improved the FET performance. TMB-based polymerFETs annealed at 200 °C yielded a maximum hole mobility of 1.28 cm2V1 -1

s , which is far higher than the 0.43 cm2V-1s-1 obtained from the CF-based device. This enhancement was

attributed to increased interchain interactions as well as improved long range interconnection between fibrous domains. Moreover, all the non-chlorinated solutions generated purely edge-on orientations of the polymer chains, which is highly beneficial for carrier transport in FET devices. Furthermore, we fabricated an array of flexible TMB-processed PDPP2DT-F2T2 FETs on the plastic PEN substrates. These devices demonstrated excellent carrier mobilities and negligible degradation after 300 bending cycles. Overall, we demonstrated that the organized assembly of polymer chains can be achieved by slow drying using high bp non-chlorinated solvents and a post thermal treatment. Furthermore, we showed that polymer FETs processed using high bp non-halogenated solvents may outperform those processed using halogenated solvents.

Keywords: organic transistor, non-chlorinated solvent, low bandgap polymer, carrier mobility, flexible electronics, mechanical stability

2


Page 3 of 28


1. INTRODUCTION 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

Semiconducting conjugated polymers have been developed for various applications of polymer field effect transistors (FETs), including radio frequency-identification, chemical sensors, switching elements, and logic circuits in electronics.1-5 Carrier mobilities of conjugated polymer-based FETs have exceeded 1 cm2V1 -1

s , which is even higher than the carrier mobility of amorphous silicon (a-Si) FETs.6-8 Most of the reported

high-performance semiconducting polymers are based on alternating linkages of electron rich donor (D) units9-12 and electron-deficient acceptor (A) units.13-15 Combinations of the chemical structures of D and A units can be used to modulate the optical and electrical properties of conjugated polymers and can affect the morphology in film state. Side alkyl chains in these polymers also play a significant role in determining the solubility and the molecular interactions in the film state.7,

16-19

Among the D-A type polymers,

diketopyrrolopyrrole (DPP) has been widely employed as an acceptor unit because DPP-containing polymers can provide high quality crystalline films based on the planar backbone structure, which results in high carrier mobilities. Oligothiophene donor units such as bithiophene, thieno[3,2-b]thiophene, thiophenevinylene-thiophene, selenophene-vinylene-selenophene have been employed as a linkage of DPP units.20-26 A new linkage donor structure should be developed to further improve carrier mobility of the DPP-based polymers. Chlorinated solvents such as chloroform (CF), chlorobenzene (CB), and o-dichlorobenzene (DCB) have been exclusively used in preparing polymer FETs. This is mainly because the solubility of conjugated polymers is high in such solvents, especially when the polymer molecular weight is large. However, the environmental risks and waste removal costs of chlorinated solvents have rarely been considered in the PFET-research community.27, 28 Thus, it is of paramount importance to replace commonly-used chlorinated solvents with environmentally harmless non-chlorinated solvents for practical commercialization of polymer FET devices. To date, only a few studies have attempted to replace halogenated solvents with nonhalogenated solvents such as toluene (TOL)29, xylene (XY)30, and tetralin.25, 31, 32 Moreover, the drying speed of semiconducting polymer films influences the film morphology and FET performance, and this aspect needs to be investigated using a series of different boiling point (bp) non-chlorinated solvents. According to previous studies that have employed chlorinated solvent systems such as CB, DCB, or binary solvents (e.g., CF:CB or CB:DCB), the use of high bp solvent systems (rather than using CF) assisted the growth of crystalline domains and thus enhanced device performance.4, 33 Note that CB and DCB, which have been used in previous studies, have different dipole moments and surface energies (in addition to the bp difference),33 while those for TOL, XY, 1,2,4-trimethylbenzene (TMB)34 are similar to one another (see Figure S1). This fact suggests that we can examine the pure dependence of solvent drying speed on the electrical properties of polymer FETs by using non-halogenated solvents of TOL, XY, and TMB whose bp values are 110, 144, and 168 ºC, respectively.

3



Page 4 of 28

Here we report the development of a DPP-based polymer of poly(2,5-bis(2-decyltetradecyl)-31 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

(3'',4'-difluoro-[2,2':5',2''-terthiophen]-5-yl)-6-(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione) (PDPP2DT-F2T2) by polymerizing DPP and 3,3'-difluoro-2,2'-bithiophene (F2T2) units for highperformance flexible polymer FET devices. The F2T2 unit is quite planar due to the non-covalent F···S interactions in the neighboring thiophene.35, 36 The synthesized PDPP2DT-F2T2 is highly soluble in nonchlorinated solvents. The PDPP2DT-F2T2 polymer was processed with TOL, XY, and TMB as well as CF to fabricate top-gate bottom-contact (TGBC) FETs. PDPP2DT-F2T2-based FETs have shown ambipolar behavior with more efficient hole transport than electron transport. The carrier mobilities increased with increasing bp of the non-chlorinated solvent used for processing. Moreover, thermal annealing treatment on spin-coated polymer films further increased carrier mobilities. For example, 200 °C-annealed polymer FETs prepared from a TMB solution displayed a high hole mobility of 1.28 cm2V-1s-1 and a good electron mobility of 0.39 cm2V-1s-1. This performance is attributed to the increased crystallinity and highly fibril structure of PDPP2DT-F2T2 polymer films due to the use of high bp non-chlorinated solvents, demonstrating that high bp non-chlorinated solvents have a high potential for use in fabricating polymer FET devices. Furthermore, flexible PEN substrate-used PDPP2DT-F2T2 polymer FETs were fabricated. High carrier mobility and excellent bending stability were demonstrated.

2. EXPERIMENTAL SECTION 2.1 Synthesis The synthetic route to prepare PDPP2DT-F2T2 polymer is shown in Scheme 1. The synthetic details are described below and for compounds 1-3 reported procedures were followed and confirmed by comparing 1

H-NMR and 13C-NMR spectra with the reported data.37-39

Synthesis of 11-(iodomethyl)tricosane, 1 : 2-decyltetradecan-1-ol (5 g, 14.1 mmol), triphenylphosphine (4.44 g, 16.9 mmol), and imidazole (1.44 g, 21.1 mmol) were added to anhydrous dichloromethane (38.3 mL) and were then cooled down to 0 °C in an ice-bath. Iodine (4.65 g, 18.3 mmol) was added to the reaction solution. After 15 min, the reaction mixture was stirred at RT. After 18 h, a saturated aqueous Na2S2O3 solution (20 mL) was added to quench the reaction. The organic solution was concentrated, and the mixture was dissolved in n-hexane (200 mL) and washed with deionized water (100 mL) three times. The hexane solution was dried using anhydrous Na2SO4. The resulting organic layer was purified by silica gel flash column chromatography (silica gel, n-hexane as eluent) to attain colorless oil compound 1 (6.64 g, 99% yield). 1H-NMR (300 MHz, CDCl3): δ =3.277-3.263 (d, J = 4.2 Hz, 2H), 1.35-1.19 (m, 40H), 0.903-0.859 (m, 6H) (see the 1H-NMR spectrum in Figure S2).37, 38 Synthesis of 2,5-bis(2-decyltetradecyl)-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione, 2 : 4


Page 5 of 28


3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (1 g, 3.33 mmol), compound 1 (5.15 g, 11.09 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

mmol), K2CO3 (1.53 g, 11.09 mmol) and 18-crown-6 (4.7 mg, 0.018 mmol) were dissolved in anhydrous DMF (40 mL). The reaction solution was stirred at 130 °C. After 24 h, the reaction mixture was cooled down to RT and the organic solvent was removed using a rotary evaporator. Deionized water (40 mL) was added into the reaction solution, and then the crude product was extracted with ether (50 mL) three times. The collected ether solution was dried using anhydrous Na2SO4. The resulting crude product was purified by column chromatography (silica gel, 0-30% chloroform in n-hexane as eluent) to yield a product, which was then recrystallized using chloroform/methanol to afford pure compound 2 (0.769 g, 23.7%). 1H-NMR (300 MHz, CDCl3): δ = 8.879-8.866 (d, J = 3.9 Hz, 2H), 7.625-7.608 (d, J = 5.1 Hz, 2H), 7.279-7.266 (d, J = 8.89 Hz, 2H), 4.028-4.003 (d, J = 7.5 Hz, 4H), 1.900 (m, 2H), 1.4-1.1 (m, 80H), 0.892-0.852 (m, 12H) (see the 1

H-NMR spectrum in Figure S3).39

Synthesis

of

3,6-bis(5-bromothiophen-2-yl)-2,5-bis(2-decyltetradecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-

dione, 3 : compound 2 (0.7 g, 0.719 mmol) was diluted in anhydrous chloroform (70 mL). NBS (0.256 g, 1.438 mmol) dissolved in anhydrous DMF (3 mL) was added slowly into the reaction solution. The solution was stirred at RT under dark conditions. After 28 h, the solution was poured into deionized water (80 mL) and was extracted with chloroform followed by drying using anhydrous Na2SO4. The resulting organic layer solvent was evaporated under reduced pressure. The resulting crude product was purified by flash column chromatography (silica gel, chloroform and n-hexane (3:1) as an eluent). The resulting deep purple solid was recrystallized using chloroform/methanol to afford compound 3 (0.732 g, 90%). 1H-NMR (300 MHz, CDCl3): δ = 8.635-8.621 (d, J = 4.2 Hz, 2H), 7.223-7.209 (d, J = 4.2 Hz, 2H), 3.934-3.909 (d, J = 7.5 Hz, 4H), 1.875 (m, 2H), 1.35-1.15 (m, 80H), 0.895-0.851 (m,12H).

13

C-NMR (75MHz, CDCl3): δ = 161.42,

139.42, 135.34, 131.45, 131.19, 118.97, 108.03, 46.37, 37.78, 31.95, 31.19, 30.01, 29.73, 29.71, 29.69, 29.67, 29.58, 29.39, 26.20, 22.72, 14.15 ppm. (see the 1H-NMR and

13

C-NMR spectra in Figure S4-S5).39

Elemental Analysis: Calculated percent C, 65.82; H, 9.09; N, 2.48. Found percent C, 66.37; H, 9.11; N, 2.43. Synthesis of poly(2,5-bis(2-decyltetradecyl)-3-(3'',4'-difluoro-[2,2':5',2''-terthiophen]-5-yl)-6-(thiophen-2yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione), PDPP2DT-F2T2 : 3 (0.300 g, 0.265 mmol), (3,3'-difluoro[2,2'-bithiophene]-5,5'-diyl)bis(trimethylstannane)

(0.140

g,

0.265

mmol)

and

tetrakis(triphenylphosphine)palladium (0) (0.0141 g, 0.0122 mmol) were added into a flame-dried 10 mL reaction flask with a magnetic bar. Anhydrous toluene (5 mL) and anhydrous DMF (1 mL) that were degassed separately using the freeze-pump-thaw technique for four cycles were then added into the reaction mixture. Reaction temperature was raised from 60 °C to 90 °C gradually at a rate of 2 °C/min, and then the reaction mixture was stirred for 23 min at 90 °C under an argon atmosphere. Next, the reaction mixture was cooled to 60 °C and was diluted with chloroform (6 mL). Subsequently, diethylammonium diethyldithiocarbamate (10.0 mg) dissolved in deionized water (2 mL) was added to the polymer solution, which was stirred at 50 °C for 60 min. The desired polymer was extracted using CHCl3 (20 mL) and 5



Page 6 of 28

deionized water (20 mL). The organic solvent of the collected organic layer was removed using a rotary 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

evaporator, and the polymer was re-dissolved in a small amount of CHCl3 and precipitated in methanol. The collected polymer precipitates were further purified via Soxhlet extraction using methanol, acetone, hexane, cyclohexane, dichloromethane, and chloroform. The chloroform fraction was collected and precipitated in methanol and was collected via gravity filtration. The polymer was dried under vacuum to yield PDPP2DTF2T2 polymer (0.261 g, 84% yield). 1H-NMR (300 MHz, CDCl3): δ = 9.5-8.4 (4H), 5.0-4.8 (4H), 1.5350.35 (92H). Gel-permeation chromatography (GPC) (o-dichlorobenzene, 80 °C) gave the following results: Mn = 71,000 Da, Mw = 137,000 Da, PDI = 1.93. Td,95% = 410 °C (1H-NMR spectrum, GPC curve, and thermogravimetric analysis (TGA) thermogram are shown in Figure S6-8).

2.2. Device Fabrication and Measurements Polymer FETs with top-gate bottom-contact (TGBC) geometries were fabricated to evaluate the electrical characteristics of the PDPP2DT-F2T2 polymer. A Si wafer with a thermally-grown 300 nm-thick SiO2 was used as the substrate. Si substrates were cleaned by sonication in acetone, isopropanol (IPA), and deionized water for 10 min each and dried by N2 stream. The source and drain electrodes were patterned via sequential thermal evaporation of Cr (3 nm) as an adhesion layer and Au (17 nm) through a shadow mask onto the cleaned Si wafer substrate. The channel width (W) and channel length (L) were 1000 and 100 µm, respectively. The PDPP2DT-F2T2 solution dissolved in CF, TOL, XY, or TMB (5 mg/mL) was spin-coated at a spin-rate of 2000 rpm on the substrate. The resulting polymer films were annealed thermally at RT, 100, and 200 °C for 60 min. The thickness of PDPP2DT-F2T2 films prepared from four different solvents were around 40 nm, regardless of solvents. A poly(methyl methacrylate) (PMMA) (Mw = 120 kDa, Sigma Aldrich)-dissolved in n-butyl acetate solution (70 mg/mL) was spin-coated atop the PDPP2DT-F2T2 film to form a 500 nm-thick gate dielectric layer. The gate dielectric PMMA films were further dried at 80 °C for 6 h. Finally, an aluminum gate electrode with a thickness of 40 nm was patterned onto the PMMA layer via thermal evaporation through a shadow mask. For the fabrication of a flexible polymer FET array, the same process was conducted using plastic polyethylene naphthalate (PEN) substrates (Teijin DuPont Films, Teonex Q65HA) in place of Si wafers. Cr/Au (5/20 nm) source and drain electrodes were patterned onto the PEN substrate via thermal evaporation. The W and L were 1000 and 100 µm, respectively. A PDPP2DTF2T2 solution in TBM (5 mg/mL) was spin-coated on the substrate, and the semiconductor film was annealed at 150 °C for 60 min. The 500 nm-thick PMMA gate dielectric layer was then deposited and dried. To form a gate electrode, 40 nm-thick Al was patterned onto the channel region. The electrical properties of the polymer FETs were measured at room temperature in the dark using a Keithley 4200 semiconductor parameter analyzer system. The electrical properties of each type FET devices were obtained from more than ten devices

6


Page 7 of 28

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


3. RESULTS AND DISCUSSION The synthetic route for the PDPP2DT-F2T2 polymer is shown in Scheme 1. 2-Decyltetradecyl alcohol was converted to 2-decyltetradecyl iodide (1), which was attached to 3,6-di(thiophen-2yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione

to

yield

2,5-bis(2-decyltetradecyl)-3,6-di(thiophen-2-

yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (2). Compound 2 was then brominated with NBS to give 3,6bis(5-bromothiophen-2-yl)-2,5-bis(2-decyltetradecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione

(3).

Stille

coupling of compound 3 and (3,3'-difluoro-[2,2'-bithiophene]-5,5'-diyl)bis(trimethylstannane) with Pd(PPh3)4 catalyst in a toluene:DMF co-solvent (vol. ratio = 5:1) produced crude PDPP2DT-F2T2 polymer. The polymer solution in chloroform was treated with an aqueous solution containing diethyldithiocarbamic acid diethylammonium salt to get rid of Pd catalyst and was condensed and precipitated in methanol to yield the PDPP2DT-F2T2 polymer. This polymer was further purified by a Soxhlet extraction procedure. The chloroform fraction was collected and dried. The weight average molecular weight (Mw) of the purified PDPP2DT-F2T2 polymer was 137,000 Da with a PDI of 1.93 (Figure S7). PDPP2DT-F2T2 polymer was soluble in common organic solvents such as CF, CB, DCB, TOL, XY, and TMB. Thermogravimetric analysis of the PDPP2DT-F2T2 polymer revealed a 95%-decomposition temperature of 410 oC (Figure S8). UV-visible absorption spectra of PDPP2DT-F2T2 polymer in solution and film states are shown in Figure 1. In the film state, the absorption spectra displayed three distinct peaks at around 450, 731, and 810 nm with a shoulder at 650 nm. The peak at 450 nm had low absorption, whereas the vibronic peaks at 731 and 810 nm exhibited much higher absorptions. There was a slight red shift along with a slight enhancement in the ratio between the absorption at 810 nm and the absorption at 700 nm as the solvents used to prepare the films changed from CF, to TOL, XY, and TMB (Figure 1a). This observation indicates that the interchain interactions between PDPP2DT-F2T2 polymer chains increased in this order and that the nonchlorinated solvents TOL, XY, and TMB can improve interchain interactions.4, 25, 40, 41 This argument is also supported by comparing these spectra with the optical properties of the PDPP2DT-F2T2 polymer in solution. The maximum absorption peaks of polymer solutions in TMB and CF were 794 and 788 nm, respectively (see Figure 1b and Figure S9a). Additionally, the PDPP2DT-F2T2 polymer formed J-aggregates in the TMB solution, which was only partly disaggregated even at an elevated solution temperature of 115 °C. These observations indicate that non-halogenated solvents can induce stronger interactions than CF, even in solution. The interchain interactions were further enhanced upon thermal annealing of polymer films; the peak at 810 nm observed at RT was slightly red-shifted to 813 nm at 200 °C, and its relative intensity was enhanced compared to that at 731 nm. To understand the role of fluorine atoms in the interchain interactions of PDPP2DT-F2T2 polymer, we separately synthesized poly(2,5-bis(2-decyltetradecyl)-3-(3'',4'-difluoro[2,2':5',2''-terthiophen]-5-yl)-6-(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione) (PDPP2DT-T2) (Mw 7



Page 8 of 28

= 160,000 Da, PDI = 6.4) in the same way as described for PDPP2DT-F2T2 and measured its optical 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

properties in the TMB solution as a function of temperature (see Figure S9b). The maximum absorption peak of PDPP2DT-T2 polymer was found at 782 nm, which is smaller than that of the PDPP2DT-F2T2 polymer in solution. The dissolution of PDPP2DT-T2 polymer aggregates at high temperature was easier than that for PDPP2DT-F2T2 polymer aggregates. Both these observations indicate that fluorine-contained bithiophene units promoted interchain interactions. Cyclic voltammetry was carried out to examine the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the PDPP2DT-T2 polymer using an anhydrous acetonitrile solution containing 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF6). A cyclic voltammogram of the polymer is shown in Figure 1d. Multiple oxidation and reduction potentials were found, and the onsets of oxidation and reduction potentials were determined to be 0.58 and -1.34 V, corresponding to -5.38 eV for the HOMO and -3.46 eV for the LUMO level, respectively. This HOMO level is slightly deeper than the HOMO of PDPP2DT-T2 (-5.33 eV) (Figure S10) due to the presence of electronwithdrawing fluorine atoms. Density functional theory (DFT) calculations were carried out to obtain insight into the electronic structure of the PDPP2DT-F2T2 polymer. The (DPP2Me-F2T2)4 molecule was used as a model compound for the electronic properties of PDPP2DT-F2T2 polymer. It consisted of four repeating units where the long 2-decyltetradecyl groups were replaced with methyl (Me) groups. The geometry and electronic properties of (DPP2Me-F2T2)4 have been investigated with the Gaussian 09 program package at a density functional theory (DFT) level (B3LYP, 6-311G(d)). Surface plots and energy levels of the model molecule are displayed in Figure 2a. HOMO and LUMO levels were located at -5.02 and -3.33 eV, respectively. A welldistributed electronic contribution was observed in the HOMO orbital, which is slightly more extended than a quinoidal electronic distribution of the LUMO orbital. DPP units played a major role in forming HOMO-1, HOMO-2, LUMO+1, and LUMO+2 orbitals. Additionally, the energy minimized molecular geometries are shown in Figure 2b. The molecular backbone is quite planar, which is mainly due to the near-zero degree dihedral angles (DAs) observed in the difluorobithiophene and the dithienyldiketopyrrolopyrrole units. The distance between F and S atoms was approximately 2.93 Å. This value is slightly larger than the distance between S and H atom (2.99 Å, see Figure S11) in the bithiophene units, reflecting the presence of F•••S interactions in the difluorobithiophene units. Slight twists (DA = ~17°) were observed between the thiophenes and the diflurobithiophenes. This fact supported the strong interchain interactions found in the UV-visible absorption feature (above) and the two-dimensional grazing-incidence X-ray diffraction (GIXD) data (below). Additionally, we compared these data with the optimized geometry and electronic structure of (DPP2Me-T2)4, a model molecule for the PDPP2DT-T2 polymer (see Figure S11). This molecule has a slightly higher HOMO level (-4.90 eV) and a higher LUMO level (-3.21 eV), and it also has a more distorted geometry. DAs between thiophenes connected to the DPP units and bithiophenes are similar, but 8


Page 9 of 28


there is an extra twist in the center of the bithiophene units (DA = ~19°). Based on a comparison between 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

(DPP2Me-F2T2)4 and (DPP2Me-T2)4, we concluded that the fluorine atoms lower the HOMO/LUMO levels and make the polymer backbone more planar. GIXD experiments were carried out to gain insight into the interchain stacking of the PDPP2DTF2T2 polymer in a film state. Polymer films were spin-coated from CF, TOL, XY, and TMB solutions and were then annealed at RT and 200 °C. The GIXD images of the PDPP2DT-F2T2 films are displayed in Figure 3, and line-cut profiles are shown in Figure 4. The PDPP2DT-F2T2 film processed from a CF solution at RT displayed highly-ordered crystalline features. Strong lamellar (h00) peaks from (100) to (400) were clearly observed in the qz direction, while the (100) peak was distributed in other directions, even reaching the qy direction. The π‒π stacking (010) peak was observed with a radial distribution and strong intensities both in the qy direction and in the qz direction. These characteristics indicated that a majority of polymer chains adopted an edge-on orientation, while a minority of polymer chains assumed the face-on orientation. Thermal annealing at 200 °C increased the film crystallinity significantly and switched the faceon orientation of a small portion of polymer chains into an edge-on orientation. In contrast, it is quite interesting to observe that the semiconductors prepared from all the non-chlorinated solvents (TOL, XL, and TMB) did not contain the face-on oriented polymer chains in the film state. That is, the lamellar peaks were only observed in the qz direction, and the (010) peak was only observed in the qy direction. We note that the purer edge-on orientation behavior in the non-chlorinated solvents was critical in carrier transport in the FET device geometry.38, 42-44 This feature affected polymer FET device characteristics, providing better charge transport from the non-chlorinated solutions-processed polymer FETs (see below). The peak fitting of the line-cut profiles in the qy and qz directions allowed us to estimate the interchain stacking. Figure 4 shows the curves fitted with a Lorentzian function. The parameters associated with the π‒π spacing and lamellar spacing were obtained from the (010) peaks in the qy direction and the (200) peaks in the qz direction, respectively. These values are also summarized in Table 1. According to the (010) peaks, as-cast films increased the correlation length slightly from 7.19 to 7.35 nm by replacing CF with non-chlorinated solvents. The π‒π spacing distance of the non-chlorinated solvent-processed films was estimated to be 3.64 Å, which is indicative of close interchain stacking.45-48 Upon thermal annealing at 200 °C, all the films enhanced the correlation length up to 8.91, 9.07, 9.89, and 10.4 nm for CF, TOL, XY, and TMB-processed films, respectively. Note that the higher bp non-chlorinated solvents further promoted crystalline long-range order. Upon thermal annealing, the lamellar peaks became stronger and narrower, indicating that the correlation lengths increased significantly from ~ 8 to ~11 nm. The lamellar spacing values decreased slightly (e.g., from 23.6 Å at RT to 22.8 Å at 200 °C for TMB), which suggests that the interdigitation of side alkyl chains became consolidated. Overall, these results suggested that the use of high bp solvents and thermal annealing increase the interchain interactions and also promote the edge-on orientation of the polymers. 9



Page 10 of 28

The surface morphology of the PDPP2DT-F2T2 polymer films prepared from CF, TOL, XY, and 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

TMB solutions and thermal annealing were imaged using AFM. Figure 5 shows the topographic and phase images. CF processed films exhibited uneven-sized aggregates with a root-mean-square (rms) roughness value of 1.8 nm. Upon 200 °C annealing, the CF-processed film became highly aggregated and slightly rougher with an rms of 2.0 nm. The TOL-processed films displayed fine fibrous aggregation, which was further aggregated to show better interconnection upon thermal annealing at 200 °C. The XY-processed films were slightly more aggregated than the TOL-processed films and exhibited further aggregation upon annealing at 200 °C. On the other hand, the TMB-processed films displayed thick fibrillar features at RT, which were observed in topographic and phase images. Annealing the film at 200 °C significantly promoted the fibrillar structure, which can be clearly seen in the phase image. Considering these results together with the FET performances of each solvent-processed films (see below), the crystallinity and interconnection between polymer chains/domains appeared to be important and the fibrillar connections seemed to be desirable for enhanced carrier transport. The electrical properties of the PDPP2DT-F2T2 films were examined from TGBC geometry FETs. The polymer films were processed from four different solvents (CF, TOL, XY, and TMB) and were then annealed thermally at RT, 100, and 200 °C for 60 min. Figures 6a ‒ 6d show the representative transfer curves (drain current (ID) versus gate voltage (VG)) of the PDPP2DT-F2T2 FETs measured at a drain voltage of VD = –60 or +60 V. Ambipolar charge transport was observed based on the V-shaped transfer curves of four different solution-based PFETs. Negligible current hysteresis between the forward and reverse VG traces was observed in the curves. The hole or electron mobilities of the FETs were calculated in the respective saturation regimes based on the equation ID = CSµW(VG – VTH)2/2L,16, 49, 50 where CS is the specific capacitance of the gate dielectric, µ is carrier mobility, VTH is the threshold voltage, W is the channel width, and L is the channel length. The carrier mobility values of all the devices in all the different conditions are summarized in Table 2. The threshold voltages and on/off current ratios of the devices are summed up in Table 3. Figure 6e displays the dependence of carrier mobilities on both the solvent and the thermal annealing temperature. The carrier transport of all the solution-processed polymer FETs were improved with increasing annealing temperature because of the increased interchain interactions and the consolidated edge-on orientation in the films. Among the various samples, the CF-processed films showed the largest improvements in transport parameters because the CF-processed films originally contained a large portion of face-on oriented polymer domains and an irregularly-aggregated rough morphology at RT (see GIXD and AFM). The face-on oriented polymer chains transitioned to an edge-on orientation with larger crystalline domains after annealing at 200 °C. In contrast, the TMB-processed films had an edge-on crystalline, fibrous morphology (even at RT) so that the carrier mobilities were the highest among the series. The thermal annealing at higher temperature improved the film crystallinity and fibril structure even more, resulting in further enhancements in carrier mobilities. It is interesting to note that the hole mobilities were 10


Page 11 of 28


similar to (or sometimes lower than) the electron mobilities at RT for the same solution-processed PFETs, 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

but the hole mobilities were significantly enhanced (more than twofold) compared to the electron mobilities as the annealing temperature increased. This observation suggests that the formation of the J-aggregation and edge-on orientation upon thermal annealing are more favorable for hole transport in the case of the PDPP2DT-F2T2 polymer. Figure 6f shows the carrier mobilities of the PDPP2DT-F2T2 PFETs that were prepared from four different solutions and were annealed at 200 °C. The non-chlorinated solvent-processed FETs performed far better than the CF-processed FETs, and their carrier mobilities increased with increasing bps of the non-chlorinated solutions. The TMB-processed FETs displayed a maximum hole mobility of 1.28 cm2V-1s-1 and a maximum electron mobility of 0.39 cm2V-1s-1, which are among the highest carrier mobilities of non-chlorinated solvent-based polymer FETs.

25, 31, 32

The output curves (ID versus VD)

of the 200 °C–annealed PDPP2DT-F2T2 FETs in Figure S12 showed non-ohmic behavior at a low VG and saturation behavior at a high VG. We further fabricated an array of flexible PDPP2DT-F2T2 FETs using a non-chlorinated solvent (TMB) and a plastic PEN substrate and examined its electrical properties. Note the two differences in the device fabrication process: (i) the flexible PEN substrates were used in place of Si-wafers and (ii) the PDPP2DT-F2T2 films spin-coated from TBM solution were annealed at 150 °C instead of 200 °C because 150 °C was the highest temperature that prevented deformation of the PEN substrates. Figure 7a shows the schematic device structure and photographic image of the array of flexible PDPP2DT-F2T2 FETs fabricated on the PEN substrate. Transfer and output characteristics were obtained as shown in Figures 7b and 7c. The transfer curves exhibited ambipolar characteristics with negligible hysteresis. Even though the devices were fabricated on a plastic substrate without using any planarization layers, we obtained excellent hole and electron mobilities of 0.96 (0.84 ± 0.11) and 0.26 (0.23 ± 0.03) cm2V-1s-1, respectively. These mobilities are comparable to the highest values for flexible polymer FETs.30, 51, 52 Output curves exhibited a transition from non-ohmic to saturation behavior with increasing VG, as found in the Si-wafer substrate-based FETs. Finally, fatigue tests with bending and release cycles (tensile strain = 1%, bending radius = 6.4 mm) were performed on the array of the flexible PDPP2DT-F2T2 FETs. Even after 300 cycles, the device characteristics, i.e., carrier mobility, on/off current ratio, and threshold voltage were well maintained (Figures 7d and 7e).

4. CONCLUSION We synthesized a

PDPP2DT-F2T2

polymer

having

a

planar geometry

enforced

by

difluorobithiophene (F2T2) units, and we characterized the crystallinity and morphology of the polymer films that were coated from CF, TOL, XT, and TMB solutions and subsequently annealed at RT, 100, and 200 °C. As the bp of the non-chlorinated solvent used for processing increased, the polymer films were more crystalline, showing almost exclusive edge-on orientation and enhanced connection between polymer 11



Page 12 of 28

domains. These features were further enhanced by the subsequent thermal annealing process. For these 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

reasons, the PDPP2DT-F2T2 based FETs processed using the non-chlorinated solvents had performances in the order of TOL < XY < TMB, and all performed better than CF-processed polymer FETs. The 200 °Cannealed TMB-processed PDPP2DT-F2T2 FET devices displayed a maximum hole mobility of 1.28 cm2V1 -1

s and a maximum electron mobility of 0.39 cm2V-1s-1. Additionally, we fabricated an array of flexible

PDPP2DT-F2T2 FETs on plastic PEN substrates. These devices demonstrated excellent electrical performance and robust operation in the fatigue test. Therefore, this work demonstrates that high bp nonchlorinated solvents, which are environmentally benign, can facilitate the formation of highly crystalline features and provide high carrier mobility in polymer FETs

12


Page 13 of 28


Acknowledgement 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

This work was supported by a grant (NRF–2015M1A2A2056218) from the Technology Development Program to Solve Climate Change of the National Research Foundation (NRF) funded by the Ministry of Science, ICT and Future Planning and a grant (NRF–2015R1D1A1A01058493) from the Basic Science Program through the NRF funded by the Ministry of Education, the New & Renewable Energy of the Korean Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korean Government Ministry of Knowledge Economy (20163030013900), and Center for Advanced Soft Electronics (CASE) under the Global Frontier Research Program (NRF−2013M3A6A5073177).

Supporting Information Contact angles of organic solvents, H-NMR spectra of compounds and polymer, TGA, UV-visible absorption spectra, CVs, line-cut profile GIXD data, additional DFT calculations for (DPP2Me-T2), and output curves of polymer FETs.

13



Page 14 of 28

5. REFERENCES 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

(1) Baeg, K. J.; Caironi, M.; Noh, Y. Y. Toward Printed Integrated Circuits Based on Unipolar or Ambipolar Polymer Semiconductors. Adv. Mater. 2013, 25, 4210-4244. (2) Han, A.-R.; Dutta, G. K.; Lee, J.; Lee, H. R.; Lee, S. M.; Ahn, H.; Shin, T. J.; Oh, J. H.; Yang, C. Ε‐ Branched Flexible Side Chain Substituted Diketopyrrolopyrrole‐Containing Polymers Designed for High Hole and Electron Mobilities. Adv. Funct. Mater. 2015, 25, 247-254. (3) Sokolov, A. N.; Tee, B. C.; Bettinger, C. J.; Tok, J. B.-H.; Bao, Z. Chemical and Engineering Approaches to Enable Organic Field-Effect Transistors for Electronic Skin Applications. Acc. Chem. Res. 2011, 45, 361-371. (4) Kim, M. J.; Park, J. H.; Kang, B.; Kim, D.; Jung, A.-R.; Yang, J.; Kang, M. S.; Lee, D. Y.; Cho, K.; Kim, H.; Kim, B.; Cho, J. H. Low-Band-Gap Polymer-Based Ambipolar Transistors and Inverters Fabricated Using a Flow-Coating Method. J. Phys. Chem. C 2016, 120, 13865-13872. (5) Ostroverkhova, O. Organic Optoelectronic Materials: Mechanisms and Applications. Chem. Rev. 2016, 116, 13279-13412. (6) Lee, H.-S.; Lee, J. S.; Cho, S.; Kim, H.; Kwak, K.-W.; Yoon, Y.; Son, S. K.; Kim, H.; Ko, M. J.; Lee, D.-K.; Kim, J. Y.; Park, S.; Choi, D. H.; Oh, S. Y.; Cho, J. H.; Kim, B. Crystallinity-Controlled Naphthalenealt-Diketopyrrolopyrrole Copolymers for High-Performance Ambipolar Field Effect Transistors. J. Phys. Chem. C 2012, 116, 26204-26213. (7) Lee, J.; Han, A.-R.; Kim, J.; Kim, Y.; Oh, J. H.; Yang, C. Solution-Processable Ambipolar Diketopyrrolopyrrole–Selenophene Polymer with Unprecedentedly High Hole and Electron Mobilities. J. Am. Chem. Soc. 2012, 134, 20713-20721. (8) Venkateshvaran, D.; Nikolka, M.; Sadhanala, A.; Lemaur, V.; Zelazny, M.; Kepa, M.; Hurhangee, M.; Kronemeijer, A. J.; Pecunia, V.; Nasrallah, I.; Romanov , I.; Broch, K.; McCulloch, I.; Emin, D.; Olivier, Y.; Cornil, J.; Beljonne, D.; Sirringhaus, H. Approaching Disorder-Free Transport in High-Mobility Conjugated Polymers. Nature 2014, 515, 384-388. (9) Sirringhaus, H.; Friend, R.; Li, X.; Moratti, S.; Holmes, A.; Feeder, N. Bis(dithienothiophene) Organic Field-Effect Transistors with a High ON/OFF Ratio. Appl. Phys. Lett. 1997, 71, 3871-3873. (10) Li, J.; Qin, F.; Li, C. M.; Bao, Q.; Chan-Park, M. B.; Zhang, W.; Qin, J.; Ong, B. S. HighPerformance Thin-Film Transistors from Solution-Processed Dithienothiophene Polymer Semiconductor Nanoparticles. Chem. Mater. 2008, 20, 2057-2059. (11) McCulloch, I.; Heeney, M.; Chabinyc, M. L.; DeLongchamp, D.; Kline, R. J.; Cölle, M.; Duffy, W.; Fischer, D.; Gundlach, D.; Hamadani, B.; Hamilton, R.; Richter, L.; Salleo, A.; Shkunov, M.; Sparrowe, D.; Tierney, S.; Zhang, W. Semiconducting Thienothiophene Copolymers: Design, Synthesis, Morphology, and Performance in Thin‐Film Organic Transistors. Adv. Mater. 2009, 21, 1091-1109. (12) He, M.; Li, J.; Sorensen, M. L.; Zhang, F.; Hancock, R. R.; Fong, H. H.; Pozdin, V. A.; Smilgies, D.M.; Malliaras, G. G. Alkylsubstituted Thienothiophene Semiconducting Materials: Structure−Property Relationships. J. Am. Chem. Soc. 2009, 131, 11930-11938. (13) Meager, I.; Ashraf, R. S.; Rossbauer, S.; Bronstein, H.; Donaghey, J. E.; Marshall, J.; Schroeder, B. C.; Heeney, M.; Anthopoulos, T. D.; McCulloch, I. Alkyl Chain Extension as a Route to Novel Thieno[3,2b]thiophene Flanked Diketopyrrolopyrrole Polymers for Use in Organic Solar Cells and Field Effect Transistors. Macromolecules 2013, 46, 5961-5967. (14) Chen, M. S.; Niskala, J. R.; Unruh, D. A.; Chu, C. K.; Lee, O. P.; Fréchet, J. M. Control of PolymerPacking Orientation in Thin Films through Synthetic Tailoring of Backbone Coplanarity. Chem. Mater. 2013, 25, 4088-4096. (15) Kim, G.; Kang, S.-J.; Dutta, G. K.; Han, Y.-K.; Shin, T. J.; Noh, Y.-Y.; Yang, C. A ThienoisoindigoNaphthalene Polymer with Ultrahigh Mobility of 14.4 cm2/V·s that Substantially Exceeds Benchmark Values for Amorphous Silicon Semiconductors. J. Am. Chem. Soc. 2014, 136, 9477-9483. (16) Zaumseil, J.; Sirringhaus, H. Electron and Ambipolar Transport in Organic Field-Effect Transistors. Chem. Rev. 2007, 107, 1296-1323. (17) Hoeben, F. J.; Jonkheijm, P.; Meijer, E.; Schenning, A. P. About Supramolecular Assemblies of πConjugated Systems. Chem. Rev. 2005, 105, 1491-1546. (18) Lee, J.; Chung, J. W.; Kim, D. H.; Lee, B.-L.; Park, J.-I.; Lee, S.; Häusermann, R.; Batlogg, B.; Lee, 14


Page 15 of 28

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


S.-S.; Choi, I.; Kim, I. W.; Kang, M. S. Thin Films of Highly Planar Semiconductor Polymers Exhibiting Band-Like Transport at Room Temperature. J. Am. Chem. Soc. 2015, 137, 7990-7993. (19) Yamashita, Y.; Hinkel, F.; Marszalek, T.; Zajaczkowski, W.; Pisula, W.; Baumgarten, M.; Matsui, H.; Müllen, K.; Takeya, J. Mobility Exceeding 10 cm2/(V·s) in Donor–Acceptor Polymer Transistors with BandLike Charge Transport. Chem. Mater. 2016, 28, 420-424. (20) Hendriks, K. H.; Heintges, G. H.; Wienk, M. M.; Janssen, R. A. Comparing Random and Regular Diketopyrrolopyrrole–Bithiophene–Thienopyrrolodione Terpolymers for Organic Photovoltaics. J. Mater. Chem. A 2014, 2, 17899-17905. (21) Li, Y.; Singh, S. P.; Sonar, P. A High Mobility P‐Type DPP‐Thieno[3,2‐b]thiophene Copolymer for Organic Thin‐Film Transistors. Adv. Mater. 2010, 22, 4862-4866. (22) Nielsen, C. B.; Turbiez, M.; McCulloch, I. Recent Advances in the Development of Semiconducting Dpp‐Containing Polymers for Transistor Applications. Adv. Mater. 2013, 25, 1859-1880. (23) Bronstein, H.; Chen, Z.; Ashraf, R. S.; Zhang, W.; Du, J.; Durrant, J. R.; Shakya Tuladhar, P.; Song, K.; Watkins, S. E.; Geerts, Y.; Wienk, M. M.; Janssen, R. A.; Anthopoulos, T.; Sirringhaus, H.; Heeney, M.; McCulloch, I. Thieno[3,2‐b]thiophene−Diketopyrrolopyrrole-Containing Polymers for High-Performance Organic Field-Effect Transistors and Organic Photovoltaic Devices. J. Am. Chem. Soc. 2011, 133, 32723275. (24) Li, Y.; Sonar, P.; Murphy, L.; Hong, W. High Mobility Diketopyrrolopyrrole (DPP)-Based Organic Semiconductor Materials for Organic Thin Film Transistors and Photovoltaics. Energy Environ. Sci. 2013, 6, 1684-1710. (25) Yun, H. J.; Lee, G. B.; Chung, D. S.; Kim, Y. H.; Kwon, S. K. Novel Diketopyrroloppyrrole Random Copolymers: High Charge‐Carrier Mobility from Environmentally Benign Processing. Adv. Mater. 2014, 26, 6612-6616. (26) Zhang, W.; Shi, K.; Huang, J.; Gao, D.; Mao, Z.; Li, D.; Yu, G. Fluorodiphenylethene-Containing Donor–Acceptor Conjugated Copolymers with Noncovalent Conformational Locks for Efficient Polymer Field-Effect Transistors. Macromolecules 2016, 49, 2582-2591. (27) Martin, E. T.; McGuire, C. M.; Mubarak, M. S.; Peters, D. G. Electroreductive Remediation of Halogenated Environmental Pollutants. Chem. Rev. 2016, 116, 15198-15234. (28) Chueh, C.-C.; Yao, K.; Yip, H.-L.; Chang, C.-Y.; Xu, Y.-X.; Chen, K.-S.; Li, C.-Z.; Liu, P.; Huang, F.; Chen, Y.; Chen, W.-C.; Jen, A. K.-Y. Non-Halogenated Solvents for Environmentally Friendly Processing of High-Performance Bulk-Heterojunction Polymer Solar Cells. Energy Environ. Sci. 2013, 6, 3241-3248. (29) Guo, X.; Zhang, M.; Cui, C.; Hou, J.; Li, Y. Efficient Polymer Solar Cells Based on Poly(3Hexylthiophene) and Indene–C60 Bisadduct Fabricated with Non-Halogenated Solvents. ACS Appl. Mater. Interfaces 2014, 6, 8190-8198. (30) Yan, H.; Chen, Z.; Zheng, Y.; Newman, C.; Quinn, J. R.; Dötz, F.; Kastler, M.; Facchetti, A. A HighMobility Electron-Transporting Polymer for Printed Transistors. Nature 2009, 457, 679-686. (31) Lee, W. Y.; Giri, G.; Diao, Y.; Tassone, C. J.; Matthews, J. R.; Sorensen, M. L.; Mannsfeld, S. C.; Chen, W. C.; Fong, H. H.; Tok, J. B. H.; Toney, M. F.; He, M.; Bao, Z. Effect of Non‐Chlorinated Mixed Solvents on Charge Transport and Morphology of Solution‐Processed Polymer Field‐Effect Transistors. Adv. Funct. Mater. 2014, 24, 3524-3534. (32) Choi, H. H.; Baek, J. Y.; Song, E.; Kang, B.; Cho, K.; Kwon, S. K.; Kim, Y. H. A Pseudo‐Regular Alternating Conjugated Copolymer Using an Asymmetric Monomer: A High‐Mobility Organic Transistor in Nonchlorinated Solvents. Adv. Mater. 2015, 27, 3626-3631. (33) Kim, M. J.; Choi, J. Y.; An, G.; Kim, H.; Kang, Y.; Kim, J. K.; Son, H. J.; Lee, J. H.; Cho, J. H.; Kim, B. A New Rigid Planar Low Band Gap PTTDPP-DT-DTT Polymer for Organic Transistors and Performance Improvement through the Use of a Binary Solvent System. Dyes Pigm. 2016, 126, 138-146. (34) Tada, K.; Onoda, M. Poor Man's Green Bulk Heterojunction Photocells: A Chlorine-Free Solvent for Poly(3-Hexylthiophene)/C60 Composites. Solar Energy Mater. Solar Cells 2012, 100, 246-250. (35) Nketia‐Yawson, B.; Lee, H. S.; Seo, D.; Yoon, Y.; Park, W. T.; Kwak, K.; Son, H. J.; Kim, B.; Noh, Y. Y. A Highly Planar Fluorinated Benzothiadiazole‐Based Conjugated Polymer for High‐Performance Organic Thin‐Film Transistors. Adv. Mater. 2015, 27, 3045-3052. (36) Liu, X.; Sun, Y.; Hsu, B. B.; Lorbach, A.; Qi, L.; Heeger, A. J.; Bazan, G. C. Design and Properties of Intermediate-Sized Narrow Band-Gap Conjugated Molecules Relevant to Solution-Processed Organic 15



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

Page 16 of 28

Solar Cells. J. Am. Chem. Soc. 2014, 136, 5697-5708. (37) Letizia, J. A.; Salata, M. R.; Tribout, C. M.; Facchetti, A.; Ratner, M. A.; Marks, T. J. N-Channel Polymers by Design: Optimizing the Interplay of Solubilizing Substituents, Crystal Packing, and FieldEffect Transistor Characteristics in Polymeric Bithiophene-Imide Semiconductors. J. Am. Chem. Soc. 2008, 130, 9679-9694. (38) Lee, J. S.; Son, S. K.; Song, S.; Kim, H.; Lee, D. R.; Kim, K.; Ko, M. J.; Choi, D. H.; Kim, B.; Cho, J. H. Importance of Solubilizing Group and Backbone Planarity in Low Band Gap Polymers for High Performance Ambipolar Field-Effect Transistors. Chem. Mater. 2012, 24, 1316-1323. (39) Cho, S.; Lee, J.; Tong, M.; Seo, J. H.; Yang, C. Poly(Diketopyrrolopyrrole‐Benzothiadiazole) with Ambipolarity Approaching 100% Equivalency. Adv. Funct. Mater. 2011, 21, 1910-1916. (40) Lin, C.-J.; Lee, W.-Y.; Lu, C.; Lin, H.-W.; Chen, W.-C. Biaxially Extended Thiophene–Fused Thiophene Conjugated Copolymers for High Performance Field Effect Transistors. Macromolecules 2011, 44, 9565-9573. (41) Lin, H.-W.; Lee, W.-Y.; Chen, W.-C. Selenophene-DPP Donor–Acceptor Conjugated Polymer for High Performance Ambipolar Field Effect Transistor and Nonvolatile Memory Applications. J. Mater. Chem. 2012, 22, 2120-2128. (42) Choi, J. Y.; Kang, W.; Kang, B.; Cha, W.; Son, S. K.; Yoon, Y.; Kim, H.; Kang, Y.; Ko, M. J.; Son, H. J.; Cho, K.; Cho, J. H.; Kim, B. High Performance of Low Band Gap Polymer-Based Ambipolar Transistor Using Single-Layer Graphene Electrodes. ACS Appl. Mater. Interfaces 2015, 7, 6002-6012. (43) Lee, S.; Jo, G.; Kang, S. J.; Wang, G.; Choe, M.; Park, W.; Kim, D. Y.; Kahng, Y. H.; Lee, T. Enhanced Charge Injection in Pentacene Field‐Effect Transistors with Graphene Electrodes. Adv. Mater. 2011, 23, 100-105. (44) Lee, W. H.; Park, J.; Sim, S. H.; Lim, S.; Kim, K. S.; Hong, B. H.; Cho, K. Surface-Directed Molecular Assembly of Pentacene on Monolayer Graphene for High-Performance Organic Transistors. J. Am. Chem. Soc. 2011, 133, 4447-4454. (45) Jung, M.; Yoon, Y.; Park, J. H.; Cha, W.; Kim, A.; Kang, J.; Gautam, S.; Seo, D.; Cho, J. H.; Kim, H.; Choi, J. Y.; Chae, K. H.; Kwak, K.; Son, H. J.; Ko, M. J.; Kim, H.; Lee, D.-K.; Kim, J. Y.; Choi, D. H.; Kim, B. Nanoscopic Management of Molecular Packing and Orientation of Small Molecules by a Combination of Linear and Branched Alkyl Side Chains. ACS nano 2014, 8, 5988-6003. (46) Lei, T.; Dou, J. H.; Pei, J. Influence of Alkyl Chain Branching Positions on the Hole Mobilities of Polymer Thin‐Film Transistors. Adv. Mater. 2012, 24, 6457-6461. (47) Tsao, H. N.; Cho, D. M.; Park, I.; Hansen, M. R.; Mavrinskiy, A.; Yoon, D. Y.; Graf, R.; Pisula, W.; Spiess, H. W.; Müllen, K. Ultrahigh Mobility in Polymer Field-Effect Transistors by Design. J. Am. Chem. Soc. 2011, 133, 2605-2612. (48) Lee, J.; Han, A.-R.; Yu, H.; Shin, T. J.; Yang, C.; Oh, J. H. Boosting the Ambipolar Performance of Solution-Processable Polymer Semiconductors via Hybrid Side-Chain Engineering. J. Am. Chem. Soc. 2013, 135, 9540-9547. (49) Kang, M. S.; Frisbie, C. D. A Pedagogical Perspective on Ambipolar FETs. ChemPhysChem 2013, 14, 1547-1552. (50) Horowitz, G. Organic Field-Effect Transistors. Adv. Mater. 1998, 10, 365-377. (51) Fukuda, K.; Takeda, Y.; Yoshimura, Y.; Shiwaku, R.; Tran, L. T.; Sekine, T.; Mizukami, M.; Kumaki, D.; Tokito, S. Fully-Printed High-Performance Organic Thin-Film Transistors and Circuitry on One-MicronThick Polymer Films. Nat. Commun. 2014, 5, 4147. (52) Xu, J.; Wang, S.; Wang, G.-J. N.; Zhu, C.; Luo, S.; Jin, L.; Gu, X.; Chen, S.; Feig, V. R.; To, J. W.; Rondeau-Gagné, S.; Park, J.; Schroeder, B. C.; Lu, C.; Oh, J. Y.; Wang, Y.; Kim, Y. H.; Yan, H.; Sinclair, R.; Zhou, D.; Xue, G.; Murmann, B.; Linder, C.; Cai, W.; Tok, J. B.-H.; Chung, J. W.; Bao, Z. Highly Stretchable Polymer Semiconductor Films through the Nanoconfinement Effect. Science 2017, 355, 59-64.

16


Page 17 of 28

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


Scheme 1. Synthetic route to PDPP2DT-F2T2.

17



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

Page 18 of 28

Figure 1. (a) UV-visible absorption spectra of PDPP2DT-F2T2 films spin-coated from CF, TOL, XY, and TMB. (b) UV-visible absorption spectra of PDPP2DT-F2T2 in TMB solution as a function of solution temperature. (c) UV-visible absorption spectra of PDPP2DT-F2T2 films spin-coated from TMB and annealed at RT, 100, and 200 °C. (d) Cyclic voltammogram of PDPP2DT-F2T2 film.

18


Page 19 of 28

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


Figure 2. (a) Surface plots and energy levels of the frontier orbitals of (DPP2Me-F2T2)4. (b) Optimized geometry of (DPP2Me-F2T2)4. Dihedral angles and F•••S distances are indicated.

19



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

Page 20 of 28

Figure 3. GIXD images of (a,e) CF, (b,f) TOL, (c,g) XY, and (d,h) TMB‒used PDPP2DT-F2T2 films that were annealed at RT (top) and 200 °C (bottom).

20


Page 21 of 28

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


Figure 4. Line-cut profiles in the qy (left) and qz (right) directions of PDPP2DT-F2T2 films annealed at RT (top) and 200 °C (bottom) for films processed in (a) CF, (b) TOL, (c) XY, and (d) TMB.

21



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

Figure 5. Topography and phase images of PDPP2DT-F2T2 films processed in: (a,a’, e,e’) CF, (b,b’,f,f’) TOL, (c,c’,g,g’) XY, and (d,d’,h,h’) TMB.

22


Page 22 of 28

Page 23 of 28

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


Figure 6. (a-d) Transfer characteristics at a fixed VD of –60 V or +60 V for the PFETs based on the PDPP2DT-F2T2 films that were coated from CF, TOL, XY, or TMB solutions and annealed at RT, 100, and 200 °C. (e) Average hole and electron mobilities of the PDPP2DT-F2T2 FETs in all the conditions. (f) Average hole and electron mobilities of the FETs based on the PDPP2DT-F2T2 films annealed at 200 °C.

23



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

Page 24 of 28

Figure 7. (a) Schematic device structure and photographic image of the PDPP2DT-F2T2 FET array fabricated on a flexible PEN substrate. The PDPP2DT-F2T2 film was spin-coated from TMB solutions and annealed at 150 °C. (b) Transfer and (c) output characteristics of the flexible PDPP2DT-F2T2 FETs. (d) Evolution of transfer curves during bending (1% tensile strain) and release cycles. (e) Variation of carrier mobility, on/off current ratio, and threshold voltage as a function of bending-release cycles.

24


Page 25 of 28

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


Table 1. Parameters associated with the π‒π spacing and lamellar spacing. Annealing temp./ solvent

π‒π spacing from (010) in the qy direction -1

q(010)(Å )

-1

FWHM(Å )

d(Å)a

CF 1.740 0.0786 3.611 TOL 1.724 0.0808 3.645 RT XY 1.727 0.0765 3.639 TMB 1.725 0.0771 3.642 CF 1.729 0.0635 3.635 1.715 0.0623 3.664 200 TOL °C XY 1.719 0.0572 3.656 TMB 1.718 0.0541 3.657 a π‒π spacing distance; b Lamellar spacing distance

lamellar spacing from (200) in the qz direction -1

-1

LC(nm)

q(200)(Å )

FWHM(Å )

d(Å)b

LC(nm)

7.192 7.001 7.394 7.339 8.911 9.070 9.886 10.448

0.527 0.535 0.531 0.531 0.522 0.552 0.551 0.551

0.0594 0.0750 0.0778 0.0698 0.0449 0.0556 0.0508 0.0493

22.844 23.472 23.658 23.646 24.078 22.760 22.824 22.814

9.517 7.543 7.265 8.099 12.589 10.163 11.124 11.476

25



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

Table 2. Carrier mobilities of PDPP2DT-F2T2 TGBC transistors (units: cm2V–1s–1). Solvent Carrier 25 °C 100 °C

Page 26 of 28

200 °C

hole electron

0.014 (0.011±0.001) 0.013 (0.007±0.001)

0.127 (0.11±0.02) 0.059 (0.041±0.005)

0.427 (0.40±0.04) 0.180 (0.15±0.02)

Hole

0.028 (0.021±0.002)

0.165 (0.15±0.01)

0.518 (0.45±0.06)

electron

0.046 (0.041±0.004)

0.093 (0.088±0.008)

0.229 (0.21±0.02)

XY

hole electron

0.053 (0.047±0.005) 0.096 (0.088±0.008)

0.189 (0.18±0.01) 0.167 (0.15±0.01)

0.805 (0.80±0.09) 0.343 (0.31±0.03)

TMB

hole electron

0.100 (0.10±0.01) 0.129 (0.12±0.02)

0.307 (0.27±0.03) 0.195 (0.17±0.02)

1.28 (1.1±0.2) 0.39 (0.36±0.03)

CF TOL

The numbers are provided in the following order: maximum mobility, average, and standard deviation.

26


Page 27 of 28

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


Table 3. Threshold voltages and on/off current ratios of PDPP2DT-F2T2 TGBC transistors. Solvent

CF

TOL

XY

TMB

25 °C

100 °C

200 °C

Vth (hole)

-62.0 (±6.2) V

-61.3 (±5.9) V

-58.3 (±6.0) V

Vth (electron)

76.0 (±7.3) V

76.6 (±7.6) V

76.6 (±7.8) V

5

Ion/Ioff (hole)

2.2 (±0.2) × 10

1.0 (±0.4) × 10

3.2 (±0.6) × 106

Ion/Ioff (electron)

5.6 (±0.1) × 104

4.9 (±0.4) × 105

9.2 (±0.6) × 105

Vth (hole)

-54.1 (±5.2) V

-58.4 (±5.8) V

-57.6 (±5.7) V

Vth (electron)

78.7 (±7.9) V

77.1 (±7.7) V

79.5 (±8.0) V

5

6

Ion/Ioff (hole)

2.3 (±0.2) × 10

1.2 (±0.8) × 10

3.4 (±1.1) × 106

Ion/Ioff (electron)

2.6 (±0.2) × 105

5.1 (±0.6) × 105

2.1 (±0.6) × 106

Vth (hole)

-56.4 (±5.6) V

-53.9 (±4.9) V

-60.6 (±5.2) V

Vth (electron)

78.2 (±8.3) V

76.1 (±6.0) V

77.5 (±6.6) V

Ion/Ioff (hole)

3.5 (±0.3) × 105

1.3 (±0.6) × 106

3.6 (±1.4) × 106

Ion/Ioff (electron)

5.2 (±0.5) × 105

1.5 (±0.9) × 106

3.4 (±1.1) × 106

Vth (hole)

-60.2 (±4.9) V

-60.6 (±5.5) V

-55.0 (±5.8) V

Vth (electron)

77.6 (±8.3) V

76.3 (±8.0) V

76.1 (±7.1) V

5

6

Ion/Ioff (hole)

5.3 (±0.5) × 10

1.3 (±0.8) × 10

8.2 (±3.1) × 106

Ion/Ioff (electron)

6.3 (±0.4) × 105

1.8 (±0.6) × 106

3.9 (±1.3) × 106

27


6


TOC Figure 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

28


Page 28 of 28

A Nonchlorinated Solvent-Processable Fluorinated Planar Conjugated

Recommend Documents