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Article

Development of Dithieno[3,2-b:2′,3′-d]thiophene (DTT) Derivatives as Solution-Processable Small Molecular Semiconductors for Organic Thin Film Transistors

by
Eunjin Choi
1,†,
Yuhyeon Jang
2,†,
Dongil Ho
1,
Wookil Chae
3,
Taeshik Earmme
3,
Choongik Kim
1,* and
SungYong Seo
2,4,*
1
Department of Chemical and Biomolecular Engineering, Sogang University, Seoul 04107, Korea
2
Department of Smart Green Technology Engineering, Pukyong National University, Busan 48513, Korea
3
Department of Chemical Engineering, Hongik University, Seoul 04066, Korea
4
Department of Chemistry, Pukyong National University, Busan 48547, Korea
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Coatings 2021, 11(10), 1222; https://doi.org/10.3390/coatings11101222
Submission received: 3 September 2021 / Revised: 30 September 2021 / Accepted: 1 October 2021 / Published: 8 October 2021
(This article belongs to the Section Thin Films)
Browse Figures
Versions Notes

Abstract

:
Novel solution-processable dithieno[3,2-d:2′,3′-d]thiophene (DTT) derivatives with alkylated thiophene or alkyl chain substituents, 2,6-bis(5-octylthiophen-2-yl)dithieno[3,2-b:2′,3′-d]thiophene (compound 1), 2,6-bis(5-(2-ethylhexyl)thiophen-2-yl)dithieno[3,2-b:2′,3′-d]thiophene (compound 2), and 2,6-dioctyldithieno[3,2-b:2′,3′-d]thiophene (compound 3), have been synthesized and employed as small molecular organic semiconductors for organic field-effect transistors (OFETs). All compounds exhibited good thermal stability over 290 °C, while different side groups of DTT compounds afforded different melting temperatures. The molecular orbital energy levels were experimentally and theoretically calculated, and their trend was almost the same. The developed compounds were employed as active layers for top-contact/bottom-gate OFETs with average charge carrier mobility as high as 0.10 cm2/Vs and current on/off ratio > 107 in ambient atmosphere. Notably, DTT derivative with linear alkyl chain (-octyl) substituents showed the best device performance. High device performance could be attributed to the large grains and continuous surface coverages as well as high film texture of the corresponding semiconductor films.

1. Introduction

For decades, studies on organic semiconductors (OSCs) have been conducted for various optoelectronic applications in mechanically flexible, cost-effective, and large-area electronics such as organic field-effect transistors (OFETs), organic light-emitting diodes (OLEDs), and organic photovoltaics (OPVs) [1,2,3,4,5,6,7,8,9,10,11]. Research advances on OFETs have focused on improving the electrical performance and stability of π-bonded organic semiconductors. Accordingly, there have been several reports in which organic semiconductors exhibited very high electrical performance with carrier mobility > 1–10 cm2/Vs [12,13,14,15,16,17,18,19]. Among two types of organic semiconductors, small molecular organic semiconductors generally show higher purity, better synthetic reproducibility, and higher solubility in common solvents with enhanced electrical performance, than polymeric counterparts.
Among the various chemical structures that make up organic semiconductors, fused-thiophene derivatives have attracted much attention [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]. Along with the properties of fused-thiophene, dithieno[3,2-d:2′,3′-d]thiophene (DTT) moiety is considered as a promising backbone structure because of its rigid and flat molecular structure, and extended π-conjugation, affording compact molecular packing in thin films and enhanced electrical performance [34,35,36,37,38,39,40,41,42,43,44,45,46,47]. In addition to π-π interactions, intermolecular S-S interactions, coming from the S atoms in the DTT structure, furnish more pathways for charge transport with the effective dimensionality of the electronic structure [48]. Furthermore, DTT derivatives exhibit large bandgap energy due to their high resonance stabilization energy, resulting in excellent ambient stability [34,35]. Note that compounds including DTT derivatives are generally treated as the ambient stable materials when they have larger energy band gaps (>2.09 eV) and lower HOMO levels (<−5.02 eV) than pentacene [49].
There have been several reports on the characterization of DTT derivatives as active layers in OFETs [34,35,36,37,38,39,40,41,42,43,44,45,46,47]. For instance, Shi et al. reported a vacuum-deposited DTT-based small molecule with terminal phenyl groups with high carrier mobility of 2.2 cm2/Vs [45]. In the case of solution-processed DTT derivatives, Ho et al. showed that solution-sheared DTT-based material afforded uniaxially aligned fiber-based morphology with hole mobility of 0.32 cm2/Vs [46]. In addition, Vegiraju et al. reported 3,5-dithioalkyl DTT-based small molecular semiconductors end-capped with diverse fused thiophenes and the resulting solution processed OFETs showed high device performance with hole mobility as high as 2.6 cm2/Vs [47]. To this end, it is worth further developing solution-processable DTT derivatives as OSC for OFETs.
In this study, we newly designed and synthesized three DTT-based compounds with terminal alkyl chains (Figure 1). Our research team previously reported a study that improved conjugation by additional thiophene rings. In order to achieve the same effect, thiophene rings were attached to DTT moiety [50]. The solution-processability of the compounds was enhanced with a linear (octyl) or branched (2-ethylhexyl) terminal chain, and the solution-shearing (SS) method was performed to produce semiconductor thin film. To analyze thermal, optical, and electrochemical properties of the corresponding materials, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), UV-vis spectroscopy, and cyclic voltammetry (CV) were conducted. Density functional theory (DFT) calculation was carried out to examine the molecular structure and theoretical orbital distribution of each compound. Furthermore, the developed compounds were characterized and employed as active layers for top-contact and bottom-gate OFETs. All the compounds showed p-channel activity with hole mobility as high as 0.10 cm2/Vs and a current on/off ratio >107. Thin-film microstructure and surface morphology of thin films were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM) to correlate with performance. In particular, compound 2, which showed the best average hole mobility, exhibited relatively high XRD peak intensity and smooth terrace-like film morphology, facilitating the extension of the π orbital overlap.

2. Materials and Methods

2.1. General Materials and Methods

Under an Ar environment, air and/or moisture sensitive reactions were implemented in oven-dried glassware and with anhydrous solvents. Unless otherwise specified, all compounds were purchased from commercial sources and used without further purification. Tributyl(5-(2-ethylhexyl)thiophen-2-yl)stannane and tributyl(5-octylthiophen-2-yl)stannane were synthesized, as stated in the literature [51]. Solvents were used after freshly distilled or dried by passing through an alumina column. In previous work, General analysis method of the synthesized compounds was already described [36].
Poly(styrene) (ω-hydroxy-terminated, 32,000 g/mol) was purchased from Polymer Source. Thermogravimetric analysis (TGA, NETZSCH instrument TG 209 F3 Tarsus, Selb, Germany) was implemented in a N2 atmosphere with a flow rate of 20 mL/min. The temperature range was from 40 to 700 °C at a heating rate of 10 °C/min. Differential scanning calorimetry (DSC, TA instrument Q20-2487, New castle, DE, USA) was performed from 20 to 260 °C with a heating or cooling rate of 10 °C /min. UV-vis (JASCO V-770 spectrometer, Tokyo, Japan) spectroscopy was implemented from 190 to 900 nm for chloroform solution of each compound. Three-electrode cyclic voltammetry (CV, PGSTAT204 electrochemical analyzer, Metrohm Autolab, Utrecht, The Netherlands) method was performed with working electrode (platinum), counter electrode (platinum wire), and reference electrode (Ag/AgCl in saturated KCl). Tetrabutylammonium perchlorate, dichloromethane, and ferrocene/ferrocenium (Fc/Fc+) were used as electrolyte, solvent, and internal standard, respectively.

2.2. Synthesis

Dithieno[3,2-b:2′,3′-d]thiophene (4) [52] and 2,6-diiododithieno[3,2-b:2′,3′-d]thiophene (4a) [53] were synthesized in accordance with reference methods. Accordingly, 2,6-Dioctyldithieno[3,2-b:2′,3′-d]thiophene (1) was synthesized through lithiation and alkylation, as shown in Scheme 1. Sonogashira coupling of compound 4a with proper tin compounds afforded 2,6-bis(5-octylthiophen-2-yl)dithieno[3,2-b:2′,3′-d]thiophene (2) and 2,6-bis(5-(2-ethylhexyl)thiophen-2-yl)dithieno[3,2-b:2′,3′-d]thiophene (3).

2.2.1. Synthesis of Dithieno[3,2-b:2′,3′-d]thiophene (4)

Compound 4 was synthesized, following process from previous literature [52]. 1H NMR (400 MHz, CDCl3): δ 7.35 (d, J = 5.0 Hz, 2H), 7.28 (d, J = 5.0 Hz, 2H).

2.2.2. Synthesis of 2,6-Diiododithieno[3,2-b:2′,3′-d]thiophene (4a)

Compound 4a was synthesized, following process from previous literature [53]. 1H NMR (400 MHz, CDCl3): δ 7.40 (s, 2H).

2.2.3. Synthesis of 2,6-Dioctyldithieno[3,2-b:2′,3′-d]thiophene (1)

To a −78 °C solution of compound 4 (100 mg, 0.51 mmol) in anhydrous THF (20 mL), 2.5 M n-BuLi solution (1.0 mL) under a N2 atmosphere was added, dropwise. The solution was stirred at −78 °C for 30 min, and 1-bromooctane (246 mg, 1.27 mmol) was added to this solution. Then, the reaction mixture was stirred overnight at room temperature. The reaction was quenched by water and extracted with CH2Cl2. The organic layers were collected, washed with water, brine, and dried over anhydrous MgSO4. The solvent was removed under reduced pressure. The crude product was purified by flash column chromatography on silica gel using hexanes as the eluent to afford compound 1 as white solid (47.7 mg, 22.3%) [54]. 1H NMR (400 MHz, CDCl3): δ 6.92 (s, 2H), 2.86 (t, J = 7.3 Hz, 4H), 1.73–1.66 (m, 4H), 1.40–1.26 (m, 20H), 0.86 (t, J = 6.9 Hz, 6H) 13C NMR (101 MHz, CDCl3): δ 146.4, 139.3, 129.1, 117.5, 32.0, 31.7, 31.2, 29.4, 29.3, 29.1, 22.8, 14.2. HRMS-El(m/z): [M + H+] calcd. for C24H36S3, 421.2052; found, 421.2055.

2.2.4. Synthesis of 2,6-Bis(5-octylthiophen-2-yl)dithieno[3,2-b:2′,3′-d]thiophene (2)

Compound 4a (200 mg, 0.45 mmol), tributyl(5-octylthiophen-2-yl)stannane (477 mg, 0.98 mmol), and Pd(PPh3)4 (26 mg, 0.02 mmol) were dissolved in dry toluene (15 mL) and refluxed for 12 h under N2 atmosphere. After cooling to room temperature, the mixture was extracted with CH2Cl2 and dried over anhydrous MgSO4. The solvent was removed under reduced pressure and the residue was purified by flash column chromatography on silica gel using hexanes as the eluent to afford compound 2 as yellow solid (77.8 mg, 29.8%) [55]. 1H NMR (400 MHz, CD2Cl2): δ 7.29 (s, 2H), 7.06 (d, J = 3.7 Hz, 2H), 6.73 (d, J = 3.7 Hz, 2H), 2.81 (t, J = 7.5 Hz, 4H), 1.73–1.66 (m, 4H), 1.40–1.29 (m, 20H), 0.90–0.89 (m, 6H) 13C NMR (101 MHz, CDCl3): δ 146.2, 141.3, 138.3, 134.9, 129.2, 125.0, 123.7, 116.3, 32.0, 31.7, 30.3, 29.4, 29.3, 29.2, 22.8, 14.2. HRMS-El(m/z): [M + H+] calcd. for C32H40S5, 585.1806; found, 585.1807.

2.2.5. Synthesis of 2,6-Bis(5-(2-ethylhexyl)thiophen-2-yl)dithieno[3,2-b:2′,3′-d]thiophene (3)

Compound 4a (200 mg, 0.45 mmol), tributyl(5-(2-ethylhexyl)thiophen-2-yl)stannane (477 mg, 0.98 mmol), and Pd(PPh3)4 (26 mg, 0.02 mmol) were dissolved in dry toluene (15 mL) and refluxed for 12 h under N2 atmosphere. After cooling to room temperature, the mixture was extracted with CH2Cl2 and dried over anhydrous MgSO4. The solvent was removed under reduced pressure and the residue was purified by flash column chromatography on silica gel using hexanes as the eluent to afford compound 3 as red solid (106 mg, 40.6%) [55]. 1H NMR (400 MHz, CD2Cl2) δ 7.30 (s, 2H), 7.06 (d, J = 3.7 Hz, 2H), 6.72 (d, J = 3.7 Hz, 2H), 2.76 (d, J = 6.9 Hz, 4H), 1.61 (t, J = 5.7 Hz, 2H), 1.41–1.27 (m, 16H), 0.93–0.89 (m, 12H) 13C NMR (101 MHz, CDCl3): δ 144.7, 141.3, 138.6, 135.1, 129.1, 126.1, 123.6, 116.2, 41.5, 34.2, 32.4, 29.0, 25.6, 23.1, 14.3, 10.9. HRMS-El(m/z): [M + H+] calcd. for C32H40S5, 585.1806; found, 585.1809.

2.3. Theoretical Calculation

Density functional theory (DFT) calculations on DTT derivatives were performed to estimate optimized HOMO and LUMO energy profiles using B3LYP method (Becke’s 3 parameters, the Lee-Yang-Parr) with 6-31G(d) basis sets, as implemented in Gaussian 09W program (9.5 version).

2.4. Device Fabrication

Highly n-doped Si wafers (resistivity <0.005 Ω·cm) with a 300 nm thermally grown SiO2 gate dielectric (areal capacitance: 11.4 nF/cm2) were used as substrates for the top-contact/bottom-gate OTFTs. The Si/SiO2 substrates were sonicated in isopropyl alcohol (IPA) for 15 min and treated with O2 plasma for 10 min (Harrick Plasma, 18 W). For PS-brush treatment, a toluene solution (0.5 wt%) of ω-hydroxy-terminated polystyrene (PS) (Mw: 32,000 g/mol) was spin-coated at the spin rate of 3000 rpm for 30 s onto the Si/SiO2 substrates, followed by thermal annealing at 170 °C for 48 h in a vacuum oven. Then the PS-brush-treated substrates were rinsed with toluene and placed in the vacuum oven for annealing at 100 °C for 24 h. Organic semiconductor layers were deposited by solution-shearing (SS) method with different solvents (chloroform, toluene), concentration, coating speed, and substrate temperature to optimize semiconductor performance. To remove the residual solvent, the solution-sheared films were placed in a vacuum oven at the same temperature as the shearing temperature. Source/drain electrodes of 40 nm Gold were thermally evaporated with a decomposition rate of 0.2 Å/s utilizing a shadow mask with a channel length of 50 μm and width of 500 μm.

2.5. Device Characterization

The microstructure and surface morphology of the thin film semiconductor was characterized by X-ray diffractometer (D8 Advance (TRIO/TWIN), Bruker, Billerica, MA, USA) and atomic force microscope (AFM, Park Systems, Suwon, Korea), respectively. The electrical performance parameters of OTFTs were determined in ambient utilizing a semiconductor parameter analyzer (Keithley 4200-SCS, Keithley Instruments, OH, USA). Charge carrier mobility in the saturation regime ( μ s a t ) was calculated by the general equation, µsat = (2IDS × L)/[WCi × (VG − VTH)2]. (IDS; the source-drain current, L; the channel length, W; the channel width, Ci; the areal capacitance of the gate dielectric, VG; the gate voltage, VTH; the threshold voltage) [56,57].

3. Results

3.1. Thermal, Optical, and Electrochemical Properties

Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were carried out to characterize the thermal properties of newly synthesized DTT derivatives. Due to the molecular structure, thermal stability was anticipated to be good and suitable for the solution process method. Compounds 1, 2, and 3 showed the decomposition temperatures (5% weight loss) of 292, 396, and 392 °C, respectively, (Figure S1 and Table 1), showing high thermal stability of the developed compounds. The DSC measurements of compounds 1–3 revealed sharp endotherms above 42, 139, and 127 °C, respectively, (Figure S2 and Table 1). Higher melting temperature of compounds 2 and 3 than that of compound 1 is due to stronger intermolecular interaction with more thiophene rings [58]. Similarly, linear alkyl chain (-octyl) of compound 2 could promote stronger intermolecular interactions than branched alkyl side chain (-ethylhexyl) of compound 3, resulting in slightly higher melting temperature of compound 2 [59,60].
The optical properties of the compounds in diluted chloroform solution were investigated by the UV-vis spectroscopy (Figure 2). As shown, compounds 2 and 3 with more thiophene rings exhibited significantly red-shifted maximum absorption peaks because of the extended conjugation length, compared to compound 1. The optical energy band gaps obtained from the UV-vis onset wavelengths (λonset) of each compound were 3.75, 2.78, and 2.73 eV, for compounds 1, 2, and 3, respectively, (Table 1).
Electrochemical properties of compounds were determined by cyclic voltammetry (CV) using CH2Cl2 at room temperature. Oxidation potentials of the compounds 1–3 were 1.14, 0.81, and 0.90 V, respectively, (Figure 3). The HOMO level was calculated by ferrocene/ferrocenium internal standard with the regular formula:
EHOMO (eV) = − e(Eoxonset − EFc/Fc + onset) − 4.80 eV
where Eoxonset is the onset of oxidation potential. Hence, HOMO levels were calculated as −5.42, −5.09, and −5.19 eV, ensuring high oxidative stability [61,62]. Moreover, the experimental HOMO level of compound 2 fits well with the work function of gold, which can contribute to high device performance by facilitating charge injection [41]. The LUMO level was obtained by adding the energy band gap obtained from UV-vis spectra to the HOMO level, which resulted in −1.67, −2.31, and −2.46 eV for compound 1, 2, and 3, respectively.

3.2. Theoretical Calculation

Density functional theory (DFT) calculations were implemented to optimize the molecular geometry and HOMO/LUMO orbital energy distribution of DTT derivatives. As shown in Figure 4, the theoretically optimized HOMO/LUMO energy of the compounds 1–3 were −5.21/−0.86 eV for compound 1, −4.91/−1.68 eV for compound 2, and −4.92/−1.70 eV for compound 3, respectively. Hence, the calculated energy band gaps were 4.35, 3.23, and 3.22 eV for compounds 1, 2, and 3, respectively, showing similar trend to the experimentally determined band gap energies (Table 1). For all the compounds, HOMO and LUMO orbitals were dispersed on the main backbone and thiophene derivative moiety.

3.3. Thin-Film Transistor Characterization

To evaluate the semiconducting properties of the DTT derivatives, OFET devices were fabricated in a top-contact, bottom-gate configuration employing each compound as an active layer. The thin films of each compound were deposited by the solution-shearing method on the PS-treated SiO2/Si substrate. All solution-processed semiconductor films exhibited p-channel activity in ambient conditions (Figure 5 and Figure S3). As shown, compounds with more extended conjugation (compound 2 and 3) exhibited higher electrical performance of 0.067 and 0.0091 cm2/Vs, respectively, than compound 1 (carrier mobility of 0.000028 cm2/Vs). Lower electrical performance of compound 3, compared to compound 2, can be ascribed to the reduced intermolecular π-π interaction and molecular packing from steric hindrance around the aromatic plane with the branched (2-ethylhexyl) side chain (Table 2) [63]. Relatively large threshold voltages might be due to interface trap states between semiconductor and dielectric, as reported in several studies in the literature on DTT-based small molecules [34,35,64,65,66]. Note that a “kink” feature in Figure 5a could be caused by contact resistance, and mobility can be overestimated higher than the actual value. Therefore, in order to prevent the overestimation of mobility, actual carrier mobility was extracted, as specified in the literature [56,67].

3.4. Thin-Film Microstructure and Morphology

Solution-sheared semiconductor films of compounds 1–3 were characterized by θ–2θ XRD and AFM to evaluate thin-film microstructure and surface morphology. As shown in Figure 6, thin films of compounds 2 and 3 exhibited higher XRD peak intensity than compounds 1, in accordance with the device performance of the corresponding devices (vide supra). The primary diffraction peaks (001) of the compounds 1–3 appeared at 2θ = 4.70° (d-spacing = 18.8 Å), 2θ = 3.66° (d-spacing = 24.1 Å), and 2θ = 4.13° (d-spacing = 21.4 Å), respectively. The theoretically estimated molecular lengths obtained by DFT calculation were 28.7 Å for compound 1, 30.6 Å for compound 2, and 23.4 Å for compound 3, respectively. The molecular lengths were longer than the corresponding d-spacing values, suggesting that the molecules were vertically aligned but slightly tilted on the surface.
Surface morphologies of thin films of compounds 1–3 were characterized by AFM (Figure 7). The fabricated thin films of compound 1 showed rod-like morphology with relatively high roughness with root-mean-square (RMS) roughness of 30.4 nm. Conversely, thin films of compounds 2 and 3 exhibited interconnected terrace-like layered morphologies with relatively small RMS roughness of 1.67 and 1.20 nm, respectively. High electrical performance of compound 2 and 3 could be ascribed to large grains and continuous surface coverages. Notably, the step heights of the large islands were 2.3–2.5 nm for compound 2 and 2.1–2.3 nm for compound 3, corresponding to the d-spacing of thin films of each compound (vide supra).

4. Conclusions

In summary, we have developed a new class of solution-processable dithieno[3,2-b:2′,3′-d]thiophene-based semiconductors through reasonable molecular design to accomplish environmental stability, excellent solution processability, and high transistor performance. Compared to pentacenes or oligothiophenes, these DTT derivatives show low HOMO levels, affording high oxidative stability. Furthermore, we have successfully fabricated OTFTs based on a new series of organic semiconductors. Thin films of all DTT compounds exhibited p-channel field-effect performance, with mobilites as high as 0.10 cm2/Vs and current on/off ratio ~107. In particular, linear alkyl chains in compound 2 facilitate molecular packing to enhance π-π interaction and charge transport, resulting in the highest device performance. Our study suggests that dithieno[3,2-b:2′,3′-d]thiophene derivatives are attractive candidates for solution-processable, small molecule semiconductors.

Supplementary Materials

The following are available online at https://www.mdpi.com/article/10.3390/coatings11101222/s1, Figure S1: Thermogravimetric analysis (TGA) of (a) compound 1, (b) compound 2, and (c) compound 3, Figure S2: Differential scanning calorimetry (DSC) analysis of (a) compound 1, (b) compound 2, and (c) compound 3, Figure S3: Representative transfer characteristics of the fabricated OFETs of (a) compound 1 and (b) compound 3.

Author Contributions

Conceptualization, E.C., C.K. and S.S.; Formal analysis, E.C. and Y.J.; Investigation, E.C. and Y.J.; Resources, Y.J., D.H., W.C., T.E., C.K. and S.S.; Writing–Original Draft, E.C., Y.J., C.K. and S.S.; Writing–Review and Editing, E.C., C.K. and S.S.; Visualization, E.C. and C.K.; Supervision, C.K. and S.S.; Funding Acquisition, C.K. and S.S. All authors have read and agreed to the published version of the manuscript.

Funding

The research was funded by the National Research Foundation of Korea (NRF) (NRF-2020R1C1C1003606 and NRF-2021R1F1A1050933).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Chan, C.-Y.; Tanaka, M.; Lee, Y.-T.; Wong, Y.-W.; Nakanotani, H.; Hatakeyama, T.; Adachi, C. Stable pure-blue hyperfluorescence organic light-emitting diodes with high-efficiency and narrow emission. Nat. Photonics 2021, 15, 203–207. [Google Scholar] [CrossRef]
  2. Chen, L.-H.; Lin, P.; Chen, M.-C.; Huang, P.-Y.; Kim, C.; Ho, J.-C.; Lee, C.-C. Silver nanowire-polymer composite electrode for high performance solution-processed thin-film transistors. Org. Electron. 2012, 13, 1881–1886. [Google Scholar] [CrossRef]
  3. Gélinas, S.; Rao, A.; Kumar, A.; Smith, S.L.; Chin, A.W.; Clark, J.; Van Der Poll, T.S.; Bazan, G.C.; Friend, R.H. Ultrafast long-range charge separation in organic semiconductor photovoltaic diodes. Science 2014, 343, 512–516. [Google Scholar] [CrossRef] [Green Version]
  4. Ho, D.; Ozdemir, R.; Kim, H.; Earmme, T.; Usta, H.; Kim, C. BODIPY-based semiconducting materials for organic bulk heterojunction photovoltaics and thin-film transistors. Chempluschem 2019, 84, 18–37. [Google Scholar] [CrossRef]
  5. Kondo, Y.; Yoshiura, K.; Kitera, S.; Nishi, H.; Oda, S.; Gotoh, H.; Sasada, Y.; Yanai, M.; Hatakeyama, T. Narrowband deep-blue organic light-emitting diode featuring an organoboron-based emitter. Nat. Photonics 2019, 13, 678–682. [Google Scholar] [CrossRef]
  6. Kwon, G.; Kim, K.; Choi, B.D.; Roh, J.; Lee, C.; Noh, Y.Y.; Seo, S.; Kim, M.G.; Kim, C. Multifunctional organic-semiconductor interfacial layers for solution-processed oxide-semiconductor thin-film transistor. Adv. Mater. 2017, 29, 1607055. [Google Scholar] [CrossRef]
  7. Li, H.; Shi, W.; Song, J.; Jang, H.J.; Dailey, J.; Yu, J.; Katz, H.E. Chemical and biomolecule sensing with organic field-effect transistors. Chem. Rev. 2019, 119, 3–35. [Google Scholar] [CrossRef] [PubMed]
  8. 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. [Google Scholar] [CrossRef]
  9. Nikolka, M.; Nasrallah, I.; Rose, B.; Ravva, M.K.; Broch, K.; Sadhanala, A.; Harkin, D.; Charmet, J.; Hurhangee, M.; Brown, A.; et al. High operational and environmental stability of high-mobility conjugated polymer field-effect transistors through the use of molecular additives. Nat. Mater. 2017, 16, 356–362. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  10. Park, Y.; Baeg, K.J.; Kim, C. Solution-processed nonvolatile organic transistor memory based on semiconductor blends. ACS Appl. Mater. Interfaces 2019, 11, 8327–8336. [Google Scholar] [CrossRef] [PubMed]
  11. Ren, X.; Yang, F.; Gao, X.; Cheng, S.; Zhang, X.; Dong, H.; Hu, W. Organic field-effect transistor for energy-related applications: Low-Power-consumption devices, near-infrared phototransistors, and organic thermoelectric devices. Adv. Energy Mater. 2018, 8, 1801003. [Google Scholar] [CrossRef]
  12. Cho, H.; Lee, S.; Cho, N.S.; Jabbour, G.E.; Kwak, J.; Hwang, D.H.; Lee, C. High-mobility pyrene-based semiconductor for organic thin-film transistors. ACS Appl. Mater. Interfaces 2013, 5, 3855–3860. [Google Scholar] [CrossRef] [PubMed]
  13. Hofmockel, R.; Zschieschang, U.; Kraft, U.; Rödel, R.; Hansen, N.H.; Stolte, M.; Würthner, F.; Takimiya, K.; Kern, K.; Pflaum, J.; et al. High-mobility organic thin-film transistors based on a small-molecule semiconductor deposited in vacuum and by solution shearing. Org. Electron. 2013, 14, 3213–3221. [Google Scholar] [CrossRef]
  14. Kanimozhi, C.; Yaacobi-Gross, N.; Chou, K.W.; Amassian, A.; Anthopoulos, T.D.; Patil, S. Diketopyrrolopyrrole—diketopyrrolopyrrole-based conjugated copolymer for high-mobility organic field-effect transistors. J. Am. Chem. Soc. 2012, 134, 16532–16535. [Google Scholar] [CrossRef]
  15. 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. [Google Scholar] [CrossRef]
  16. Mei, Y.; Loth, M.A.; Payne, M.; Zhang, W.; Smith, J.; Day, C.S.; Parkin, S.R.; Heeney, M.; McCulloch, I.; Anthopoulos, T.D.; et al. High mobility field-effect transistors with versatile processing from a small-molecule organic semiconductor. Adv. Mater. 2013, 25, 4352–4357. [Google Scholar] [CrossRef]
  17. Sakanoue, T.; Sirringhaus, H. Band-like temperature dependence of mobility in a solution-processed organic semiconductor. Nat. Mater. 2010, 9, 736–740. [Google Scholar] [CrossRef] [PubMed]
  18. Sirringhaus, H. 25th anniversary article: Organic field-effect transistors: The path beyond amorphous silicon. Adv. Mater. 2014, 26, 1319–1335. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  19. Takimiya, K.; Shinamura, S.; Osaka, I.; Miyazaki, E. Air-stable and high-mobility organic semiconductors based on heteroarenes for field-effect transistors. Heterocycles 2011, 83, 1187–1204. [Google Scholar] [CrossRef]
  20. Bourass, M.; Touimi Benjelloun, A.; Benzakour, M.; McHarfi, M.; Jhilal, F.; Serein-Spirau, F.; Marc Sotiropoulos, J.; Bouachrine, M. DFT/TD-DFT characterization of conjugational electronic structures and spectral properties of materials based on thieno[3,2-b][1]benzothiophene for organic photovoltaic and solar cell applications. J. Saudi Chem. Soc. 2017, 21, 563–574. [Google Scholar] [CrossRef]
  21. Chen, H.; Cui, Q.; Yu, G.; Guo, Y.; Huang, J.; Zhu, M.; Guo, X.; Liu, Y. Synthesis and characterization of novel semiconductors based on thieno[3,2-b][1]benzothiophene cores and their applications in the organic thin-film transistors. J. Phys. Chem. C 2011, 115, 23984–23991. [Google Scholar] [CrossRef]
  22. Cinar, M.E.; Ozturk, T. Thienothiophenes, dithienothiophenes, and thienoacenes: Syntheses, oligomers, polymers, and properties. Chem. Rev. 2015, 115, 3036–3140. [Google Scholar] [CrossRef] [PubMed]
  23. Huang, P.Y.; Chen, L.H.; Chen, Y.Y.; Chang, W.J.; Wang, J.J.; Lii, K.H.; Yan, J.Y.; Ho, J.C.; Lee, C.C.; Kim, C.; et al. Enhanced performance of benzothieno[3,2-b]thiophene (BTT)-based bottom-contact thin-film transistors. Chem. Eur. J. 2013, 19, 3721–3728. [Google Scholar] [CrossRef]
  24. Liu, Y.; Liu, Y.; Zhan, X. High-mobility conjugated polymers based on fused-thiophene building blocks. Macromol. Chem. Phys. 2011, 212, 428–443. [Google Scholar] [CrossRef]
  25. McCulloch, I.; Heeney, M.; Chabinyc, M.L.; DeLongchamp, D.; Kline, R.J.; Cölle, M.; Duffy, W.; Fischer, D.; Gundlach, D.; Hamadani, B.; et al. Semiconducting thienothiophene copolymers: Design, synthesis, morphology, and performance in thin-film organic transistors. Adv. Mater. 2009, 21, 1091–1109. [Google Scholar] [CrossRef]
  26. Mori, T.; Nishimura, T.; Yamamoto, T.; Doi, I.; Miyazaki, E.; Osaka, I.; Takimiya, K. Consecutive thiophene-annulation approach to π-extended thienoacene-based organic semiconductors with [1] benzothieno [3,2-b][1] benzothiophene (BTBT) substructure. J. Am. Chem. Soc. 2013, 135, 13900–13913. [Google Scholar] [CrossRef]
  27. Ozdemir, M.; Choi, D.; Kwon, G.; Zorlu, Y.; Kim, H.; Kim, M.-G.; Seo, S.; Sen, U.; Citir, M.; Kim, C.; et al. Design, synthesis, and characterization of α,ω-disubstituted indeno[1,2-b]fluorene-6,12-dione-thiophene molecular semiconductors. Enhancement of ambipolar charge transport through synthetic tailoring of alkyl substituents. RSC Adv. 2016, 6, 212–226. [Google Scholar] [CrossRef]
  28. Pandey, M.; Gowda, A.; Nagamatsu, S.; Kumar, S.; Takashima, W.; Hayase, S.; Pandey, S.S. Rapid formation and macroscopic self-assembly of liquid-crystalline, high-mobility, semiconducting thienothiophene. Adv. Mater. Interfaces 2018, 5, 1700875. [Google Scholar] [CrossRef]
  29. Takimiya, K.; Osaka, I.; Mori, T.; Nakano, M. Organic semiconductors based on [1] benzothieno [3,2-b][1] benzothiophene substructure. Acc. Chem. Res. 2014, 47, 1493–1502. [Google Scholar] [CrossRef]
  30. Takimiya, K.; Shinamura, S.; Osaka, I.; Miyazaki, E. Thienoacene-based organic semiconductors. Adv. Mater. 2011, 23, 4347–4370. [Google Scholar] [CrossRef]
  31. Turkoglu, G.; Cinar, M.E.; Ozturk, T. Thiophene-based organic semiconductors. Top. Curr. Chem. 2017, 375, 84. [Google Scholar] [CrossRef]
  32. Wang, C.; Nakamura, H.; Sugino, H.; Takimiya, K. Methylthionated benzo [1,2-b:4, 5-b′] dithiophenes: A model study to control packing structures and molecular orientation in thienoacene-based organic semiconductors. Chem. Commun. 2017, 53, 9594–9597. [Google Scholar] [CrossRef]
  33. Xue, Z.; Chen, S.; Gao, N.; Xue, Y.; Lu, B.; Watson, O.A.; Zang, L.; Xu, J. Structural design and applications of stereoregular fused thiophenes and their oligomers and polymers. Polym. Rev. 2019, 60, 318–358. [Google Scholar] [CrossRef]
  34. Kim, C.; Chen, M.-C.; Chiang, Y.-J.; Guo, Y.-J.; Youn, J.; Huang, H.; Liang, Y.-J.; Lin, Y.-J.; Huang, Y.-W.; Hu, T.-S.; et al. Functionalized dithieno[2,3-b:3′,2′-d]thiophenes (DTTs) for organic thin-film transistors. Org. Electron. 2010, 11, 801–813. [Google Scholar] [CrossRef]
  35. Sun, Y.M.; Ma, Y.Q.; Liu, Y.Q.; Lin, Y.Y.; Wang, Z.Y.; Wang, Y.; Di, C.A.; Xiao, K.; Chen, X.M.; Qiu, W.F.; et al. High-performance and stable organic thin-film transistors based on fused thiophenes. Adv. Funct. Mater. 2006, 16, 426–432. [Google Scholar] [CrossRef]
  36. Chen, M.-C.; Vegiraju, S.; Huang, C.-M.; Huang, P.-Y.; Prabakaran, K.; Yau, S.L.; Chen, W.-C.; Peng, W.-T.; Chao, I.; Kim, C.; et al. Asymmetric fused thiophenes for field-effect transistors: Crystal structure–film microstructure–transistor performance correlations. J. Mater. Chem. C 2014, 2, 8892–8902. [Google Scholar] [CrossRef]
  37. Li, P.; Cui, Y.; Song, C.; Zhang, H. Electronic and charge transport properties of dimers of dithienothiophenes: Effect of structural symmetry and linking mode. RSC Adv. 2015, 5, 50212–50222. [Google Scholar] [CrossRef]
  38. Liu, Y.; Di, C.A.; Du, C.; Liu, Y.; Lu, K.; Qiu, W.; Yu, G. Synthesis, structures, and properties of fused thiophenes for organic field-effect transistors. Chem. Eur. J. 2010, 16, 2231–2239. [Google Scholar] [CrossRef] [PubMed]
  39. Chen, M.C.; Chiang, Y.J.; Kim, C.; Guo, Y.J.; Chen, S.Y.; Liang, Y.J.; Huang, Y.W.; Hu, T.S.; Lee, G.H.; Facchetti, A.; et al. One-pot [1 + 1 + 1] synthesis of dithieno[2,3-b:3′,2′-d]thiophene (DTT) and their functionalized derivatives for organic thin-film transistors. Chem. Commun. 2009, 1846–1848. [Google Scholar] [CrossRef]
  40. Tsuzuki, S.; Orita, H.; Sato, N. Intermolecular interactions of oligothienoacenes: Do S⋯S interactions positively contribute to crystal structures of sulfur-containing aromatic molecules? J. Chem. Phys. 2016, 145, 174503. [Google Scholar] [CrossRef] [PubMed]
  41. Youn, J.; Vegiraju, S.; Emery, J.D.; Leever, B.J.; Kewalramani, S.; Lou, S.J.; Zhang, S.; Prabakaran, K.; Ezhumalai, Y.; Kim, C.; et al. Diperfluorophenyl fused thiophene semiconductors for n-type organic thin film transistors (OTFTs). Adv. Electron. Mater. 2015, 1, 1500098. [Google Scholar] [CrossRef]
  42. Zhang, H.; Dong, H.; Li, Y.; Jiang, W.; Zhen, Y.; Jiang, L.; Wang, Z.; Chen, W.; Wittmann, A.; Hu, W. Novel air stable organic radical semiconductor of dimers of dithienothiophene, single crystals, and field-effect transistors. Adv. Mater. 2016, 28, 7466–7471. [Google Scholar] [CrossRef]
  43. Zhang, L.; Tan, L.; Hu, W.; Wang, Z. Synthesis, packing arrangement and transistor performance of dimers of dithienothiophenes. J. Mater. Chem. 2009, 19, 8216–8222. [Google Scholar] [CrossRef]
  44. Zhu, M.; Luo, H.; Wang, L.; Guo, Y.; Zhang, W.; Liu, Y.; Yu, G. The synthesis of 2,6-dialkylphenyldithieno[3,2-b:2′,3′-d]thiophene derivatives and their applications in organic field-effect transistors. Dye. Pigment. 2013, 98, 17–24. [Google Scholar] [CrossRef]
  45. Shi, J.; Li, Y.; Jia, M.; Xu, L.; Wang, H. Organic semiconductors based on annelated β-oligothiophenes and its application for organic field-effect transistors. J. Mater. Chem. 2011, 21, 17612–17614. [Google Scholar] [CrossRef]
  46. Ho, D.; Jeon, M.; Kim, H.; Gidron, O.; Kim, C.; Seo, S. Solution-processable dithieno[3,2-b:2′,3′-d]thiophene derivatives for organic thin-film transistors and complementary-like inverters. Org. Electron. 2018, 52, 356–363. [Google Scholar] [CrossRef]
  47. Vegiraju, S.; Luo, X.-L.; Li, L.-H.; Afraj, S.N.; Lee, C.; Zheng, D.; Hsieh, H.-C.; Lin, C.-C.; Hong, S.-H.; Tsai, H.-C.; et al. Solution processable pseudo n-thienoacenes via intramolecular S···S lock for high performance organic field effect transistors. Chem. Mater. 2020, 32, 1422–1429. [Google Scholar] [CrossRef]
  48. Zhang, L.; Tan, L.; Wang, Z.; Hu, W.; Zhu, D. High-performance, stable organic field-effect transistors based on trans-1, 2-(dithieno [2,3-b:3′,2′-d] thiophene) ethene. Chem. Mater. 2009, 21, 1993–1999. [Google Scholar] [CrossRef]
  49. Kim, C.; Huang, P.-Y.; Jhuang, J.-W.; Chen, M.-C.; Ho, J.-C.; Hu, T.-S.; Yan, J.-Y.; Chen, L.-H.; Lee, G.-H.; Facchetti, A.; et al. Novel soluble pentacene and anthradithiophene derivatives for organic thin-film transistors. Org. Electron. 2010, 11, 1363–1375. [Google Scholar] [CrossRef]
  50. Lee, J.; Yun, C.; Reddy, M.R.; Ho, D.; Kim, C.; Seo, S. Synthesis and characterization of fluorenone-based donor-acceptor small molecule organic semiconductors for organic field-effect transistors. Macromol. Res. 2020, 28, 654–659. [Google Scholar] [CrossRef]
  51. Hu, T.; Han, L.; Xiao, M.; Bao, X.; Wang, T.; Sun, M.; Yang, R. Enhancement of photovoltaic performance by increasing conjugation of the acceptor unit in benzodithiophene and quinoxaline copolymers. J. Mater. Chem. C 2014, 2, 8047–8053. [Google Scholar] [CrossRef]
  52. Park, K.H.; Park, J.B.; Zong, K. A convenient synthesis of dithieno [3,2-b:2′,3′-d] thiophenes from thiophene. Synthesis 2016, 48, 4126–4130. [Google Scholar]
  53. Sánchez-Carrera, R.S.; Odom, S.A.; Kinnibrugh, T.L.; Sajoto, T.; Kim, E.-G.; Timofeeva, T.V.; Barlow, S.; Coropceanu, V.; Marder, S.R.; Bredas, J.-L. Electronic properties of the 2, 6-diiododithieno [3,2-b:2′,3′-d] thiophene molecule and crystal: A joint experimental and theoretical study. J. Phys. Chem. B 2010, 114, 749–755. [Google Scholar] [CrossRef]
  54. Lu, Z.Z.; Peng, J.D.; Wu, A.K.; Lin, C.H.; Wu, C.G.; Ho, K.C.; Lin, Y.C.; Lu, K.L. Heteroleptic ruthenium sensitizers with hydrophobic fused-thiophenes for use in efficient dye-sensitized solar cells. Eur. J. Inorg. Chem. 2016, 2016, 1214–1224. [Google Scholar] [CrossRef]
  55. Navacchia, M.L.; Melucci, M.; Favaretto, L.; Zanelli, A.; Gazzano, M.; Bongini, A.; Barbarella, G. Alkylenesulfanyl-bridged Bithienyl cores for simultaneous tuning of electronic, filming, and thermal properties of oligothiophenes. Org. Lett. 2008, 10, 3665–3668. [Google Scholar] [CrossRef] [PubMed]
  56. Choi, H.H.; Cho, K.; Frisbie, C.D.; Sirringhaus, H.; Podzorov, V. Critical assessment of charge mobility extraction in FETs. Nat. Mater. 2017, 17, 2–7. [Google Scholar] [CrossRef]
  57. McCulloch, I.; Salleo, A.; Chabinyc, M. Avoid the kinks when measuring mobility. Science 2016, 352, 1521–1522. [Google Scholar] [CrossRef] [PubMed]
  58. Tamayo, A.B.; Tantiwiwat, M.; Walker, B.; Nguyen, T.-Q. Design, synthesis, and self-assembly of oligothiophene derivatives with a diketopyrrolopyrrole core. J. Phys. Chem. C 2008, 112, 15543–15552. [Google Scholar] [CrossRef]
  59. Jung, M.; Yoon, Y.; Park, J.H.; Cha, W.; Kim, A.; Kang, J.; Gautam, S.; Seo, D.; Cho, J.H.; Kim, H.; et al. 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. [Google Scholar] [CrossRef]
  60. Rancatore, B.J.; Kim, B.; Mauldin, C.E.; Fréchet, J.M.J.; Xu, T. Organic semiconductor-containing supramolecules: Effect of small molecule crystallization and molecular packing. Macromolecules 2016, 49, 833–843. [Google Scholar] [CrossRef]
  61. Wu, Y.; Li, Y.; Gardner, S.; Ong, B.S. Indolo [3,2-b] carbazole-based thin-film transistors with high mobility and stability. J. Am. Chem. Soc. 2005, 127, 614–618. [Google Scholar] [CrossRef]
  62. Zschieschang, U.; Ante, F.; Yamamoto, T.; Takimiya, K.; Kuwabara, H.; Ikeda, M.; Sekitani, T.; Someya, T.; Kern, K.; Klauk, H. Flexible low-voltage organic transistors and circuits based on a high-mobility organic semiconductor with good air stability. Adv. Mater. 2010, 22, 982–985. [Google Scholar] [CrossRef] [PubMed]
  63. Khatun, M.N.; Dey, A.; Meher, N.; Iyer, P.K. Long alkyl chain induced OFET characteristic with low threshold voltage in an n-type perylene monoimide semiconductor. ACS Appl. Electron. Mater. 2021, 3, 3575–3587. [Google Scholar] [CrossRef]
  64. Galindo, S.; Tamayo, A.; Leonardi, F.; Mas-Torrent, M. Control of polymorphism and morphology in solution sheared organic field-effect transistors. Adv. Funct. Mater. 2017, 27, 1700526. [Google Scholar] [CrossRef] [Green Version]
  65. Liu, Z.; Becerril, H.A.; Roberts, M.E.; Nishi, Y.; Bao, Z. Experimental study and statistical analysis of solution-shearing processed organic transistors based on an asymmetric small-molecule semiconductor. IEEE Trans. Electron. Devices 2009, 56, 176–185. [Google Scholar] [CrossRef]
  66. Possanner, S.K.; Zojer, K.; Pacher, P.; Zojer, E.; Schürrer, F. Threshold voltage shifts in organic thin-film transistors due to self-assembled monolayers at the dielectric surface. Adv. Funct. Mater. 2009, 19, 958–967. [Google Scholar] [CrossRef]
  67. Okachi, T. Mobility overestimation due to minority carrier injection and trapping in organic field-effect transistors. Org. Electron. 2018, 57, 34–44. [Google Scholar] [CrossRef]
Coatings 11 01222 g001 550
Figure 1. Chemical structures of DTT-derivatives developed in this study.
Figure 1. Chemical structures of DTT-derivatives developed in this study.
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Coatings 11 01222 sch001 550
Scheme 1. Synthetic scheme for compounds 1–3 employed in this study.
Scheme 1. Synthetic scheme for compounds 1–3 employed in this study.
Coatings 11 01222 sch001
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Figure 2. The optical absorption spectra of the compounds 1–3 in chloroform solution.
Figure 2. The optical absorption spectra of the compounds 1–3 in chloroform solution.
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Coatings 11 01222 g003 550
Figure 3. Cyclic voltammetry (CV) curves of newly synthesized DTT derivatives at room temperature in CH2Cl2.
Figure 3. Cyclic voltammetry (CV) curves of newly synthesized DTT derivatives at room temperature in CH2Cl2.
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Coatings 11 01222 g004 550
Figure 4. Optimized HOMO/LUMO energy profiles of (a) compound 1, (b) compound 2, and (c) compound 3.
Figure 4. Optimized HOMO/LUMO energy profiles of (a) compound 1, (b) compound 2, and (c) compound 3.
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Coatings 11 01222 g005 550
Figure 5. Representative (a) transfer and (b) output curves of organic thin-film transistor fabricated with compounds 2.
Figure 5. Representative (a) transfer and (b) output curves of organic thin-film transistor fabricated with compounds 2.
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Figure 6. θ-2θ XRD patterns of the solution-processed thin films of three synthetic compounds.
Figure 6. θ-2θ XRD patterns of the solution-processed thin films of three synthetic compounds.
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Coatings 11 01222 g007a 550Coatings 11 01222 g007b 550
Figure 7. Atomic force microscope (AFM) topographical images and step-height profiles of thin film of compound (a) 1, (b) 2, and (c) 3; scale bars are 2 μm with area size of 10 μm × 10 μm.
Figure 7. Atomic force microscope (AFM) topographical images and step-height profiles of thin film of compound (a) 1, (b) 2, and (c) 3; scale bars are 2 μm with area size of 10 μm × 10 μm.
Coatings 11 01222 g007aCoatings 11 01222 g007b
Table
Table 1. Physicochemical Properties of DTT Derivatives developed in this study.
Table 1. Physicochemical Properties of DTT Derivatives developed in this study.
DSC
Tm (°C) a		TGA
Td (°C) b		UV-Vis
λmax (nm) c		Egap
(eV) d		Eoxonset
(eV) e		HOMO
(eV) e		LUMO
(eV) f
1422922623.751.14−5.42−1.67
21393964002.780.81−5.09−2.31
31273923992.730.90−5.19−2.46
a Melting temperature, b Decomposition temperature(5%), c Measured in chloroform solution, d Band gap was estimated using the tangent line at the onset of UV-vis spectra, e Measured by cyclic voltammetry in CH2Cl2 at room temperature (using ferrocene/ferrocenium as internal standard), f ELUMO = EHOMO + Egap.
Table
Table 2. Optimized OTFT Device Performance based on the Thin Films of DTT Derivatives a.
Table 2. Optimized OTFT Device Performance based on the Thin Films of DTT Derivatives a.
Compoundµmax (cm2/Vs)
(µavg (cm2/Vs))		Ion/IoffVTH (V)
10.000028 ± 0.000002
(0.000030)		(4.6 ± 2.0) × 103−13 ± 4
20.067 ± 0.033
(0.10)		(1.4 ± 0.8) × 107−23 ± 4
30.0091 ± 0.0019
(0.011)		(7.6 ± 1.3) × 106−22 ± 1
a µ: charge carrier mobility, Ion/Ioff: current on/off ratio, VTH: threshold voltage. The average values were obtained from 5 devices under ambient condition.
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Choi, E.; Jang, Y.; Ho, D.; Chae, W.; Earmme, T.; Kim, C.; Seo, S. Development of Dithieno[3,2-b:2′,3′-d]thiophene (DTT) Derivatives as Solution-Processable Small Molecular Semiconductors for Organic Thin Film Transistors. Coatings 2021, 11, 1222. https://doi.org/10.3390/coatings11101222

AMA Style

Choi E, Jang Y, Ho D, Chae W, Earmme T, Kim C, Seo S. Development of Dithieno[3,2-b:2′,3′-d]thiophene (DTT) Derivatives as Solution-Processable Small Molecular Semiconductors for Organic Thin Film Transistors. Coatings. 2021; 11(10):1222. https://doi.org/10.3390/coatings11101222

Chicago/Turabian Style

Choi, Eunjin, Yuhyeon Jang, Dongil Ho, Wookil Chae, Taeshik Earmme, Choongik Kim, and SungYong Seo. 2021. "Development of Dithieno[3,2-b:2′,3′-d]thiophene (DTT) Derivatives as Solution-Processable Small Molecular Semiconductors for Organic Thin Film Transistors" Coatings 11, no. 10: 1222. https://doi.org/10.3390/coatings11101222

APA Style

Choi, E., Jang, Y., Ho, D., Chae, W., Earmme, T., Kim, C., & Seo, S. (2021). Development of Dithieno[3,2-b:2′,3′-d]thiophene (DTT) Derivatives as Solution-Processable Small Molecular Semiconductors for Organic Thin Film Transistors. Coatings, 11(10), 1222. https://doi.org/10.3390/coatings11101222

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