Thin-film transistors based on molecular and polymeric organic materials have been proposed for a number of applications, such as displays and radio-frequency identification tags. The main factors motivating investigations of organic transistors are their lower cost and simpler packaging, relative to conventional inorganic electronics, and their compatibility with flexible substrates. In most digital circuitry, minimal power dissipation and stability of performance against transistor parameter variations are crucial. In silicon-based microelectronics, these are achieved through the use of complementary logic-which incorporates both p- and n-type transistors-and it is therefore reasonable to suppose that adoption of such an approach with organic semiconductors will similarly result in reduced power dissipation, improved noise margins and greater operational stability. Complementary inverters and ring oscillators have already been reported. Here we show that such an approach can realize much larger scales of integration (in the present case, up to 864 transistors per circuit) and operation speeds of approximately 1 kHz in clocked sequential complementary circuits.

Electronic systems that use rugged lightweight plastics potentially offer attractive characteristics (low-cost processing, mechanical flexibility, large area coverage, etc.) that are not easily achieved with established silicon technologies. This paper summarizes work that demonstrates many of these characteristics in a realistic system: organic active matrix backplane circuits (256 transistors) for large (Ϸ5 ؋ 5-inch) mechanically flexible sheets of electronic paper, an emerging type of display. The success of this effort relies on new or improved processing techniques and materials for plastic electronics, including methods for (i) rubber stamping (microcontact printing) high-resolution (Ϸ1 m) circuits with low levels of defects and good registration over large areas, (ii) achieving low leakage with thin dielectrics deposited onto surfaces with relief, (iii) constructing highperformance organic transistors with bottom contact geometries, (iv) encapsulating these transistors, (v) depositing, in a repeatable way, organic semiconductors with uniform electrical characteristics over large areas, and (vi) low-temperature (Ϸ100°C) annealing to increase the on͞off ratios of the transistors and to improve the uniformity of their characteristics. The sophistication and flexibility of the patterning procedures, high level of integration on plastic substrates, large area coverage, and good performance of the transistors are all important features of this work. We successfully integrate these circuits with microencapsulated electrophoretic ''inks'' to form sheets of electronic paper.T he backplane circuit consists of a square array of 256 suitably interconnected p-channel transistors. Fig. 1 shows the circuit layout. Fig. 2 presents a cross-sectional illustration of a transistor and a top view of a unit cell. The completed display (total thickness Ϸ1 mm) comprises a transparent frontplane electrode of indium tin oxide (ITO) and a thin unpatterned layer of flexible electronic ''ink'' mounted against a sheet that supports square pixel electrode pads and pinouts; these pixel pads attach, via a conductive adhesive, to the back planes. Each transistor functions as a switch that locally controls the color of the ink, which consists of a layer of polymeric microcapsules filled with a suspension of charged pigments in a colored fluid (1, 2). In each of the four quadrants of the display, transistors in a given column have connected gates, and those in a given row have connected source electrodes. Applying a voltage to a column (gate) and a row (source) electrode turns on the transistor located at the cell where these electrodes intersect. Activating the transistor generates an electric field between the frontplane ITO and the corresponding pixel electrode. This field causes movement of a pigment within the microcapsules, which changes the color of the pixel, as observed through the ITO: when the pigments flow to the ITO side of the capsules, the color of the pigment (white in this case) determines the color of the pixel; when they ...

We present a comparative study of ultrafast photoconversion dynamics in tetracene (Tc) and pentacene (Pc) single crystals and Pc films using optical pump-probe spectroscopy. Photoinduced absorption in Tc and Pc crystals is activated and temperature-independent, respectively, demonstrating dominant singlet-triplet exciton fission. In Pc films (as well as C60-doped films) this decay channel is suppressed by electron trapping. These results demonstrate the central role of crystallinity and purity in photogeneration processes and will constrain the design of future photovoltaic devices.

We show that organic thin-film transistors have suitable properties for use in gas sensors. Such sensors possess sensitivity and reproducibility in recognizing a range of gaseous analytes. A wealth of opportunities for chemical recognition arise from the variety of mechanisms associated with different semiconductor–analyte interactions, the ability to vary the chemical constitution of the semiconductor end/side groups, and also the nature of the thin-film morphology.

Organic transistor based circuits that can be employed for chemical vapor sensing, are described. Such circuits have improved sensing characteristics in comparison with discrete transistor based sensors. Complementary ring oscillator based sensors have a stronger response to analytes such as octanol and allyl propionate compared to a single transistor. A fabrication process that combines organic semiconductor circuitry with Si is described. The design and advantages of adaptive differential amplifiers with high gain and feedback are described. Voltage gains of ∼20 allow the detection of weak odorant inputs and the adaptive feedback allows for improved background elimination.

Organic scintillators are widely used in radiation-detection applications due to their low cost, ease of fabrication, and fast response times.[1] Their ionization energy is about 60 eV/ photon and is nonlinear with particle energy for strongly ionizing radiation, such as alpha particles.[1] Because of their large and nonlinear ionization energy, they are unsuitable for applications that require high energy resolution or detection of strongly ionizing particles. In contrast, inorganic semiconductors have ionization energies of about three times their energy gap (e.g., Si requires 3.6 eV per electron-hole pair), and they respond linearly to strongly ionizing particles.[1] The ionization energy of a semiconductor quantum dot (qdot) is expected to be less than the bulk material and may approach the energy gap of the quantum dot. [2,3] Here, we propose a new class of radiation-detection materials, composites of inorganic semiconductor quantum dots and organic semiconductors, that possess the cost and processing advantages of organic scintillators and the ionization characteristics of inorganic semiconductors.The qdot/organic semiconductor composite is designed so that ionizing radiation produces excitations predominantly in the inorganic semiconductor qdots, and these excitations are subsequently Förster-transferred [4] to the organic material.Depending upon the application, the Förster-excited organic material(s) are chosen either to emit a Stokes-shifted photon or to dissociate the excitation and produce mobile charges. For scintillators, the composite material must be transparent to the emitted photon, and the large Stokes shift of the organic material is essential. Förster transfer can occur on subnanosecond timescales, so the fast response times of organic scintillators can be preserved. For charge-collection devices the composite material must be trap free to allow efficient charge collection. Trap-free, conjugated organic materials are now available.[5] Pure qdot solids are impractical radiation-detection materials because they are not transparent to their emission wavelength and have significant charge-carrier trapping.[6] However, qdot/organic semiconductor composites can be designed that have promising optical and electrical transport characteristics. [7,8] Gamma-ray, neutron, and charged-particle detection involves measuring the energy deposited by electrons or charged particles produced by the incident radiation. The deposited energy is measured by counting photons or mobile charges produced in the detecting material.[1] The electron or charged-particle energy is transferred to the electrons of the detection material via Coulomb interactions that scale with electron density. Because inorganic qdots have a higher density than organic materials, most of the energy is deposited in the qdots for qdot volume fractions above about 0.15. Here, we investigate a composite scintillator that uses a luminescent polymer as the organic semiconductor host. We first present optical properties of the composite that de...

Oligothiophene thin film transistors have recently been shown to respond to organic vapors, suggesting possible applicability in the field of olfactory sensor arrays. Here, we present a study of the correlation between the morphological structure of the active semiconductor thin film and the response to the vapor. The study was carried out by combining the measurement of the transient source-drain current of the transistor under vapor flow with the morphological characterization of the organic thin films by transmission electron microscopy.

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