Eilaf Ahmed

High Mobility Single-Crystal Field-Effect Transistors from Bisindoloquinoline Semiconductors

A novel heptacyclic bisindoloquinoline-based organic semiconductor has been synthesized, characterized, and used to fabricate single-crystal field-effect transistors. A synthetic route was developed for the synthesis of heptacyclic bis(indolo{1,2-a})quinoline via an intramolecular cyclization of anthrazoline derivatives. Single-crystal X-ray structure revealed that the seven fused rings of bis(indolo{1,2-a})quinoline are relatively coplanar and lead to a slipped face-to-face π-stacking with the shortest intermolecular spacing of 3.3 A. Single-crystal field-effect transistors based on the bis(indolo{1,2-a})quinoline had carrier mobility as high as 1.0 cm2/V·s with on/off ratios greater than 104.

A highly effective one-pot synthesis of quinolines from o-nitroarylcarbaldehydes.

A highly effective one-pot Friedländer quinoline synthesis using inexpensive reagents has been developed. o-Nitroarylcarbaldehydes were reduced to o-aminoarylcarbaldehydes with iron in the presence of catalytic HCl (aq.) and subsequently condensed in situ with aldehydes or ketones to form mono- or di-substituted quinolines in high yields (66-100%).

Nanowires of oligothiophene-functionalized naphthalene diimides: self assembly, morphology, and all-nanowire bulk heterojunction solar cells

We report the solution-phase self-assembly of nanowires of a series of six oligothiophene-functionalized naphthalene diimides (NDI-nTH and NDI-nT) and their use as electron acceptors in all-nanowire bulk heterojunction organic solar cells. The dimensions and detailed morphology of the nanowires varied greatly with molecular structure of the NDI molecules and the solution concentration and solvent composition. Nanowires of NDI-3TH have typical dimensions of 80–250 nm in width, 2–10 μm in length, and 14.2–15.3 nm in thickness. Significant red-shift and enhancement of optical absorption in the low energy region (>600 nm) were observed in the nanowire suspension compared with solution and thin film, suggesting an increased supramolecular order in the nanowires. All-nanowire bulk heterojunction solar cells fabricated using NDI-3TH nanowires as electron acceptor and poly(3-hexylthiophene) nanowires as donor had a power conversion efficiency of 1.15%. External quantum efficiency of the photovoltaic cells showed that the n-type organic semiconductor nanowires contributed significantly to light harvesting. Our results represent the first demonstration of all-nanowire organic solar cells and show that non-fullerene n-type organic semiconductor nanowires can be effectively incorporated into bulk heterojunction solar cells.

Air-stable ambipolar field-effect transistors and complementary logic circuits from solution-processed n/p polymer heterojunctions.

We demonstrate the use of n/p polymer/polymer heterojunctions deposited by sequential solution processing to fabricate ambipolar field-effect transistors and complementary logic circuits. Electron and hole mobilities in the transistors were ∼0.001-0.01 cm(2)/(V s) in air without encapsulation. Complementary circuits integrating multiple ambipolar transistors into NOT, NAND, and NOR gates were fabricated and shown to exhibit sharp signal switching with a high voltage gain.