Light-emitting Organic Field Effect Research Articles

Achieving Bright Organic Light-Emitting Field-Effect Transistors with Sustained Efficiency through Hybrid Contact Design.

Organic light-emitting field-effect transistors (OLEFETs) with bilayer structures have been widely studied due to their potential to integrate high-mobility organic transistors and efficient organic light-emitting diodes. However, these devices face a major challenge of imbalance charge transport, leading to a severe efficiency roll-off at high brightness. Here, we propose a solution to this challenge by introducing a transparent organic/inorganic hybrid contact with specially designed electronic structures. Our design aims to steadily accumulate the electrons injected into the emissive polymer, allowing the light-emitting interface to effectively capture more holes even when the hole current increases. Our numerical simulations show that the capture efficiency of these steady electrons will dominate charge recombination and lead to a sustained external quantum efficiency of 0.23% over 3 orders of magnitude of brightness (4 to 7700 cd/m2) and current density (1.2 to 2700 mA/cm2) from -4 to -100 V. The same enhancement is retained even after increasing the external quantum efficiency (EQE) to 0.51%. The high and tunable brightness with stable efficiency offered by hybrid-contact OLEFETs makes them ideal light-emitting devices for various applications. These devices have the potential to revolutionize the field of organic electronics by overcoming the fundamental challenge of imbalance charge transport.

The construction of white-light-emitting anisotropic hydrogel

In this work, hybrid anisotropic hydrogel is developed through dispersing carbon quantum dots, ultrahigh magnetic nanoparticle-coated alumina (Fe/Al2O3) platelets in acrylamide aqueous solution in the assistance of magnetic field, then fix the oriented structure via gelation. The aligned Fe/Al2O3 platelets result in formation of anisotropic structure, thus endows the hydrogels mechanical anisotropy and fluorescent anisotropy. White-light emission is obtained via varying the weight ratio of yellow-emitting ZnO QDs and blue-emitting N,S-CDs. This strategy not only enriches the mechanical/fluorescent dual anisotropic soft materials, but also have great potential application in the fields of organic light-emitting diodes, nonlinear optics and field effect transistors.

Application of graphene vertical field effect to regulation of organic light-emitting transistors**Project supported by the National Natural Science Foundation of China (Grant No. 31872901) and the National Key Research and Development Program of China (Grant No. 2016YFA0501602).

The luminescence intensity regulation of organic light-emitting transistor (OLED) device can be achieved effectively by the combination of graphene vertical field effect transistor (GVFET) and OLED. In this paper, we fabricate and characterize the graphene vertical field-effect transistor with gate dielectric of ion–gel film, confirming that its current switching ratio reaches up to 102. Because of the property of high light transmittance in ion–gel film, the OLED device prepared with graphene/PEDOT:PSS as composite anode exhibits good optical properties. We also prepare the graphene vertical organic light-emitting field effect transistor (GVOLEFET) by the combination of GVFET and graphene OLED, analyzing its electrical and optical properties, and confirming that the luminescence intensity can be significantly changed by regulating the gate voltage.

Study on the Photoresponse Characteristics of Organic Light-Emitting Field-Effect Transistors

Organic photodetectors have attracted great attention because of their promising applications in the fields of imaging, optical communication, and biosensing. Although the optical and electrical performances of the organic light-emitting field effect transistors (OLEFETs) have improved substantially in the past decade, the photodetection property of the OLEFETs has rarely been studied. Here, we investigated the photoresponse characteristics of the heterostructured OLEFETs, which unexpectedly shows performance comparable to some organic phototransistor-only devices, without sacrificing the light emission performance of the device. The device shows photoresponse ability in a wide visible light range and a maximum photon-to-electron efficiency of 45 300% with millisecond-scale switching on and off time when under the illumination of 405 nm. It is found that the photoresponse characteristics of the devices are mainly determined by the hole injection layer, as light absorption happens mainly in this layer. Our...

Nano-Alignment in Semiconducting Polymer Films: A Path to Achieve High Current Density and Brightness in Organic Light Emitting Transistors

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 semiconducting 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.

Near-Infrared to Visible Organic Upconversion Devices Based on Organic Light-Emitting Field Effect Transistors.

The near-infrared (NIR) to visible upconversion devices have attracted great attention because of their potential applications in the fields of night vision, medical imaging, and military security. Herein, a novel all-organic upconversion device architecture has been first proposed and developed by incorporating a NIR absorption layer between the carrier transport layer and the emission layer in heterostructured organic light-emitting field effect transistors (OLEFETs). The as-prepared devices show a typical photon-to-photon upconversion efficiency as high as 7% (maximum of 28.7% under low incident NIR power intensity) and millisecond-scale response time, which are the highest upconversion efficiency and one of the fastest response time among organic upconversion devices as referred to the previous reports up to now. The high upconversion performance mainly originates from the gain mechanism of field-effect transistor structures and the unique advantage of OLEFETs to balance betweenthe photodetection and light emission. Meanwhile, the strategy of OLEFETs also offers the advantage of high integration so that no extra OLED is needed in the organic upconversion devices. The results would pave way for low-cost, flexible and portable organic upconversion devices with high efficiency and simplified processing.

Low-voltage organic light-emitting field-effect transistors using n-Dodecylphosphonic acid-passivated HfOx dielectrics

Abstract In this paper, organic light-emitting field effect transistors (OLEFETs) operating at low voltages |Vop| below 10 V were first produced and characterized. n-Dodecylphosphonic acid (PA-C12)-self-assembled monolayer (SAM)-passivated HfOx dielectrics prepared using sol-gel chemistry decreased the device-operating voltages. Crystalline organic active layers of pentacene and N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (P13) acted as p-and n-type materials, respectively. 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran doped onto a tris(8-hydroxyquinoline) aluminum (Alq3:DCM) layer was used as a light-emitting medium to enhance the luminescence efficiency. Based on a tri-layered structure with balanced ambipolar transports and the combined high capacitance-low leakage current of the PA-C12-SAM-treated HfOx dielectrics, the OLEFETs demonstrated good device performance with light emission at |Vop|

Harvesting Triplet Excitons with Exciplex Thermally Activated Delayed Fluorescence Emitters toward High Performance Heterostructured Organic Light-Emitting Field Effect Transistors.

The utilization of triplet excitons plays a key role in obtaining high emission efficiency for organic electroluminescent devices. However, to date, only phosphorescent materials have been implemented to harvest the triplet excitons in the organic light-emitting field effect transistors (OLEFETs). In this work, we report the first incorporation of exciplex thermally activated delayed fluorescence (TADF) emitters in heterostructured OLEFETs to harvest the triplet excitons. By developing a new kind of exciplex TADF emitter constituted by m-MTDATA (4,4',4″-tris(N-3-methylphenyl-N-phenylamino)triphenylamine) as the donor and OXD-7 (1,3-bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazo-5-yl]benzene) as the acceptor, an exciton utilization efficiency of 74.3% for the devices was achieved. It is found that the injection barrier between hole transport layer and emission layer as well as the ratio between donor and acceptor would influence the external quantum efficiency (EQE) significantly. Devices with a maximum EQE of 3.76% which is far exceeding the reported results for devices with conventional fluorescent emitters were successfully demonstrated. Moreover, the EQE at high brightness even outperformed the result for organic light-emitting diode based on the same emitter. Our results demonstrate that the exciplex TADF emitters can be promising candidates to develop OLEFETs with high performance.

Improved Performance of Organic Light-Emitting Field-Effect Transistors by Interfacial Modification of Hole-Transport Layer/Emission Layer: Incorporating Organic Heterojunctions.

Organic heterojunctions (OHJs) consisting of a strong electron acceptor 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN) and an electron donor N,N'-di(naphthalene-1-yl)-N,N'-diphenyl-benzidine (NPB) were demonstrated for the first time that they can be implemented as effective modification layers between hole transport layer (HTL) and emission layer in the heterostructured organic light-emitting field effect transistors (OLEFETs). The influence of both HAT-CN/NPB junction (npJ) and NPB/HAT-CN junction (pnJ) on the optoelectronic performance of OLEFETs were conscientiously investigated. It is found that both the transport ability of holes and the injection ability of holes into emissive layer can be dramatically improved via the charge transfer of the OHJs and that between HAT-CN and the HTL. Consequently, OLEFETs with pnJ present optimal performance of an external quantum efficiency (EQE) of 3.3% at brightness of 2630 cdm(-2) and the ones with npJs show an EQE of 4.7% at brightness of 4620 cdm(-2). By further utilizing npn OHJs of HAT-CN/NPB/HAT-CN, superior optoelectronic performance with an EQE of 4.7% at brightness of 8350 cdm(-2) and on/off ratio of 1 × 10(5) is obtained. The results demonstrate the great practicality of implementing OHJs as effective modification layers in heterostructured OLEFETs.

Single crystal biphenyl end-capped furan-incorporated oligomers: influence of unusual packing structure on carrier mobility and luminescence

We report the synthesis and characterization of two new furan-based biphenyl end-capped oligomers, 2-([1,1′-biphenyl]-4-yl)-5-(5-([1,1′-biphenyl]-4-yl)thiophen-2-yl)furan (BPFT) and 5,5′-di([1,1′-biphenyl]-4-yl)-2,2′-bifuran (BP2F) as candidate semiconductors for organic light-emitting field effect transistors (OLETs). Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) showed the high thermostability of these furan-based semiconductors. X-Ray crystallography of single crystals grown by physical vapor transfer (PVT) method revealed a complicated herringbone packing of BPFT stacking with unusual flat and bent structures, which is different from that of BP2F and the bithiophene-based analogue 5,5′-di([1,1′-biphenyl]-4-yl)-2,2′-bithiophene (BP2T). BPFT single crystal showed a higher absolute quantum yield (51%) compared to that of BP2F and BP2T. Density Functional Theory (DFT) calculations showed that the different excitation energies between flat and bent structures led to the asymmetric transition dipoles in dark state of BPFT H-aggregates, which explains the highest PLQY of BPFT single crystal. Single crystal FET based on BPFT showed an ambipolar characteristic with high hole and electron mobilities, while single crystal FET based on BP2F exhibited p-type characteristic with a high hole mobility. Light emission was observed from the single-crystal FET based on BPFT.

Organic light emitting field effect transistors based on an ambipolar p-i-n layered structure

A bottom contact/top gate ambipolar “p-i-n” layered light emitting field effect transistor with the active medium inserted between two doped transport layers, is reported. The doping profile results crucial to the capability of emitting light, as well as to the electrical characteristics of the device. In this sense, high output current at relative low applied gate/drain voltage and light emission along the whole large area transistor channel are observed, putting the basis to full integration of organic light emitting field effect transistors in planar complex devices.

Encapsulation of organic light-emitting devices using a perfluorinated polymer

Films of Cytop™, a perfluorinated polymer, are spin cast as a single barrier layer for evaluation of barrier properties on organic light-emitting devices and on Ca thin films. Cytop™ is water repellant, resulting in encapsulated organic light-emitting field effect transistors and organic light-emitting diodes (OLEDs), which remain active even after immersion into water or exposure to water droplets on the Cytop™ surface. OLEDs encapsulated with Cytop™ exhibit up to five times longer continuous operation under identical environmental and driving conditions compared with devices that are not encapsulated with Cytop™.

Organic Light‐Emitting Field‐Effect Transistors Operated by Alternating‐Current Gate Voltages

Organic light-emitting field-effect transistors are operated by a novel method characterized by the application of ac voltages to the gate electrode. This prompts carrier injection from both source and drain electrodes into the organic layer (a thin film or a crystal) without altering the device constitution. Stronger emissions are observed from the device with increasing gate voltage frequencies.

On the width of the recombination zone in ambipolar organic field effect transistors

The performance of organic light emitting field effect transistors is strongly influenced by the width of the recombination zone. We present an analytical model for the recombination profile. By assuming Langevin recombination, the recombination zone width W is found to be given byW=4.34dδ, with d and δ the gate dielectric and accumulation layer thicknesses, respectively. The model compares favorably to both numerical calculations and measured surface potential profiles of an actual ambipolar device.

Environmentally stable light emitting field effect transistors based on 2-(4-pentylstyryl)tetracene

Organic light emitting field effect transistors based on 2-(4-pentylstyryl)tetracene are able to operate in ambient air and have a shelf lifetime of several months.

発光性有機トランジスタ用材料の分子設計とデバイス特性

In this study, we report on material design of light-emitting organic field effect transistors (LE-OFETs). Some of newly synthesized pyrene and bis-styryl derivatives as an active layer demonstrated high field effect mobility (μh = 0.11 cm /Vs, C6-BSBP) and high photoluminescence efficiency (φPL-80%, symmetrical di-substituted pyrene derivatives). Further, external electroluminescence quantum efficiency was improved from 0.01% in TPPy to 0.15-0.54% in pyrene dimmers. In addition, we demonstrate an increase of EL efficiency by introducing guest-host system and ambipolar operation mechanism.

Organic Light Emitting Field Effect Transistors: Advances and Perspectives

AbstractLight emitting field effect transistors based on molecular and polymeric organic semiconductors are multifunctional devices that integrate light emission with the current modulating function of a transistor. The planar geometry of organic light emitting field effect transistors (OLEFETs) offers direct access to the light emission region, providing a unique experimental configuration to investigate fundamental optical and electronic properties in organic semiconductors. OLEFETs show great potential for technological applications such as active matrix full color electroluminescent displays. In this Feature Article we review advances in OLEFETs since their first demonstration in 2003 and we highlight exciting challenges associated with their future development.

Ambipolar organic light emitting field effect transistors with modified asymmetric electrodes

The authors report on gate-controlled light emission from an organic field effect transistor composed of a vapor-deposited thin film of α,ω-bis(biphenyl-4-yl)-terthiophene (BP3T) with an electron injection layer of pentacene for the drain electrode. A n-triacontane thin film vapor deposited on a Si∕SiO2 wafer was used as a buffer layer for the gate dielectric. The location of emission zones within the channel where both injected carriers recombine was controlled by the gate voltage. The insertion of the pentacene and n-triacontane layers improved the threshold voltage and mobility for electrons, resulting in balanced ambipolar carrier injection and transport.

Bipolar Characteristics of an Organic Light-Emitting Filed Effect Transistor Using a TPTPT and NTCDA Co-Deposited Layer

We fabricated an organic light-emitting field effect transistors (OLEFET) using a co-deposited layer of TPTPT and NTCDA which has p-type and n-type semiconducting behaviors, respectively. The organic layer was formed on a comb type electrode (source-drain electrodes) with a channel length of 25μm on a p-Si/SiO2 substrate. Bipolar and EL characteristics were investigated by changing co-deposition ratio of TPTPT and NTCDA. In the optimum deposition ratio, we observed typical ambipolar characteristics, demonstrating saturation current characteristics at low Vd (source-drain voltage), followed by divergent current characteristics at high Vd.

High mobility ambipolar charge transport in a cross-linked reactive mesogen at room temperature

By photochemically cross linking the molecules of a reactive end group functionalized calamitic liquid crystal (bis(heptylphenyl)-bithiophene-oxetane) in the smectic mesophase, an insoluble rigid molecular network is formed which remains structurally unchanged on cooling to room temperature. The charge transport is investigated by the time-of-flight method and the resulting material shows long-range (∼10μm) ambipolar transport with nondispersive field independent hole mobility, μhole=0.016cm2∕Vs and dispersive field dependent electron mobility, typically μelectron=0.028cm2∕Vs (both at 4×104Vcm−1 and at 15 °C). These desirable charge transport properties make this system a promising candidate for organic electronic applications, such as charge transport layers in organic light-emitting diodes and field effect transistors.