Use In Organic Thin-film Transistors Research Articles

Formation of Large Crystalline Domains in a Semiconducting Polymer with Semi-fluorinated Alkyl Side Chains and Application to High-Performance Thin-Film Transistors.

The semi-fluorinated alkyl (SFA) side chain introduced thienylenevinylene (TV)-based p-type polymer, PC12TVC5F7T, was synthesized for use in organic thin-film transistors (OTFTs). Herein, we investigated the influence of SFA side chains on the morphology, molecular orientation, and crystalline structure using a combination of atomic force microscopy (AFM), scanning electron microscopy (SEM), two-dimensional (2D) grazing-incidence wide-angle X-ray scattering (GIWAXS), and density functional theory (DFT) calculations. Interestingly, the incorporation of SFA side chains led to the evolution of plate-like large-sized domains and also strongly intermolecular stacked high crystalline structures. Furthermore, due to the strong interactions between SFA side chains, several (00h) peaks could be observed for PC12TVC5F7T, in spite of their fairly large dihedral angle. As a result, due to the well-developed microstructure of PC12TVC5F7T, the OTFT devices based on it exhibited a high hole mobility of 1.91 cm2 V-1 s-1, which is an outstanding value among the poly(thiophene) derivative polymers. These observations indicate that large-sized domains and strongly intermolecular stacked high crystalline structures, which are beneficial for charge carrier transport, could be attained by the introduction of SFA side chains, further enhancing the performance of the OTFTs.

Phthalocyanine-Based Organic Thin-Film Transistors: A Review of Recent Advances

Metal phthalocyanines (MPcs) are versatile conjugated macrocycles that have attracted a great deal of interest as active components in modern organic electronic devices. In particular, the charge transport properties of MPcs, their chemical stability, and their synthetic versatility make them ideal candidate materials for use in organic thin-film transistors (OTFTs). This article reviews recent progress in both the material design and device engineering of MPc-based OTFTs, including the introduction of solubilizing groups on the MPcs and the surface modification of substrates to induce favorable MPc self-assembly. Finally, a discussion on emerging niche applications based on MPc OTFTs will be explored, in addition to a perspective and outlook on these promising materials in OTFTs. The scope of this review is focused primarily on the advances made in the field of MPc-based OTFTs since 2008.

Electrically and thermally stable gate dielectrics from thiol–ene cross-linked systems for use in organic thin-film transistors

Novel solution-processable thiol–ene gate dielectrics for use in organic thin-film transistors (OTFTs) have been designed and fabricated in this study. Incorporation of UV-sensitive functional groups in the thiol–ene system affords electrical and thermal stability to the gate dielectric layers by a simple photocuring method. The very smooth thiol–ene gate dielectric layer exhibits excellent insulating properties (leakage current densities ∼10−7 to 10−8 A cm−2 at 2 MV cm−1) and a relatively high dielectric constant (>5) with high environmental stability. Furthermore, the electrical properties of this gate dielectric layer are stable up to 300 °C and show no changes even when the dielectric is kept for 100 days in air; this stability can be attributed to the densely cross-linked structure of the thiol–ene layer. OTFTs utilizing the thiol–ene gate dielectrics with various organic semiconductors show enhanced TFT performances; in particular, they show no hysteresis without a threshold-voltage shift. These observations are in contrast to those for a representative organic gate dielectric polymer, cross-linked poly(4-vinylphenol).

Formation of intra-island grain boundaries in pentacene monolayers

To assess the formation of intra-island grain boundaries during the early stages of pentacene film growth, we studied sub-monolayers of pentacene on pristine silicon oxide and silicon oxide with high pinning centre density (induced by UV/O(3) treatment). We investigated the influence of the kinetic energy of the impinging molecules on the sub-monolayer growth by comparing organic molecular beam deposition (OMBD) and supersonic molecular beam deposition (SuMBD). For pentacene films fabricated by OMBD, higher pentacene island-density and higher polycrystalline island density were observed on UV/O(3)-treated silicon oxide as compared to pristine silicon oxide. Pentacene films deposited by SuMBD exhibited about one order of magnitude lower island- and polycrystalline island densities compared to OMBD, on both types of substrates. Our results suggest that polycrystalline growth of single islands on amorphous silicon oxide is facilitated by structural/chemical surface pinning centres, which act as nucleation centres for multiple grain formation in a single island. Furthermore, the overall lower intra-island grain boundary density in pentacene films fabricated by SuMBD reduces the number of charge carrier trapping sites specific to grain boundaries and should thus help achieving higher charge carrier mobilities, which are advantageous for their use in organic thin-film transistors.

High Surface Area Contorted Conjugated Microporous Polymers Based on Spiro-Bipropylenedioxythiophene

Conjugated polymers derived from thiophene or 3,4-ethylenedioxythiophene derivatives have been widely investigated for use in organic thin-film transistors and organic photovoltaic devices. We describe here the synthesis of a series of conjugated microporous polymers formed by reaction of spiro-bis(2,5-dibromopropylenedioxythiophene) with one of three di- or triethynyl monomers. These polymers have surface areas up to 1631 m2/g and exhibit significant microporosity, suggesting possible applications in the fields of organic electronics or optoelectronics.

Organic thin-film transistor properties and the structural relationships between various aromatic end-capped triisopropylsilylethynyl anthracene derivatives

Abstract We describe the preparation and characterization of single crystals and thin films composed of three new small molecules based on soluble triisopropylsilylethynyl ( TIPS )-substituted anthracene ( TIPSAnt ) for use in organic thin-film transistors (TFTs); the three molecules examined were TIPSAnt derivatives containing thiophene ( TIPSAntT ), benzothiophene ( TIPSAntBeT ), or phenyl thiophene ( TIPSAntPT ) end cappers. We elucidated the relationship between the molecular structures and TFT performances by measuring the thermal, optical, electrochemical, crystalline, and morphological properties of these molecules. TIPSAntPT was able to achieve a “bricklayer” type of molecular stacking structure, facilitated by the bulky phenyl thiophene substituents. This is the first report of a “bricklayer” stacking structure of triisopropylsilylethynyl anthracene derivatives. Among the three molecules, TIPSAntPT showed the highest TFT mobility, 0.063 cm 2 /Vs for the film state and 0.12 cm 2 /Vs for single crystals. By contrast, in the case of in TIPSAntBeT , the introduction of the rigid substituent group led to poor TFT device performance. TFT device performances could be explained in terms of thin-film morphology, investigated by atomic force microscopy (AFM) and X-ray diffraction (XRD) analysis.

Material and device considerations for organic thin-film transistor sensors

The rapid development of the field of organic electronics has sparked great interest in the use of organic thin-film transistors (OTFTs) as low-cost electronic sensors. The direct coupling of the electronic and the sensor media to provide real time electrical output has already demonstrated high sensitivity to a variety of chemical species. The synthetic versatility of organic materials also provides endless routes to impart functionality for specifically targeted chemical interactions. Owing to their compatibility with flexible materials and simple fabrication methods, OTFTs are poised to have a tremendous impact on future portable detection technology. This article reviews recent progress made toward improved sensitivity, selectivity and stability of OTFT sensors through material and device engineering. Specific consideration is paid to the interaction of the electronic materials with the analytes as a means of providing insight into mechanistic principles as well as the future direction of OTFTs.

Frequency Dependences of Displacement Current and Channel Current in Pentacene Thin-Film Transistors

We demonstrate the gate voltage (VGS) frequency dependences of displacement current (Idis) and channel current (IDS), which were simultaneously measured under the application of a triangular wave of VGS and a constant drain voltage in top-contact pentacene organic thin-film transistors (OTFTs). Carrier injection and carrier transport properties, such as field-effect mobility, threshold voltage, and carrier injection voltages at the source and drain electrodes, were evaluated; they showed no frequency dependences at frequencies between 1 and 50 kHz. From the source current -VGS and drain current -VGS characteristics, a charge sheet at the interface of the pentacene thin-film and gate dielectric was found to form below the source and drain electrodes in this frequency range. For the practical use of OTFTs, a simultaneous measurement system for Idis and IDS is a simple and powerful technique for evaluating both carrier injection and carrier transport properties under OTFT operations.

Synthesis of 5,7,12,14-Tetraarylpentacenes from Pentacene-5,7,12,14-tetrone and Characterisation of the Tetrol Intermediates

Pentacene has excellent semi-conducting properties but its practical use in organic thin-film transistors (OTFTs) has some drawbacks caused by its sensitivity to oxygen and low solubility. In order to overcome these problems one can introduce substituents on the ring system. In this context, we are investigating the possibility of introduction of aryl substituents on the pentacene backbone. 5,7,12,14-Tetraaryl-substituted pentacenes are described in this article. They have been prepared from the 5,7,12,14-aryl-substituted pentacene-5',7',12',14'-tetrol. We isolated all isomers of the tetrol. We also found that the 5,7,12,14-thienylpentacene-5',7',12',14'-tetrol can undergo rearrangement to afford both 5,5',7,7'-tetrathienylpentacene-12,14-one and 5,5',12,12'-tetrathienylpentacene-7,14-one.

Effect of measuring environment on the electrical characteristics of NiPc based thin film transistors: The effects of ozone

Electrical characteristics of Organic Thin Film Transistors (OTFT) are found to be sensitive to ambient atmosphere. The electrical properties of Metal-Phthalocyanines (M-Pc) are affected upon exposure to an atmosphere containing oxidizing molecules like oxygen, nitrogen oxides or ozone. This phenomenon finds application in the use of OTFT based on nickel-phthalocyanine (NiPc) as gas sensors. In this work, tests of ozone detecting were carried out exhibiting a high sensitivity to ozone. The observed changes in the electrical characteristics, when the OTFT is exposed to an ambient atmosphere, are discussed in terms of ozone doping process. Our results show that NiPc-based OTFTs can represent a new class of ozone sensors.

Organic thin-film transistors as transducers for (bio) analytical applications

The use of organic thin-film transistors (OTFTs) in sensorics is relatively new. Although electronic noses, electronic textiles and disposable biochemical sensors appear to be viable applications for this type of devices, the benefits of the technology still have to be proven. This paper aims to provide a review of the recent advances in the area of chemically sensitive field-effect devices based on organic thin-film transistors (OTFTs), with emphasis on bioanalytical applications. Detection principle, device configuration, materials and fabrication processes as well as sensor performances will be discussed, with emphasis on the potential for implementation in real applications and the important challenges ahead.

Phthalocyanine Composites as High‐Mobility Semiconductors for Organic Thin‐Film Transistors

A new class of organic semiconductors based on composites of copper phthalocyanine and nickel phthalocyanine for use in organic thin-film transistors show relatively high mobilities. X-ray diffraction of the composite films, which consist of homogenously sized crystals (see Figure), indicates the presence of a new crystalline phase incorporating both copper and nickel phthalocyanine molecules.

Materials Requirements and Fabrication of Active Matrix Arrays of Organic Thin-Film Transistors for Displays

An overview of the materials requirements and the fabrication processes for the use of organic thin-film transistors in active-matrix backplanes for displays is presented. A summary of current knowledge of the electrical performance of both molecular and polymeric semiconductors is discussed with emphasis on the performance requirements needed for displays. Patterning and deposition processes for conductors, dielectrics, and organic semiconductors that have been used to fabricate organic thin-film transistors are reviewed. Examples of backplanes fabricated with these processes are given, and directions for the future research are outlined.