Ambipolar Light-emitting Field-effect Transistors Research Articles

Mechanisms of radiative recombination in ambipolar light-emitting field-effect transistors based on organic polymers and inorganic nanoparticles

Mechanisms of radiative recombination in ambipolar light-emitting field-effect transistors with composite active layers based on the PFO organic polymer and inorganic ZnO nanoparticles are considered. Theoretical analysis of the radiative recombination in the accumulation layer of the structure is performed in the framework of a model permitting one to obtain an analytical description of the process. An expression for the total recombination rate has been obtained and numerical calculations have been carried out. Correspondence between the calculation results and experimental data has been obtained for the integral intensity of electrical luminescence in the composite structure under consideration.

High-Mobility, Heterostructure Light-Emitting Transistors and Complementary Inverters

Light-emitting field effect transistors (LEFETs) are optoelectronic devices that can simultaneously execute light emission and the standard logic functions of a transistor in a single device architecture. In this article, we show that ambipolar LEFETs can be made in a bilayer structure using Super Yellow, a light-emitting polymer layer, and a high-mobility diketopyrrolo-pyrrole-based copolymer as an ambipolar charge-transporting layer. The LEFETs were fabricated in the bottom gate architecture with top-contact, air-stable, symmetric Au–Au electrodes. The devices show light emission in both electron and hole accumulation modes with an external quantum efficiency (EQE) of 0.1% at a brightness of 650 cd/m2 in electron accumulation mode, and an EQE of 0.001% at a brightness of 4 cd/m2 in hole accumulation mode. We have also demonstrated a light-emitting inverter by combining two LEFETs into the inverter architecture. The light-emitting inverter generates both electrical and optical signals with an electrical gain of 112.

Enhanced Ambipolar Charge Injection with Semiconducting Polymer/Carbon Nanotube Thin Films for Light-Emitting Transistors

We investigate the influence of small amounts of semiconducting single-walled carbon nanotubes (SWNTs) dispersed in polyfluorenes such as poly(9,9-di-n-octylfluorene-alt-benzothiadiazole (F8BT) and poly(9,9-dioctylfluorene) (F8) on device characteristics of bottom contact/top gate ambipolar light-emitting field-effect transistors (LEFETs) based on these conjugated polymers. We find that the presence of SWNTs within the semiconducting layer at concentrations below the percolation limit significantly increases both hole and electron injection, even for a large band gap semiconductor like F8, without leading to significant luminescence quenching of the conjugated polymer. As a result of the reduced contact resistance and lower threshold voltages, larger ambipolar currents and thus brighter light emission are observed. We examine possible mechanisms of this effect such as energy level alignment, reduced bulk resistance above the contacts, and field-enhanced injection at the nanotube tips. The observed ambipolar injection improvement is applicable to most conjugated polymers in staggered transistor configurations or similar organic electronic devices where injection barriers are an issue.

Green light emission from the edges of organic single-crystal transistors

We have fabricated ambipolar light-emitting field-effect transistors made of 1,4-bis(5-phenylthiophen-2-yl)benzene (AC5) single crystals, which have 35% fluorescent quantum efficiency. The obtained hole and electron mobilities were 2.9×10−1 cm2/V s and 6.7×10−3 cm2/V s, respectively. These are the highest values among AC5 transistors. Importantly, although the light emission from the crystal surface was less than the detection level of the camera, we observed bright and polarized light emission from the edge of the single crystals. This polarized edge emission is attributed to the strong self-assembled light-confining nature and perfectly aligned transition dipole moments, which are advantageous for future laser devices.

Characterization of Perylene and Tetracene-Based Ambipolar Light-Emitting Field-Effect Transistors

Herein is presented systematic analysis of air-stable, ambipolar heterojunction-based organic light-emitting field-effect transistors (OLEFETs). Top-contact OLEFETs with multidigitated, long channel-width geometry were produced by the successive deposition of electron-transporting N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (P13) and hole-transporting tetracene layers, using the neutral cluster beam deposition (NCBD) method. The morphological, structural, and photoluminescence properties of the untreated and thermally post-treated P13/tetracene active layers were examined by atomic force microscopy, X-ray diffraction, and laser scanning confocal microscopy. From the comparative analysis of the NCBD thin films, the neutral cluster beams led to the preparation of smooth, uniform bilayer films consisting of well-packed grain crystallites. The OLEFETs demonstrated good field-effect characteristics, stress-free operational stability, and electroluminescence under ambient conditions. The operating ...

Simultaneous Optimization of Light Gain and Charge Transport in Ambipolar Light-Emitting Polymer Field-Effect Transistors

Ambipolar light-emitting field-effect transistors (LEFETs) based on poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) are able to combine electrical switching capability with the generation of light within a well-defined recombination zone inside the channel. Therefore, they are an attractive architecture not only for low-loss light signal transmission in optoelectronic integrated circuits but also for the potential realization of electrically pumped organic lasers. However, these applications require a simultaneous optimization of transistor performance and waveguiding of emitted light. Here we show that to achieve efficient waveguiding and optical gain the annealing temperature of the F8BT film has to be kept at 120 °C below its glass transition temperature. At such low processing temperatures it is difficult to achieve efficient ambipolar charge injection from gold source/drain electrodes and charge transport at the active transistor interface. We show that modification of the gold electrodes with ...

Electroluminescence imaging and microstructure of organic light-emitting field-effect transistors

The effect of morphology and microstructure on the emission characteristics of ambipolar light-emitting field-effect transistors is studied using the polyfluorene copolymer F8BT [poly(9,9-di-n-octylfluorene-alt-benzothiadiazole)] as a model system. Different intensity distributions of the emission zones of amorphous, polycrystalline, and aligned F8BT films are demonstrated. Electroluminescence maps of the channel region are produced by overlaying a series of images recorded during gate voltage sweeps. They show a correlation to the microcrystalline structure of the F8BT and are assumed to visualize the current density distribution within the transistor channel.

Light emission from an ambipolar semiconducting polymer field-effect transistor

Ambipolar light-emitting field-effect transistors are fabricated with two different metals for the top-contact source and drain electrodes; a low-work-function metal defining the channel for the source electrode and a high-work-function metal defining the channel for the drain electrode. A thin film of polypropylene-co-1-butene on SiNx is used as the gate dielectric on an n++-Si wafer, which functioned as the substrate and the gate electrode. Transport data show ambipolar behavior. Recombination of electrons and holes results in a narrow zone of light emission within the channel. The location of the emission zone is controlled by the gate bias.