High-mobility Organic Semiconductors Research Articles

Preparation of highly oriented copper phthalocyanine film by molecular templating effects for organic field-effect transistor

Highly oriented copper phthalocyanine (CuPc) film consisting of many crystal domains was prepared by introducing titanyl-phthalocyanine (TiOPc) as molecular template at high substrate temperature. CuPc molecules stand up on the top of TiOPc domains exhibiting herringbone structure and high-order arrangement investigated by atomic force microscopy and X-ray diffraction. Then organic transistors were fabricated that exhibited improved device performances, a 0.12 cm 2/V s of mobility and a 10 5 of on/off ratio. Furthermore, template thickness dependence on device performance was disclosed. These results indicated that molecular template is a very effective method to prepare high-mobility organic semiconductor film.

Experimental Study and Statistical Analysis of Solution-Shearing Processed Organic Transistors Based on an Asymmetric Small-Molecule Semiconductor

Solution processed organic field-effect transistors (SPOFETs) are crucial for realizing low-cost large-area/ubiquitous flexible electronics. Currently, both soluble high-mobility organic semiconductors and efficient solution processes are in demand. In this paper, we report the systematic experimental study and statistical modeling/analysis for the SPOFETs based on an asymmetric small-molecule organic semiconductor, trimethyl-[2, 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">'</sup> ; 5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">'</sup> , 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">''</sup> ; 5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">''</sup> , 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">'''</sup> ] quarter-thiophen-5-yl-silane (4 T-TMS), which was deposited as the active layer through a recently developed low-temperature solution-shearing process. Three-dimensional statistical modeling and analysis bas ed on 46 different processing conditions was used to comprehensively study the solution-shearing process control and optimization for fabricating high-performance 4T-TMS SPOFETs. Various effects including solution concentration effect, shearing speed effect, and deposition temperature effect were investigated and discussed. Under optimized processing conditions, well-oriented crystalline 4 T-TMS thin films were deposited for the SPOFETs, which showed remarkable effective field-effect mobility up to 0.3 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V middots in the saturation region and current on/off ratios over 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> . Gaussian fitted uniformity and good air stability of these devices stored and tested under ambient conditions for six months suggest that 4 T-TMS SPOFETs based on the optimized solution-shearing process are promising for applications in organic electronic circuits and displays. Importantly, the systematic experiment design and the corresponding statistical modeling/analysis presented here provide a general guideline for process optimization for fabricating high-performance SPOFETs.

Electronic functionalization of solid-to-liquid interfaces between organic semiconductors and ionic liquids: Realization of very high performance organic single-crystal transistors

High-performance electronic function of current amplification is realized with the use of solid-to-liquid interfaces between organic semiconductors and ionic liquid. To hold in place the ionic liquid of 1-ethyl-3-methyl-imidazolium bis(trifluoromethanesulfonyl)imide known for low viscosity and high ionic conductivity, an elastomeric well structure is fabricated with polydimethylsiloxane on which organic single crystals of rubrene are electrostatically attached. As the result of rapid formation of electric double layers in the ionic liquid interfacing, the high-mobility organic semiconductor crystals’ fast-switching transistor function is demonstrated with the application of gate voltage, realizing the highest sheet transconductance, namely, amplifying performance, ever achieved.

Synthesis, Characterization of 9, 9′-Bianthracene and Fabrication of 9, 9′-Bianthracene Field-Effect Transistors

We synthesize and purify 9, 9′-bianthracene with the purity up to 96.4%. The electronic and crystallographic structures of 9, 9′-bianthracene are studied. The results of a joint experimental investigation based on a combination of x-ray diffraction (XRD) spectra, hydrogen nuclear magnetic (HNMR) spectra, infrared absorption (FT-IR) spectra, and mass spectra (MS) of 9,9′-bianthracene are obtained. The uniform compact film is observed by an atomic-force microscope (AFM). Organic field effect transistors (OFETs) with an active layer based on the synthesized 9, 9′-bianthracene are fabricated for the first time. Its field-effect mobility is as large as 0.067cm2/(V-s) and the on/off ratio is above 5 × 10.4 The result demonstrates that the oligomerization of a small semiconductor molecule is an effective method to develop high-mobility organic semiconductors.

Organic transistors manufactured using inkjet technology with subfemtoliter accuracy

A major obstacle to the development of organic transistors for large-area sensor, display, and circuit applications is the fundamental compromise between manufacturing efficiency, transistor performance, and power consumption. In the past, improving the manufacturing efficiency through the use of printing techniques has inevitably resulted in significantly lower performance and increased power consumption, while attempts to improve performance or reduce power have led to higher process temperatures and increased manufacturing cost. Here, we lift this fundamental limitation by demonstrating subfemtoliter inkjet printing to define metal contacts with single-micrometer resolution on the surface of high-mobility organic semiconductors to create high-performance p-channel and n-channel transistors and low-power complementary circuits. The transistors employ an ultrathin low-temperature gate dielectric based on a self-assembled monolayer that allows transistors and circuits on rigid and flexible substrates to operate with very low voltages.

Soluble and Easily Crystallized Anthracene Derivatives: Precursors of Solution-Processable Semiconducting Molecules

New soluble anthracene derivatives containing thiophene and phenylenevinylene derivatives were synthesized via well-known synthetic routes. TIPS derivatives were added at the 9,10-positions of anthracene for the solubility and crystallinity. Both of the molecules were found to be promising for high charge mobility and stable organic semiconductors. The soluble anthracene core (TIPSAnt) is a potential precursor for the synthesis of novel semiconducting materials.

Improved Synthesis of the High-Mobility Organic Semiconductor Dithio­phene-Tetrathiafulvalene

Dithiophene-tetrathiafulvalene (DT-TTF) has been shown to be a promising organic semiconductor for organic transistors, since it combines high mobility with processability. A novel synthesis to prepare this material is described here. It involves the coupling of a 1,3-dithiol-2-one. The yield of this route is higher than previously reported yields.

Organic Complementary D Flip-Flops Enabled by Perylene Diimides and Pentacene

The development of organic complementary circuits has been largely limited by the development of suitable organic n-channel transistors. However, recent advances have led to materials such as the high-mobility air-stable n-channel organic semiconductor, N,N'-bis(n-octyl)-dicyanoperylene-3, 4 : 9, 10-bis(dicarboximide), PDI-8CN2. Here, the fabrication of an organic complementary D flip-flop using PDI-8CN2 n-channel transistors and pentacene p-channel transistors is described. The measured clock-to-output delay is 25 mus for 1 kHz, and 14 mus at the clock frequency of 5 kHz. This is the fastest clock speed for an organic complementary circuit yet achieved

Investigation into the modelling of field-effect carrier mobility in disordered organic semiconductors

Organic semiconductors have attracted significant interest because of their potential application in electronic devices. One of the most important parameters in such an application is the carrier mobility, which is low when compared with inorganic semiconductors. In the past, significant effort has been spent to produce high mobility organic semiconductors, even though the best room temperature value reported is only a few cm2/V.s. In the work, the field-effect carrier mobility in organic semiconductors is examined by correlating reported data for pentacene with simulations based on the correlated disorder model. Using the rms width of the density of states (DOS) as the main variable, a good match between data and simulations has been produced. The results suggested that the carrier mobility in disordered organic semiconductors could be solely dependent on σ, the rms width of the DOS. The rather small value of σ used in the calculations pointed to the need for a better understanding into the transport mechanism within this regime. Other fitting parameters affected the carrier mobility included the site spacing and the barrier height, both of which were capable of changing the carrier mobility. A more careful examination revealed that there were physical constraints limiting the values of these parameters.

Substituted Indolo[3,2-b]Carbazoles: A New Class of Stable, High Mobility Organic Semiconductors for Thin Film Transistors

AbstractProperly functionalized indolo[3,2-b]carbazoles represent a new class of stable, high-mobility organic semiconductors for organic thin-film transistor applications. Both 5,11-disubstituted and peripherally substituted indolo[3,2-b]carbazoles with proper substituents self-organized into highly crystalline terrace-layered structures under suitable processing conditions. Organic TFTs using channel semiconductors of this nature exhibited excellent field-effect transistor properties, with mobility to 0.14 cm2 V-1 s-1 and current on/off ratio to 107. By virtue of their relatively low HOMO levels and large band gaps, this class of semiconductors also displayed excellent environmental stability under ambient conditions, an appealing characteristic for organic TFT applications.

Low-voltage organic transistors with an amorphous molecular gate dielectric

Organic thin film transistors (TFTs) are of interest for a variety of large-area electronic applications, such as displays, sensors and electronic barcodes. One of the key problems with existing organic TFTs is their large operating voltage, which often exceeds 20 V. This is due to poor capacitive coupling through relatively thick gate dielectric layers: these dielectrics are usually either inorganic oxides or nitrides, or insulating polymers, and are often thicker than 100 nm to minimize gate leakage currents. Here we demonstrate a manufacturing process for TFTs with a 2.5-nm-thick molecular self-assembled monolayer (SAM) gate dielectric and a high-mobility organic semiconductor (pentacene). These TFTs operate with supply voltages of less than 2 V, yet have gate currents that are lower than those of advanced silicon field-effect transistors with SiO2 dielectrics. These results should therefore increase the prospects of using organic TFTs in low-power applications (such as portable devices). Moreover, molecular SAMs may even be of interest for advanced silicon transistors where the continued reduction in dielectric thickness leads to ever greater gate leakage and power dissipation.

New Phenomena in High Mobility Organic Semiconductors

Field-effect devices on the basis of high-quality molecular single crystals have been used to study charge transport properties of two-dimensional electron and hole systems in organic semiconductor materials. The improvement of crystalline quality and purity leads to the observation of a variety of new phenomena in these materials, such as the quantum Hall effect, ballistic charge transport, or superconductivity, which are summarized in this article.