Difluorobenzothiadiazole and Selenophene Based Conjugated

Subscriber access provided by Kaohsiung Medical University

Organic Electronic Devices

Difluorobenzothiadiazole and Selenophene Based Conjugated Polymer Demonstrating an Effective Hole Mobility Exceeding 5 cm2V-1s-1 with Solid-State Electrolyte Dielectric Benjamin Nketia-Yawson, A-Ra Jung, Hieu Dinh Nguyen, Kyung-Koo Lee, BongSoo Kim, and Yong Young Noh ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b14176 • Publication Date (Web): 21 Aug 2018 Downloaded from http://pubs.acs.org on August 24, 2018

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 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 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.

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 26 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

Difluorobenzothiadiazole and Selenophene Based Conjugated Polymer Demonstrating an Effective Hole Mobility Exceeding 5 cm2V-1s-1 with Solid-State Electrolyte Dielectric Benjamin Nketia-Yawson,†,ǁ A-Ra Jung,‡,ǁ Hieu Dinh Nguyen,§ Kyung-Koo Lee,§ BongSoo Kim,*,‡ and Yong-Young Noh*,†

†

Department of Energy and Materials Engineering, Dongguk University, 30 Pildong-ro, 1-gil

Jung-gu, Seoul, 04620, Republic of Korea. ‡

Department of Science Education, Ewha Womans University, 52 Ewhayeodae-gil, Seodaemun-

gu, Seoul 03760, Republic of Korea. §

Department of Chemistry, Kunsan National University, 558 Daehak-ro, Kunsan-si 54150,

Republic of Korea.

Keywords: organic thin film transistors, donor-acceptor conjugated polymers, chain orientation, carrier mobility, solid-state electrolyte

1

ACS Paragon Plus Environment

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

ABSTRACT We report synthesis of a new PDFDSe polymer based on a planar 4,7-bis(4,4-bis(2-ethylhexyl)4H-silolo[3,2-b:4,5-b']dithiophen-2-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole (DFD) moieties and selenophene linkages. The planar backboned PDFDSe polymer exhibits highest occupied molecular orbital and lowest unoccupied molecular orbital levels of -5.13 and -3.56 eV, respectively, and generates a well-packed highly crystalline states in films with exclusive edgeon orientations. PDFDSe thin film was incorporated as a channel material in top gate bottom contact organic thin film transistor (OTFT) with a solid-state electrolyte gate insulator (SEGI) composed

of

P(VDF-TrFE)/poly(vinylidene

fluoride-co-hexafluroropropylene)/1-ethyl-3-

methylimidazolium bis(trifluoromethylsulfonyl)imide, which exhibited a remarkably high hole mobility up to µ = 20.3 cm2V-1s-1 corresponding to effective hole mobility exceeding 5 cm2V-1s-1, and a very low threshold voltage of -1 V. These device characteristics are associated with the high carrier density in the semiconducting channel region, induced by the high capacitance of the SEGI layer. The excellent carrier mobility from the PDFDSe/SEGI device demonstrates a great potential of semiconducting polymer TFTs as electronic components in future electronic applications.

2


Page 2 of 26

Page 3 of 26 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


INTRODUCTION Conjugated polymers have been actively developed to improve electrical performance of solution processed organic thin film transistors (OTFTs).1,2 The merits of conjugated polymers include light weight, high flexibility, and low cost to fabricate electronic devices by high throughput and large area printing.3,4 Conjugated polymers can achieve high charge carrier mobility due to charge delocalization in the well-overlapped π orbital system and close π-π interchain stacking.2,5 Conjugated polymer electronic structure and conductivity can be tuned by employing a combination of various electron rich (donor) and electron deficient (acceptor) moieties in the polymer backbone.2,6,7 Planar backbone structures are desirable to facilitate good interchain packing, which can enhance charge carrier mobility. Carrier mobilities (µ) of TFTs based on donor-acceptor conjugated polymers with high backbone planarity have recently exceeded 10 cm2V-1s-1,8–11 and further improvements by the use of ionic additives are being pursued.12,13 To improve OTFT performance, one must optimize semiconducting film microstructures, contact electrodes, and gate dielectric. High capacitance gate dielectric materials, such as high kmaterials,14–16 crosslinked insulating polymers,17–20 and ionic composites,21–23 have been developed in addition to the most commonly used octadecylsilyl group treated SiO2 gate dielectric layer. These high capacitance dielectric materials can induce high charge density at the semiconducting layer/gate dielectric interface, enabling not only high carrier mobility, but also low operating voltage. Several research groups have demonstrated high mobility and low voltage operation OTFTs with high-k polymeric dielectrics, such as poly(vinylidenefluoridetrifluoroethylene) chlorotrifluoroethylene)

(P(VDF-TrFE)),10,24

poly(vinylidenefluoride-trifluoroethylene-

(P(VDF-TrFE-CTFE)),24,25

3


poly(vinylidene

fluoride-


bromotrifluoroethylene) (P(VDF-BTFE)),26 poly(vinylidene fluoride-co-hexafluroropropylene) (P(VDF-HFP)),27 and engineered blend dielectrics.28–30 In this regard, we recently developed high capacitance solid-state electrolyte gate insulators (SEGIs), formed by blending P(VDFTrFE) polymer and an ion gel composed of a mixture of P(VDF-HFP) with 1-ethyl-3methylimidazolium bis(trifluoromethylsulfonyl) imide ([EMIM][TFSI]) ion liquid.31 In particular, the devised SEGI gate dielectric has significantly enhanced OTFT performance for conjugated polymers. Operating voltages were 2 V or lower, and excellent carrier mobilities were obtained for 3–13 cm2V-1s-1 with known conjugated polymers, such as poly(3hexylthiophene) and diketopyrrolopyrrole thieno[3,2-b]thiophene polymer. In contrast to ion gel or liquid ion based dielectric films, thin metal films as the gate electrode can be directly deposited on the insulating layer, which greatly improves device stability and reproducibility. To further improve device performance, we need to develop an optimal conjugated polymer that can be well coordinated with the SEGI dielectric layer. We synthesize a new conjugated polymer poly(4-(4,4-bis(2-ethylhexyl)-4H-silolo[3,2b:4,5-b’]dithiophene-2-yl)-7-(4,4-bis(2-ethylhexyl)-6-(selenophene-2-yl)-4H-silolo[3,2-b:4,5b’]dithiophene-2-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole (PDFDSe). Previous studies have shown that poly(4-(4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b’]dithiophene-2-yl)-7-(4,4-bis(2ethylhexyl)-6-(thiophene-2-yl)-4H-silolo[3,2-b:4,5-b’]dithiophene-2-yl)-5,6difluorobenzo[c][1,2,5]thiadiazole (PDFDT) polymer exhibited excellent performance,24,31 because the PDFDT polymer is planar and has high chain-to-chain interactions through its polymer backbone geometry. To enforce the interchain interaction, selenophenes were adopted as

links

between

4,7-bis(4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b']dithiophen-2-yl)-5,6-

difluorobenzo[c][1,2,5]thiadiazole (DFD) moieties, which are highly conjugated planar systems

4


Page 4 of 26

Page 5 of 26 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


through non-covalent F···S interactions, and facilitate π‒π, C-H···F, and C-F···π interchain interactions.24,32,33 Also, selenophene-contained polymers have often displayed superior performance to thiophene-based analog polymers,11,34,35 because selenophenes have stronger heteroaromatic interaction than thiophenes and promote well-ordered morphology. In addition, when selenophenes are replaced with thiophenes in the conjugated backbone, the highest occupied molecular orbital (HOMO) level tends increase slightly.36 The current study shows that PDFDSe polymer HOMO is 0.1 eV higher than that of PDFDT polymer, which implies the PDFDSe polymer can be more oxidizable, and hence PDFDSe based OTFT devices can be more easily tuned by gate bias modulation. In contrast to PDFDT films, crystalline domains of PDFDSe films are predominantly edge-on orientation, which is beneficial for carrier transport in TFT device geometries. Thus, we found PDFDSe TFT devices exhibited enhanced carrier mobility compared to PDFDT devices. In particular, we achieved an extremely high hole mobility, µ = 20.3 cm2V-1s-1 with the high-k gate dielectric P(VDF-TrFE)/P(VDFHFP)/[EMIM][TFSI] SEGI.

5



RESULTS AND DISCUSSION Synthesis and Characterization. Scheme 1 displays the synthetic routes to PDFDSe and PDFDT polymers by Stille polymerization. The synthetic details of PDFDSe polymer are described in in Supporting Information and the PDFDT polymer was re-prepared for the further characterizations following our previous report.24 Both polymers were purified by sequential Soxhlet extraction using methanol, acetone, dichloromethane, and chloroform. Chloroform batches were used for electrical characterization. The number average molecular weight (Mn) and polydispersity index (PDI) of the obtained PDFDSe polymer were 28,000 Da and 2.64, respectively. UV-visible absorption spectra of polymers in solution and film states were obtained to compare PDFDT and PDFDSe polymer the optical properties. The PDFDSe polymer was highly aggregating in solution (Figure 1a), significantly more than PDFDT (Figure S6).24 In film, PDFDSe absorbed UV-visible light up to 790 nm, corresponding to 1.57 eV optical bandgap, with peaks at 491, 659, and 717 nm. As reported previously,24 the 491 nm peak was attributed to the HOMO-3 to LUMO+2 and HOMO to LUMO+3 transitions (Figure S7). The absorption maximum position changed from 693 in solution to 717 nm in film, which indicated that interchain interaction between polymer chains was intensified during solidification. UV-visible absorption features between PDFDSe and PDFDT films were very similar in the long wavelength region, with slightly more (3 nm) red-shift for PDFDSe (Figure 1b). Thermal annealing did not change light absorption features for either polymer (Figure S8). Cyclic voltammetry provided polymer film energy levels using a standard three electrode cell with acetonitrile solution containing 0.1 M tetrabutylammonium hexafluorophosphate. Oxidation potentials were determined to be 0.33 and 0.44 V with respect to ferrocene oxidation potential for PDFDSe and PDFDT films (Figure 1c), which correspond to -5.13 and -5.24 eV,

6


Page 6 of 26

Page 7 of 26 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


respectively. We note that the PDFDSe film was electrochemically reversible and stable over several cycles (Figure S9). Additionally, quantum mechanical density functional theory (DFT) calculations were performed for the three repeat units of each polymer, (DFDSe)3 and (DFDT)3. HOMO and LUMO overall electron density distributions were almost identical between the molecules (Figure 1d). A well-conjugated system was observed for the HOMOs. A strong contribution of difluorobenzothiazole moieties was found for the LUMOs, and the slightly lower LUMO of (DFDSe)3 than the LUMO of (DFDT)3 (-3.08 and -3.05 eV, respectively) was found.

Microstructure and Surface Morphology. Interchain stacking and chain orientation were examined using grazing incidence X-ray diffraction (GIXD). Both PDFDSe and PDFDT polymer films showed improved crystallinity as thermal annealing temperature increased (Figure 2a–c). We note that PDFDSe polymers adopted mainly edge-on orientation, where the high order lamellar peaks appeared clearly in the out-of-plane direction and the strong (010) peak appeared in the in-plane direction. Thermally annealed PDFDT showed a mixture of edge-on and face-on orientations, with both lamellar and π‒π stacking (010) peaks observed in the out-of-plane direction. Figure 2d compares polymer chain orientations. The intensity-azimuth angle dependence revealed a narrow Gaussian shape and an arc shape for PDFDSe and PDFDT films, respectively, indicating that PDFDSe films have more uniform edge-on orientation than PDFDT films. Line-cut profiles in the qz and qy directions (Figure S10 and S11) show nearly the same lamellar spacings at 16.5 Å (qz = 0.381 Å-1) and 16.9 Å (qz = 0.371 Å-1) for 200°C annealed PDFDSe and 150°C annealed PDFDT polymer films, respectively. The π‒π stacking distances were nearly the same (3.64 Å (qy = 1.724 Å-1) and 3.65 Å (qy = 1.723 Å-1) for 200°C annealed PDFDSe and 150°C annealed PDFDT polymer films, respectively). More importantly, lamellar

7



and (010) peak intensities were stronger for PDFDSe than PDFDT. The tighter and more crystalline packing of PDFDSe chains in film can be attributed to the fact that selenophenes have stronger heteroaromatic interaction than thiophenes. Polymer film surface morphology of PDFDSe films were investigated using atomic force microscopy (AFM) as a function of thermal annealing temperature (Figure S12). As-cast PDFDSe film was composed of fine nanoscale fibers, and more aggregated nanofibril line features with annealing were developed, consistent with crystalline feature development on the thermally annealed PDFDSe films.

TFT Device Performance. To examine electrical properties of the PDFDSe polymer, top gate bottom contact (TGBC) PDFDSe TFTs with PMMA and P(VDF-TrFE) gate dielectric were fabricated. Figure 3a displays chemical structure of PMMA and P(VDF-TrFE) polymers and schematic TGBC device structure. TGBC PDFDSe/PMMA TFTs with channel width (W) of 1 mm and channel length (L) of 10 µm were first made to find optimal thermal annealing temperature. PDFDSe films were thermally annealed at 150, 200, 250°C, and 200°C-annealed PDFDSe device displayed the best performance (Figure S13a). However, the output curves of 10 µm-L devices exhibited no saturation at high drain voltage (Vd) (Figure S13b), evidence of short channel effects due to high contact resistance.24,38,39 Thus, the channel length was extended to be 50 µm. The 50 µm-L devices with 200°C annealed PDFDSe films exhibited saturation behavior (Figure 3b). The representative output characteristics of PDFDSe/PMMA TFT devices is shown in Figure 3b(top). Figure 3c shows representative transfer characteristics of optimized 200°C annealed PDFDSe TFT with 1 mm-W and 50 µm-L. The PDFDSe/PMMA TFTs exhibited the maximum hole mobility µh = 0.18 cm2V-1s-1 (average ≈ 0.16±0.01cm2V-1s-1), and a threshold voltage Vth = -29.3±1.4 V. On the other hand, devices employing high capacitance neat P(VDF8


Page 8 of 26

Page 9 of 26 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


TrFE) dielectric layer provided even higher carrier mobility at significantly lower voltage. The output and transfer characteristics of PDFDSe/P(VDF-TrFE) based devices are shown in Figure 3b(bottom) and Figure 3c, respectively. Average µh = 0.62±0.05 cm2V-1s-1 and Vth = -4.3±0.9 V were achieved for 50 µm-L devices operating at Vg = -30 V (Vd = -30 V). PDFDSe/P(VDF-TrFE) TFTs showed a bit larger hysteresis in the transfer curve than devices with PMMA due to the ferroelectric nature of the P(VDF-TrFE).29,37 The enhanced mobility and reduced operational voltage are associated with increased hole accumulation density at the semiconductor/dielectric interface because of the much higher capacitance (Ci ≈ 36.8 nF cm−2). On the other hand, the – C–F dipoles in P(VDF-TrFE) destructively induced depletion or trapping of electrons in the ntransport region, leading to pure p-transport behavior.29,40,41 We note that PDFDSe TFTs with PMMA (containing few electron-trapping groups)42 showed electron transport behavior under positive gate bias with an electron mobility ≈ 10-3 cm2V-1s-1, whereas PDFDT/PMMA TFTs displayed negligible electron transport (Figure S14). This more distinct ambipolar transport behavior of the PDFDSe TFT device might be associated with two observations: the lower lying LUMO level of PDFDSe than the LUMO of PDFDT and highly edge-on oriented, highly crystalline feature of PDFDSe films. Taking advantage of the ambipolar characteristic of PDFDSe/PMMA TFTs, a complementary inverter was fabricated by a single layer of PDFDSe. Figure 3d shows inverter characteristics of PDFDSe film with Wp/Lp = Wn/Ln = 1 mm/20 µm, which achieved a high absolute gain of 18 at VDD = 100 V. The asymmetric static voltage transfer curves were attributed to the PDFDSe polymer hole transport dominant nature.

The carrier mobility and operational voltage were remarkably enhanced by employing the SEGI layer as a gate dielectric. The SEGI layer was formulated by blending P(VDF-TrFE) (99 vol%) and ion gel (1 vol%) based on P(VDF-HFP) and [EMIM][TFSI] ion liquid. Consistent with 9



previous studies,31 this SEGI layer showed impressively high capacitance over 1 µF/cm2 due to the combined effects of strong polarization through C-F interface dipoles of the fluorinated P(VDF-TrFE) dielectric and formation of electrical double layers by EMIM and TFSI ion movement.31,43 This high capacitance implies that we can induce high charge carrier density and fill disorder induced carrier traps with low gate bias, allowing smooth charge transport.21-23 Figures 4a and 4b shows typical transfer and output characteristics of PDFDSe/SEGI TFTs, respectively, with channel lengths of L = 10 µm and 50 µm (W = 1 mm). As expected from the high capacitance, operational voltage decreased to -2 V, average µh = 6.56±0.74 cm2V-1s-1, and Vth = -0.78±0.10 V for PDFDSe/SEGI (99:1) TFTs with L = 10 µm. It should be noted that the mobility was markedly improved to µh = 19.58±0.55 cm2V-1s-1 for PDFDSe/SEGI (99:1) TFTs with L = 50 µm (Figure 4c and Figure S15). The maximum µh = 20.3 cm2V-1s-1 achieved is currently the record mobility among OTFTs using ionic gate dielectrics,21-23 including PDFDT/SEGI (99:1) TFTs (µh = 12.95±0.67 cm2V-1s-1).31 These mobilities correspond to effective carrier mobility (equation (1): µeff = µh × rsat ) of 2.49±0.17 cm2V-1s-1 and 5.20±0.43 cm2V-1s-1 for devices with L = 10 µm and 50 µm respectively, using a recently proposed reliability factor,44 (rsat, see equation (2) in Experimental Section). rsat of 37.8±5.5% and 26.6±2.7% were extracted for devices with L = 10 µm and 50 µm respectively (Figure S15e). Figure 4c displays a typical effective saturation mobility of PDFDSe/SEGI TFTs with L = 10 and 50 µm as a function of the gate voltage. The mobility increases with gate voltage (Vg) to about 1.35 V and -1.60 V in 10 µm and 50 µm L devices, respectively and then decreases above these high gate voltages, which is attributed to non-ohmic metal/semiconductor contacts.45-49 Additionally, under such a high carrier density condition, a large portion of the hole transport states are already occupied at these high gate voltages. Thus, a reduced carrier hopping from one

10


Page 10 of 26

Page 11 of 26 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


site to another is followed, reducing the hole-carrier mobility at high Vg (Figure 4b).

45-47

Consequently, the mobilities in Table 1 are estimated in the high Vg region (~0.4-0.7 V less than |Vg| = 2 V) to prevent any carrier mobility overestimation. The peaking behavior in Figure 4b could also be attributed to electrochemical doping or voltage operation.50 Figure S16 presents that similar Vg dependence of mobility was observed for PDFDSe TFTs with high capacitance P(VDF-TrFE) dielectric, whereas the mobility increased with Vg was continued for PDFDSe TFTs with low capacitance PMMA dielectric because the increasing number of charge carriers (but the number is still lower than the numbers for high capacitance P(VDF-TrFE) or SEGI gate dielectrics) kept induced with increasing Vg. An improved on/off ratio > 105 was also obtained for PDFDSe/SEGI TFTs. Also, contact resistance (Rc) was estimated using Y-function method (YFM), a widely used method to extract Rc of organic transistors,51,52 and summarized in Table 1. PDFDSe/SEGI (99:1) TFT devices presented much lower contact resistance (Rc ~ 0.13-0.27 kΩ.cm and 0.06-0.26 kΩ.cm for devices with L = 10 and 50, respectively) compared to PDFESe devices based on PMMA and P(VDF-TrFE) dielectrics. The different estimated Rc in the PDFDSe TFTs with different gate dielectrics (PMMA, P(VDF-TrFE) and SEGI) and metal gate electrodes (Al, Au) originates from the diverse Schottky barrier during the charge transport modulation. Alteration of the Schottky barrier by the gate field which can be significantly influenced by the metal gate electrode and the dielectrics has recently been observed in OTFTs, which is a key origin of contact resistance.53,54 Additionally, the short channel effects, observed in PMMA gated devices with 10 µm channel length, were effectively suppressed using SEGI due to the high capacitance over 1 µFcm-2 (Figure S16).55

Finally, we measured bias stress of PDFDSe/P(VDF-TrFE) and PDFDSe/SEGI TFTs in a nitrogen atmosphere (Figure 4d and S17). Hysteresis behavior in the both PDFDSe/P(VDF11



TrFE) and PDFDSe/SEGI TFTs were observed. For PDFDSe/P(VDF-TrFE) TFTs, the phenomenon originated mainly from the ferroelectric nature of the P(VDF-TrFE) dielectric and the ambipolar nature of PDFDSe polymer giving rise to trapping of the minority electron carrier at the PDFDSe/SEGI interface.29,31,40,41 After 100 sweeps, high on-current (Id) ≈ 0.31 mA was maintained with no noticeable change in off current in the PDFDSe/SEGI TFT recording on/off ratio > 104, higher than bias stressed neat P(VDF-TrFE) gated PDFDSe device (Figure S17). The steady bias stress induced decay was attributed to interfacial charge trapping at the PDFDSe/SEGI interface, presumably caused by residual oxygen and moisture, and continuous constant voltages applied during the bias stress.56

CONCLUSIONS A planar donor-acceptor type PDFDSe polymer was successfully synthesized by Stille polymerization. The PDFDSe polymer was strongly aggregated even in solution and highly crystalline film states. Thermal annealing promoted growth of fibrous PDFDSe aggregates in films. Strong interchain interactions were induced by the PDFDSe polymer backbone planar geometry. TGBC PDFDSe TFT devices exhibited excellent performance using PMMA, P(VDFTrFE), and SEGI gate dielectric layers. PMMA and P(VDF-TrFE) gate dielectrics produced maximum µh = 0.18 and 0.67 cm2V-1s-1, respectively, in 50 µm L devices. SEGI produced record maximum µh = 20.3 cm2V-1s-1 corresponding to effective hole mobility exceeding 5 cm2V-1s-1. These high carrier mobilities were produced by the interplay of (i) intense interchain interactions, (ii) highly edge-on oriented polymer chains in the TFT devices, (iii) high carrier density due to high polarizability of gate insulator and low oxidation potential of selenophene-based conjugated system, and (iv) channel length optimization for reducing the effect of contact resistance. The

12


Page 12 of 26

Page 13 of 26 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


current study demonstrates the high potential of selenophene incorporated semiconducting polymers in TFT devices.

EXPERIMENTAL SECTION Device Fabrication. Top-gate/bottom-contact geometry OTFT devices were fabricated. Au was deposited on 3 nm Ni adhesive layer on Corning Eagle XG glass substrates to provide the charge injection electrode. Source and drain electrodes (Au/Ni = 13/3 nm) were patterned by photolithography on the glass substrates, with channel lengths 10 and 50 µm, and width 1000 µm. The substrates were sequentially cleaned in an ultrasonic bath with de-ionized water, acetone and isopropanol for 10 min each and then dried in an oven. PDFDSe (5 mg/ml) and PDFDT (2 mg/ml) solutions in chlorobenzene were spin coated at 2000 rpm for 60 s, thermally annealed at 150–250 °C for 30 min, and then allowed to cool slowly in a N2 filled glove box. After thermal annealing, PMMA (Sigma–Aldrich, Mn: 120 kDa) film was spin coated on the active layer from 80 mg/ml solution in n-butyl acetate at 2000 rpm for 60 s (thickness ≈ 500 nm) and then thermally annealed at 80°C for 2 h to provide the gate dielectric layer. For fluorinated dielectric gated devices, P(VDF-TrFE) (Solvay, 70:30 mol% random copolymer) was dissolved in 2-butanone at 30 mg/ml, then spin coated on the active layer at 2000 rpm for 60 s (thickness ≈ 250 nm) and thermally annealed at 80°C for 2 h. OTFTs were completed by depositing 50 nm top gate Al electrodes via thermal evaporation using a metal shadow mask. For SEGI gated devices, the oven-dried substrates were then subjected to ozone surface treatment for 20 min before spin coating the PDFDSe layer. The SEGI was prepared by blending P(VDF-TrFE) and P(VDF-HFP)-[EMIM][TFSI] gel solutions at 99:1 vol% ratio.29 The SEGI solution was then spin

13



coated at 2000 rpm for 60 s, and thermally annealed at 80°C for 1 h. OTFTs were completed by depositing 40 nm top gate Au electrodes using a metal shadow mask.

Electrical characterization and TFT measurement. Au/SEGI/PDFDSe/Au MIS capacitance voltage characteristics were measured using a precision LCR meter (HP4284A, Agilent) and semiconductor parameter analyzer (Keithley 4200-SCS). All current-voltage characteristics were examined using a semiconductor parameter analyzer (Keithley 4200-SCS) in a N2 filled glove box. Current-voltage characteristics of PMMA gated devices at various temperatures (T) were placed on measured using a hot chuck in a customized vacuum chamber with probe tips. Device temperature was controlled by liquid nitrogen gas flow and heating the chuck. The µ and Vth were calculated in the saturation regime using the standard equation: Id = (W/2L) µCi(Vg-Vth)2, where Ci is the dielectric capacitance/unit area. The effective carrier mobility is defined by equation (1): µeff = rsat × µ. The rsat is calculated using the following equation (2):

rsat

  =  

Id

max

Vg

− max

I d0

max

    

2

 ∂ Id   ∂V g 

2

    claimed

0 where |Id|max is the drain current at the maximum gate voltage |Vd|max. I d is the drain current at Vg

= 0.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on ACS Publication website at DOI: 14


Page 14 of 26

Page 15 of 26 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


Detailed synthesis procedures and characterization for PDFDSe polymer. Additional figures: thermal analysis, DFT calculation, UV-visible absorption spectra, GIXD data, and AFM images. Additional figures detailing PDFDSe TFTs characteristics with PMMA and P(VDFTrFE) gate dielectrics.

AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected] *E-mail: [email protected]

Author Contributions ǁ

B.N.-Y. and A-R.J contributed equally to this work.

Notes The authors declare no competing financial interest.

Acknowledgements This work was supported by the Center for Advanced Soft Electronics (2013M3A6A5073183), funded by the Ministry of Science & ICT, Republic of Korea and by a grant (NRF– 2015R1D1A1A01058493) from the Basic Science Program through the NRF funded by the Ministry of Education.

REFERENCES (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) Sirringhaus, H. 25th Anniversary Article: Organic Field-Effect Transistors: The Path Beyond Amorphous Silicon. Adv. Mater. 2014, 26, 1319-1335. 15



(3) Caironi, M.; Noh, Y.-Y.; Large Area and Flexible Electronics, Wiley-VCH, Weinheim, Germany 2015. (4) Bucella, S. G.; Luzio, A; Gann, E.; Thomsen, L; McNeill, C. R.; Pace, G.; Perinot, A.; Chen, Z.; Facchetti, A.; Caironi, M. Macroscopic and High-Throughput Printing of Aligned Nanostructured Polymer Semiconductors for MHz Large-Area Electronics. Nat. Commun. 2015, 6, 8394. (5) Nikolka, M.; Nasrallah, I.; Rose, B.; Ravva, M. K.; Broch, K.; Sadhanala, A.; Harkin, D.; Charmet, J.; Hurhangee, M.; Brown, A.; Illig, S.; Too, P.; Jongman, J.; McCulloch, I.; Bredas, J.-L.; Sirringhaus, H. High Operational and Environmental Stability of HighMobility Conjugated Polymer Field-Effect Transistors Through the Use of Molecular Additives. Nat. Mater. 2017, 16, 356-362. (6) Sun, B.; Hong, W.; Yan, Z.; Aziz, H.; Li, Y. Record High Electron Mobility of 6.3 cm2V-1s-1 Achieved for Polymer Semiconductors Using a New Building Block. Adv. Mater. 2014, 26, 2636-2642. (7) Back, J. Y.; Yu, H.; Song, I.; Kang, I.; Ahn, H.; Shin, T. J.; Kwon, S.-K.; Oh, J. H.; Kim, Y.H. Investigation of Structure-Property Relationships in Diketopyrrolopyrrole-Based Polymer Semiconductors via Side-Chain Engineering. Chem. Mater. 2015, 27, 1732-1739. (8) Tseng, H.-R.; Phan, H.; Luo, C.; Wang, M.; Perez, L. A.; Patel. S. N.; Ying, L.; Kramer, E. J.; Nguyen, T.-Q.; Bazan, G. C.; Heeger, A. J. High-Mobility Field-Effect Transistors Fabricated with Macroscopic Aligned Semiconducting Polymers. Adv. Mater. 2014, 26, 2993-2998. (9) Paterson, A. F.; Treat, N. D.; Zhang, W.; Fei, Z.; Wyatt-Moon, G.; Faber, H.; Vourlias, G.; Patsalas, P. A.; Solomeshch, O.; Tessler, N.; Heeney, M.; Anthopoulos, T. D. Small Molecule/Polymer Blend Organic Transistors with Hole Mobility Exceeding 13 cm2V-1s-1. Adv. Mater. 2016, 28, 7791-7798. (10) Kim, G.; Kang, S.-J.; Dutta, G. K.; Han, Y.-K.; Shin, T. J.; Noh, Y.-Y.; Yang C. A Thienoisoindigo-Naphthalene 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. (11) Zhao, Z.; Yin, Z.; Chen, H.; Zheng, L.; Zhu, C.; Zhang, L.; Tan, S.; Wang, H.; Guo, Y.; Tang, Q.; Liu Y. High-Performance, Air-Stable Field-Effect Transistors Based on 16


Page 16 of 26

Page 17 of 26 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


Heteroatom-Substituted

Naphthalenediimide

Benzothiadiazole

Copolymers

Exhibiting

Ultrahigh Electron Mobility up to 8.5 cmV-1s-1. Adv. Mater. 2017, 29, 1602410. (12) Luo, H.; Yu, C.; Liu, Z.; Zhang, G.; Geng, H.; Yi, Y.; Broch, K.; Hu, Y.; Sadhanala, A.; Jiang, L.; Qi, P.; Cai, Z.; Sirringhaus, H.; Zhang, D. Remarkable Enhancement of Charge Carrier Mobility of Conjugated Polymer Field-Effect Transistors upon Incorporating an Ionic Additive. Sci. Adv. 2016, 2, e1600076. (13) Snaith, H. J.; Grätzel, M. Enhanced Charge Mobility in a Molecular Hole Transporter via Addition of Redox Inactive Ionic Dopant: Implication to Dye-Sensitized Solar cells. Appl. Phys. Lett. 2006, 89, 262114. (14) Kim, J.-W.; Oh, J.-D.; Kim, D.-K.; Lee. H.-Y.; Ha, Y.-G.; Choi J.-H. Low-Voltage Organic Devices Based on Pristine and Self-Assembled Monolayer-Treated HfTiOx Gate Dielectrics. J. Mater. Chem. C, 2016, 4, 7999-8005. (15) Yun, D.-J.; Lee, S.; Yong, K.; Rhee, S.-W. Low-Voltage Bendable Pentacene Thin-Film Transistor with Stainless Steel Substrate and Polystyrene-Coated Hafnium Silicate Dielectric. ACS Appl. Mater. Interfaces 2012, 4, 2025-2032. (16) Ono, S.; Hausermann, R.; Chiba, D.; Shimamura, K.; Ono, T.; Batlogg, B. High Performance Organic Field-Effect Transistors with Ultra-Thin HfO2 Gate Insulator Deposited Directly onto the Organic Semiconductor. Appl. Phys. Lett. 2014, 104, 013307. (17) Kim, C.; Wang, Z.; Choi, H.-J.; Ha, Y.-G.; Facchetti, A.; Marks, T. J. Printable Cross-Linked Polymer Blend Dielectrics. Design Strategies, Synthesis, Microstructures, and Electrical Properties, with Organic Field-Effect Transistors as Testbeds. J. Am. Chem. Soc. 2008, 130, 6867-6878. (18) Noh, Y.-Y.; Zhao, N.; Caironi, M.; Sirringhaus, H. Downscaling of Self-Aligned, AllPrinted Polymer Thin-Film Transistors. Nat. Nanotechnol. 2007, 2, 784-789. (19) Roberts, M. E.; Queralto´, N.; Mannsfeld, S. C. B.; Reinecke, B. N.; Knoll, W.; Bao, Z. Cross-Linked Polymer Gate Dielectric Films for Low-Voltage Organic Transistors. Chem. Mater. 2009, 21, 2292-2299. (20) Wang, C.; Lee, W.-Y.; Nakajima, R.; Mei, J.; Kim, D. H. Bao, Z. Thiol−ene Cross-Linked Polymer Gate Dielectrics for Low-Voltage Organic Thin-Film Transistors. Chem. Mater. 2013, 25, 4806-4812. 17



(21) Ono, S.; Miwa, K.; Seki, S.; Takeya, A Comparative Study of Organic Single-Crystal Transistors Gated with Various Ionic liquid Electrolytes. J. Appl. Phys. Lett. 2009, 94, 063301. (22) Yang, H. M.; Kwon, Y. K.; Lee, S. B.; Kim, S.; Hong, K.; Lee, K. H. Physically CrossLinked Homopolymer Ion Gels for High Performance Electrolyte-Gated Transistors. ACS Appl. Mater. Interfaces 2017, 9, 8813-8818. (23) Lee, J.; Kaake, L. G.; Cho, J. H.; Zhu, X.-Y.; Lodge, T. P.; Frisbie, C. D. Ion Gel-Gated Polymer Thin-Film Transistors: Operating Mechanism and Characterization of Gate Dielectric Capacitance, Switching Speed, and Stability. J. Phys. Chem. C 2009, 113, 8972-8981. (24) 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. (25) Lee, J.; Chung, J. W.; Yoon, G. B.; Lee, M. H.; Kim, D. H.; Park, J.; Lee, J.-K.; Kang, M. S. Influence of Dielectric Layers on Charge Transport through Diketopyrrolopyrrole-Containing Polymer Films: Dielectric Polarizability vs Capacitance. ACS Appl. Mater. Interfaces 2016, 8, 30344-30350. (26) Adhikari, J. M.; Gadinski, M. R.; Li, Q.; Sun, K. G.; Reyes-Martinez, M. A.; Iagodkine, E.; Briseno, A. L.; Jackson, T. N.; Wang, Q.; Gomez, E. D. Controlling Chain Conformations of High-k Fluoropolymer Dielectrics to Enhance Charge Mobilities in Rubrene Single-Crystal Field-Effect Transistors. Adv. Mater. 2016, 28, 10095-10102. (27) Wang, C.; Lee, W.-Y.; Kong, D.; Pfattner, R.; Schweicher, G.; Nakajima, R.; Lu, C.; Mei, J.; Lee, T. H.; Wu, H.-C.; Lopez, J.; Diao, Y.; Gu, X.; Himmelberger, S.; Niu, W.; Matthews, J. R.; He, M.; Salleo, A.; Nishi Y.; Bao, Z. Significance of the Double-Layer Capacitor Effect in Polar Rubbery Dielectrics and Exceptionally Stable Low-Voltage High Transconductance Organic Transistors. Sci. Rep. 2015, 5, 17849. (28) Lu, C.; Lee, W.-Y.; Shih, C.-C.; Wen, M.-Y.; Chen, W.-C. Stretchable Polymer Dielectrics for Low-Voltage-Driven Field-Effect Transistors. ACS Appl. Mater. Interfaces 2017, 9, 25522-25532. (29) Khim, D.; Xu, Y.; Baeg, K.-J.; Kang, M.; Park, W.-T.; Lee, S.-H.; Kim, I.-B.; Kim, J.; Kim, D.-Y.; Liu, C.; Noh, Y.-Y. Large Enhancement of Carrier Transport in SolutionProcessed

18


Page 18 of 26

Page 19 of 26 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


Field-Effect Transistors by Fluorinated Dielectric Engineering. Adv. Mater. 2016, 28, 518526. (30) Baeg, K.-J.; Khim, D.; Kim, J.; Han, H.; Jung, S.-W.; Kim, T.-W.; Kang, M.; Facchetti, A.; Hong, S.-K.; Kim, D.-Y.; Noh, Y.-Y. Controlled Charge Transport by Polymer Blend Dielectrics in Top Gate Organic Field-Effect Transistors for Low-Voltage-Operating Complementary Circuits. ACS Appl. Mater. Interfaces 2012, 4, 6176-6184. (31) Nketia-Yawson, B.; Kang, S.-J.; Tabi, G. D.; Perinot, A.; Caironi, M.; Facchetti, A.; Noh, Y.Y. Ultrahigh Mobility in Solution-Processed Solid-State Electrolyte-Gated Transistors. Adv. Mater. 2017, 29, 1605685. (32) Okamoto, T.; Nakahara, K.; Saeki, A.; Seki, S.; Oh, J. H.; Akkerman, H. B.; Bao, Z.; Matsuo, Y. Aryl-Perfluoroaryl Substituted Tetracene: Induction of Face-to-Face π-π Stacking and Enhancement of Charge Carrier Properties. Chem. Mater. 2011, 23, 1646-1649. (33) Reichenbächer, K.; Süss, H. I.; Hulliger, J. Fluorine in Crystal Engineering-‘‘The Little Atom That Could’’. Chem. Soc. Rev. 2005, 34, 22-30. (34) Kronemeijer, A. J.; Gili, E.; Shahid, M.; Rivnay, J.; Salleo, A.; Heeney, M.; Sirringhaus H. A Selenophene-Based Low-Bandgap Donor-Acceptor Polymer Leading to Fast Ambipolar Logic. Adv. Mater. 2012, 24, 1558-1565. (35) Ha, J. S.; Kim, K. H.; Choi, D. H. 2,5-Bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4-(2H,5H)dione-Based Donor-Acceptor Alternating Copolymer Bearing 5,50-Di (thiophen-2-yl)-2,20biselenophene Exhibiting 1.5 cm2.V-1.s-1 Hole Mobility in Thin-Film Transistors. J. Am. Chem. Soc. 2011, 133, 10364-10367. (36) Al-Hashimi, M.; Han, Y.; Smith, J.; Bazzi, H. S.; Alqaradawi, S. Y. A.; Watkins, S. E.; Anthopoulos, T. D.; Heeney, M. Influence of The Heteroatom on the Optoelectronic Properties and Transistor Performance of Soluble Thiophene-, Selenophene- and Tellurophene-Vinylene Copolymers. Chem. Sci. 2016, 7, 1093-1099. (37) Naber, R. C. G.; Tanase, C.; Blom, P. W. M.; Gelinck, G. H.; Marsman, A. W.; Touwslager, F. J.; Setayesh, S.; Leeuw, D. M. High-Performance Solution-Processed Polymer Ferroelectric Field-Effect Transistors. Nat. Mater. 2005, 4, 243-248. (38) Payne, M. M.; Parkin, S. R.; Anthony,J. E.; Kuo, C.-C.; Jackson T. N. Organic Field-Effect Transistors from Solution-Deposited Functionalized Acenes with Mobilities as High as 1 cm2/V.s. J. Am. Chem. Soc. 2005, 127, 4986-4987. 19



(39) Wang, C.; Rivnay, J.; Himmelberger, S.; Vakhshouri, K.; Toney, M. F.; Gomez, E. D.; Salleo A. Ultrathin Body Poly(3-hexylthiophene) Transistors with Improved Short-Channel Performance. ACS Appl. Mater. Interfaces 2013, 5, 2342-2346. (40) Baeg, K.-J.; Khim, D.; Jung, S.-W.; Kang, M.; You, I.-K.; Kim, D.-Y.; Facchetti, A.; Noh, Y.-Y. Remarkable Enhancement of Hole Transport in TopGated N-Type Polymer Field-Effect Transistors by a High-k Dielectric for Ambipolar Electronic Circuits. Adv. Mater. 2012, 24, 5433-5439. (41) Tabi, G. D.; Nketia-Yawson, B.; Lee, J. Y.; Cho, K.; Lim, B.; Noh Y.-Y. Fluorinated Benzothiadiazole and Indacenodithieno[3,2-B]thiophene Based Regioregular-Conjugated Copolymers for Ambipolar Organic Field-Effect Transistors and Inverters. RSC Adv. 2017, 7, 1110-1117. (42) Chen, Z.; Lee, M. J.; Ashraf, R. S.; Gu, Y.; Albert-Seifried, S.; Nielsen, M. M.; Schroeder, B.; Anthopoulos, T. D.; Heeney, M.; McCulloch, I.; Sirringhaus H. High-Performance Ambipolar Diketopyrrolopyrrole Thieno[3,2-b]thiophene Copolymer Field-Effect Transistors with Balanced Hole and Electron Mobilities. Adv. Mater. 2012, 24, 647-652. (43) Sakanoue, T.; Li, J.; Tanaka, H.; Ito, R.; Ono, S.; Kuroda, S.; Takenobu T. High Current Injection into Dynamic p–n Homojunction in Polymer Light-Emitting Electrochemical Cells. Adv. Mater. 2017, 29, 1606392. (44) Choi, H. H.; Cho, K.; Frisbie, C. D.; Sirringhaus, H.; Podzorov, V. Nat. Mater. 2018, 17, 2-7. (45) Bittle, E.; Basham, J.; Jackson, T.; Jurchescu, O.; Gundlach, D. Mobility Overestimation Due to Gated Contacts in Organic Field-Effect Transistors. Nat. Commun. 2016, 7, 10908. (46) Liu, C.; Li, G.; Pietro, R. D.; Huang, J.; Noh, Y.-Y.; Liu, X.; Minari, T. Device Physics of Contact Issues for the Overestimation and Underestimation of Carrier Mobility in Field-Effect Transistors. Phys. Rev. Applied 2017, 8, 034020. (47) Uemura, T.; Rolin, C.; Ke, T.-H.; Fesenko, P.; Genoe, J.; Heremans, P.; Takeya, J. On the Extraction of Charge Carrier Mobility in High-Mobility Organic Transistors. Adv. Mater. 2016, 28, 151-155. (48) Lee, J.; Chung, J. W.; Yoon, G. B.; Lee, M. H.; Kim, D. H.; Park, J.; Lee, J.-K.; Kang M. S. Influence of Dielectric Layers on Charge Transport through Diketopyrrolopyrrole-Containing Polymer Films: Dielectric Polarizability vs Capacitance. ACS Appl. Mater. Interfaces 2016, 8, 30344-30350. 20


Page 20 of 26

Page 21 of 26 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


(49) Stassen, A. F.; de Boer, R. W. I.; Iosad, N. N.; Morpurgo A. F. Influence Of The Gate Dielectric on the Mobility of Rubrene Single-Crystal Field-Effect Transistors. Appl. Phys. Lett. 2004, 85, 3899. (50)

Laihoa, A.; Herlogsson, L.; Forchheimer, R.; Crispin, X.; Berggren, M. PNAS 2011, 108, 15069-15073.

(51) Xu, Y.; Minari, T.; Tsukagoshi, K.; Chroboczek, J.A.; Ghibaudo, G. Direct Evaluation of Low-Field Mobility and Access Resistance in Pentacene Field-Effect Transistors. J. Appl. Phys. 2010, 107, 114507. (52) Yoo, D.; Nketia-Yawson, B.; Kang, S.-J.; Ahn, H.; Shin, T. J.; Noh, Y.-Y.; Yang, C. A Timely Synthetic Tailoring of Biaxially Extended Thienylenevinylene-Like Polymers for Systematic Investigation on Field-Effect Transistors. Adv. Funct. Mater. 2015, 25, 586-596. (53)

Lee, S.; Nathan, A. Science 2016, 354, 302-304.

(54)

Xu Y.; Sun, H. B.; Li, W. W.; Lin, Y. F.; Balestra, F.; Ghibaudo, G.; Noh, Y. Y. Adv. Mater. 2017, 29, 1702729.

(55) Herlogsson, L.; Noh, Y.-Y.; Zhao, N.; Crispin, X.; Sirringhaus, H.; Berggren M. Downscaling of Organic Field-Effect Transistors with a Polyelectrolyte Gate Insulator**. Adv. Mater. 2008, 20, 4708-4713. (56) Choi, H. H.; Lee, W. H.; Cho K. Bias-Stress-Induced Charge Trapping at Polymer Chain Ends of Polymer Gate-Dielectrics in Organic Transistors. Adv. Funct. Mater. 2012, 22, 48334839.

Scheme 1. Synthetic routes to PDFDSe and PDFDT polymers

21



Figure 1. (a) UV-visible absorption spectra of PDFDSe solution in chlorobenzene at various temperatures. (b) UV-visible absorption spectra of PDFDSe and PDFDT in solution state and film state at room temperature. (c) Cyclic voltammograms of PDFDSe and PDFDT polymer films. (d) DFT-calculated HOMO and LUMO surface plots and energy levels of (DFDSe)3 and (DFDT)3 model compounds.

22


Page 22 of 26

Page 23 of 26 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) Grazing incidence X-ray diffraction (GIXD) images of PDFDSe films annealed at RT, 150, 200, and 250°C left to right, respectively. (b) GIXD images of PDFDT films annealed at RT, 150, 200, and 250°C left to right, respectively. (c) Line cut profiles for thermally annealed PDFDSe and PDFDT films near the (100) peak in the qz direction. (d) Radial line cut profiles of 200°C annealed PDFDSe and 150°C annealed PDFDT films at (100) peaks. (e) Energy minimum molecular geometry of (DFDSe)3 calculated by the DFT method.

23



Figure 3. (a) Chemical structure of PMMA and P(VDF-TrFE) dielectrics (top), and TGBC TFT geometry (bottom). (b) Output curves of 200 oC annealed PDFDSe TFTs with PMMA (top) and P(VDF-TrFE) (bottom) gate dielectrics (channel W/L = 1 mm/50 µm). (c) Transfer characteristics of TFT devices based on 200oC annealed PDFDSe films with PMMA and P(VDF-TrFE) gate dielectric layers (channel W/L = 1 mm/50 µm). (d) Input-output voltage characteristics, and corresponding gain at 80 and 100 V driver voltage for 200°C annealed PDFDSe/PMMA inverters. Inset shows circuit configuration of the complementary inverter.

24


Page 24 of 26

Page 25 of 26 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. PDFDSe/SEGI TFT (a) transfer and (b) output characteristics for channel lengths of 10 and 50 µm. The Vg was swept at a rate of 189 mVs-1. (c) Typical effective saturation mobility of PDFDSe/SEGI TFTs as a function of the gate voltage. (d) PDFDSe/SEGI TFT device bias stress test, L = 50 µm. For clarity, only forward sweeps were shown here.

25



Page 26 of 26

Table 1 PDFDSe TFT parameters with PMMA, P(VDF-TrFE), and SEGI gate dielectrics. µ Dielectric

max 2

[cm /V/s]

µavg

V th [V]

2

[cm /V/s]

S.S [V/dec.]

Rc•W [kΩ•cm]

PMMA 0.18 0.16±0.01 -29.3±1.4 -17.3±1.1 51.4–75.4 P(VDF-TrFE) 0.67 0.62±0.05 -4.3±0.9 -5.5±1.3 4.6–39.7 SEGI 20.30 19.58±0.55 -0.98±0.06 -0.20±0.03 0.06–0.26 Averages were calculated from 8–12 measurements of the 200 oC annealed PDFDSe TFT devices, W = 1 mm/50 µm. Capacitances used for mobility estimation were 6.2 nF/cm2, 36.8 nF/cm2, and 4.9 µF/cm2 for PMMA, P(VDF-TrFE), and SEGI dielectrics, respectively.

TOC GRAPHIC

26


Difluorobenzothiadiazole and Selenophene Based Conjugated

Recommend Documents