Development of a new class of luminescent materials that show high-speed response, high charge carrier mobility, and high brightness is desirable toward realization of next generation of devices, such as electrically pumped organic lasers, visible light communication instruments, and organic light-emitting transistors. In this paper, high-speed organic light-emitting diodes (OLEDs) and high-performance hybrid light-emitting transistors from a new type of solution processable luminescent material, poly[thiophene-2,5-diyl-alt-5,10-bis((2-hexyldecyl)oxy)dithieno[3,2-c:3 ',2 '-h][1,5]naphthyridine-2,7-diyl] (PTNT), are reported. The OLEDs based on PTNT polymer exhibit a peak brightness of 8 x 10(5) cd m(-2) and 40 MHz modulation frequency under 10 ns pulse operation. This modulation frequency is significantly higher than that of commercially available LEDs, used for visible light communication. Additionally, solution-processed area-emitting hybrid light-emitting transistors with an external quantum yield of 0.25% at brightness of 250 cd m(-2) are demonstrated. Finally, the paper provides device physics and optoelectronic properties of PTNT polymer using ultraviolet photon spectroscopy, inversed photoelectron spectroscopy, and photophysical measurements.

Improved performance of p-type organic light-emitting transistors (OLETs) is demonstrated by introducing a conjugated polyelectrolyte (CPE) layer and symmetric high work function (WF) source and drain metal electrodes. The OLET comprises a tri-layer film consisting of a hole transporting layer, an emissive layer, and a CPE layer as an electron injection layer. The thickness of the CPE layer is critical for achieving good performance and provides an important structural handle for consideration in future optimization studies. We also demonstrate for the first time, good performance solution-processed blue-emitting OLETs. These results further demonstrate the simplification of device fabrication and improved performance afforded by integrating CPE interlayers into organic optoelectronic devices.

We have studied triplet-triplet annihilation in neat films of electrophosphorescent fac-tris(2-phenylpyridine) iridium(III) [Ir(ppy)(3)]-cored dendrimers containing phenylene- and carbazole-based dendrons with 2-ethylhexyloxy surface groups using time-resolved photoluminescence. From measured annihilation rates, the limiting current densities above which annihilation would dominate in dendrimer light-emitting devices are found to be > 1 A/cm(2). The triplet exciton diffusion length varies in the range of 2-10 nm depending on the dendron size. The distance dependence of the nearest-neighbor hopping rate shows that energy transfer is dominated by the exchange mechanism. (C) 2005 American Institute of Physics.

Two new heteroleptic Pt(II) complexes bearing an n-hexyloxy substituted phenyllepidine-based ligand and either a picolinate (pic) or acetylacetonate (acac) coligand are synthesized for use in organic light-emitting field-effect transistors (LEFETs). Both compounds are obtained in good yields via a short and straightforward synthetic route. It is found that while both Pt(II) complexes show good chemical stability and solubility, the coligand affects the photoluminescence quantum yield and crystal packing of the complexes. Although aggregate induced phosphorescence enhancement is not observed, it is found that high concentrations of the emitters in a poly[bis(4-phenyl) (2,4,6-trimethylphenyl) amine] host lead to improved charge injection in hybrid LEFETs. LEFETs with area emission, high ON/OFF ratios (> 10(6)) and mobilities (approximate to 1.3 cm(2) V-1 s(-1)), and external quantum efficiencies of up to 0.1% at the highest brightness of 855 cd m(-2) are demonstrated.

The optoelectronic gate light-emitting field-effect transistor (OEG LEFET) containing alternate SiO(2) and SiN(x) dielectric stacks allows enhanced light emission for a designed spectrum range and provides reliable strength for a wide operating voltage. The device can improve the emission efficiency by 4.5 times in comparison to a reference LEFET with a SiN(x) gate dielectric and can reach a brightness as high as 4500 cd/m(2).

The role of triplet excitons in rubrene/C-60 heterojunctions is investigated through detailed spectroscopic studies of triplet generation routes in the neat and heterojunction films of rubrene and C-60. Time-correlated single-photon counting experiments on rubrene and rubrene/C-60 give a long-lived component with lifetime >200 ns, and triplets are found to live longer in rubrene/C-60. A distinct reduction at short time scales in fluorescence lifetime of rubrene/C-60 gives the indication of singlet exciton dissociation via formation of charge-transfer (CT) states. Using ultrafast transient absorption spectroscopy, it is found that triplets are generated via singlet-fission in neat rubrene films at t approximate to 1.8 ps, whereas a delayed population buildup of triplets in rubrene/C-60 occurs at t approximate to 8 ps. The slow rise of triplet population confirms the role of CT-state-mediated triplet energy transfer in rubrene/C-60. The recombination of triplets via triplet-triplet annihilation in organic light-emitting diode (OLED) operation of rubrene/C-60 is shown to generate extra singlets, which lift the spin branching ratio to values >25%. It is concluded that triplet excitons in rubrene/C-60 are instrumental in bringing lower turn-on voltages, brighter emission, and higher external quantum efficiency of electroluminescence in OLED and light-emitting field effect transistors.

Light-emitting field-effect transistors (LEFETs) are an emerging type of devices that combine light-emitting properties with logical switching function. One of the factors limiting their efficiency stems from the spin statistics of electrically generated excitons. Only 25% of them, short lived singlet states, are capable of light emission, with the other 75% being long lived triplet states that are wasted as heat due to spin-forbidden processes. Traditionally, the way to overcome this limitation is to use phosphorescent materials as additional emission channel harnessing the triplet excitons. Here, an alternative strategy for triplet usage in LEFETs in the form of thermally activated delayed fluorescence (TADF) is presented. Devices employing a TADF capable material, 4CzIPN (2,4,5,6-tetra[9H-carbazol-9-yl]isophthalonitrile), in both n-type and p-type configurations are shown. They manifest excellent electrical characteristics, consistent brightness in the range of 100-1,000 cd m(-2) and external quantum efficiency (EQE) of up to 0.1%, which is comparable to the equivalent organic light-emitting diode (OLED) based on the same materials. Simulation identifies the poor light out-coupling as the main reason for lower than expected EQEs. Transmission measurements show it can be partially alleviated using a more transparent top contact, however more structural optimization is needed to tap the full potential of the device.

A split-gate field effect transistor containing four electrodes, source, drain, two gates allows enhanced transport for specific carrier species and separate control of carrier polarity over two gate regimes. The device can be operated as a transistor or a diode by controlling gate biases.

Solution-processable non-polymeric organic semiconductors are attractive for opto-electronic applications due to their relatively simple synthetic reproducibility and characterization, and enhanced capability for fine-tuning of their properties. We report the synthesis, charge transport, photophysics, and photovoltaic properties of three non-polymeric materials based upon bisarylthiophenyl diketopyrrolopyrrole [DPP(ThAr)(2)]. The DPP(ThAr)(2) molecules are comprised of solubilizing alkyl groups, 2-ethylhexyl (for 1a) and 2-octyldodecyl (for 1b and 2), which are capped with "electron accepting" moieties -fluorenone (1) or benzothiadiazole (2). While the materials could be prepared under standard SuzukiMiyaura cross-coupling conditions, a simple direct arylation afforded 2 and 1b in good yields. We found 1a with a short alkyl chain lacked sufficient solubility for solution processing but 1b and 2 are solution processable and form good quality films. All three materials exhibited ambipolar charge transport in field effect transistors, with 1b showing balanced charge mobilities of about 10(-3) cm(2) V-1 s(-1). Bulk heterojunction solar cells of 1b or 2 with PC71BM were found to have high opencircuit voltages (up to 0.9 V) with power conversion efficiencies of up to 4.5% and 2.6%, respectively. (C) 2017 Elsevier B.V. All rights reserved.

Organic light emitting field effect transistors (LEFETs) integrate light emission of a diode with logic functions of a transistor into a single device architecture. This integration has the potential to provide simplified displays at low costs and access to injection lasing. However, the charge carrier mobility in LEFETs is a limiting factor in realizing high current densities along with a trade-off between brightness and efficiency. Herein, we present a technique controlling the nanoscale morphology of semi-conducting polymers using nanoscale grooved substrates and dip-coating deposition to achieve high current density. We then applied this approach to heterostructure LEFETs and demonstrated brightness exceeding 29000 cd m(-2) at an EQE of 0.4% for a yellow emitter and 9600 cd m(-2) at an EQE of 0.7% for a blue emitter. These results represent a significant advancement in organic optoelectronics and are an important milestone toward the realization of new applications in displays and electrically pumped lasing.

Light-emitting field-effect transistors (LEFETs) integrate functions of an organic light-emitting diode (OLED) and a field-effect transistor, and hence offer significant advantages in simplifying the device architecture for next-generation active matrix full-color displays as well as having potential in communications and electrically pumped lasers. There is little work on phosphorescent light-emitting field-effect transistors, particularly those based on host-free phosphorescent light-emitting materials. In this report, we demonstrate solution-processed host-free LEFETs and OLEDs based on a blue phosphorescent dendrimer as the active emitter and compare their performance. The LEFETs exhibit excellent electrical and optical characteristics with a luminance of 650 cd m(-2) and an EQE of 2.1%, which is comparable to the equivalent OLEDs based on the same dendrimer. The LEFETs were fabricated in a heterostructure bilayer configuration using a p-type charge transport material, poly(2,5-bis(3-n-hexadecylthiophene-2-yOthieno[3,2-b]thiophene) (PBTTT), underneath the emissive layer. The equivalent OLEDs were fabricated using PBTTT and MoOx, as the hole-injecting and -transporting layers. Remarkably, negligible EQE roll -off in the LEFETs at high current density and brightness was observed. These results indicate that for phosphorescent materials there could be an advantage in using LEFETs over OLEDs at high current density or brightness. In addition, we discuss the operating mechanism and effects of solvent used to deposit the dendrimer layer on the interface formed with the PBTTT layer. X-ray reflectometry showed that the interface between the PBTTT and dendrimer layer changed in terms of the lamellar ordering of the PBTTT layer upon solution deposition of the dendrimer layer, resulting in a lower charge carrier mobility in the devices.