Semiconductors For Organic Thin-film Transistors Research Articles

Improvement charge injection in P-type polymer field-effect transistors with low-cost molybdenum electrodes through dodecanoic acid self assembled monolayer

ABSTRACTMost of the merit of organic thin film transistors (OTFTs) is that they can be manufactured using cost effective processes. However, expensive gold (Au) electrodes have usually been used as a source/drain (S/D), due to their benign energy level matching, high air stability, and easy patternability. In this article, we report a simple method for improving the charge injection from a low cost molybdenum (Mo) electrode to organic semiconductors in OTFTs by incorporating a dodecanoic acid (DA)–based self-assembled monolayer (SAM). The OTFT performance is remarkably improved when compared to the devices with a pristine Au electrode. The hole carrier mobilities (hole μFET) were ∼0.13 (rr-P3HT), ∼0.55 (PC12TV12T) and ∼0.72 (P2100) cm2/V·sec.

Synthesis and Characterization of Diketopyrrolopyrrole Derivatives as Organic Semiconductors for Organic Thin-Film Transistors

Synthesis and Characterization of Diketopyrrolopyrrole Derivatives as Organic Semiconductors for Organic Thin-Film Transistors

Benzothiadiazole-Based Small-Molecule Semiconductors for Organic Thin-Film Transistors and Complementary-like Inverters.

New benzothiadiazole derivatives, 4,7-bis(5-phenylthiophen-2-yl)benzo[c][1,2,5]thiadiazole (PT-BTD) and 4,7-bis[4-(thiophen-2-yl)phenyl]benzo[c][1,2,5]thiadiazole (TP-BTD), were synthesized and characterized as small-molecule organic semiconductors for organic thin-film transistors (OTFTs) and complementary inverters. The thermal, optical, and electrochemical properties of the new compounds were fully characterized. Vacuum-deposition and solution-shearing methods were used to fabricate thin films based on these compounds. Thin films based on PT-BTD exhibited p-channel characteristics with hole mobilities as high as 0.10 cm2 V-1 s-1 and current on/off ratios >107 for top-contact/bottom-gate OTFT devices. With an optimized blending ratio of PT-BTD and the representative n-channel semiconductor N,N'-1H,1H-perfluorobutyl dicyanoperylenediimide, bulk heterojunction ambipolar transistors were fabricated with balanced hole and electron mobilities of 0.10 and 0.07 cm2 V-1 s-1 , respectively. Furthermore, a complementary-like inverter was fabricated using ambipolar thin-film transistors, which showed a high voltage gain of 84.

Organic thin-film transistors based on solution-processable benzodithiophene dimers modified with hexyl groups

Benzodithiophene dimers modified with hexyl groups (2C6-BDT-dimer) were investigated as solution-processable organic semiconductors for organic thin-film transistors (OTFTs). Since 2C6-BDT-dimer crystals have an anisotropic shape, flow coating was adopted to grow polycrystalline films. The flow-coated films were inferior to the vacuum-evaporated ones in terms of their crystallinity estimated from X-ray diffraction data. However, the hole mobility of the OTFTs with the flow-coated films, which was 1.7 cm2 V−1 s−1 at maximum, was higher than that of the OTFTs with vacuum-evaporated films because the one-dimensional thin crystals of the flow-coated films were aligned in the flow-coating direction.

Synthesis and Characterization of Arylacetylene Derivative as Solution Processable Organic Semiconductors for Organic Thin-Film Transistors

Synthesis and Characterization of Arylacetylene Derivative as Solution Processable Organic Semiconductors for Organic Thin-Film Transistors

Synthesis and characterization of 2,7-diethynyl-benzo[b]benzo[4,5]thieno[2,3-d]thiophene derivative as organic semiconductors for organic thin-film transistors

New benzo[b]benzo[4,5]thieno[2,3-d]thiophene derivatives were synthesized and characterized as organic semiconductors in top-contact/bottom-gate organic thin-film transistors (OTFTs). New compounds were fully characterized by thermogravimetric analysis, differential scanning calorimetry, UV–vis spectroscopy, cyclic voltammetry, and density functional theory calculation. New compounds were vacuum-deposited as thin films, and investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM). Thin-film transistors based on compound 1 showed decent p-channel characteristics with mobility as high as 0.58cm2V−1s−1 and current on/off ratio of 106–109. Thin film microstructure and surface morphologies have been correlated with the corresponding device performance.

Synthesis and Characterization of Benzothiadiazole Derivatives as Organic Semiconductors for Organic Thin-Film Transistors.

New benzothiadiazole derivatives end-functionalized with carbazole and a-carboline, 4,7-di(9H-carbazol-9-yl)benzo[c][1,2,5]thiadiazole (1) and 4-(9H-carbazol-9-yl)-7-(9H-pyrido[2,3-bindol-9-yl) benzo[c][1,2,5]thiadiazole (2) were synthesized and characterized as organic semiconductors for organic thin-film transistors (OTFTs). Thermal, optical, and electrochemical properties of the corresoponding compounds were characterized. Thin films of compound 1 exhibited p-channel characteristics with carrier mobility as high as 10⁻⁴ cm²/Vs and a current on/off ratio of 10⁵ for top-contact/bottom-gate OTFT devices.

Novel Organic Semiconductors Based on Phenyl and Phenylthienyl Derivatives for Organic Thin-Film Transistors

New phenyl and phenylthienyl derivatives end-functionalized with carbazole and α-carboline, 9-(4- (9H-carbazol-9-yl)phenyl)-9H-carbazole, 9-(4-(9H-carbazol-9-yl)phenyl)-9H-pyrido[2,3-b]indole, 9-(3-(9H-carbazol-9-yl)phenyl)-9H-carbazole, 9-(3-(9H-carbazol-9-yl)phenyl)-9H-pyrido[2,3-b]indole, 9-(4-(5-(9H-carbazol-9-yl)thiophen-2-yl)phenyl)-9H-carbazole, and 9-(3-(5-(9H-carbazo-9-yl) thiophen-2-yl)phenyl)-9H-carbazole were synthesized and characterized as organic semiconductors for organic thin-film transistors (OTFTs). Most compounds exhibited p-channel characteristics with carrier mobility as high as 1.7 x 10⁻⁵ cm²/Vs and a current on/off ratio of 10²-10⁴ for top-contact/bottom-gate OTFT devices.

α-Modified Naphthodithiophene Diimides—Molecular Design Strategy for Air-Stable n-Channel Organic Semiconductors

Molecular modifications of naphtho[2,3-b:6,7-b′]dithiophene diimide (NDTI) by introducing electron-deficient substituents, such as p-(trifluoromethyl)phenyl-, 5-pyrimidyl-, and chlorine groups, on the thiophene α-positions were examined to develop superior n-channel organic semiconductors for organic thin-film transistors (OTFTs). Among newly developed NDTI derivatives, N,N′-dioctyl-2,7-dichloro-NDTI (5) was found to be a superior semiconductor over N,N′-dioctyl-NDTI (1a). The OTFTs based on 5 showed electron mobility as high as 0.73 cm2 V–1 s–1, whereas the mobility of α-unsubstituted 1a based OTFTs was 0.05 cm2 V–1 s–1. The improved mobility by the introduction of chlorine groups can be explained by the electronic structure in the solid state. In contrast to an one-dimensional (1D) electronic structure of 1a elucidated by single crystal X-ray analysis and theoretical calculations, 5 can be characterized as a two-dimensional (2D) bricklayer structure, in which the chlorine groups at the thiophene α-posit...

Design of High-Mobility Diketopyrrolopyrrole-Based π-Conjugated Copolymers for Organic Thin-Film Transistors.

Since the report of the first diketopyrrolopyrrole (DPP)-based polymer semiconductor, such polymers have received considerable attention as a promising candidate for high-performance polymer semiconductors in organic thin-film transistors (OTFTs). This Progress Report summarizes the advances in the molecular design of high-mobility DPP-based polymers reported in the last few years, especially focusing on the molecular design of these polymers in respect of tuning the backbone and side chains, and discussing the influences of structural modification of the backbone and side chains on the properties and device performance of corresponding DPP-based polymers. This provides insights for the development of new and high-mobility polymer semiconductors.

Trapped charge mapping in crystalline organic transistors by using scanning Kelvin probe force microscopy

Trapped charge distributions at the interfaces between gate insulators and crystalline organic semiconductors in thin-film transistors are visualized by using a technique based on scanning Kelvin probe force microscopy (SKFM). For the charge density measurement, an ac voltage is applied to the gate electrode and its amplitude is adjusted so as to keep the electrostatic force constant between the SKFM tip and the semiconductor surface. The trapped charge density shows characteristic spatial distributions in the channel region, which varies by voltage stresses applied to the transistors. By comparing the charge distributions with the surface-potential profiles, trap mechanisms are discussed.

Synthesis and characterization of carbazole- and α-carboline-based thiophene derivatives as organic semiconductors for organic thin-film transistors

New thiophene derivatives, end-functionalized with carbazoles (9-(5-(9H-carbazol-9-yl)thiophen-2-yl)-9H-carbazole), carbazole and α-carboline (9-(5-(9H-carbazol-9-yl)thiophen-2-yl)-9H-pyrido[2,3-b]indole), and α-carbolines (9-(5-(9H-pyrido[2,3-b]indol-9-yl)thiophen-2-yl)-9H-pyrido[2,3-b]indole) were synthesized and characterized as organic semiconductors for organic thin-film transistors (OTFTs). The best device performance was achieved via a hexamethyldisilazane dielectric surface treatment of thermally grown Si–SiO2 substrates prior to vapor-phase semiconductor deposition. Within this family, the semiconductor having an electron-donating (carbazole) and an electron-withdrawing (α-carboline) substituent exhibited the highest p-channel characteristic with a carrier mobility as high as 0.014 cm2 V−1 s−1 and a current on/off ratio of 7 × 105 for top-contact/bottom-gate OTFT devices. The device characteristics have been correlated with the film morphologies and microstructures of the corresponding compounds.

High-Mobility Pyrene-Based Semiconductor for Organic Thin-Film Transistors

Numerous conjugated oligoacenes and polythiophenes are being heavily studied in the search for high-mobility organic semiconductors. Although many researchers have designed fused aromatic compounds as organic semiconductors for organic thin-film transistors (OTFTs), pyrene-based organic semiconductors with high mobilities and on-off current ratios have not yet been reported. Here, we introduce a new pyrene-based p-type organic semiconductor showing liquid crystal behavior. The thin film characteristics of this material are investigated by varying the substrate temperature during the deposition and the gate dielectric condition using the surface modification with a self-assembled monolayer, and systematically studied in correlation with the performances of transistor devices with this compound. OTFT fabricated under the optimum deposition conditions of this compound, namely, 1,6-bis(5'-octyl-2,2'-bithiophen-5-yl)pyrene (BOBTP) shows a high-performance transistor behavior with a field-effect mobility of 2.1 cm(2) V(-1) s(-1) and an on-off current ratio of 7.6 × 10(6) and enhanced long-term stability compared to the pentacene thin-film transistor.

Synthesis and characterization of a new π-conjugated polymer with cyanoacrylate side chain for organic thin film transistors

A new copolymer, poly(carbazol-9-yl)phenyl)-2-cyanoacrylate)-alt-(2,2′-(1,5-bis(hexyloxy)naph thalene-2,6-diyl)dithiophene)) (PCCNT) with cyanoacrylate, was synthesized by the Stille coupling reaction for p-type semiconductors in OTFTs. FTIR and 1H NMR spectroscopes confirmed the structure of PCCNT. The molecular weight of polymer was 14.6 kDa with polydispersity index of 1.72 using GPC. The obtained polymer with long alkyl side chains demonstrated good solubility. PCCNT has good thermal stability of (Td=324) as well as good oxidation stability with a HOMO level of −5.35 eV. UV-Vis absorption maximum of the polymer was found at 431 nm in solution and at 444 nm for the film, respectively. In the photoluminescence (PL), the large red-shift was observed from solution emission (λmax 493 nm) to film emission (λmax 539 nm) due to an intermolecular interaction. The fabricated bottom gate-top contact organic thin film transistors (OTFTs) showed field-effect mobility of 9.02×10−5 cm2/Vs and threshold voltage of −3 V. Open image in new window

Synthesis and thin-film transistor performance of benzodipyrrolinone and bithiophene donor-acceptor copolymers

Three novel benzodipyrrolinone–bithiophene based donor-acceptor polymers are synthesized and used as p-type semiconductors in organic thin-film transistors (OTFTs). Hole mobility of up to 0.03 cm2 V−1 s−1 is achieved. A new acetal-type branched substituent is introduced to significantly improve the solubility of the resulting polymer.

A furan-containing conjugated polymer for high mobility ambipolar organic thin film transistors

Furan substituted diketopyrrolopyrrole (DBF) combined with benzothiadiazole based polymer semiconductor PDPP-FBF has been synthesized and evaluated as an ambipolar semiconductor in organic thin-film transistors. Hole and electron mobilities as high as 0.20 cm(2) V(-1) s(-1) and 0.56 cm(2) V(-1) s(-1), respectively, are achieved for PDPP-FBF.

Novel liquid crystalline conjugated oligomers based on phenanthrene for organic thin film transistors

Three thiophene/phenanthrene hybrid oligomers were synthesized and their liquid crystalline (LC) properties were characterized by differential scanning calorimetry (DSC), polarized optical microscopy (POM), temperature-dependent X-ray diffraction (XRD) and electron diffraction. Highly ordered LC phases with a broad temperature range were observed for all three oligomers probably owing to the absence of symmetry against the long axis of phenanthrene unit. Highly ordered smectic LC thin films were prepared by vacuum deposition and their organic thin film transistors (OTFTs) exhibited high mobilities up to 0.34 cm2 V−1s−1. Solution processed films showed self-healing behaviors upon thermal annealing, and OTFTs prepared by solution drop casting showed mobilities up to 0.05 cm2 V−1s−1. These results indicate that thiophene/phenanthrene hybrid oligomers are promising high mobility organic semiconductors for OTFTs.

Organic Thin-Film Transistors Processed from Relatively Nontoxic, Environmentally Friendlier Solvents

Poly(2,6-bis(3-alkylthiophen-2-yl)dithieno- [3,2-b;2′,3′-d]-thiophene)s represent a new class of solution-processable polymer semiconductors for organic thin-film transistors. This class of polymer semiconductors offers not only high field-effect transistor mobility, but also processability from relatively nontoxic, environmentally friendlier solvents. Thin-film transistors utilizing these polymer semiconductors fabricated even from environmentally friendlier organic solvents of generally low solvency such as hexane and toluene have exhibited high field-effect mobility and current on/off ratio as well as excellent thermal stability and high resistance to photoinduced oxidative doping. This is in sharp contrast to most high-mobility polymer semiconductors, which require toxic chlorinated aromatic solvents for fabrication to achieve high mobility. The use of relatively nontoxic processing solvent would eliminate the safety concerns associated with use of chlorinated aromatic solvents, potentially enabling l...

4,4′,4″-Tris(4-naphthalen-1-yl-phenyl)amine as a multifunctional material for organic light-emitting diodes, organic solar cells, and organic thin-film transistors

We have developed the first multifunctional organic material, 4,4′,4″-tris(4-naphthalen-1-yl-phenyl)amine ( 1-TNPA), which can be used as a deep blue emitting and hole-transporting material in organic light-emitting diodes (OLEDs), as a donor material in organic solar cells (OSCs), and as an active material in organic thin-film transistors (OTFTs). In particular, in the case of 1-TNPA-based OLEDs, efficient emission characteristics, the emission of deep-blue light similar to the National Television Standard Committee (NTSC) standard blue, and more efficient hole transport than that in the case of NPD-based OLEDs were observed. 1-TNPA can be also used as a donor in OSCs and as an organic semiconductor in OTFTs.

Azine- and Azole-Functionalized Oligo´ and Polythiophene Semiconductors for Organic Thin-Film Transistors

In the organic electronics research field, several strategies have been used to modulate the transport properties of thiophene-derived semiconductors via sequential functionalization of their π-conjugated cores. This review summarizes the major design and synthetic strategies for tuning thiophene-containing small molecule and polymer properties by introducing electron-deficient nitrogen-containing azine and azole moieties. Several examples are presented which elucidate the structural, optical, and electronic consequences of incorporating these electron-deficient fragments in the conjugated skeletons, particularly relating to applications in organic thin-film transistors.