Polymer Organic Field-effect Transistors Research Articles

Free radical fast photo-cured gate dielectric for top-gate polymer field effect transistors

We demonstrated top-gate organic field effect transistors (OFETs) made with free radical photo-cured polymer gate dielectrics and poly(3-hexylthiophene). We introduced a new approach of cross linking dielectric polymers in OFETs by using acrylate monomers cured with UV irradiation directly on the semiconductor. Three different blends were formulated: one self-initiating acrylate oligomer and two epoxy acrylate monomers mixed with 4-phenylbenzophenone as photo initiator and N-methyldiethanolamine as amine synergist. Thin films of these blends were cured in air within one minute. The curing process was monitored with FT-IR spectroscopy and the effect of a wetting agent was studied by measuring the CV characteristics of metal–insulator-semiconductor (MIS) structures made with these formulations. OFETs made with the demonstrated formulations showed high on/off ratios (105–106) and low sub-threshold slopes (0.44–1.42V/dec).

Easily Attainable Phenothiazine-Based Polymers for Polymer Solar Cells: Advantage of Insertion of S,S-dioxides into its Polymer for Inverted Structure Solar Cells

Two donor– (D−) acceptor (A) type polymers based on a soluble chromophore of phenothiazine (PT) unit that is a tricyclic nitrogen–sulfur heterocycle, have been synthesized by introducing an electron-deficient benzothiadiazole (BT) building block copolymerized with either PT or phenothiazine-S,S-dioxide (PT-SS) unit as an oxidized form of PT. The resulting polymers, PPTDTBT and PPTDTBT-SS are fully characterized by UV–vis absorption, electrochemical cyclic voltammetry, X-ray diffraction (XRD), and DFT theoretical calculations. We find that the maximum absorption of PPTDTBT is not only markedly red-shifted with respect to that of PPTDTBT-SS but also its band gap as well as molecular energy levels are readily tuned by the insertion of S,S-dioxides into the polymer. The main interest is focused on the electronic applications of the two polymers in organic field-effect transistors (OFETs) as well as conventional and inverted polymeric solar cells (PSCs). PPTDTBT is a typical p-type polymer semiconductor for OFETs and conventional PSCs based on this polymer and PC71BM show a power conversion efficiency (PCE) of 1.69%. In case of PPTDTBT-SS, the devices characteristics result in: (i) 1 order of magnitude higher hole mobility (μ = 6.9 × 10–4 cm2 V–1 s–1) than that obtained with PPTDTBT and (ii) improved performance of the inverted PSCs (1.22%), compared to its conventional devices. Such positive features can be accounted for in terms of closer packing molecular characteristics owing either to the effects of dipolar intermolecular interactions orientated from the sulfonyl groups or the relatively high coplanarity of PPTDTBT-SS backbone.

Au‐Doped Polyacrylonitrile–Polyaniline Core–Shell Electrospun Nanofibers Having High Field‐Effect Mobilities

Au-doped polyacrylonitrile–polyaniline core–shell nanofibers are fabricated via electrospinning and subsequent gas-phase polymerization, providing a very high field-effect mobility of up to 11.6 cm2 V−1 s−1. This method is also suitable for other conducting polymers and may eventually lead to a new and simplified fabrication of high-performance polymer organic field-effect transistors.

Bithiophene-Imide-Based Polymeric Semiconductors for Field-Effect Transistors: Synthesis, Structure−Property Correlations, Charge Carrier Polarity, and Device Stability

Developing new high-mobility polymeric semiconductors with good processability and excellent device environmental stability is essential for organic electronics. We report the synthesis, characterization, manipulation of charge carrier polarity, and device air stability of a new series of bithiophene-imide (BTI)-based polymers for organic field-effect transistors (OFETs). By increasing the conjugation length of the donor comonomer unit from monothiophene (P1) to bithiophene (P2) to tetrathiophene (P3), the electron transport capacity decreases while the hole transport capacity increases. Compared to the BTI homopolymer P(BTimR) having an electron mobility of 10(-2) cm(2) V(-1) s(-1), copolymer P1 is ambipolar with balanced hole and electron mobilities of ∼10(-4) cm(2) V(-1) s(-1), while P2 and P3 exhibit hole mobilities of ∼10(-3) and ∼10(-2) cm(2) V(-1) s(-1), respectively. The influence of P(BTimR) homopolymer M(n) on film morphology and device performance was also investigated. The high M(n) batch P(BTimR)-H affords more crystalline film microstructures; hence, 3× increased electron mobility (0.038 cm(2) V(-1) s(-1)) over the low M(n) one P(BTimR)-L (0.011 cm(2) V(-1) s(-1)). In a top-gate/bottom-contact OFET architecture, P(BTimR)-H achieves a high electron mobility of 0.14 cm(2) V(-1) s(-1), only slightly lower than that of state-of-the-art n-type polymer semiconductors. However, the high-lying P(BTimR)-H LUMO results in minimal electron transport on exposure to ambient. Copolymer P3 exhibits a hole mobility approaching 0.1 cm(2) V(-1) s(-1) in top-gate OFETs, comparable to or slightly lower than current state-of-the-art p-type polymer semiconductors (0.1-0.6 cm(2) V(-1) s(-1)). Although BTI building block incorporation does not enable air-stable n-type OFET performance for P(BTimR) or P1, it significantly increases the OFET air stability for p-type P2 and P3. Bottom-gate/top-contact and top-gate/bottom-contact P2 and P3 OFETs exhibit excellent stability in the ambient. Thus, P2 and P3 OFET hole mobilities are almost unchanged after 200 days under ambient, which is attributed to their low-lying HOMOs (>0.2 eV lower than that of P3HT), induced by the strong BTI electron-withdrawing capacity. Complementary inverters were fabricated by inkjet patterning of P(BTimR)-H (n-type) and P3b (p-type).

Crystallization and microstructure change of semiconductor active thin layer in polymer organic field-effect transistors

The crystallization and microstructure change of self-organization and the related conduction mechanisms of polymer semiconductor active thin layer in polymer organic field-effect transistors (OFET) are investigated by synchrotron radiation grazing incident X-ray diffraction (GIXRD) for understanding the relationships between polymer self-organization and charge carry. The change of the crystalline microstructure of RR-P3HT clarifies the effect of SAMs for improving the interface between the insulator layer and the organic semiconductor layer. The self-organiztion of RR-P3HT modified by SAMs improves the crystalliztion to pack form the thiophene rings along the perpendicular direction of substrate and results in that the π-π interchains are stacked to parallel the substrate. The two-dimensional charge transport is improved. Furthermore, we find that two-dimensional, conjugated, and self-organized crystalline lamellae are easier to gain with slow grown film than with fast grown film.

Frequency Characteristics of Polymer Field-Effect Transistors with Self-Aligned Electrodes Investigated by Impedance Spectroscopy

Solution-based organic field-effect transistors (OFETs) with low parasitic capacitance have been fabricated using a self-aligned method. The self-aligned processes using a cross-linking polymer gate insulator allow fabricating electrically stable polymer OFETs with small overlap area between the source-drain electrodes and the gate electrode, whose frequency characteristics have been investigated by impedance spectroscopy (IS). The IS of polymer OFETs with self-aligned electrodes reveals frequency-dependent channel formation process and the frequency response in FET structure.

Non-solvent addition induced self-organization for enhancement of performance of poly(3-hexylthiophene) organic field-effect transistors

In order to enhance the performance of poly(3-hexylthiophene) (RR-P3HT) organic field-effect transistors (OFET) by low temperature solution-process of non-solvent addition (acetonitrile and ethanol), the resulting self-organization of polymer semiconductor layer and performance of RR-P3HT OFET are studied in this paper. The results fshow that an appropriate non-solvent addition (acetonitrile and ethanol) promotes the formation of more microcrystalline lamellae and improves the self-organization of polymer semiconductor layer, resulting in electrical properties enhancement of polymer OFET. The results indicate that the field-effect of RR-P3HT OFET with 5% acetonitrile addition can reach 3.39×10-3 cm2/V ·s, which is higher by a factor of 8 than that with 0% acetonitrile addition. Encessive non-solvent addition (acetonitrile and ethanol) leads to more precipitates which reduce microcrystalline lamellae and lowers the quality of polymer film, resulting in performance degradation of polymer OFET.

Polythiophenes: Important Conjugated Semiconducting Polymers for Organic Field-Effect Transistors

Polythiophenes (PTs) are one of the most important classes of conjugated polymers employed as semiconductors in organic field-effect transistors (OFETs). In the last few years, versatile thiophene-based polymers have received great interest for applications in large-area, flexible, and low-cost electronics attributing to their excellent optoelectronic properties. Significant progress has been made in PT-based semiconductors for high performance transistors. We review here the achievements gained in conjugated PT-based semiconductors and demonstrate their structural modifications and design principles. We highlight the most important semiconducting polymers created from PT derivatives obtained through rational monomer design, controlled π-conjugation and appropriately positioned pendant side-chain distribution. Finally, we discuss remaining challenges and outline our views on future developments. Keywords: Polythiophenes, organic field-effect transistors

Solvent‐Assisted Re‐annealing of Polymer Films for Solution‐Processable Organic Field‐Effect Transistors

The introduction of solvent to a polymer film, which is generally believed to have a negative influence on device performance, is an effective way for improving device performances of polymer organic field-effect transistors (OFETs) if the treatment is combined with a re-annealing process and film-thickness optimization. The so-called solvent-assisted re-annealing offers a simple and novel approach towards polymer OFETs with excellent device characteristics (see figure).

Comparative Study on Gate Insulators of Polymers and SiO2 in Transport Properties of p- and n-Type Organic Field-Effect Transistors

Field-effect mobilities and threshold voltages in organic field-effect transistors (OFETs) were studied to elucidate the difference of the OFETs performance between Si/SiO2 and flexible polymer substrates. The polymer OFETs were built on poly(ethylene naphthalate) (PEN) film as the substrate with polyimide (PI) as the gate-insulators. Pentacene and N,N'-ditridecylperylene-3,4,9,10-tetracarboxylicdiimide (PTCDI-C13) were employed as p- and n-type semiconductors. The n-type OFET on polymer substrates exhibited higher electron mobility and smaller threshold voltages compared with those on Si/SiO2. On the contrary, the p-type OFET on the Si/SiO2 substrate showed better transport performance than that on the polymer substrate. The results are discussed taking the difference of surface potential between SiO2 and PI gate-insulator, which possibly modifies OFET characteristics.

Rational Optimization of Benzo[2,1‐b;3,4‐b′]dithiophene‐Containing Polymers for Organic Field‐Effect Transistors

Rational Optimization of Benzo[2,1‐b;3,4‐b′]dithiophene‐Containing Polymers for Organic Field‐Effect Transistors

Synthesis and Carrier Transport Properties of Triarylamine-based Amorphous Polymers for Organic Field-effect Transistors

Abstract Twenty-three kinds of triarylamine-based polymers, which are a new class of p-type semiconducting materials for organic field-effect transistors (OFETs), were synthesized by Pd-catalyzed amination of the corresponding aryldihalide and arylamine. All triarylamine-based polymers in this study exhibited p-channel behavior in OFETs, and field-effect hole mobilities ranged from 10−6 to 10−3 cm2 V−1 s−1.