Triethylsilylethynyl Anthradithiophene Research Articles

Synthesis and characterization of triethylsilylethynyl anthradithiophene with bithiophene end-groups for OTFT device

The new organic semiconducting material, triethylsilylethynyl anthradithiophene with bithiophene end groups, was designed and synthesized by Suzuki coupling reaction for the application of the OTFT. The synthesized oligomer was characterized by TGA and DSC for thermal stability, by UV-vis absorption for optical property, and by CV for electrochemical property. ((2,8-Di([2,2'-bithiophen]-5-yl)-11-((diethyl (methyl)silyl)ethynyl)anthra [2,3-b:6,7-b'] dithiophen-5-yl)ethynyl) triethylsilane showed typical p-channel activity with hole carrier mobility of 0.00005 cm2/Vs, the threshold voltage of −1.6 V, and the on/off ratio of 1.0x103. In order to study of morphology and crystallinity of ((2,8-di([2,2'-bithiophen]-5-yl)-11-((diethyl(methyl)silyl)ethynyl) anthra [2,3-b:6,7-b'] dithiophen-5-yl)ethynyl) triethyl silane, AFM and XRD was analyzed.

Investigation on the Electrical Stability of 5,11-Bis(triethylsilylethynyl)anthradithiophene Thin-Film Transistors.

We investigate the effects of environmental conditions on the electrical stability of spin-coated 5,11-bis(triethylsilylethynyl)anthradithiophene (TES-ADT) thin-film transistors (TFTs) in which crosslinked poly(4-vinylphenol-co-methyl methacrylate) (PVP-co-PMMA) was utilized as a gate insulator layer. Atomic force microscopy observations show molecular terraces with domain boundaries in the spin-coated TEST-ADT semiconductor film. The TFT performance was observed to be superior in the ambient air condition. Under negative gate-bias stress, the TES-ADT TFTs showed a positive threshold voltage shift in ambient air and a negative threshold voltage shift under vacuum. These results are explained through a chemical reaction between water molecules in air and unsubstituted hydroxyl groups in the cross-linked PVP-co-PMMA as well as a charge-trapping phenomenon at the domain boundaries in the spin-coated TES-ADT semiconductor.

Optimization of gate-bias stability and gas-sensing properties of triethylsilylethynyl anthradithiophene micro-strip field-effect transistors by incorporating insulating polymer

Abstract The control of the microstructure and patterning of 5,11-bis(triethylsilylethynyl)anthradithiophene (TES-ADT) film is essential for high-performance TES-ADT field-effect transistors (FETs) as a NO2 gas sensor. In this study, a binary blend film based on TES-ADT and insulating polymer was annealed by solvent vapor with patterned PDMS molds. The solvent-containing PDMS mold led to the TES-ADT crystallization under the phase-separation between TES-ADT and PMMA. This resulted in highly crystalline micro-strip films where TES-ADT and the insulating polymer were phase-separated on top and bottom, respectively. The micro-strip structures can have superior gas sensor performance because they have additional gas diffusion paths compared to non-patterned structures. Initial investigations to clarify morphology and microstructure of the films revealed that lateral phase separation got dominant with increasing the portion of the insulating polymer. The blended films were then used as the active layer in the FET-based gas sensors. The use of blended films instead of non-blended TES-ADT film in FETs is advantageous in reducing both the threshold voltage and subthreshold slope while compromising the field-effect mobility. The sensing response as the gas sensors is slightly lower in the blended TES-ADT FET than in the non-blended TES-ADT FET. However, the utilization of blended films significantly enhanced the bias-stress stability. Accordingly, a uniform baseline of the sensor performance was achieved in TES-ADT: insulating polymer blended FETs. This trend was in contrast to an abrupt decrease in the sensing signals of the non-blended TES-ADT FETs. The enhanced bias stability of the blended FETs was exhibited as a result of covering the silanol groups in SiO2 with a phase-separated insulating polymer. Our results provide a route for to the optimization of bias stability and response in TES-ADT micro-strip gas sensors through the application of a one-step blend technology.

Gas Sensors: Enhanced Gas Sensing Performance of Organic Field‐Effect Transistors by Modulating the Dimensions of Triethylsilylethynyl‐Anthradithiophene Microcrystal Arrays (Adv. Mater. Interfaces 4/2020)

In article number 1901696, Wi Hyoung Lee and co-workers report a method to increase sensitivity of the 5,11-bis(triethylsilylethynyl)-anthradithiophene (TES-ADT) gas sensors by adopting TES-ADT crystal arrays of various shapes and dimensions. The patterning and crystallization of spin-cast TES-ADT films are simultaneously achieved by the use of a solvent-containing engraved polydimethylsiloxane mold. The increased sensing performance in patterned TES-ADT film is mainly due to the increased area of crystal edges, which provides a diffusion pathway for gas molecules to arrive at the semiconductor-dielectric interface.

Enhanced Gas Sensing Performance of Organic Field‐Effect Transistors by Modulating the Dimensions of Triethylsilylethynyl‐Anthradithiophene Microcrystal Arrays

AbstractThis paper systematically compares the gas sensing properties of organic field‐effect transistors (OFETs) based on patterned 5,11‐bis(triethylsilylethynyl)anthradithiophene (TES‐ADT) films, by adopting TES‐ADT crystal arrays of various shapes and dimensions. The patterning and crystallization of spin‐cast TES‐ADT layers are achieved by the use of a solvent‐containing engraved polydimethylsiloxane (PDMS) mold. Decreasing width of the TES‐ADT pattern enhances gas sensing performance, as well as field‐effect mobility of OFETs. The decreased grain boundary density at narrower line width contributes to the increase of field‐effect mobility. On the other hand, the increased sensing performance is mainly due to the increased area of crystal edges, which provides a diffusion pathway for gas molecules to arrive at the semiconductor‐dielectric interface. This study provides new perspectives on the diffusion pathway of gas molecules in OFET‐based gas sensor, and will be useful for the design of active channel to boost the gas sensing properties of OFETs.

Annealing Behavior with Thickness Hindered Nucleation in Small-Molecule Organic Semiconductor Thin Films

We introduce a comprehensive overview of spontaneous and thermal induced structure changes in thin films of the high performance small-molecular organic semiconductor 5,11-bis(triethyl silylethynyl) anthradithiophene (TES-ADT). Most importantly, we find that nucleation of the TES-ADT high temperature beta phase can be induced only for films thicker than a critical thickness, while it is hindered for thinner films. The described limited crystal phase nucleation, the circumstances of which are unique in the realm of small-molecule organic semiconductors, is explained in terms of a two step nucleation mechanism while taking into account the anisotropic surface energy of crystal grains. Furthermore, we identify changes in the optical absorption spectra observed during aging of as deposited films with a spontaneous transformation from the amorphous phase to the alpha(2) phase via the alpha(1) phase of TES-ADT. The transformation takes place on the time scale of several days. Finally, we determine temperature dependence of lattice parameters of the alpha(1) and alpha(2) phases and the lattice parameters of the beta phase. Thermal expansion of the alpha(1) phase is found to be much lower than that of the alpha(2) phase.

Effects of thermal annealing conditions on the electrical characteristics of TES-ADT thin-film transistors

We investigated the annealing temperature and exposure period dependence of electrical characteristics of bottom-gate/top-contact solution-processed organic thin-film transistors (TFTs) fabricated on ITO-patterned substrates using 5,11-bis(triethylsilylethynyl)anthradithiophene(TES-ADT), PVP-co-PMMA, and silver as the semiconductor, gate dielectric, and drain and source electrodes, respectively. The semiconductor films were thermally annealed at 60, 80, and 90 °C for 60 min; then, the optimal annealing temperature, which proved to be 80 °C, was considered to investigate the impact of exposure time by exposing the film for 30, 60, and 90 min. Experimental results indicate that the medium temperature resulted in the better electrical performance, whereas the high temperature proved to be detrimental by causing ruptures through the film. According to our study, TES-ADT film annealed at 80 °C for 60 min results in the finest semiconductor microstructure, which improves the electrical characteristics, whereas lower or higher temperatures and shorter or longer annealing times lead to an unfavorable structure that hampers charge transport in the film.

Effects of Grain Boundary Density on the Gas Sensing Properties of Triethylsilylethynyl‐Anthradithiophene Field‐Effect Transistors

AbstractIn this study, triethylsilylethynyl‐anthradithiophene (TES‐ADT) films with different density of grain boundaries are used for systematic investigation of effects of grain boundary density on gas sensing properties of TES‐ADT field‐effect transistors (FETs). Grain boundary density is simply controlled by changing mixing time of TES‐ADT solution. Higher mixing time leads to higher grain boundary density, and field‐effect mobility decreases with increased grain boundary density. However, gas sensing properties exhibit the opposite behavior. Drain current and field‐effect mobility of FETs based on TES‐ADT film with higher grain boundary density increase much more upon exposure of NO2 with electron withdrawing character. In addition, dynamic gas sensing tests reveal that response rate and sensitivity of a TES‐ADT sensor are enhanced remarkably by an increase of grain boundary density in TES‐ADT films. Grain boundaries provide a pathway for diffusion of gas molecules into channel regions and thus increase of grain boundary density is beneficial for development of highly sensitive OFET gas sensors.

High-resolution charge carrier mobility mapping of heterogeneous organic semiconductors

Organic electronic device performance is contingent on charge transport across a heterogeneous landscape of structural features. Methods are therefore needed to unravel the effects of local structure on overall electrical performance. Using conductive atomic force microscopy, we construct high-resolution out-of-plane hole mobility maps from arrays of 5000 to 16 000 current-voltage curves. To demonstrate the efficacy of this non-invasive approach for quantifying and mapping local differences in electrical performance due to structural heterogeneities, we investigate two thin film test systems, one bearing a heterogeneous crystal structure [solvent vapor annealed 5,11-Bis(triethylsilylethynyl)anthradithiophene (TES-ADT)—a small molecule organic semiconductor] and one bearing a heterogeneous chemical composition [p-DTS(FBTTh2)2:PC71BM—a high-performance organic photovoltaic active layer]. TES-ADT shows nearly an order of magnitude difference in hole mobility between semicrystalline and crystalline areas, along with a distinct boundary between the two regions, while p-DTS(FBTTh2)2:PC71BM exhibits subtle local variations in hole mobility and a nanoscale domain structure with features below 10 nm in size. We also demonstrate mapping of the built-in potential, which plays a significant role in organic light emitting diode and organic solar cell operation.

Understanding the Crystal Packing and Organic Thin-Film Transistor Performance in Isomeric Guest-Host Systems.

In order to understand how additives influence the structure and electrical properties of active layers in thin-film devices, a compositionally identical but structurally different guest-host system based on the syn and anti isomers of triethylsilylethynyl anthradithiophene (TES ADT) is systematically explored. The mobility of organic thin-film transistors (OTFTs) comprising anti TES ADT drops with the addition of only 0.01% of the syn isomer and is pinned at the mobility of OTFTs having pure syn isomer after the addition of only 10% of the isomer. As the syn isomer fraction increases, intermolecular repulsion increases, resulting in a decrease in the unit-cell density and concomitant disordering of the charge-transport pathway. This molecular disorder leads to an increase in charge trapping, causing the mobility of OTFTs to drop with increasing syn-isomer concentration. Since charge transport is sensitive to even minute fractions of molecular disorder, this work emphasizes the importance of prioritizing structural compatibility when choosing material pairs for guest-host systems.

Simultaneous control of molecular orientation and patterning of small-molecule organic semiconductors for organic transistors

Triethylsilylethynyl anthradithiophene (TES-ADT) has been shown to be a promising soluble semiconductor for the active layer of organic field-effect transistors (OFETs) due to its solution processability, chemical stability and excellent electrical properties. However, there are still some problems that need to be resolved for the utilization of TES-ADT in OFETs. One of these problems is a patterning issue to minimize crosstalk between neighboring TES-ADT FETs. To this end, TES-ADT crystals of various shapes need to be patterned at the desired positions. Here, we demonstrated a simple method to fabricate patterned TES-ADT crystals by using a PDMS mold containing 1,2–dichloroethane (DCE) solvent. This method serves the dual purpose of preparing a variety of pattern shapes while simultaneously changing as-spun TES-ADT thin films into crystal patterns. The top-contact OFETs with the TES-ADT crystal patterns exhibited high performance, reaching a field-effect mobility of ∼0.3 cm2 V−1s−1.

Grain Boundary Induced Bias Instability in Soluble Acene-Based Thin-Film Transistors.

Since the grain boundaries (GBs) within the semiconductor layer of organic field-effect transistors (OFETs) have a strong influence on device performance, a substantial number of studies have been devoted to controlling the crystallization characteristics of organic semiconductors. We studied the intrinsic effects of GBs within 5,11-bis(triethylsilylethynyl) anthradithiophene (TES-ADT) thin films on the electrical properties of OFETs. The GB density was easily changed by controlling nulceation event in TES-ADT thin films. When the mixing time was increased, the number of aggregates in as-spun TES-ADT thin films were increased and subsequent exposure of the films to 1,2-dichloroethane vapor led to a significant increase in the number of nuleation sites, thereby increasing the GB density of TES-ADT spherulites. The density of GBs strongly influences the angular spread and crystallographic orientation of TES-ADT spherulites. Accordingly, the FETs with higher GB densities showed much poorer electrical characteristics than devices with lower GB density. Especially, GBs provide charge trapping sites which are responsible for bias-stress driven electrical instability. Dielectric surface treatment with a polystyrene brush layer clarified the GB-induced charge trapping by reducing charge trapping at the semiconductor-dielectric interface. Our study provides an understanding on GB induced bias instability for the development of high performance OFETs.

Thermal resistances of thin films of small molecule organic semiconductors

We have measured the thermal resistances of thin films of the small molecule organic semiconductors bis(triisopropylsilylethynyl) pentacene (TIPS-pn), bis(triethylsilylethynyl) anthradithiophene (TES-ADT) and difluoro bis(triethylsilylethynyl) anthradithiophene (diF-TES-ADT).

Unified film patterning and annealing of an organic semiconductor with micro-grooved wet stamps

A unified patterning and annealing approach was successfully demonstrated for 5,11-bis(triethylsilylethynyl)-anthradithiophene (TES-ADT) films spun-cast on polymer-treated SiO2 dielectrics.

Functionalized soluble triethylsilylethynyl anthradithiophenes (TESADTs) for organic electronic devices

Four new solution-processable triethylsilylethynyl anthradithiophene-(TESADT) based organic semiconductors, end-capped with phenyl (DP-; 1), thien-2-yl (DT-; 2), thienothien-2-yl (DTT-; 3), and perfluorophenyl (DFP-; 4) groups have been synthesized, characterized, and incorporated in organic thin-film transistors (OTFTs) and organic photovoltaics (OPVs). For the fabrication of solution-processed OTFT, thin films of all four compounds have been fabricated via a solution process of solution-shearing (SS), droplet-pinned crystallization (DPC), and drop-casting (DC). Among various solution-processing methods, solution-shearing produced TFTs the highest electrical performance. Thin films of compound 1 formed via the SS method exhibited p-channel characteristics, with hole mobilities as high as ∼0.034 cm2V−1s−1. The film morphologies and microstructures of these compounds have been characterized by atomic force microscopy and X-ray diffraction to rationalize device performance trends. Furthermore, DP-TESADT (1) and DFP-TESADT (4) has been employed for the fabrication of OPVs. Especially, pseudo-bilayer polymer solar cells based on an underlayer of poly(3-hexylthiophene) (P3HT) doped with 2.4% DP-TESADT and 9.1% DFP-TESADT and an upper layer of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) achieved power conversion efficiency up to 2.1%.

Al2O3/TiO2 nanolaminate gate dielectric films with enhanced electrical performances for organic field-effect transistors

Nanolamination has entered the spotlight as a novel process for fabricating highly dense nanoscale inorganic alloy films. OFET commercialization requires, above all, excellent dielectric properties of gate dielectric layer. Here, we describe the fabrication and characterization of Al–O–Ti (AT) nanolaminate gate dielectric films using a PEALD process, and their OFET applications. The AT films exhibited a very smooth surface (Rq < 0.3 nm), a high dielectric constant (17.8), and a low leakage current (8.6 × 10−9 A/cm2 at 2 MV/cm) compared to single Al2O3 or TiO2 films. Importantly, a 50 nm thick AT film dramatically enhanced the value of μFET (0.96 cm2/V) on a pentacene device, and the high off-current level in a single TiO2 film was effectively reduced. The nanolamination process removes the drawbacks inherent in each single layer so that the AT film provides excellent dielectric properties suitable for fabricating high-performance OFETs. Triethylsilylethynyl anthradithiophene (TES-ADT), a solution-processable semiconductor, was combined with the AT film in an OFET, and the electrical properties of the device were characterized. The excellent dielectric properties of the AT film render nanolamination a powerful strategy for practical OFET applications.

Quantifying the Energy Barriers and Elucidating the Charge Transport Mechanisms across Interspherulite Boundaries in Solution‐Processed Organic Semiconductor Thin Films

Grain boundaries act as bottlenecks to charge transport in devices comprising polycrystalline organic active layers. To improve device performance, the nature and resulting impact of these boundaries must be better understood. The densities and energy levels of shallow traps within and across triethylsilylethynyl anthradithiophene (TES ADT) spherulites are quantified. The trap density is 7 × 1010 cm−2 in devices whose channels reside within a single spherulite and up to 3 × 1011 cm−2 for devices whose channels span a spherulite boundary. The activation energy for charge transport, EA, increases from 34 meV within a spherulite to 50–66 meV across a boundary, depending on the angle of molecular mismatch. Despite being molecular in nature, these EA’s are more akin to those found for charge transport in polymer semiconductors. Presumably, trapped TES ADT at the boundary can electrically connect neighboring spherulites, similar to polymer chains connecting crystallites in polymer semiconductor thin films.

Synthesis and Characterization of Naphthalene End‐capped Triethylsilylethynyl Anthradithiophene for Organic Thin‐Film Transistors

Naphthalene end‐capped triethylsilylethynyl anthradithiophene was synthesized by a Suzuki coupling reaction. The obtained compound had good solubility due to its bulky triethylsilylethynyl groups although the extended π‐conjugated backbone structure. The thermal stability of the new material was analyzed by thermogravimetry analysis and differential scanning calorimeter thermograms. The optical and electrochemical properties were examined. A thin film of compound was fabricated by spin‐coating and exhibited p‐channel organic thin film transistors (OTFTs) transport with hole mobility of 4 × 10−4 cm2/Vs.

Capillary effects in guided crystallization of organic thin films

Recently, it has been demonstrated that solvent-vapor-induced crystallization of triethylsilylethynyl anthradithiophene (TES ADT) thin films can be directed on millimeter length scales along arbitrary paths by controlling local crystal growth rates via pre-patterning the substrate. Here, we study the influence of capillary effects on crystallization along such channels. We first derive an analytical expression for the steady-state growth front velocity as a function of channel width and validate it with numerical simulations. Then, using data from TES ADT guided crystallization experiments, we extract a characteristic channel width, which provides the smallest feature size that can be obtained by this technique.

Damaging Effect of Hot Metal Atoms on Organic Semiconducting Films during Top Contact Formation

The formation of a high quality interface between metallic and organic semiconducting thin films is critically important in achieving high-performance organic electronics devices. In this regard, the importance of understanding the multifaceted issue of structure damage incurred to organic films by the evaporated metal atoms cannot be overstated. In the present study, we have investigated the change of a structurally ordered, organic semiconducting (o.s.) thin film of 5,11-bis(triethylsilylethynyl)anthradithiophene (TESADT) effected by gold atoms by means of synchrotron-based soft X-ray spectroscopies including ultraviolet photoemission spectroscopy (UPS) and X-ray photoemission spectroscopies (XPS) with imaging capability, near edge X-ray absorption fine structure (NEXAFS) spectroscopy, and atomic force microscopy (AFM). This work shows that gold atoms readily diffuse into the organic films and nucleate into nanometer-size clusters, damage chemical structure, destroy structural ordering of the organic fi...