Influences of Structural Modification of S,N-Hexacenes on the

Subscriber access provided by BUFFALO STATE

Organic Electronic Devices

Influences of Structural Modification of S,N-Hexacenes on the Morphology and OFET Characteristics Yi-Fan Huang, Chun-Kai Wang, Bo-Han Lai, Chin-Lung Chung, ChinYi Chen, Guan-Ting Ciou, Ken-Tsung Wong, and Chien-Lung Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 23 May 2019 Downloaded from http://pubs.acs.org on May 23, 2019

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 29 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

Influences of Structural Modification of S,N‑Hexacenes on the Morphology and OFET Characteristics Yi-Fan Huang, †∥ Chun-Kai Wang, ‡∥ Bo-Han Lai, † Chin-Lung Chung, ‡ Chin-Yi Chen, † GuanTing Ciou, † Ken-Tsung Wong‡§* and Chien-Lung Wang†* ∥Author

Contributions: These authors contributed equally to this work.

†Department

of Applied Chemistry, National Chiao Tung University, Hsinchu 30010, Taiwan

‡Department

of Chemistry, National Taiwan University, Taipei 10617, Taiwan

§Institute

of Atomic and Molecular Science, Academia Sinica, Taipei 10617, Taiwan.

KEYWORDS: S,N-hexacenes, organic field-effect transistor, chemical modification, GIWAXS, morphology

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

Page 2 of 29

ABSTRACT

Although chemical modifications on conjugated molecules are widely applied for the purpose of improving processability and device performances, effect of the modification was far less investigated. Here, five S,N-hexacenes are studied to reveal the influences of (1) the lateral alkyl chain, (2) the terminal group (thiophene vs. benzene) and (3) the end-capping phenyl group of the hexacenes on the morphology and OFET performances. Crystal arrays of the hexacenes were prepared via PDMS-assisted crystallization prior to morphological and OFET characterizations. The lattice structures and crystal quality of the hexacenes were evaluated by microscope, and diffraction techniques including single-crystal diffractometer, electron diffraction and GIWAXS. The systematic analyses led to the following conclusions. (1) The bulkier alkyl side chain assists to form more densely packed crystals with less structural defects. (2) The terminal thiophene rings bring about higher-lying EHOMO, more ordered phase and crystal orientation whereas the terminal benzene rings deteriorate the structural order of active layer and result in liquid crystal phase. (3) The phenyl endcaps ameliorate morphological order, intermolecular overlapping, thermal stability and elevate EHOMO. Thus, EH-DTPTt-Ph deliver the highest μh, contributing to high-lying EHOMO, well-oriented crystal array with longer correlation length and suitable lattice orientation. This systematic research provides the aspects about the effects of the functionalized S,N-hexacenes on the morphology and OFET characteristics, which is anticipated to be useful for molecular design of heteroacenes.


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


1. INTRODUCTION During the past decade, multi-fused acenes have played important roles in the progress of organic semiconductors. The coplanar and extended conjugated backbone provides intermolecular π-overlap, which facilitates efficient charge transport.1 Moreover, substituents on oligoacenes at the end- and side-position have also been intensively investigated to enhance the solubility, processability and molecular packing of multi-fused acenes. Highest hole mobility (μh) and improved solubility have been reached by well-oriented crystal array of TIPS-pentancene that adopts a brickwall-like packing to afford two-dimensional network charge transport.2-3 Rubrene is also a laterally functionalized acene that forms cofacial herringbone molecular packing to deliver high hole mobility of 15-40 cm2 V-1 s-1.4-5 In terms of end-substituent acene derivatives, extending the conjugation length has been shown as a facile strategy to obtain high mobility.6 Other approach to enhance π-stacking interaction, such as using intramolecular static dipole moment to induce electrostatic self-complementarity, was reported as well.7 Acenes, such as tetracene and pentacene, show high mobility but suffering from oxidative instability and poor solubility.8 To improve chemical stability, heteroatoms, such as sulfur, nitrogen and so on, are introduced to provide heteroacenes. For example, Howard E. Katz and coworkers first replaced the two terminal benzene rings of a pentacene with two thiophenes, affording the formation of anthracenedithiophene, which offers much better stability and interstack electronic coupling than pentacene.9-10 Afterwards, more thiophene rings were incorporated into the heteroacenes to promote cofacial arrangement of fused acenes. With the assistance of the physical interaction among sulfurs, the heteroacenes form 2D charge-carrier transport channel in OFET device and delivered hole mobility (μh) of 1.7 cm2 V-1 s-1.11 For heteroacenes, the nitrogen



Page 4 of 29

atom on pyrrole ring presents an avenue for side substitution so that the processability of the heteroacenes are more easily modified.12-16 Besides the chemical structure, the assembly structure and thin-film morphology of conjugated molecules are also critical to the OFET performances. The self-assembly structure of a conjugated molecule can significantly affect OFET mobility, because it changes the inter-molecular electron coupling between the neighboring molecules.17 High OFET performances were generally delivered by conjugated molecules that form compact π-stacking and crystalline domains with low density of structural disorder and grain boundary. Although solution processing techniques have been widely explored to optimize the thin-film morphology of active materials,18-21 the wide diversity in the chemical structures of conjugated molecules still causes great challenges in understanding the structure-property relationship of organic semiconductors.22 The attempts to improve the performances of acenes and heteroacenes have led to flourish developments of acene-based materials. To our best knowledge, alkyl side chains have been investigated to affirm their influence on thin film morphology, molecular packing and furthermore device performance.23 Compared with shorter alkyl chain, longer alkyl side chains (i.e. n-hexyl group or n-octyl group) not merely offer solubility but provide greater incommensurability to induce the segregation between conjugated backbone and lateral alkyl side chain. Thermodynamically, tendency of the same subunits to self-assemble with each other reinforce the potential to form the more compact π-π stacking of rigid conjugated backbone to minimize the Gibbs free energy of mixing.24 The effect of variable alkyl chain length on optoelectronic property has been reported by Dr. Bäuerle and co-workers.25 In comparison with linear alkyl substituents, branched alkyl side chains have been reported to result in longer-range ordering and closer intermolecular π-π stacking distance,26 as the critical factors contributing to form efficient charge


Page 5 of 29 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


transport channel. However, the influences of other molecular modifications on the morphology and OFET performances are largely unknown. To address this issue and provide information regarding the structure-property relationships of acene-based materials, in this study, five S,Nhexacenes shown in Chart 1 are studied in this paper. The two conjugated backbones of these molecules, DTPTt and PPTt, are made with a central thienothiophene unit fused with two flanking units on the both sides. The flanking group of DTPTt is constructed with a pyrrole ring and a thiophene ring, –Th, whereas that of PPTt is built with a pyrrole ring and a benzene ring, denoted as –Bz here. The two backbones are thus different in their terminal aromatic rings. The two backbones can be further functionalized by lateral alkyl chains at the N-positions of the pyrrole rings or/and end-capped by aromatic rings at the terminal positions of the backbones to provide the five S,N-hexacenes shown in Chart 1. Inspired by literature research, by replacing the straight alkyl chain with the branched counterparts to afford EH-DTPTt- and EH-PPTt-based derivatives were expected to form denser molecular packing and to induce more planar structure as well. By comparing the properties of the following pairs of the S,N-hexacenes: (1) EH-DTPTt vs. EtDTPTt, (2) EH-DTPTt vs. EH-PPTt, and (3) EH-DTPTt vs. EH-DTPTt-Ph and EH-PPTt vs. EHPPTt-Ph, the influences of (1) lateral alkyl chains, (2) terminal rings and (3) end-capping units on the OFET performances and the morphological behaviors of these S,N-hexacenes will be discussed.



Page 6 of 29

Chart 1. Molecular structures of the five S,N-hexacenes. 2. MATERIAL AND INSTRUMENT Syntheses and Materials: Unless otherwise stated, all chemicals and reagents were used as received from commercial sources without further purification. Solvents for reactions were purified by distillation with drying agent prior to use. Nuclear Magnetic Resonance (NMR) Spectroscopy: 1H

and 13C NMR spectra of molecules were recorded on a Varian 400 Unity plus (400 MHz)

spectrometer in deuterated chloroform (or other given solvents) as internal reference. The Chemical shift δ was reported in ppm. The definitions of splitting pattern were: s, singlet; d, doublet; t, triplet; q, quartet; qn, quintet; sex, sextet; m, multiplet. Coupling constant was represented by J and reported in Hz. Mass Spectrometry:


Page 7 of 29 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


Mass spectra were obtained from JEOL SX-102A using fast atom bombardment (FAB) as ionization method. Thermogravimetric analysis (TGA): Decomposed temperature (Td, 5% weight loss) were measured with a Dynamic Q500 ThermoGravimetric Analyzer under nitrogen atmosphere with heating and cooling rates of 10 °C·min-1. Differential Scanning Calorimetry (DSC). The melting and crystallization temperatures were measured using Perkin Elmer Jade DSC 4000 under nitrogen flow with heating and cooling rates of 10 °C·min-1. Polarizing Optical Microscope (POM): Polarizing optical microscopy (POM) images were recorded by a Leica DM2700 optical microscopy. Via the PDMS assisted crystallization (PAC) method (Details are available in Supporting Information.), the Et-DTPTt, EH-DTPTt, EH-PPTt, EH-PPTt-Ph crystal array were prepared from chlorobenzene solution of each molecules (concentration: 5 mg mL-1). The EHDTPTt-Ph crystal array was prepared from CS2 solution of EH-DTPTt-Ph (concentration: 3 mg mL-1). Ultraviolet Photoelectron Spectroscopy (UPS) Measurement: Neat Films were prepared by spin-coating at a spin-rate of 1000 rpm from 20 mg/mL CHCl3 solutions on ITO/glass substrates. The spectra of films were measured by ULVAC-PHI PHI 5000 Versaprobe II using He-I light source. UV-Vis Absorption Measurement: The absorption spectra of in CH2Cl2 solutions (1 – 10 μM) were measured by spectrophotometers JASCO V-670 spectrophotometer. Neat films were prepared by spin-coating at a spin-rate of 1000



Page 8 of 29

rpm from 20 mg/mL CHCl3 solutions on ITO/glass substrates and the corresponding spectra were measured by Thermo Scientific Evolution 220 spectrophotometer. Transmission Electron Microscopy (TEM): TEM images have been acquired with a JEOL JEM-2010 microscope operating at an accelerating voltage of 200 kV. TEM observations were conducted in bright-field, high-resolution mode. All the samples were dried under vacuum overnight before the TEM observation. Grazing Incidence Wide-Angle X-ray Scattering (GIWAXS) characterization: All GIWAXS patterns of S,N-hexacenes derivatives were acquired at BL17A1 beamline in the National Synchrotron Radiation Research Center (NSRRC), Taiwan. A Mar345 image plate detector was used to capture the scattering patterns. Sample-to-detector distance is 261.5 mm, which was calibrated from AgBe standard. The wavelength of the incident X-rays is 1.33 Å. Typical GIWAXS patterns were obtained at a fixed incidence angle of 0.20°. Calibration process was performed via POLAR X-ray data analysis software. All GIWAXS patterns were obtained from the crystal arrays of heterohexacenes on Si wafer which were prepared by the same procedure and preparation conditions for the OFET device fabrications. The details are described in following part. OFET Device Fabrication and Characterization: A 300 nm thick silicon oxide gate dielectric with capacitance Ci=11.3 nF cm–2 was thermally grown on an n-type highly doped silicon wafer, which was used as the gate electrode and dielectric layer. First, the Si wafers were soaked in Piranha solution (H2SO4:H2O2= 3:1) for 1 hr, sonicated for 40 min, rinsed by deionized water and dried under house nitrogen stream, subsequently followed by UV-ozone treatment for 40 min. In this research, octadecyltrichlorosilane (ODTS) are coated on Si wafer as self-assembled monolayer (SAM) to improve the charge mobility. For


Page 9 of 29 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


ODTS-modified surface, the gate dielectric was treated with ODTS in toluene solution for 3 hr to form the self-assembled monolayer under N2. After formation of SAM, the Si wafer was rinsed by isopropanol and dried under nitrogen stream. The crystal arrays of Et-DTPTt, EH-DTPTt, EHDTPTt-Ph, EH-PPTt, EH-PPTt-Ph were deposited on ODTS-treated SiO2 / Si substrates from their solutions at 11oC. The PDMS sheet was removed after the solvent was completely adsorbed by the PDMS sheet, and then sent into the vacuum chamber for the following vacuum deposition of the Au electrodes. Then, the Au source and drain electrodes (40 nm in thickness) were deposited by vacuum evaporation on the crystal arrays through a shadow mask, affording a bottom-gate, topcontact device configuration. Characterization of the OFET devices was carried out at room temperature under N2 atmosphere using a Keithley 4156C Semiconductor Parameter Analyzers, Agilent Technologies. The field-effect mobility was calculated in the saturation regime by using the equation IDS = (μWCi /2L) (VG – Vth)2, where IDS is the drain–source current, μ is the field-effect mobility, W is the channel width (1000 μm), L is the channel length (100 μm), Ci is the capacitance per unit area of the gate dielectric layer, VG is the gate voltage and Vth is threshold voltage.

3. RESULTS AND DISCUSSION 3.1 Syntheses of S,N-hexacenes



Br

Br S

ethylamine hydrochloride

S

S Br

N

Pd(dba)2, dppf, NaOtBu toluene, reflux, overnight 58%

S Br

Page 10 of 29

S

S

S

S

N

Et-DTPTt

R N

S

S

1. tBuLi, -78 oC, THF then SnBu3Cl

S

S

R N

2. bromobenzene, PdCl2(PPh3)2 toluene, reflux, overnight 63%

N R

S

R = 2-ethylhexyl O 2N

1. nBuLi , -78 oC, THF

S

PdCl2(PPh3)2

Br

toluene, reflux 6h 54% for 2 steps

Br

H N

S

PPh3, o-DCB

Br

Br

180 oC, 12 h

Br

I

2. SnBu3Cl, -78 oC to r.t.

S

Br

S

S N R EH-DTPTt-Ph

EH-DTPTt R = 2-ethylhexyl

S

O 2N

NO2

S

Br

1 R N

S

NaH, 2-ethylhexylbromide

Br

Br S

N R

r.t., 12 h 12% for 2 steps

S

N H

S

2

3 R = 2-ethylhexyl B(OH)2 , Pd(PPh3)4

R N

S

Br

Br N R

Na2CO3(aq), DME reflux, 72 h 71%

S

N R

EH-PPTt-Ph R = 2-ethylhexyl

S 3

R N

S

1. tBuLi, -78 oC, THF, 1 h 2. MeOH, -78 oC to r.t. 98%

R N

S

R = 2-ethylhexyl

N R

S EH-PPTt

R = 2-ethylhexyl

Scheme 1. Synthetic routes of the DTPTt- and PPTt-based S,N-hexacenes. The syntheses of the S,N-hexacenes are shown in Scheme 1. EH-DTPTt was synthesized according to the literature procedure developed by previous work.27 Et-DTPTt was synthesized according to the same Buchwald coupling procedure similar to EH-DTPTt. For end-capping DTPTt-based molecules, EH-DTPTt was treated with t-BuLi and then quenched by SnBu3Cl, and then the stannylated EH-DTPTt was underwent Pd(II) catalyzed Stille cross coupling reaction with bromobenzene to afford EH-DTPTt-Ph. For PPTt-based molecules, we started from Pd(II) catalyzed Stille cross coupling reaction between distannyled thienothiophene28 and 4-bromo-1iodo-2-nitrobenzene29 to afford compound 1. Cadogan reaction of compound 1 treated with triphenylphosphine gave intermediate 2, and then the alkylation of intermediate 2 gave compound 10 ACS Paragon Plus Environment

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


3. Pd (0) catalyzed Suzuki coupling between compound 3 and phenylboronic acid gave EH-PPTtPh. For EH-PPTt, compound 3 was treated with t-BuLi and then quench with methanol to afford EH-PPTt in nearly quantitative yield. Thermal stability of all the S,N-hexacenes was studied by thermogravimetric analysis (TGA). As shown in Figure S2, all S,N-hexacenes have 5% mass loss temperature (Td) higher than 200 ˚C. The DTPTt-based molecules exhibit better thermal stability than the PPTt-based counterparts. Moreover, the –phenyl (–Ph) endcaps further improve the thermal stability of the hexacenes.

Figure 1. DSC thermograms of S,N-hexacenes during (a) heating scan and (b) cooling scan. Differential scanning calorimetry (DSC) thermograms (Figure 1) were used to investigate the influences of the chemical structure on the phase behaviors of all S,N-hexacenes. The highest temperature in the DSC scan was set according to the Td of the molecules. In Figure 1, all molecules exhibit typical enantiotropic phase behavior except for Et-DTPTt and EH-DTPTt-Ph. Melting temperature (Tm) and crystallization temperature (Tc) of the molecules were summarized in Table 1. It can be found that EH-DTPTt shows higher Tm, Tc and transition enthalpy than those of EHPPTt. This result reveals that the terminal –Th rings of EH-DTPTt facilitate the formation of more ordered phase than the terminal –Bz rings of EH-PPTt. Although Et-DTPTt (hollow circle black line) shows no phase transition in its DSC thermogram, it actually forms a crystallinity phase, which is verified by the morphological analyses below. Et-DTPTt thus has a high Tm above the 11 ACS Paragon Plus Environment


Page 12 of 29

temperature range of the DSC scan because of its short -Et chains. EH-DTPTt-Ph shows the typical monotropic phase behavior with Tm at 243 oC upon heating and two exothermic signals at 165 oC and 220 oC in the subsequent cooling scan. This indicates that during the cooling scan, EH-DTPTtPh first formed a less-ordered liquid crystalline phase at 220 oC, and then transformed into a more ordered phase at 165 oC.30-31 Moreover, as compared with the non-end-capped heteroacenes, the higher Tm and Tc of the –Ph end-capped molecules shown in Table 1 indicate that the –Ph endcaps facilitate both DTPTt- and PPTt-based S,N-hexacenes to form the more ordered phases with improved thermal stability. 3.2 UV-Vis and UPS

Figure 2. UV-Vis absorption spectra of the S,N-hexacenes (a) in solution state and (b) in thin film state. (c) UPS spectra of the S,N-hexacenes film deposited on ITO/glass. EF means Fermi level, corresponding to zero binding energy. Table 1. Photophysical properties, energy levels and thermal properties of DTPTt- and PPTtbased molecules. Molecule

λ

max

a/b

(nm)

λ

ε -1

onset

-1

(M cm

)a

a/b

(nm)

T

T

T

o

o

o

Egopt (eV) c

EHOMO (eV) d

ELUMO (eV) e

( C)

( C)

( C)

d

m

c

Et-DTPTt

380/ 367

58900

395/ 421

2.95

-5.22

-2.27

273

-

-

EH-DTPTt

381/

44700

395/

2.98

-5.12

-2.14

249

153

123


Page 13 of 29 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


367

416

EH-PPTt

384/ 357

52000

395/ 420

2.95

-5.23

-2.28

216

140

111

EH-DTPTt-Ph

441/ 408

97700

469/ 568

2.18

-4.96

-2.78

364

243

220, 165

EH-PPTt-Ph

409/ 396

91600

429/ 442

2.81

-5.20

-2.39

353

248

177

a UV-Vis

was carried out in dichloromethane solution. UV-Vis was carried out in thin film state. c Calculated from the onset of absorption spectra in thin film state by using b

1240

𝐸opt g (eV) = λonset (nm). d

Determined from UPS result. EHOMO =hν-(Ecutoff - Δ), where hν is incident photon energy, 21.2 eV for HeI resonance line. Ecutoff is derived from crosspoint of the two tangent lines, of which baseline and left slope of highest binding energy. Δ corresponds to energy difference between EHOMO and EF, estimated by linearly extrapolating the lowest binding energy side of the peak to baseline with zero intensity.32 de E opt LUMO = EHOMO + Eg .

The UV-Vis absorption spectra of the S,N-hexacenes in solution state and thin film state are shown in Figure 2a and Figure 2b, and the optical band-gaps (Eg) of the molecules are summarized in Table 1. In Figure 2a, Et-DTPTt (λ (λ

= 384 nm) have nearly the same λ

max

= 380 nm), EH-DTPTt (λ

max

max

= 381 nm) and EH-PPTt

max

because of their similar conjugation length. Thus, the

differences in the terminal units and lateral alkyl chains have insignificant influences on the optical properties of the S,N-hexacenes. On the contrary, the end-capping –Ph groups extend the effective conjugation of the DTPTt and PPTt cores, which results in red-shifted absorption with higher extinction coefficient of EH-DTPTt-Ph (λ

= 441 nm, ε = 97700 M-1cm-1) and EH-PPTt-Ph

max

(λ

= 409 nm, ε = 91600 M-1cm-1) as compared with EH-DTPTt (λ

max

1cm-1)

= 381 nm, ε = 44700 M-

max

and EH-PPTt (384 nm, ε = 52000 M-1cm-1). Besides, the higher quinoidal character and

greater electron donating ability of thiophene than benzene contribute to bathochromic-shifted absorption with higher extinction coefficient of EH-DTPTt-Ph than EH-PPTt-Ph.



Page 14 of 29

While measured the absorption of molecules in thin film, all the molecules exhibited bathochromic onset absorption (λonset) compared to the absorption in solution. Et-DTPTt (λonset = 421 nm), EH-DTPTt (λonset = 416 nm) and EH-PPTt (λonset = 420 nm) also show nearly similar onset absorption wavelength while the end-capped EH-DTPTt-Ph (λonset = 568 nm) and EH-PPTtPh (λonset = 442 nm) exhibit greater bathochromic shift compared to those without end-capped –Ph groups, which indicates the end-caps facilitate closer π-π molecular packing as indicated from the XRD characterization results showing below. To correlate the relationship between energy levels and chemical structures for more efficient charge transport, the S,N-hexacenes were studied by ultraviolet photoelectron spectroscopy (UPS). The results were shown in Figure 2c and the values of EHOMO and ELUMO were concluded in Table 1. The results of molecules with different side chains (Et-DTPTt vs. EH-DTPTt) show that bulkier side chains lead to elevated EHOMO while the more quinoidal character of the terminal –Th rings than the –Bz rings leads to the shallower EHOMO of EH-DTPTt than EH-PPTt (-5.12 eV vs. -5.23 eV). Moreover, the end-capping –Ph groups elevate the EHOMOs of EH-DTPTt-Ph and EH-PPTtPh to -4.96 eV and -5.20 eV, respectively, resulting from extension of conjugation length. 3.3 Morphology and OFET Characteristics


Page 15 of 29 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 3. (a) The schematic illustration of the PDMS-assisted crystallization (PAC). POM micrograms of (b) Et-DTPTt, (c) EH-DTPTt, (d) EH-DTPTt-Ph, (e) EH-PPTt and (f) EH-PPTtPh crystal arrays prepared via the PAC method. The darker regions on the left and right sides of the images represent the covered areas with the Au source and drain electrodes. To investigate the organic field-effect transistor (OFET) characteristics of the S,N-hexacenes, the crystal arrays of the S,N-hexacenes were prepared via PDMS-assisted crystallization (PAC) on octadecyltrichlorosilane (ODTS)-treated Si/SiO2 substrates.33 The PAC procedure is illustrated in Figure 3a (Details are described in Supporting Information). All the crystal arrays have been optimized to the highest quality (i.e. higher tunnel coverage, less crystal boundaries and cracks) after several solvents were tried in PAC procedure for OFET device characterization. Figure S3 shows the morphology of the crystal arrays of EH-DTPTt, EH-DTPTt-Ph, EH-PPTt and EH-PPTtPh that were prepared from different solvents. Figure 3b-3f show the polarized light optical microscope (POM) micrographs of the obtained active layers. The POM results reveal that how the lateral alkyl chains, the end-capping units and the terminal aromatic rings affect the crystal morphology differently. First, by comparing Figure 3b with Figure 3c, it can be found that although 15 ACS Paragon Plus Environment


Page 16 of 29

both crystal arrays are well-aligned, the bulkier –EH side chains facilitate the formation of more densely packed crystals, which provides the higher channel coverage between the source and drain electrodes. Second, as shown in Figure 3d, the presence of the –Ph endcaps on EH-DTPTt-Ph widen the crystals in the crystal array, and further improves the channel coverage. Finally, the influences of the terminal aromatic rings are found by comparing Figure 3c with Figure 3e. There are no well-oriented or clear identified crystalline domains in the EH-PPTt thin film. Since the terminal aromatic ring is the only structural difference between EH-PPTt and EH-DTPTt, it is possible that the terminal –Bz rings of EH-PPTt degrade structural order of the film. It is also interesting to found in Figure 3f and Figure 3e that although EH-PPTt cannot form ordered crystal array, the attached –Ph endcaps of EH-PPTt-Ph facilitate to form wide and aligned crystals in the PAC procedure. From Figure 3d and Figure 3f, it is thus confirmed that the –Ph endcap groups not only extend the conjugation length but also help to improve the structural order of the active thin films. Figure 4 shows output and transfer plots of the S,N-hexacenes in the bottom-gate/top-contact OFET devices under N2 atmosphere at room temperature. Table 2 summarizes the µh, On/Off current ratio (Ion/Ioff) and threshold voltage (Vth) of the devices deduced from the transfer characteristics in the saturation regime. All crystal arrays exhibit typical p-type channel OFET characteristics. Nevertheless, the differences in the OFET characteristics suggest that the quality of the charge-transport channels formed by the S,N-hexacenes are different. First, Et-DTPTt does not give stable saturated regime in the output plot (Figure 4a) as EH-DTPTt does (Figure 4b), and it delivers μh that is one order of magnitude lower than EH-DTPTt (Table 2). The poorer OFET performances of Et-DTPTt is related to its lower channel coverage between the source and drain electrodes (Figure 4b). Since all the OFET devices are operated in thin film


Page 17 of 29 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


state, the packing structures of the hexacenes in the thin film state were further characterized from the electron diffraction (ED) patterns shown in Figure 5a and Figure 5b. The ED patterns first revealed the reciprocal lattices of Et-DTPTt and EH-DTPTt in the crystal arrays. The d-spacings and the lattice angle deduced from the reciprocal lattices are a = 8.56 Å, c = 7.99 Å, β = 105 ˚ for Et-DTPTt and a = 14.28 Å, b = 11.20 Å, γ = 107 ˚ for EH-DTPTt, respectively. The lattice parameters match with those parameters resolved from the single crystals of Et-DTPTt, summarized in Table S2. Note that different lattice parameters of EH-DTPTt in thin film from those of for single crystal were obtained with extended b-axis and larger γ. Since metastable phase may be attained prior to the equilibrium phase during the crystal growth process in PAC method, the alkyl side chains therefore remain conformationally disordered, thus, extending b-axis.22 In this case, the lattice orientation and packing structure of Et-DTPTt and EH-DTPTt in the crystal arrays can be determined and illustrated in Figure 6a-6c and Figure 6d-6f. (Analytical details are available in Supporting Information.) In the crystal arrays, both hexacenes have their π-stacking direction point toward the charge-transport direction. The suitable lattice orientation explains why both Et-DTPTt and EH-DTPTt show p-type semiconducting behaviors in the OFET devices. Nevertheless, in the ED pattern of Et-DTPTt (Figure 5a), the diffused and weaker diffraction spots as compared to the sharper and clearer diffraction spots of EH-DTPTt (Figure 5b) suggest that EtDTPTt formed crystals arrays with shorter correlation length and higher density of structural defects.34 The comparison between Et-DTPTt and EH-DTPTt thus demonstrates that the bulkier – EH lateral chain is beneficial for the formation of crystal arrays that have high channel coverage and less structural defects. As a result, better OFET characteristics were attained by the crystal array of EH-DTPTt. The lower IDS however were observed in backward sweep than in the forward sweep of the gate voltage (VGS), between 0 V to -100 V, in the transfer characteristics of Et-DTPTt



Page 18 of 29

and EH-DTPTt, which exhibited that charges are trapped in the transfer channel, normally hysteresis, arising from defects in crystal and disorder molecular packing.35 The influences of the –Ph endcap on OFET characteristics of the hexacenes are revealed by comparing EH-DTPTt with EH-DTPTt-Ph. Comparing Figure 4b to Figure 4c, with the –Ph endcaps, not only the hysteresis phenomenon was improved but also an even better OFET performances and more stable transfer characteristics were delivered by the crystal array of EHDTPTt-Ph. Since the hysteresis featuring lower back sweep current results from trapped charge in active layer,36 higher-lying EHOMO of EH-DTPTt-Ph prevents charges from being trapped, leading to improved hysteresis.37 Similar to Et-DTPTt and EH-DTPTt, the packing structure of EHDTPTt-Ph was also studied via ED shown in Figure 5c. The d-spacings and the lattice angle of EH-DTPTt-Ph deduced from the ED pattern are b = 8.80 Å, c = 26.67 Å, α = 90˚, which are similar to those parameters of the single crystal, as shown in Table S3. Figure 6g-6i show the lattice orientation and model of EH-DTPTt-Ph on silicon substrate. In the crystal arrays, EH-DTPTt-Ph also has the π-stacking direction parallel to the charge-transport direction. The sharp diffraction spots of EH-DTPTt-Ph suggest that EH-DTPTt-Ph forms crystalline domains with longer correlation length.34 Additionally, in Figure S6, the π-π distance of EH-DTPTt is 3.64 Å while EHDTPTt-Ph exhibits 3.33 Å. The more compact π- π stacking facilitating charge transports stems from intermolecular interaction because of the end-caps, which coincides well with the DSC and UV-Vis results. In Figure 5a, the diffused diffraction peaks interpret relatively shorter correlation length and the distinctly diminished intensity of long-range order diffraction spots along a-axis exhibit some microstrains, serving as intrinsic trapping sites, probably scattering in the charge transport channel of Et-DTPTt to restrict the effective charge transport.38 In contrast, most sharp diffraction spots with uniform intensity and size in Figure 5b and Figure 5c suggest that both EH-


Page 19 of 29 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


DTPTt and EH-DTPTt-Ph form crystalline domains with longer correlation length and negligible microstrains along charge-transport direction but two blurred diffraction spots observed only in Figure 5b indicate several defects existing in the crystal array of EH-DTPTt. Suitable lattice orientation, less microstrains and defects as well as longer correlation length explain why EHDTPTt-Ph shows higher charge mobility and almost hysteresis-free reversible scan in transfer characteristics. Finally, the influences of the –Bz and –Th terminal units on the morphology and the OFET characteristics are discussed by comparing the grazing incident wide-angle X-ray scattering (GIWAXS) patterns of EH-DTPTt (Figure S7a) and EH-PPTt (Figure S7b). Less diffraction peaks featuring ring-like shapes was observed in the GIWAXS pattern of EH-PPTt. It confirms that the terminal –Bz rings disrupt the orientation and packing structure of EH-PPTt and shows that EHPPTt forms an active film with randomly oriented liquid crystalline domains.39 On the contrary, in Figure S7c, the active film of EH-PPTt-Ph provides sharp diffraction spots in the GIWAXS pattern. This indicates that the –Ph endcaps improve crystal morphology and induce highlyoriented crystalline domains, which is in agreement with POM results. Consequently, one order of magnitude higher μh was delivered by EH-PPTt-Ph. Moreover, the morphological characterization results clearly show that the –Ph endcap is an important component for the DTPTt- and PPTtrelated hexacenes to form well-ordered active films.



Page 20 of 29


Page 21 of 29 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. Output (left) (VG = 0 to −75 V, −15 V interval) and transfer (right) (VDS = −100 V) characteristics of (a) Et-DTPTt, (b) EH-DTPTt, (c) EH-DTPTt-Ph, (d) EH-PPTt, and (e) EH-PPTtPh OFET devices. Table 2. OFET characteristics of the crystal arrays.

aµ

h, ave

Molecule

µh, ave (cm2 V-1 s-1) a

Ion/Ioff

Et-DTPTt

(1.84 ± 0.78) ×10-4

2.40×104

-57.0±21.5

EH-DTPTt

(1.55 ± 0.73) × 10-3

3.84 × 104

-5.43 ± 5.41

EH-DTPTt-Ph

(2.77 ± 1.06) × 10-2

3.08 × 104

-1.43 ± 1.76

EH-PPTt

(3.21 ± 0.96) × 10-3

4.38 × 105

-11.1 ± 9.77

EH-PPTt-Ph

(2.56 ± 0.92) × 10-2

4.10 × 104

-0.30 ± 0.64

Vth (V)

is based on the average of ten devices.



Page 22 of 29

Figure 5. The experimental ED pattern (top) and simulated ED patterns (bottom) generated from the [010], [001], [100] zone of (a) Et-DTPTt, (b) EH-DTPTt and (c) EH-DTPTt-Ph lattice models. The insets on the top right are the TEM images of individual crystal (dark part) and yellow arrows indicate the crystal growth direction.


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


Figure 6. (a), (d), (g) are the illustrates the configuration of charge transport direction in crystal arrays of Et-DTPTt, EH-DTPTt, EH-DTPTt-Ph, respectively. The direction of the lattice vectors, a, b, c, are determined from the single-crystal structures and the ED analyses of the hexacenes. The side view of the lattice models of Et-DTPTt, EH-DTPTt and EH-DTPTt-Ph are demonstrated in (b), (e), (h), whereas the top views of the lattice models are shown in (c), (f), (i), respectively.

4. CONCLUSION In this work, five S,N-hexacenes were synthesized and investigated to reveal the effects of (1) lateral alkyl chain (–Et vs. –EH), (2) terminal group (–Th vs. –Bz) and (3) end-caps (–Ph) on the molecular properties, morphology and OFET characteristics of the S,N-hexacenes. The UPS results show that bulkier side chains result in elevated EHOMO. On the other hand, terminal –Th rings push up the EHOMOs of EH-DTPTt as compared to those of EH-PPTt. Furthermore, –Ph endcaps further shallow the EHOMOs of EH-DTPTt-Ph and EH-PPTt-Ph, which was found to benefit the charge injection in the OFET devices. From DSC results, –Ph endcaps induce the more ordered phases, thus, leading to the higher Tm and Tc and improved thermal stability for both DTPTt- and PPTt-based S,N-hexacenes. Since structure-property relationship attributes to hierarchical assembly of the S,N-hexacenes over length scales from lattice structure to the crystal quality (i.e. size and orientation of the crystalline domains) in the charge transport channel, to optimize the crystal quality, the active layers of the S,N-hexacenes were first prepared via the PAC procedure. POM, ED and GIWAXS were then used to reveal the morphological details of the active films. The characterization results show that the bulkier lateral chain, –EH, facilitates to form larger, dense-packed crystal arrays with less defects and higher channel coverage to offer the higher mobility of EH-DTPTt than that of EtDTPTt. Moreover, the terminal –Bz rings were found to degrade the structural order. Unlike the 23 ACS Paragon Plus Environment


Page 24 of 29

crystal arrays of DTPTt-related derivatives with the terminal –Th rings, EH-PPTt with the terminal –Bz rings forms liquid crystalline film without preferred orientation. In terms of the influence of end-capping group, all results confirm that the –Ph endcaps facilitate better morphological order, intermolecular overlapping, thermal stability and elevate EHOMO. The improved morphological order and elevated EHOMO were found to be benefit for the OFET performances. Among these five heteroacenes, the highest μh delivered by EH-DTPTt-Ph attributes to high-lying EHOMO, welloriented crystal array with longer correlation length and suitable lattice orientation, as the indispensable features of efficient charge transport channel. The systematic study uncovers how the possible chemical modifications of the S,N-hexacenes affect the morphology and OFET characteristics of the molecules and provides useful knowledge for the further design of heteroacenes. ASSOCIATED CONTENT Supporting Information 1H, 13C

NMR spectra, phase transition parameters from TGA and DSC, lattice parameters, single

crystal CIF. of Et-DTPTt, EH-DTPTt and EH-DTPTt-Ph are available in supporting information. Supporting Information is available from on the ACS Publications website or from the author. AUTHOR INFORMATION Corresponding Author * Prof. Chien-Lung Wang, E-mail: [email protected] * Prof. Ken-Tsung Wong, E-mail: [email protected] Author Contributions ∥ Y.-F.

Huang and C.-K. Wang contributed equally to this work. 24 ACS Paragon Plus Environment

Page 25 of 29 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


ACKNOWLEDGMENT The authors acknowledge funding support from Ministry of Science and Technology, Taiwan (MOST 104-2113-M-002-006-MY3, MOST 104-2628-E-009-007-MY3 and MOST 106-2221-E009-130-MY3). The authors appreciate the National Synchrotron Radiation Research Center (NSRRC, Taiwan) for assistance with the GIWAXS measurements.

5. REFERENCE (1) Watanabe, M.; Chang, Y. J.; Liu, S.-W.; Chao, T.-H.; Goto, K.; Islam, M. M.; Yuan, C.-H.; Tao, Y.-T.; Shinmyozu, T.; Chow, T. J. The Synthesis, Crystal Structure and Charge-transport Properties of Hexacene. Nat. Chem. 2012, 4 (7), 574-578. (2) Anthony, J. E.; Brooks, J. S.; Eaton, D. L.; Parkin, S. R. Functionalized Pentacene: Improved Electronic Properties from Control of Solid-state Order. J. Am. Chem. Soc. 2001, 123 (38), 94829483. (3) Park, S. K.; Jackson, T. N.; Anthony, J. E.; Mourey, D. A. High Mobility Solution Processed 6, 13-bis (triisopropyl-silylethynyl) Pentacene Organic Thin Film Transistors. Appl. Phys. Lett. 2007, 91 (6), 063514. (4) Podzorov, V.; Pudalov, V.; Gershenson, M. Field-effect Transistors on Rubrene Single Crystals with Parylene Gate Insulator. Appl. Phys. Lett. 2003, 82 (11), 1739-1741. (5) Menard, E.; Podzorov, V.; Hur, S. H.; Gaur, A.; Gershenson, M. E.; Rogers, J. A. High‐performance N‐ and P‐type Single‐crystal Organic Transistors with Free‐space Gate Dielectrics. Adv. Mater. 2004, 16 (23‐24), 2097-2101. (6) Dong, H.; Fu, X.; Liu, J.; Wang, Z.; Hu, W. 25th Anniversary Article: Key Points for High‐Mobility Organic Field‐Effect Transistors. Adv. Mater. 2013, 25 (43), 6158-6183. (7) Jurchescu, O. D.; Popinciuc, M.; Van Wees, B. J.; Palstra, T. T. Interface‐controlled, High‐mobility Organic Transistors. Adv. Mater. 2007, 19 (5), 688-692. (8) Anthony, J. E. The Larger Acenes: Versatile Organic Semiconductors. Angew. Chem. Int. Ed. 2008, 47 (3), 452-483. (9) Takimiya, K.; Shinamura, S.; Osaka, I.; Miyazaki, E. Thienoacene‐based Organic Semiconductors. Adv. Mater. 2011, 23 (38), 4347-4370. 25 ACS Paragon Plus Environment


Page 26 of 29

(10) Laquindanum, J. G.; Katz, H. E.; Lovinger, A. J. Synthesis, Morphology, and Field-effect Mobility of Anthradithiophenes. J. Am. Chem. Soc. 1998, 120 (4), 664-672. (11) Gao, P.; Beckmann, D.; Tsao, H. N.; Feng, X.; Enkelmann, V.; Baumgarten, M.; Pisula, W.; Müllen, K. Dithieno [2, 3‐d; 2′, 3′‐d′] benzo [1, 2‐b; 4, 5‐b′] dithiophene (DTBDT) as Semiconductor for High‐performance, Solution‐processed Organic Field‐effect Transistors. Adv. Mater. 2009, 21 (2), 213-216. (12) 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 (2), 614-618. (13) Mitsudo, K.; Shimohara, S.; Mizoguchi, J.; Mandai, H.; Suga, S. Synthesis of NitrogenBridged Terthiophenes by Tandem Buchwald–Hartwig Coupling and Their Properties. Org. Lett. 2012, 14 (11), 2702-2705. (14) Mishra, A.; Popovic, D.; Vogt, A.; Kast, H.; Leitner, T.; Walzer, K.; Pfeiffer, M.; Mena‐Osteritz, E. A–D–A‐type S, N‐Heteropentacenes: Next‐generation Molecular Donor Materials for Efficient Vacuum‐processed Organic Solar Cells. Adv. Mater. 2014, 26 (42), 72177223. (15) Wetzel, C.; Brier, E.; Vogt, A.; Mishra, A.; Mena‐Osteritz, E.; Bäuerle, P. Fused Thiophene‐prrole‐containing Ring Systems up to a Heterodecacene. Angew. Chem. Int. Ed. 2015, 54 (42), 12334-12338. (16) Wang, Z.; Liang, M.; Tan, Y.; Ouyang, L.; Sun, Z.; Xue, S. Organic Dyes Containing Dithieno [2, 3-d: 2′, 3′-d′] thieno [3, 2-b: 3′, 2′-b′] dipyrrole Core for Efficient Dye-sensitized Solar Cells. J. Mater. Chem. A 2015, 3 (9), 4865-4874. (17) Pickett, A.; Torkkeli, M.; Mukhopadhyay, T.; Puttaraju, B.; Laudari, A.; Lauritzen, A. E.; Bikondoa, O.; Kjelstrup-Hansen, J.; Knaapila, M.; Patil, S. Correlating Charge Transport with Structure in Deconstructed Diketopyrrolopyrrole Oligomers: A Case Study of a Monomer in Fieldeffect Transistors. ACS Appl. Mater. Interfaces 2018, 10 (23), 19844-19852. (18) Diao, Y.; Tee, B. C.; Giri, G.; Xu, J.; Kim, D. H.; Becerril, H. A.; Stoltenberg, R. M.; Lee, T. H.; Xue, G.; Mannsfeld, S. C. Solution Coating of Large-area Organic Semiconductor Thin Films with Aligned Single-crystalline Domains. Nat. Mater. 2013, 12 (7), 665-671. (19) Tracz, A.; Jeszka, J. K.; Watson, M. D.; Pisula, W.; Müllen, K.; Pakula, T. Uniaxial Alignment of the Columnar Super-structure of a Hexa (alkyl) Hexa-peri-hexabenzocoronene on Untreated Glass by Simple Solution Processing. J. Am. Chem. Soc. 2003, 125 (7), 1682-1683. 26 ACS Paragon Plus Environment

Page 27 of 29 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


(20) Becerril, H. A.; Roberts, M. E.; Liu, Z.; Locklin, J.; Bao, Z. High‐performance Organic Thin‐film Transistors through Solution‐sheared Deposition of Small‐molecule Organic Semiconductors. Adv. Mater. 2008, 20 (13), 2588-2594. (21) Qi, Z.; Zhang, F.; Di, C.-a.; Wang, J.; Zhu, D. All-brush-painted Top-gate Organic Thin-film Transistors. J. Mater. Chem. C 2013, 1 (18), 3072-3077. (22) Huang, C.-F.; Wu, S.-L.; Huang, Y.-F.; Chen, Y.-C.; Chang, S.-T.; Wu, T.-Y.; Wu, K.-Y.; Chuang, W.-T.; Wang, C.-L. Packing Principles for Donor–acceptor Oligomers from Analysis of Single Crystals. Chem. Mater. 2016, 28 (15), 5175-5190. (23) Ata, I.; Dkhil, S. B.; Pfannmöller, M.; Bals, S.; Duché, D.; Simon, J.-J.; Koganezawa, T.; Yoshimoto, N.; Videlot-Ackermann, C.; Margeat, O. The Influence of Branched Alkyl Side Chains in A–D–A Oligothiophenes on the Photovoltaic Performance and Morphology of Solutionprocessed Bulk-heterojunction Solar Cells. Org. Chem. Front. 2017, 4 (8), 1561-1573. (24) Garnier, F.; Yassar, A.; Hajlaoui, R.; Horowitz, G.; Deloffre, F.; Servet, B.; Ries, S.; Alnot, P. Molecular Engineering of Organic Semiconductors: Design of Self-assembly Properties in Conjugated Thiophene Oligomers. J. Am. Chem. Soc. 1993, 115 (19), 8716-8721. (25) Wetzel, C.; Mishra, A.; Mena-Osteritz, E.; Walzer, K.; Pfeiffer, M.; Bäuerle, P. Development of Strongly Absorbing S, N-heterohexacene-based Donor Materials for Efficient Vacuumprocessed Organic Solar cells. J. Mater. Chem. C 2016, 4 (17), 3715-3725. (26) Kim, Y. J.; Park, K. H.; Ha, J.-j.; Chung, D. S.; Kim, Y.-H.; Park, C. E. The Effect of Branched versus Linear Alkyl Side Chains on the Bulk Heterojunction Photovoltaic Performance of Small Molecules Containing both Benzodithiophene and Thienopyrroledione. Phys. Chem. Chem. Phys. 2014, 16 (37), 19874-19883. (27) Chung, C.-L.; Chen, C.-H.; Tsai, C.-H.; Wong, K.-T. Novel Organic Dyes Containing Nbridged Oligothiophene Coplanar Cores for Dye-sensitized Solar Cells. Org. Electron. 2015, 18, 8-16. (28) Fuller, L. S.; Iddon, B.; Smith, K. A. Thienothiophenes. Part 2. 1 Synthesis, Metallation and Bromine→ lithium Exchange Reactions of Thieno [3, 2-b] thiophene and its Polybromo Derivatives. J. Chem. Soc., Perkin Trans. 1 1997, (22), 3465-3470. (29) Flatt, A. K.; Yao, Y.; Maya, F.; Tour, J. M. Orthogonally Functionalized Oligomers for Controlled Self-assembly. J. Org. Chem. 2004, 69 (5), 1752-1755.



Page 28 of 29

(30) Wang, C.-L.; Zhang, W.-B.; Hsu, C.-H.; Sun, H.-J.; Van Horn, R. M.; Tu, Y.; Anokhin, D. V.; Ivanov, D. A.; Cheng, S. Z. A Supramolecular Structure with an Alternating Arrangement of Donors and Acceptors Constructed by a Trans-di-C 60-substituted Zn Porphyrin Derivative in the Solid State. Soft Matter 2011, 7 (13), 6135-6143. (31) Cheng, S. Z.; Keller, A. The Role of Metastable States in Polymer Phase Transitions: Concepts, Principles, and Experimental Observations. Annu. Rev. Mater. Sci. 1998, 28 (1), 533562. (32) Hill, I.; Rajagopal, A.; Kahn, A. Energy-level Alignment at Interfaces between Metals and the Organic Semiconductor 4, 4′-N, N′-dicarbazolyl-biphenyl. J. Appl. Phys. 1998, 84 (6), 32363241. (33) Wu, K. Y.; Wu, T. Y.; Chang, S. T.; Hsu, C. S.; Wang, C. L. A Facile PDMS‐assisted Crystallization for the Crystal‐engineering of C60 Single‐crystal Organic Field‐effect Transistors. Adv. Mater. 2015, 27 (29), 4371-4376. (34) Huang, Y.-F.; Chang, S.-T.; Wu, K.-Y.; Wu, S.-L.; Ciou, G.-T.; Chen, C.-Y.; Liu, C.-L.; Wang, C.-L. Influences of Conjugation Length on Organic Field-effect Transistor Performances and Thin Film Structures of Diketopyrrolopyrrole oligomers. ACS Appl. Mater. Interfaces 2018, 10 (10), 8869-8876. (35) Choi, H. H.; Cho, K.; Frisbie, C. D.; Sirringhaus, H.; Podzorov, V. Critical Assessment of Charge Mobility Extraction in FETs. Nat. Mater. 2017, 17 (1), 2-7. (36) Kim, W.; Javey, A.; Vermesh, O.; Wang, Q.; Li, Y.; Dai, H. Hysteresis Caused by Water Molecules in Carbon Nanotube Field-effect Transistors. Nano Lett. 2003, 3 (2), 193-198. (37) Egginger, M.; Bauer, S.; Schwödiauer, R.; Neugebauer, H.; Sariciftci, N. S. Current versus Gate Voltage Hysteresis in Organic Field Effect Transistors. Monatsh. Chem. 2009, 140 (7), 735750. (38) Hosemann, R.; Hindeleh, A. Structure of Crystalline and Paracrystalline Condensed Matter. J. Macromol. Sci. B 1995, 34 (4), 327-356. (39) Rivnay, J.; Mannsfeld, S. C.; Miller, C. E.; Salleo, A.; Toney, M. F. Quantitative Determination of Organic Semiconductor Microstructure from the Molecular to Device Scale. Chem. Rev. 2012, 112 (10), 5488-5519.


Page 29 of 29 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


SYNOPSIS TOC


Influences of Structural Modification of S,N-Hexacenes on the

Recommend Documents