Publications by authors named "Jenner H L Ngai"

The control of the performance of single-walled carbon nanotube (SWCNT) random network-based transistors is of critical importance for their applications in electronic devices, such as complementary metal oxide semiconducting (CMOS)-based logics. In ambient conditions, SWCNTs are heavily p-doped by the HO/O redox couple, and most doping processes have to counteract this effect, which usually leads to broadened hysteresis and poor stability. In this work, we coated an SWCNT network with various common polymers and compared their thin-film transistors' (TFTs') performance in a nitrogen-filled glove box.

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The study has developed two hemi-isoindigo (HID)-based polymers for printed flexible resistor-type nitrogen oxide (NO) sensors: poly[2-ethylhexyl 3-((3'",4'-bis(dodecyloxy)-3,4-dimethoxy-[2,2':5',2'"-terthiophen]-5-yl)methylene)-2-oxoindoline-1-carboxylate] (P1) and poly[2-ethylhexyl 2-oxo-3-((3,3'",4,4'-tetrakis(dodecyloxy)-[2,2':5',2'"-terthiophen]-5-yl)methylene)indoline-1-carboxylate] (P2). These polymers feature thermally removable carbamate side chains on the HID units, providing solubility and creating molecular cavities after thermal annealing. These cavities enhance NO diffusion, and the liberated unsubstituted amide ─C(═O)NH─ groups readily form robust double hydrogen bonds (DHB), as demonstrated by computer simulations.

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For organic memristors, non-zero-crossing current-voltage (-) curves are often observed, which can be attributed to capacitive effects. If the conversion between the capacitance-dominated state (CDS) and the memristance-dominated state (MDS) can be realized in a controllable manner, more device functions can be obtained. In this work, a two-terminal memristor using a common organic dye, azobenzene (AZB), as the active layer was prepared.

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Organic semiconductors inherently have a low dielectric constant and hence high exciton binding energy, which is largely responsible for the rather low power conversion efficiency of organic solar cells as well as the requirements to achieve delicate bulk-heterojunction nanophase separation in the active layer. In this study, methyl acrylate as a weakly electron-withdrawing side chain for the electron rich thiophene to prepare a new building block, methyl thiophene-3-acrylate (TA), with increased polarity is used. A wide bandgap polymer PBDT-TA synthesized using TA and a benzodithiophene (BDT) monomer shows increased dielectric constant and reduced exciton binding energy compared to the analogous polymer PBDT-TC, which is made of BDT and methyl thiophene-3-carboxylate (TC).

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A novel electron deficient building block [2,2'-bithiophene]-4,4'-dicarboxamide (BTDCA) was designed to lower the highest occupied molecular orbital (HOMO) energy level of polythiophenes in order to achieve a higher open circuit voltage ( ) and thus a higher power conversion efficiency in polymer solar cells (PSCs). BTDCA dibromo monomers were conveniently synthesized in four steps, and were used to prepare three thiophene-based D-A polymers, P(BTDCA66-BT) (66BT), P(BTDCA44-BT) (44BT) and P(BTDCA44-TT) (44TT). All the polymers exhibited unipolar hole transport properties, exhibiting mobilities in the range of ∼10 to 10 cm V s with the highest hole mobility of up to 1.

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We report the design and synthesis of two novel indigo donor-acceptor (D-A) polymers, PIDG-T-C20 and PIDG-BT-C20, comprising an indigo moiety that has intramolecular hydrogen-bonds as the acceptor building block and thiophene (T) and bithiophene (BT) as the donor building block, respectively. PIDG-T-C20 and PIDG-BT-C20 exhibited characteristic p-type semiconductor performance, achieving hole mobilities of up to 0.016 and 0.

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