N-channel Semiconductor Research Articles

Design, Synthesis, and Characterization of Ladder-Type Molecules and Polymers. Air-Stable, Solution-Processable n-Channel and Ambipolar Semiconductors for Thin-Film Transistors via Experiment and Theory

The design, synthesis, and characterization of new high-performance n-channel molecular/polymeric semiconductors that are solution-processable and air-stable is of great interest for the development of p-n junctions, bipolar transistors, and organic complementary circuitry (CMOS). While over the past two decades there have been many reports on n-channel materials, solution-processability and air-stability still remain as major challenges. We report here the synthesis and detailed characterization of a highly electron-deficient class of indeno[1,2-b]fluorene-6,12-dione, 2,2'-(indeno[1,2-b]fluorene-6,12-diylidene) dimalononitrile, bisindenofluorene-12,15-dione, and 2,2'-(bisindenofluorene-12,15-diylidene) dimalononitrile-based ladder-type building blocks (1-12) and their corresponding homo- and copolymers (P1-P14), and examine in detail the effects of core size, thiophene vs core regiochemistry, carbonyl vs dicyanovinylene functionality, and alkyl chain orientation on the physicochemical properties, thin film microstructures, and OFET device performance. New compounds are characterized by DSC, TGA, melting point, single-crystal X-ray diffraction (XRD), solution/thin film optical, PL, and cyclic voltammetry measurements to evaluate frontier molecular orbital energetics and intermolecular cohesive forces. Thin films are grown by vacuum deposition and spin-coating, and investigated by X-ray diffraction (XRD) and AFM. By tuning the HOMO/LUMO energetics of the present materials over a 1.1 eV range, p-type, n-type, or ambipolar charge transport characteristics can be observed, thus identifying the MO energetic windows governing majority carrier polarity and air stability. One of these systems, thiophene-terminated indenofluorenedicyanovinylene 10 exhibits an electron mobility of 0.16 cm(2)/V x s and an I(on)/I(off) ratio of 10(7)-10(8), one of the highest to date for a solution-cast air-stable n-channel semiconductor. Here we also report solution-processed ambipolar films of thiophene-based molecule 12 and copolymers P13 and P14 which exhibit electron and hole mobilities of 1 x 10(-3)-2 x 10(-4) and I(on)/I(off) ratios of approximately 10(4), representing the first examples of molecular and polymeric ambipolar semiconductors to function in air. Analysis of the operational air-stabilities of a series of thin films having different crystallinities, orientations, and morphologies suggests that operational air-stability for thermodynamically predicted (i.e., no kinetic barrier contribution) air-stable semiconductors is principally governed by LUMO energetics with minimal contribution from thin-film microstructure. The onset LUMO energy for carrier electron stabilization is estimated as -4.0 to -4.1 eV, indicating an overpotential of 0.9-1.0 eV. Density functional theory calculations provide detailed insight into molecule/polymer physicochemical and charge transport characteristics.

A high-mobility electron-transporting polymer for printed transistors

Printed electronics is a revolutionary technology aimed at unconventional electronic device manufacture on plastic foils, and will probably rely on polymeric semiconductors for organic thin-film transistor (OTFT) fabrication. In addition to having excellent charge-transport characteristics in ambient conditions, such materials must meet other key requirements, such as chemical stability, large solubility in common solvents, and inexpensive solution and/or low-temperature processing. Furthermore, compatibility of both p-channel (hole-transporting) and n-channel (electron-transporting) semiconductors with a single combination of gate dielectric and contact materials is highly desirable to enable powerful complementary circuit technologies, where p- and n-channel OTFTs operate in concert. Polymeric complementary circuits operating in ambient conditions are currently difficult to realize: although excellent p-channel polymers are widely available, the achievement of high-performance n-channel polymers is more challenging. Here we report a highly soluble ( approximately 60 g l(-1)) and printable n-channel polymer exhibiting unprecedented OTFT characteristics (electron mobilities up to approximately 0.45-0.85 cm(2) V(-1) s(-1)) under ambient conditions in combination with Au contacts and various polymeric dielectrics. Several top-gate OTFTs on plastic substrates were fabricated with the semiconductor-dielectric layers deposited by spin-coating as well as by gravure, flexographic and inkjet printing, demonstrating great processing versatility. Finally, all-printed polymeric complementary inverters (with gain 25-65) have been demonstrated.

Air Stable Ambipolar Organic Field-Effect Transistors and Complementary-Like Inverters Prepared with Surface-Modified Gate Dielectrics

Air stable ambipolar organic field-effect transistors containing p/n heterojunctions are achieved by passivating the electron trapping sites on the SiO 2 surface. The morphology of the heterojunctions is controlled by the film thicknesses of p- and n-channel semiconductors, thereby affecting the device air stability and the electrical characteristics. Further, air stable complementary-like inverters, which are able to work both in the first and the third quadrants with a high gain up to 30, are also demonstrated.

Preparation, Characterization, and Field-effect Transistor Performance of Benzo[1,2-d:4,5-d′]bisthiazole Derivatives

Abstract Benzo[1,2-d:4,5-d′]bisthiazole (BBT) derivatives were newly synthesized, and the crystal structure, optical and electrochemical properties were investigated. They were applied for organic field-effect transistors (OFET) as n-channel semiconductors. Although their thin films have relatively rough surface, the devices showed high-performance OFET characteristics. The thin film of 2 exhibited the electron mobility of 0.24 cm2 V−1 s−1.

Anthracenedicarboximides as Air-Stable N-Channel Semiconductors for Thin-Film Transistors with Remarkable Current On−Off Ratios

A new n-type semiconductor family for organic field-effect transistors (FETs), based on core-unsubstituted and core-cyanated anthracenedicarboximides, is reported. By tuning electron affinity, these materials exhibit good electron-transport properties and stability in ambient as well as very high Ion/Ioff ratios. Unoptimized N,N‘-di-n-octyl-9,10-dicyano-2,3:6,7-anthracenedicarboximide (ADI8-CN2)−based FETs exhibit good electron mobilities (μe = 0.02 cm2/(V s)) and very high Ion/Ioff > 107 in ambient conditions.

Perylenediimide Nanowires and Their Use in Fabricating Field-Effect Transistors and Complementary Inverters

Perylenetetracarboxyldiimide (PTCDI) nanowires self-assembled from commercially available materials are demonstrated as the n-channel semiconductor in organic field-effect transistors (OFETs) and as a building block in high-performance complementary inverters. Devices based on a network of PTCDI nanowires have electron mobilities and current on/off ratios on the order of 10(-2) cm2/Vs and 10(4), respectively. Complementary inverters based on n-channel PTCDI nanowire transistors and p-channel hexathiapentacene (HTP) nanowire OFETs achieved gains as high as 8. These results demonstrate the first example of the use of one-dimensional organic semiconductors in complementary inverters.

Semiconductors for organic transistors

Organic molecules/polymers with a π-conjugated (hetero)aromatic backbone are capable of transporting charge and interact efficiently with light. Therefore, these systems can act as semiconductors in opto-electronic devices similar to inorganic materials. However, organic chemistry offers tools for tailoring materials' functional properties via modifications of the molecular/monomeric units, opening new possibilities for inexpensive device manufacturing. This article reviews the fundamental aspects behind the structural design/realization of p- (hole transporting) and n-channel (electron-transporting) semiconductors for organic field-effect transistors (OFETs). An introduction to OFET principles and history, as well as of the state-of-the-art organic semiconductor structure and performance of OFETs is provided.

Molecular Modification of 2,6-Diphenylbenzo[1,2-b:4,5-b′]dichalcogenophenes by Introduction of Strong Electron-withdrawing Groups: Conversion from p- to n-Channel OFET Materials

Abstract 2,6-Diphenylbenzo[1,2-b:4,5-b′]dithiophene (DPh-BDT) and -diselenophene (DPh-BDS) as p-channel semiconducting materials were modified by introducing fluoro, cyano, or trifluoromethyl groups into the attached phenyl moieties. On examination of organic field-effect transistors fabricated using these modified compounds, the trifluoromethyl-substituted DPh-BDT and BDS derivatives were found to act as n-channel semiconductors with high electron mobilities of 0.044 and 0.10 cm2 V−1 s−1, respectively.

Organic Thin-Film Transistors Based on Carbonyl-Functionalized Quaterthiophenes: High Mobility N-Channel Semiconductors and Ambipolar Transport

New carbonyl-functionalized quaterthiophenes, 5, 5' ''-diheptanoyl-2,2':5',2' ':5' ',2' ''-quaterthiophene (DHCO-4T), 5, 5' ''-diperfluorohexylcarbonyl-2,2':5',2' ':5' ',2' ''-quaterthiophene (DFHCO-4T), and 2,7-[bis-(5-perfluorohexylcarbonylthien-2-yl)]-4H-cyclopenta[2,1-b:3,4-b']-dithiophen-4-one (DFHCO-4TCO) have been synthesized and characterized. Field-effect transistors fabricated with these materials exhibit high electron mobilities both in a vacuum (up to 0.6 cm2 V-1 s-1) and in air (up to 0.02 cm2 V-1 s-1) and very high Ion:Ioff currents ratios (>107). DHCO-4T is the first organic material exhibiting excellent ambipolar transport (mue/muh up to 0.1/0.01 cm2 V-1 s-1, (Ion:Ioff)e/(Ion:Ioff)h up to 107/108 for the same device) over a broad range of deposition temperatures. These materials are therefore promising for organic complementary circuits.

Novel Dielectric Materials for Organic Electronics

AbstractWe present our latest results on the design and fabrication of very high capacitance dielectric materials for organic field-effect transistors. We will show that utilization of appropriate self-assembling siloxane building blocks and polymer matrices allows solution-processed, pinhole-free organic dielectrics. Electrical (MIS, TFT) data demonstrate that these insulators can be efficiently integrated into large TFT structures. These devices function for both p- and n-channel semiconductors, the molecular components of which exhibit greatly different core structures and substituent functionalities. Substantial TFT response is achieved at very low operational biases (<1V), without serious leakage currents (<10-8 A/cm at 1V).