Semiconductors For Organic Thin-film Transistors Research Articles

(F5PhO)2-F16-SiPc as an air-stable, high-performance n-type semiconductor with poor cannabinoid sensing capabilities

(F5PhO)2-F16-SiPc is an air stable, n-type semiconductor for organic thin-film transistors (OTFTs), however the structural changes that enhance its stability likely cause its lack of response to cannabinoids in a sensor.

Soluble Ruthenium Phthalocyanines as Semiconductors for Organic Thin‐Film Transistors

AbstractRuthenium phthalocyanine (RuPcs) are multipurpose compounds characterized by their remarkable reactivity and photoelectronic properties, which yield a broad synthetic scope and easy derivatization at the axial position. However, RuPcs have been underexplored for use in organic thin‐film transistors (OTFTs), and therefore new studies are necessary to provide basic insight and a first approach in this new application. Herein, two novel RuPc derivatives, containing axial pyridine substituents with aliphatic chains (RuPc(CO)(PyrSiC6) (1) and RuPc(PyrSiC6)2 (2), were synthesized, characterized, and tested as the organic semiconductor in OTFTs. RuPc thin‐films were characterized by X‐ray diffraction (XRD), and atomic force microscopy (AFM) to assess film morphology and microstructure. 1 displayed comparable p‐type device performance to other phthalocyanine‐based OTFTs of similar design, with an average field effect mobility of 2.08×10−3 cm2 V−1 s−1 in air and 1.36×10−3 cm2 V−1 s−1 in nitrogen, and threshold voltages from −11 V to −20 V. 2 was found to be non‐functional as the semiconductor in the device architecture used, likely as a result of significant differences in thin‐film formation. The results of this work illustrate a promising starting point for future development of RuPc electronic devices, particularly in this new family of OTFTs.

Solution-Processable Benzo[b]thieno[2,3-d]thiophene Derivatives as Organic Semiconductors for Organic Thin-Film Transistors

Two new benzo[b]thieno[2,3-d]thiophene (BTT) derivatives, 2-(benzo[b]thiophen-5-yl)benzo[b]thieno[2,3-d]thiophene (compound 2), and 2-(benzo[b]thieno[2,3-d]thiophene-2yl)dibenzo[b,d]thiophene (compound 3) have been synthesized and utilized as solution-processable small molecular organic semiconductors for organic field-effect transistors (OFETs). The physicochemical characteristics of the recently created substances were analyzed using thermogravimetric analysis (TGA), differential scanning calorimeter (DSC), and UV-vis spectroscopy. Subsequently, the above-mentioned substances were employed as semiconductor layers in bottom-gate/top-contact OFETs through solution shearing methods for device fabrication, and their electrical performances were meticulously evaluated. The outcoming OFET device displayed p-channel behavior, demonstrating hole mobility of up to 0.005cm2/Vs and a current on/off ratio higher than 106.

Effects of alkyl chain on the liquid crystalline properties of [1]benzothieno[3,2-b][1]benzothiophene-based organic semiconductors

New [1]benzothieno[3,2- b ] [1]benzothiophene (BTBT)-based small molecules with different substituents were synthesized and employed as solution-processable organic semiconductors for organic thin-film transistors (OTFTs). Two types of alkyl side chains (octyl/ethylhexyl) were selected for the solubility enhancement and analysis of material phase transition. Thermal, optical, and electrical properties of new compounds were analyzed and characterized. Synthesized BTBT derivatives exhibited completely different phase transition features depending on the attached side chains; linearly alkylated 2-octyl-7-(5-octylthiophen-2-yl)benzo[ b ]benzo [4,5]thieno[2,3- d ]thiophene (compound 1 ) showed decent carrier mobility up to 0.26 cm 2 /Vs at highly ordered smectic X phase, while 2-(5-(2-ethylhexyl)thiophen-2-yl)-7-octylbenzo[ b ]benzo [4,5]thieno[2,3- d ]thiophene (compound 2 ) with branched alkyl chain showed poor electrical performance. Thin film morphology and microstructure were investigated using atomic force microscopy and X-ray diffraction to reveal the dramatic property difference between the two dialkylated BTBT derivatives. • Solution-processable BTBT-based organic semiconductors were synthesized. • Analysis on alkyl side chain type; linear and branch-like substituents was conducted. • Linearly alkylated compound showed smectic liquid crystalline properties. • Organic transistors with LC phase showed mobility up to 0.26 cm 2 /Vs.

Silicon Phthalocyanines for n-Type Organic Thin-Film Transistors: Development of Structure–Property Relationships

Silicon phthalocyanines (SiPcs) have shown great potential as n-type or ambipolar organic semiconductors in organic thin-film transistors (OTFTs) and organic photovoltaics. Although properly design...

N‐Type Quinoidal Oligothiophene‐Based Semiconductors for Thin‐Film Transistors and Thermoelectrics

AbstractOrganic electronic devices have gained immense popularity in the last 30 years owing to their increasing performance. Organic thin‐film transistors (OTFTs) are one of the basic organic electronic devices with potential industrial applications. Another class of devices called organic thermoelectric (OTE) materials can directly transform waste heat into usable electrical power without causing any pollution. p‐Type transistors outperform n‐type transistors because the latter requires a lower orbital energy level for efficient electron injection and stable electron transport under ambient conditions. Aromatic building blocks can be utilized in constructing n‐type semiconductors. Quinoidal compounds are another promising platform for optoelectronic applications because of their unique properties. Since their discovery in 1970s, quinoidal oligothiophene‐based n‐type semiconductors have drawn considerable attention as candidates for high‐performance n‐type semiconductors in OTFTs and OTEs. Herein, the development history of quinoidal oligothiophene‐based semiconductors is summarized, with a focus on the molecular design and the influence of structural modification on molecular packing and thus the device performance of the corresponding quinoidal oligothiophene‐based semiconductors. Insights on the potential of quinoidal oligothiophenes for high‐performance n‐type OTFTs and OTEs are also provided.

Attribute driven inverse materials design using deep learning Bayesian framework

Much of computational materials science has focused on fast and accurate forward predictions of materials properties, for example, given a molecular structure predict its electronic properties. This is achieved with first principles calculations and more recently through machine learning approaches, since the former is computation-intensive and not practical for high-throughput screening. Searching for the right material for any given application, though follows an inverse path—the desired properties are given and the task is to find the right materials. Here we present a deep learning inverse prediction framework, Structure Learning for Attribute-driven Materials Design Using Novel Conditional Sampling (SLAMDUNCS), for efficient and accurate prediction of molecules exhibiting target properties. We apply this framework to the computational design of organic molecules for three applications, organic semiconductors for thin-film transistors, small organic acceptors for solar cells and electrolyte additives with high redox stability. Our method is general enough to be extended to inorganic compounds and represents an important step in deep learning based completely automated materials discovery.

Impact of Nonfullerene Acceptor Side Chain Variation on Transistor Mobility

AbstractOrganic photovoltaic power conversion efficiencies exceeding 14% can largely be attributed to the development of nonfullerene acceptors (NFAs). Many of these molecules are structural derivatives of IDTBR and ITIC, two common NFAs. By modifying the chemical structure of the acceptor, the optical absorption, energy levels, and bulk heterojunction morphology can be tuned. However, the effect of structural modifications on NFA charge transport properties has not yet been fully explored. In this work, the relationship between chemical structure, molecular packing, and charge transport, as measured in organic thin‐film transistors (OTFTs), is investigated for two high performance NFAs, namely O‐IDTBR and ITIC, along with their structural derivatives EH‐IDTBR and ITIC‐Th. O‐IDTBR exhibits a higher n‐type saturation field effect mobility of 0.12 cm2 V−1 s−1 compared with the other acceptors investigated. This can be attributed to the linear side chains of O‐IDTBR which direct an interdigitated columnar packing motif. The study provides insight into the transport properties and molecular packing of NFAs, thereby contributing to understanding the relationship between chemical structure, material properties, and device performance for these materials. The high electron mobility achieved by O‐IDTBR also suggests its applications can be extended to use as an n‐type semiconductor in OTFTs.

Ambipolarity and Air Stability of Silicon Phthalocyanine Organic Thin‐Film Transistors

AbstractSilicon phthalocyanines (SiPcs) are a class of conjugated, planar molecule that have recently been investigated for use in organic photovoltaics (OPVs), organic light‐emitting diodes (OLEDs), and organic thin‐film transistors (OTFTs) due to their variable structure and ease of synthesis. Bottom‐gate, bottom‐contact OTFTs with four SiPc derivatives used as the semiconducting layers are prepared using physical vapor deposition. Devices using bis(pentafluorophenoxy) silicon phthalocyanine (F10‐SiPc) deposited on 140 °C substrates demonstrate electron field‐effect mobilities (μ) of up to 0.54 cm2 V−1 s−1, among the best currently reported for N‐type phthalocyanine‐based transistors. All materials show dramatic changes in charge transport when characterized under vacuum (P < 0.1 Pa) compared to in air at atmospheric pressure, typically switching from electron majority charge carriers to holes, with the change dependent on material structure and energetics. F10‐SiPc is close to balanced ambipolar in air, with μ around 5 × 10−3 cm2 V−1 s−1 for both holes and electrons. These results demonstrate SiPcs' potential as N‐type semiconductors in OTFTs as well as their adjustable charge transport as affected by operation environment.

Solution-processable small molecules for bulk heterojunction ambipolar thin-film transistors and complementary-like inverters

Solution-processable thioalkylated bithiophene derivatives with different lengths of side chains (SBT-n; n = 10, 12, 14, 16, 18) have been synthesized and characterized as p-channel organic semiconductors for thin-film transistors (TFTs). Based on a combination of the highest performing SBT derivative (SBT-14) and quinoidals (DTTRQs) as p- and n-channel materials, solution-processed small-molecular bulk heterojunction (BHJ) ambipolar thin-film transistors were fabricated, and the resulting devices showed air-stable and high ambipolar performance with well-balanced electron and hole mobilities as high as 0.70 cm2 V−1 s−1 and 0.21 cm2 V−1 s−1, respectively. Furthermore, complementary-like inverters comprising two ambipolar thin-film transistors were demonstrated, which exhibited a high voltage gain of up to 81. Our study clearly demonstrated that side chain engineering of small molecular organic semiconductors had a significant influence on the electrical performance of TFTs and BHJ transistors, as well as complementary-like inverters.

Anion-induced N-doping of naphthalenediimide polymer semiconductor in organic thin-film transistors

Molecular doping is an important strategy to improve the charge transport properties of organic semiconductors in various electronic devices. Compared to p-type dopants, the development of n-type dopants is especially challenging due to poor dopant stability against atmospheric conditions. In this article, we report the n-doping of the milestone naphthalenediimide-based conjugated polymer P(NDI2OD-T2) in organic thin film transistor devices by soluble anion dopants. The addition of the dopants resulted in the formation of stable radical anions in thin films, as confirmed by EPR spectroscopy. By tuning the dopant concentration via simple solution mixing, the transistor parameters could be readily controlled. Hence the contact resistance between the electrodes and the semiconducting polymer could be significantly reduced, which resulted in the transistor behaviour approaching the desirable gate voltage-independent model. Reduced hysteresis was also observed, thanks to the trap filling by the dopant. Under optimal doping concentrations the channel on-current was increased several fold whilst the on/off ratio was simultaneously increased by around one order of magnitude. Hence doping with soluble organic salts appears to be a promising route to improve the charge transport properties of n-type organic semiconductors.

Solution-Processable Diketopyrrolopyrrole Derivatives as Organic Semiconductors for Organic Thin-Film Transistors.

Solution-processable diketopyrrolopyrrole derivatives having acetylene, 2,5-bis(2-ethylhexyl)-3-(5-(phenylethynyl)thiophen-2-yl)-6-(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (3), 2,5-bis (2-ethylhexyl)-3-(thiophen-2-yl)-6-(5-(thiophen-2-ylethynyl)thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c] pyrrole-1,4-dione (4), and 6,6'-((thiophene-2,5-diylbis(ethyne-2,1-diyl))bis(thiophene-5,2-diyl)) bis(2,5-bis(2-ethylhexyl)-3-(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione) (5) were synthesized and characterized as organic semiconductors for organic thin-film transistors (OTFTs). For the fabrication of thin films based on solution processable compounds, drop-casting (DC) and solution-shearing (SS) were employed. Thin films of compound 5 exhibited p-channel characteristics with carrier mobility as high as 5.7 × 10-4 cm2/Vs and a current on/off ratio of 104-106 for top-contact/bottom-gate OTFT devices.

Solid-state organization of n-type carbazole-based semiconductors for organic thin-film transistors.

The development of new organic semiconductors has been mainly led by the search for new π-conjugated cores, but recently the use of flexible side chains is attracting more and more attention to control the molecular packing and order in the solid state to improve the charge-transporting properties. In this work, the charge transport properties of a series of tricyanovinyl-substituted carbazole-based materials with different alkyl chain lengths have been investigated and correlated with the respective intermolecular interactions and molecular packings via X-ray diffraction (XRD) studies.

A chrysene-based liquid crystalline semiconductor for organic thin-film transistors

Chrysene and [1]benzothieno[3,2-b][1]benzothiophene possess a similar electronic structure, and chrysene is expected to have better semiconductor device performance than BTBT, owing to the stronger electronic couplings.

2-Thiopene[1]benzothieno[3,2-b]benzothiophene derivatives as solution-processable organic semiconductors for organic thin-film transistors

Novel [1]benzothieno[3,2-b]benzo-thiophene (BTBT) derivatives were synthesized and characterized as solution-processable organic semiconductors for top-contact/bottom-gate organic filed-effect transistors (OFETs). Physicochemical properties of the new compounds were characterized by UV–vis absorption spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimeter (DSC), cyclic voltammetry (CV), and density functional theory (DFT) calculation. The electrical properties of the corresponding compounds were investigated through the fabrication and characterization of field-effect transistors via solution-shearing. Both compounds were FET active and exhibited decent p-channel activity with carrier mobilities up to 0.10 cm2 V−1 s−1 and current on/off ratio >108. Film morphology and microstructure, as characterized by atomic force microscopy (AFM) and X-ray diffraction (XRD) were correlated with the device performance.

Solution-processable dithieno[3,2-b:2′,3′-d]thiophene derivatives for organic thin-film transistors and complementary-like inverters

Abstract Solution-processable dithieno[3,2-b:2′,3′-d]thiophene (DTT) derivatives, 2,6-bis(phenylethynyl)dithieno[3,2-b:2′,3′-d]thiophene (BP-Et-DTT) and 2,6-bis(thiophen-2-ylethynyl)dithieno[3,2-b:2′,3′-d]thiophene (BT-Et-DTT) were synthesized and characterized as organic semiconductors for organic thin-film transistors (OTFTs). Thermal, optical, and electrochemical properties of the DTT-based semiconductors were investigated. The solution-sheared thin films based on DTT derivatives exhibited p-channel characteristics as an active layer in organic thin-film transistors. The highest hole mobility was 0.32 cm2 V−1s−1 based on BP-Et-DTT thin films. The thin films exhibited micrometer-sized crystalline fiber structures which were aligned along the shearing direction, resulting in fiber-alignment-induced charge-transport anisotropy. Furthermore, bulk heterojunction (BHJ) ambipolar transistors were fabricated with an optimized blending ratio of BP-Et-DTT and the representative n-channel semiconductor, PDIFCN2. Complementary-like inverters were fabricated based on the two identical ambipolar transistors, resulting in moderate voltage gains of up to 16.

(Oligo-)Thiophene Functionalized Tetraazaperopyrenes: Donor-Acceptor Dyes and Ambipolar Organic Semiconductors.

Tetraazaperopyrenes (TAPPs) have been functionalized with thiophene and terthiophene units of different architecture resulting in a variety of organic donor-acceptor (D-A) compounds. The influence of the connection of the thiophenes to the TAPP core on their structural, photophysical and electrochemical properties has been studied in detail by a combination of X-ray crystallography, UV-vis and fluorescence spectroscopy as well as cyclic voltammetry, which allowed the establishment of structure-property relationships. The HOMO-LUMO gap is significantly decreased upon substitution of the TAPP core with electron-donating thiophene units, the extent of which is strongly influenced by the orientation of the thiophene units. The latter also crucially directs the molecular packing in the solid. Linkage at the α-position allows both inter- and intramolecular N···S interaction, whereas linkage in the β-position prevents intramolecular N···S interaction, resulting in a less pronounced conjugation of the TAPP core and the thiophene units. The new TAPP derivatives were processed as semiconductors in organic thin-film transistors (TFTs) that show ambipolar behavior. The insight into band gap and structure engineering may open up new possibilities to tailor the electronic properties of TAPP-based materials for certain desired applications.

π-Extended Isoindigo-Based Derivative: A Promising Electron-Deficient Building Block for Polymer Semiconductors.

The exploration of novel electron-deficient building blocks is a key task for developing high-performance polymer semiconductors in organic thin-film transistors. In view of the situation of the lack of strong electron-deficient building blocks, we designed two novel π-extended isoindigo-based electron-deficient building blocks, IVI and F4IVI. Owing to the strong electron-deficient nature and the extended π-conjugated system of the two acceptor units, their copolymers, PIVI2T and PF4IVI2T, containing 2,2'-bithiophene donor units, are endowed with deep-lying highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) energy levels and strong intermolecular interactions. In comparison to PIVI2T, the fluorinated PF4IVI2T exhibits stronger intra- and intermolecular interactions, lower HOMO/LUMO energy levels up to -5.74/-4.17 eV, and more ordered molecular packing with a smaller π-π stacking distance of up to 3.53 Å, resulting in an excellent ambipolar transporting behavior and a promising application in logic circuits for PF4IVI2T in ambient with hole and electron mobilities of up to 1.03 and 1.82 cm2 V-1 s-1, respectively. The results reveal that F4IVI is a promising and strong electron-deficient building unit to construct high-performance semiconducting polymers, which provides an insight into the structure-property relationships for the exploration and molecular engineering of excellent electron-deficient building blocks in the field of organic electronics.

Organic thin-film transistors incorporating a commercial pigment (Hostasol Red GG) as a low-cost semiconductor

Inexpensive carbon-based semiconducting materials are of interest for the manufacturing of organic thin-film transistors (OTFTs) for use in radio-frequency tags, gas sensors, printed logic circuits and flexible screens. The molecular organization of these materials at the interface with the dielectric layer in an OTFT is critical to device performance. We incorporated an inexpensive commercial pigment, 14H-anthra[2,1,9-m,n,a]thioxanthen-14-one (Hostasol Red GG, Solvent Orange 63), which has not been characterized before as a semiconductor in OTFTs. We found that of the four surface treatments used to modify the silicon dioxide (SiO2) dielectric, octyltrichlorosilane (OTS) had the greatest positive effect on device operation. We also illustrate the importance of moisture in the surface chemistry and its direct implications to film formation and device performance. Furthermore, increasing substrate temperature during physical vapor deposition of Red GG generally decreased device performance, despite increasing molecular organization and apparent grain size as characterized with atomic force microscopy (AFM). Optimized OTFTs had a field-effect mobility of up to 5 × 10−5 cm2/V, an on/off current ratio the order of 103 and a threshold voltage around 10 V. These results demonstrate the important role of processing conditions for Red GG-based OTFTs and could be applied to optimizing devices made with synthetic derivatives of Red GG for improved performance in this family of relatively inexpensive and unexplored semiconducting compounds.

Synthesis and Characterization of Quinoxaline Derivative as Organic Semiconductors for Organic Thin-Film Transistors

Synthesis and Characterization of Quinoxaline Derivative as Organic Semiconductors for Organic Thin-Film Transistors