Polymer-Gated Transistors with Only One Solution-Processed, Single Crystalline Organic Microwire for Light and Oxygen Detection.

Organic semiconductors employed in single crystalline form have several advantages over polycrystalline films, such as higher charge carrier mobility and better environmental stability. Herein, we report the fabrication and characterization of a solution-processed microsized single-crystalline organic wire of n-type N,N'-dipentyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C5). The crystal was applied as an active layer in polymer-gated organic field-effect transistors (OFETs) and organic complementary inverter circuits. The single crystaiiline nature of PTCDI-C5 wires were characterized using two-dimensional grazing incidence wide-angle X-ray diffraction (2D-GIXD) and polarized optical microscopy. OFETs with the PTCDI-C5 crystals exhibited high n-type performance and air stability under ambient conditions. To investigate the electrical properties of the single-crystalline PTCDI-C5 wire more precisely, OFETs with only one PTCDI-C5 microwire in the channel were fabricated, and clear n-type characteristics with satisfactory saturation behavior were observed. The device with only one crystal wire exhibited characteristics with significantly lower variation compared to the multicrystal devices, which shows that the density of crystal wires is a critical factor in precisely investigating device performance. The devices exhibited a reversible threshold voltage shift under vacuum and oxygen conditions, without changing the charge carrier mobility. Light-sensitive characteristics were also observed. Additionally, this solution-processed, highly crystalline organic semiconductor can be used in high-performance organic electronic circuits as well as in gas or light sensors.

High-Performing Thin-Film Transistors in Large Spherulites of Conjugated Polymer Formed by Epitaxial Growth on Removable Organic Crystalline Templates.

Diketopyrrolopyrrole (DPP)-based conjugated polymer PDTDPPQT was synthesized and was used to perform epitaxial polymer crystal growth on removable 1,3,5-trichlorobenzene crystallite templates. A thin-film transistor (TFT) was successfully fabricated in well-grown large spherulites of PDTDPPQT. The charge carrier mobility along the radial direction of the spherulites was measured to be 5.46-12.04 cm(2) V(-1) s(-1), which is significantly higher than that in the direction perpendicular to the radial direction. The dynamic response of charge transport was also investigated by applying a pulsed bias to TFTs loaded with a resistor (∼20 MΩ). The charge-transport behaviors along the radial direction and perpendicular to the radial direction were investigated by static and dynamic experiments through a resistor-loaded (RL) inverter. The RL inverter made of PDTDPPQT-based TFT operates well, maintaining a fairly high switching voltage ratio (Vout(ON)/Vout(OFF)) at a relatively high frequency when the source-drain electrodes are aligned parallel to the radial direction.

Laterally-stacked, solution-processed organic microcrystal with ambipolar charge transport behavior.

We report the formation of laterally stacked ambipolar crystal wire for high-mobility organic field-effect transistors (OFETs), along with a simple logic circuit through a solution process. A soluble pentacene derivative, 6,13-bis(triisopropylsilylethynyl)pentacene (Tips-pentacene), and N,N'-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) were used as p-type and n-type organic semiconductors, respectively. The laterally stacked ambipolar crystal wire is made up of Tips-pentacene and PTCDI-C8 crystals in a structure of Tips-pentacene/PTCDI-C8/Tips-pentacene (TPT). The inner part of the crystal is made up of PTCDI-C8, and Tips-pentacene is present on both sides. These TPT crystals exhibit typical ambipolar charge transport behavior in organic electronic devices, which show very balanced hole and electron mobility as high as 0.23 cm(2)/V·s and 0.13 cm(2)/V·s, respectively. Static and dynamic operational stability of the device is investigated by measuring the device performance as a function of storage time and applying voltage pulse, respectively, and it shows good air stability. In addition, a simple logic circuit based on the TPT crystal wire has been fabricated, and the static and dynamic performance has been evaluated. The results indicate that the TPT crystals are potentially useful for miniaturized organic electronic devices.

Solution-grown single-crystalline microwires of a molecular semiconductor with improved charge transport properties.

Preparation and structural analysis of highly ordered single crystalline wires of a diketopyrrolopyrrole (DPP) molecular semiconductor grown through a solution process are reported, and the static/dynamic electrical response of an organic electronic device using the DPP semiconductor has been analyzed.

A soft-template-conversion route to fabricate nanopatterned hybrid pt/carbon for potential use in counter electrodes of dye-sensitized solar cells.

Hybrid Pt(platinum)/carbon nanopatterns with an extremely low loading level of Pt catalysts derived from block copolymer templates as an alternative type of counter electrodes (CEs) in dye-sensitized solar cells (DSSCs) are proposed. DSSCs employing hybrid Pt/carbon with tailored configuration as CEs exhibit higher short-circuit current and conversion efficiencies as well as stability with a lapse of time compared with conventional cells on the basis of sputtered Pt thin films, evidencing that the new class of hybrid nanostructures possess high potential for cost-effective electrodes in energy conversion devices.

Light sensing in a photoresponsive, organic-based complementary inverter.

A photoresponsive organic complementary inverter was fabricated and its light sensing characteristics was studied. An organic circuit was fabricated by integrating p-channel pentacene and n-channel copper hexadecafluorophthalocyanine (F16CuPc) organic thin-film transistors (OTFTs) with a polymeric gate dielectric. The F16CuPc OTFT showed typical n-type characteristics and a strong photoresponse under illumination. Whereas under illumination, the pentacene OTFT showed a relatively weak photoresponse with typical p-type characteristics. The characteristics of the organic electro-optical circuit could be controlled by the incident light intensity, a gate bias, or both. The logic threshold (V(M), when V(IN) = V(OUT)) was reduced from 28.6 V without illumination to 19.9 V at 6.94 mW/cm². By using solely optical or a combination of optical and electrical pulse signals, light sensing was demonstrated in this type of organic circuit, suggesting that the circuit can be potentially used in various optoelectronic applications, including optical sensors, photodetectors and electro-optical transceivers.

Control over multifunctionality in optoelectronic device based on organic phototransistor.

Highly stable, reproducible, photosensitive organic field-effect transistors based on an n-type organic material, copper hexadecafluorophthalocyanine, and two different polymeric gate dielectrics has been reported and their performances have been compared by evaluating the surface/interface properties. The devices produced a maximum photocurrent gain (I(light)/I(dark)) of 79 at V(G) = 7 V and showed the potentiality as multifunctional optoelectronic switching applications depending upon the external pulses. The switching time of the transistor upon irradiation of light pulse, i.e., the photoswitching time of the device, was measured to be approximately 10 ms. On the basis of optical or combination of optical and electrical pulses, the electronic/optoelectronic properties of the device can be tuned efficiently. The multifunctions achieved by the single device can ensure very promising material for high density RAM and other optoelectronic applications. Furthermore, as the device geometry in the present work is not limited to rigid substrate only, it will lead to the development of flexible organic optoelectronic switch compatible with plastic substrates.

Preparation of poly(4-hydroxystyrene) based functional block copolymer through living radical polymerization and its nanocomposite with BaTiO3 for dielectric material.

Poly(4-hydroxystyrene) block copolymers containing maleic acid groups in one block were prepared through nitroxide mediated polymerization and their thin films with or without BaTiO3 nanoparticles were evaluated as a solution-processable dielectric materials. Poly(4-hydroxystyrene-co-maleic acid)-block-poly(4-hydroxystyrene) was successfully prepared through the hydrolysis of poly(4-acetoxystyrene-co-maleic anhydride)-block-poly(4-acetoxystyrene), as evidenced by GC, GPC, FT-IR and NMR. Through the incorporation of maleic acid group and BaTiO3 nanoparticles to poly(4-hydroxystyrene), higher dielectric constant was observed, suggesting that the dielectric constants of the composite films were strongly affected by the structural and compositional characteristics of polymers and nanocomposites.