Benjamin Nketia-Yawson

A Highly Planar Fluorinated Benzothiadiazole‐Based Conjugated Polymer for High‐Performance Organic Thin‐Film Transistors

High-mobility and low-voltage-operated organic field-effect transistors (OFETs) are demonstrated by the design of a new fluorinated benzothiadiazole-based conjugated polymer with fluorinated high-k polymer dielectrics. A record-breaking high hole mobility of 9.0 cm(2) V(-1) s(-1) for benzothiadiazole-based semiconducting polymers is achieved by the excellent planarity of the semiconducting polymer.

Ultrahigh Mobility in Solution-Processed Solid-State Electrolyte-Gated Transistors

A new concept of a high-capacitance polymeric dielectric based on high-k polymer and ion gel blends is reported. This solid-state electrolyte gate insulator enables remarkable field-effect mobilities exceeding 10 cm2 V-1 s-1 for common polymer and other semiconductor families at VG ≤ 2 V owing to high areal capacitance (>4 µF cm-2 ) from combined polarization of CF interface dipoles and electrical-double-layer formation.

Highly Sensitive Flexible NH3 Sensors Based on Printed Organic Transistors with Fluorinated Conjugated Polymers

Understanding the sensing mechanism in organic chemical sensors is essential for improving the sensing performance such as detection limit, sensitivity, and other response/recovery time, selectivity, and reversibility for real applications. Here, we report a highly sensitive printed ammonia (NH3) gas sensor based on organic thin film transistors (OTFTs) with fluorinated difluorobenzothiadiazole-dithienosilole polymer (PDFDT). These sensors detected NH3 down to 1 ppm with high sensitivity (up to 56%) using bar-coated ultrathin (<4 nm) PDFDT layers without using any receptor additives. The sensing mechanism was confirmed by cyclic voltammetry, hydrogen/fluorine nuclear magnetic resonance, and UV/visible absorption spectroscopy. PDFDT-NH3 interactions comprise hydrogen bonds and electrostatic interactions between the PDFDT polymer backbone and NH3 gas molecules, thus lowering the highest occupied molecular orbital levels, leading to hole trapping in the OTFT sensors. Additionally, density functional theory calculations show that gaseous NH3 molecules are captured via cooperation of fluorine atoms and dithienosilole units in PDFDT. We verified that incorporation of functional groups that interact with a specific gas molecule in a conjugated polymer is a promising strategy for producing high-performance printed OTFT gas sensors.

Fluorinated benzothiadiazole and indacenodithieno[3,2-b]thiophene based regioregular-conjugated copolymers for ambipolar organic field-effect transistors and inverters

We report the synthesis and characterization of a series of three soluble polymeric hybrids in benzothiadiazole–indacenodithieno[3,2-b]thiophene based ladder-type polymers (BT–IDTT) containing the acceptor unit 3,6-dithien-2-yl-2,5-dialkylpyrrolo[3,4-c]pyrrole-1,4-dione (DTDPP), and donor moieties 7,8-bithienyl benzo[1,2-b:4,5-b′]di-thiophene (BDTT) and 4,8-bis(5-ethylhexylselenophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene (BDTSe) in BT–IDTT–DTDPP (P1), BT–IDTT–BDTT (P2) and BT–IDTT–BDTSe (P3) copolymers to tune the strength of ambipolar charge-carrier transport properties for organic field-effect transistors (OFETs) and ambipolar complementary inverters. A narrow band gap of 1.4–1.7 eV was achieved by the careful selection of the electron donor–acceptor unit and strong packing of those polymers in the film state. In particular, a very narrow bandgap of 1.38 eV and well-balanced ambipolar transistor characteristics were achieved by replacing benzodithiophene in P2 and P3 with diketopyrrolopyrrole in P1. Optimized top gate bottom contact OFETs with P1 polymer showed electron and hole mobilities of 0.015 and 0.007 cm2 V−1 s−1 respectively, and inverter gain of ∼14 using poly(methyl methacrylate) gate dielectric. Interestingly, hole transport properties were improved to a mobility of 0.1 cm2 V−1 s−1 in all OFETs with the BT–IDTT ladder-type polymer using fluorinated P(VDF-TrFE) dielectric, which can be ascribed to the increased hole accumulation at the semiconductor–dielectric interface.

Organic thin film transistor with conjugated polymers for highly sensitive gas sensors

The ease in structural modification, redesign and development of multi-functional polymer semiconductors have led to significant advances in organic electronic device applications such as organic light emitting diodes (OLED), organic photovoltaics (OPV), organic thin film transistors (OTFT), and organic sensors. In this article, we reviewed recent techniques and strategies employed toward the optimization of conjugated polymer films for high sensing performance in OTFT-based gas sensors. Significant enhancements, particularly in gas selectivity, sensitivity, detection limit, response/recovery time of OTFT-based gas sensors by polymer film morphology and thickness control, functionalization of conjugated polymers with chemical groups and the use of doped/blended inorganic or dielectric materials and conjugated polymer composites as active layers are discussed here.

Organic field-effect transistors processed by an environmentally friendly non-halogenated solvent blend

Chlorinated solvents exhibit excellent solubility characteristics for common conjugated molecules and superior physical properties such as adequate viscosity, surface tension and high boiling point, so they are the preferred processing solvent option for realizing high-performance organic devices by cost-effective graphic art printing, despite their known adverse environmental impact. Based on Hansen solubility parameter analysis, this study employed a non-halogenated binary solvent blend of mesitylene and acetophenone to closely mimic the efficiency of dichlorobenzene, a well-known chlorinated solvent for widely used conjugated polymers used in organic field-effect transistors (OFETs) such as poly{[N,N′-bis(2-octyldodecyl)-1,4,5,8-naphthalenediimide-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} (P(NDI2OD-T2)), 3,6-bis-(5bromo-thiophen-2-yl)-N,N-bis(2-octyl-1-dodecyl)-1,4-dioxo pyrrolo[3,4-c]pyrrole (DPPT-TT) and indacenodithiophene-co-benzothiadiazole (IDT-BT). We tuned the solvent quality of the non-halogenated binary blend in various ratios and studied their effect on polymer pre-aggregation in the solution state, polymer microstructure, and morphological evolution of polymer thin films cast from the solvent blends. High-performance top-gate/bottom-contact OFETs were demonstrated with field-effect mobility values of up to ∼0.574, ∼0.634 and ∼0.785 cm2 V−1 s−1 for P(NDI2OD-T2), DPPT-TT, and IDT-BT polymers, respectively, employing a mesitylene and acetophenone blend (95 : 5 vol%) as a processing solvent.