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Merging the functionality of an organic field-effect transistor (OFET) with either a light emission or a photoelectric effect can increase the efficiency of displays or photosensing devices. In this work, we show that an organic semiconductor enables a multifunctional OFET combining electroluminescence (EL) and a photoelectric effect. Specifically, our computational and experimental investigations of a six-ring thiophene-phenylene co-oligomer (TPCO) revealed that this material is promising for OFETs, light-emitting, and photoelectric devices because of the large oscillator strength of the lowest-energy singlet transition, efficient luminescence, pronounced delocalization of the excited state, and balanced charge transport. The fabricated OFETs showed a photoelectric response for wavelengths shorter than 530 nm and simultaneously EL in the transistor channel, with a maximum at ~570 nm. The devices demonstrated an EL external quantum efficiency (EQE) of ~1.4% and a photoelectric responsivity of ~0.7 A W–1, which are among the best values reported for state-of-the-art organic light-emitting transistors and phototransistors, respectively. We anticipate that our results will stimulate the design of efficient materials for multifunctional organic optoelectronic devices and expand the potential applications of organic (opto)electronics. [ABSTRACT FROM AUTHOR]

Electroluminescence of metal halide perovskites has been widely reported via the fabrication and optimization of light-emitting diodes and light-emitting transistors. Light-emitting transistors are particularly interesting owing to the additional control of the gate voltage on the electroluminescence. In this work, the design of a microcavity, with a defect mode that can be tuned with an applied voltage, integrated with a metal halide light-emitting transistor is shown. The optical properties of the device have been simulated with the transfer matrix method, considering the wavelength-dependent refractive indexes of all the employed materials. The tunability of the microcavity has been obtained via the employment of doped semiconductor nanocrystalline films, which show a tunable plasma frequency and, thus, a tunable refractive index as a function of the applied voltage. Consequently, the tunability of the electroluminescence of the metal halide perovskite light-emitting transistor has been demonstrated.

Herein, a single‐layer light‐emitting transistor with a good on/off ratio of more than 106 is presented based on the iridium complex as a light‐emitter layer. Comprehensive experiments and simulations demonstrate that the thickness of the emitting layer can significantly improve the majority carrier injection in the source electrode. The electrode work function determines the minority carrier injection in the drain electrode, which is crucial for the light emission of the transistor. Furthermore, the increased source injection allows for a higher channel current, thereby increasing drain injection. Most importantly, although the above methods can improve the device channel current and light‐emitting brightness, the electroluminescence efficiency cannot be optimized since the increased minority carriers are much less than the increased majority carriers, resulting in most increased majority carriers cannot be contributed to the charge recombination. To achieve a higher efficient device, the channel current is supposed to be low when a conductive channel is well formed. This goal is achieved by using an ionic liquid gate to replace SiO2 gate for fabricating the light‐emitting single‐layer transistor. The efficiency is improved from ≈0.1 to 1.5 cd A−1. This work provides a new strategy for constructing high‐performance single‐layer light‐emitting transistors. [ABSTRACT FROM AUTHOR]

Unbalanced mobility and injection of charge carriers in metal‐halide perovskite light‐emitting devices pose severe limitations to the efficiency and response time of the electroluminescence. Modulation of gate bias in methylammonium lead iodide light‐emitting transistors has proven effective in increasing the brightness of light emission up to MHz frequencies. In this work, a new approach is developed to improve charge carrier injection and enhance electroluminescence of perovskite light‐emitting transistors by independent control of drain–source and gate–source bias voltages to compensate for space‐charge effects. Optimization of bias pulse synchronization induces a fourfold enhancement of the emission intensity. Interestingly, the optimal phase delay between biasing pulses depends on modulation frequency due to the capacitive nature of the devices, which is well captured by numerical simulations of an equivalent electrical circuit. These results provide new insights into the electroluminescence dynamics of AC‐driven perovskite light‐emitting transistors and demonstrate an effective strategy to optimize device performance through independent control of the amplitude, frequency, and phase of the biasing pulses. [ABSTRACT FROM AUTHOR]

Electroluminescence of metal halide perovskites has been widely reported via the fabrication and optimization of light-emitting diodes and light-emitting transistors. Light-emitting transistors are particularly interesting owing to the additional control of the gate voltage on the electroluminescence. In this work, the design of a microcavity, with a defect mode that can be tuned with an applied voltage, integrated with a metal halide light-emitting transistor is shown. The optical properties of the device have been simulated with the transfer matrix method, considering the wavelength-dependent refractive indexes of all the employed materials. The tunability of the microcavity has been obtained via the employment of doped semiconductor nanocrystalline films, which show a tunable plasma frequency and, thus, a tunable refractive index as a function of the applied voltage. Consequently, the tunability of the electroluminescence of the metal halide perovskite light-emitting transistor has been demonstrated. [ABSTRACT FROM AUTHOR]

Abstract Unbalanced mobility and injection of charge carriers in metal‐halide perovskite light‐emitting devices pose severe limitations to the efficiency and response time of the electroluminescence. Modulation of gate bias in methylammonium lead iodide light‐emitting transistors has proven effective in increasing the brightness of light emission up to MHz frequencies. In this work, a new approach is developed to improve charge carrier injection and enhance electroluminescence of perovskite light‐emitting transistors by independent control of drain–source and gate–source bias voltages to compensate for space‐charge effects. Optimization of bias pulse synchronization induces a fourfold enhancement of the emission intensity. Interestingly, the optimal phase delay between biasing pulses depends on modulation frequency due to the capacitive nature of the devices, which is well captured by numerical simulations of an equivalent electrical circuit. These results provide new insights into the electroluminescence dynamics of AC‐driven perovskite light‐emitting transistors and demonstrate an effective strategy to optimize device performance through independent control of the amplitude, frequency, and phase of the biasing pulses.

Near‐infrared light‐emitting technology is ideal for noncontact diagnostic medical imaging and high‐speed data communications. High‐quality ReSe2 nanosheets of anisotropic single‐crystal structure with a bandgap of 1.26 eV (≈984 nm) are synthesized with an atmospheric pressure chemical vapor deposition (APCVD) method. The as‐synthesized ReSe2 nanosheets‐fabricated light‐emitting transistors (LETs) exhibit nearly symmetric ambipolar characteristics in electrical transport. Judicious selection of asymmetric platinum (Pt)/chromium (Cr) electrodes, with their work functions matching respectively the conduction‐ and valence‐band edges of ambipolar ReSe2, generates a low turn‐on voltage ReSe2‐LET with the balanced number density and field‐effect mobility of bipolar carriers (i.e., electrons and holes). Room‐temperature near‐infrared electroluminescence (NIR EL) from the frequency‐modulated ReSe2‐LET has been observed unprecedentedly with the assistance of a lock‐in detection system. The NIR EL intensity is tested by varying the bias voltage applied to the ReSe2‐LET devices with different channel lengths. The wavelength of the NIR EL from ReSe2‐LET is differentiated with optical bandpass filters. Room‐temperature angle‐dependent two lobe‐shaped EL pattern manifests the inherent anisotropic in‐plane excitonic polarization of the ReSe2 crystal. The highly stable NIR EL from ReSe2‐LETs provides prospective 2D material‐based ultrathin scalable data communication electronics for future development. [ABSTRACT FROM AUTHOR]

Herein, a built‐in normally off GaN‐based high‐electron‐mobility light‐emitting transistor is designed and simulated. The proposed structure can significantly minimize the device area, eliminate the parasitic component introduced by metal interconnectors, ensure a fail‐safe operation owing to its normally off operating condition, and it affords fabrication simplicity, a preferable quality for display applications. Using 2D computer‐aided design software (Silvaco's TCAD), the device's electrical and optical features are investigated, revealing good output power linearity and light intensity control by the gate voltage. [ABSTRACT FROM AUTHOR]

Organic light‐emitting transistors (OLET) evolved from the fusion of the switching functionality of field‐effect transistors (FET) with the light‐emitting characteristics of organic light‐emitting diode (OLED) that can simplify the active‐matrix pixel device architecture and hence offer a promising pathway for future flat panel and flexible display technology. This review systematically analyzes the key device/molecular engineering tactics that assist in improving the electrode edge narrow emission to wide‐area emission for display applications via three different topics, that is, narrow to wide‐area emission, vertical architecture, and impact of high‐κ dielectric on the device performance. Source–drain electrode engineering such as symmetric/asymmetric, planar/non‐planar arrangement, semitransparent nature, multilayer approach comprising charge transport, and work function modification layers enable widening the emission zone. Vertical OLET architecture offers short channel lengths with a high aperture ratio, pixel type area emission, and stable light‐emitting area. Transistors utilizing high‐κ dielectric materials have assisted in lowering the operating voltage, enhancing luminance and air stability. The promising development in achieving wide‐area emission provides a solid basis for constructing OLET research toward display applications; however, it relies on developing highly luminescent and fast charge transporting materials, suitable semitransparent source/drain electrodes, high‐κ ‐dielectrics, and device architectural engineering. [ABSTRACT FROM AUTHOR]

Organic light‐emitting transistors (OLETs) are emerging as a type of multifunctional devices that integrate the electrical switching and the light‐emitting function. Among the various device structures, multilayer OLETs have shown superior performance due to their flexibility in structure design and material choice. However, multilayer OLETs usually work in the unipolar mode, resulting in extreme unbalance between the holes and electrons, restricting the further improvement of their performance. Here, an investigation of the hole blocking layer (HBL) is presented. The results show that a high electron mobility is not necessarily in a first place when choosing the HBL, while a deeper highest occupied molecular orbital level of the HBL can better facilitate the exciton recombination efficiency. By using bis[(4‐tert‐butylphenyl)‐1,3,4‐oxadiazolyl]phenylene instead of commonly used bathophenanthroline (Bphen) as the HBL, the external quantum efficiency (EQE) is more than doubled for a blue fluorescent OLET, and an EQE as high as 10.3% is achieved in a green phosphorescent OLET with a maximum brightness of ≈8000 cd m−2. The findings in this work highlight the importance of carrier blocking in building high efficiency OLETs and might provide some guidance for their structure design and material choice. [ABSTRACT FROM AUTHOR]

The rapid development of charge transporting and light‐emitting organic materials in the last decades has advanced device performance, highlighting the high potential of light‐emitting transistors (LETs). Demonstrated for the first time over 15 years ago, LETs have transformed from an optoelectronic curiosity to a serious competitor in the race for cheaper and more efficient displays, also showing promise for injection lasers. Thus, what is an LET, how does it work, and what are the current challenges for its integration into mainstream technologies? Herein, some light is shed on these questions. This work also provides the fundamental working principle of LETs, materials that have been used, and device physics and architectures involved in the progression of LET technology. The state‐of‐the‐art development of LETs is also explored as prospect avenues for the future of research and applications in this area. [ABSTRACT FROM AUTHOR]

Abstract: Exciton‐polaritons are quasiparticles with hybrid light–matter properties that may be used in new optoelectronic devices. Here, electrically pumped ultrastrongly coupled exciton‐polaritons in a high‐mobility donor–acceptor copolymer are demonstrated by integrating a light‐emitting field‐effect transistor into a metal‐clad microcavity. Near‐infrared electroluminescence is emitted exclusively from the lower polariton branch, which indicates efficient relaxation. A coupling strength of 24% of the exciton transition energy implies the system is in the ultrastrong coupling regime with a narrow and almost angle‐independent emission. The lower polariton energy, which can be adjusted by the cavity detuning, strongly influences the external quantum efficiency of the device. Driving the transistors at ambipolar current densities of up to 4000 A cm−2 does not decrease the coupling strength or polariton emission efficiency. Cavity‐integrated light‐emitting field‐effect transistors thus represent a versatile platform for polariton emission and polaritonic devices. [ABSTRACT FROM AUTHOR]

The fabrication of highly efficient deep-blue organic light-emitting field-effect transistors (OLEFETs) remains a challenge due to the large energy bandgap of deep-blue emitters. In this work, an effective strategy is developed by combining an ambipolar charge transport material with an efficient deep-blue fluorescent emitter that features the hybridized local and charge-transfer (HLCT) excited state character in a trilayer device architecture. The ambipolar nature of charge transport material endows the device with a relatively high hole-electron recombination efficiency, while the HLCT excited state character of the emitter offers the device a high singlet exciton yield. The device exhibits a maximum brightness of 710 cd m−2 and a maximum external quantum efficiency (EQE) of 0.28%, which is the first example of deep-blue OLEFETs. Unlike conventional OLEFETs, the devices presented herein display high EQEs during almost the entire illumination. The EQE of device at the maximum brightness reaches 0.20%, which is the highest value among the reported blue OLEFETs. Moreover, the device exhibits an excellent color purity with a sharp emission peak at 445 nm, a narrow full-width at half-maximum of 58 nm, and a Commission Internationale de l'Eclairage coordinates of (0.15, 0.06) that is very close to the National Television System Committee standard blue (0.14, 0.08). [ABSTRACT FROM AUTHOR]

Thiophene-phenylene co -oligomers (TPCOs) have shown their high potential for organic light-emitting devices because of their high luminescence and efficient charge transport. However, unsubstituted TPCOs have relatively wide optical bandgaps and the high-lying lowest unoccupied molecular orbital (LUMO) energies so that efficient electron transport is a challenge. Electron-withdrawing groups (EWGs) and fluorinated fragments embedded into the TPCO molecule structure could result in the lower LUMO energy and narrower optical bandgap. Here, we report the synthesis of two novel TPCOs series with either phenylene or perfluorinated phenylene central core and end-capped with various EWGs (aldehyde, 2-ethylhexyl cyanoacetate, hexyl rhodanine and dicyanorhodanine) and with long alkyl terminal and side chains increasing the solubility. All the oligomers synthesized were found to be thermally stable and crystalline materials with relatively low LUMO energies (down to −3.50 eV), narrow bandgaps (down to 1.9 eV), and efficient photoluminescence in the green – deep red spectral regions both in solution and solid-state. The TPCOs with 2-ethylhexyl cyanoacetate EWG were crystallized in large-area single-crystal monolayers, which showed strongly polarized photoluminescence and demonstrated their high potential as active layers in solution-processed single-layer organic light-emitting transistors. [Display omitted] • Donor-acceptor low-bandgap thiophene-phenylene co-oligomers (TPCOs) were reported. • Impact of the acceptor groups and fluorinated phenylene unit on the properties was evaluated. • TPCOs show strong photoluminescence (PL) in the green – deep red spectral regions. • CNA-based TPCOs form large-area single-crystal monolayers showing polarized PL. • Some TPCOs showed a high potential in organic light-emitting transistors. [ABSTRACT FROM AUTHOR]

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/m 2 ) and current density (1.2 to 2700 mA/cm 2 ) 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.

Highlights: [•] A double roll-printing scheme is used to implement two different types of organic nanofibers. [•] Upon AC biasing, clear multicolor (green and blue) electroluminescence is observed. [•] The electroluminescence can be both spatially and spectrally separated. [•] A correlation between the threshold voltage for transport and the onset voltage for light emission is seen. [Copyright &y& Elsevier]

Highlights: [•] We propose a novel concept for multi-color light-emission transistors. [•] RGB light emission was demonstrated in 9,10-bis-(2,2-diphenylvinyl)-anthracene. [•] Each of these different colors corresponds to a distinguishable light polarization. [Copyright &y& Elsevier]

Light-emitting transistors (LETs) have attracted tremendous academic and industrial interest due to their dual functions of electrical switching and light emission in a single device, which can considerably reduce system complexity and manufacturing costs, especially in the area of flat panel and flexible displays as well as lighting and lasers. In recent years, enhanced LET performance has been achieved by introducing multiple-layer heterostructures in the charge-carrying/light-emitting LET channel versus the best-reported performance in single active layer LETs, rendering multi-layer LETs promising candidates for next-generation display technologies. In this review, the fundamental structures and working principles of multi-layer heterostructure LETs are introduced. Next, developments in multi-layer LETs are discussed based on co-planar LETs, non-planar LETs, and vertical LETs including organic, quantum dot, and perovskite light emitters. Finally, this review concludes with a summary and a perspective on the future of this research field., (© 2021 Wiley-VCH GmbH.)

Light-emitting transistors (LETs) have attracted a significant amount of interest as multifunctional building blocks for next-generation electronics and optoelectronic devices. However, it is challenging to obtain LETs with a high carrier mobility and uniform light-emission because the semiconductor channel should provide both the electrical charge transport and optical light-emission, and typical emissive semiconductors have low, imbalanced carrier mobilities. In this work, a novel device platform that adapts the electrochemiluminescence (ECL) principle in LETs, referred to as an ECL transistor (ECLT) is proposed. ECL is a light-emission phenomenon from electrochemically excited luminophores generated by redox reactions. A solid-state ECL electrolyte consisting of a network-forming polymer, ionic liquid, luminophore, and co-reactant is employed as the light-emitting gate insulator of the ECLT. Based on this construction, high-performance LETs that make use of various conventional non-emissive semiconductors (e.g., poly(3-hexylthiophene), zinc oxide, and reduced graphene oxide) are successfully demonstrated. All the devices exhibit a high mobility (0.9-10 cm 2 V -1 s -1 ) and a uniform light-emission. This innovative approach demonstrates a novel LET platform and provides a promising pathway to achieve significant breakthroughs to develop electronic circuits and optoelectronic applications., (© 2020 Wiley-VCH GmbH.)

2D semiconductors have shown great potential for application to electrically tunable optoelectronics. Despite the strong excitonic photoluminescence (PL) of monolayer transition metal dichalcogenides (TMDs), their efficient electroluminescence (EL) has not been achieved due to the low efficiency of charge injection and electron-hole recombination. Here, multioperation-mode light-emitting field-effect transistors (LEFETs) consisting of a monolayer WSe 2 channel and graphene contacts coupled with two top gates for selective and balanced injection of charge carriers are demonstrated. Visibly observable EL is achieved with the high external quantum efficiency of ≈6% at room temperature due to efficient recombination of injected electrons and holes in a confined 2D channel. Further, electrical tunability of both the channel and contacts enables multioperation modes, such as antiambipolar, depletion,and unipolar regions, which can be utilized for polarity-tunable field-effect transistors and photodetectors. The work exhibits great potential for use in 2D semiconductor LEFETs for novel optoelectronics capable of high efficiency, multifunctions, and heterointegration., (© 2020 Wiley-VCH GmbH.)

The class of organic-inorganic lead halides with perovskite crystal structures has recently emerged as promising materials for a variety of practical optoelectronic applications. In particular, hybrid halide perovskite quantum dots possess excellent intrinsic optoelectronic properties such as high color purity (full width at half-maximum of 24.59 nm) and photoluminescence quantum yields (92.7%). In this work, we demonstrate the use of perovskite quantum dot materials as an emissive layer of hybrid light-emitting transistors. To investigate the working mechanism of perovskite quantum dots in light-emitting transistors, we investigated the electrical and optical characteristics under both p-channel and n-channel operation. Using these materials, we have achieved perovskite quantum dot light-emitting transistors with high electron mobilities of up to 12.06 cm 2 ·V -1 s -1 , high brightness of up to 1.41 × 10 4 cd m -2 , and enhanced external quantum efficiencies of up to 1.79% operating at a source-drain potential of 40 V.

Solution‐processed hybrid organic–inorganic perovskite semiconductors have demonstrated remarkable performance for both photovoltaic and light‐emitting‐diode applications in recent years, launching a new field of condensed matter physics. However, their use in other emerging optoelectronic applications, such as light‐emitting field‐effect transistors (LEFETs) has been surprisingly limited, wth only a few low‐performance devices reported. The development of hybrid LEFETs consisting of a solution‐processed self‐organized multiple‐quantum‐well lead iodide perovskite layer grown onto an electron‐transporting In2O3/ZnO heterojunction channel is reported. The multilayer transistors offer bifunctional characteristics, namely, transistor function with high electron mobility (>20 cm2 V−1 s−1) and a large current on/off ratio (>106), combined with near infrared light emission (λmax = 783 nm) and a promising external quantum efficiency (≈0.2% at 18 cd m−2). A further interesting feature of these hybrid LEFETs, in comparison to previously reported structures, is their highly uniform and stable emission characteristics, which make them attractive for smart‐pixel‐format display applications. [ABSTRACT FROM AUTHOR]

The past several years have witnessed tremendous developments of metal halide perovskite (MHP)-based optoelectronics. Particularly, the intensive research of MHP-based light-emitting diodes, photodetectors, and solar cells could probably reform the optoelectronic semiconductor industry. In comparison, in spite of the large intrinsic charge carrier mobility of MHPs, the development of MHP-based field-effect transistors (MHP-FETs) is relatively slow, which is essentially due to the gate-field screening effect induced by the ion migration and accumulation in MHP-FETs. This work mainly aims to summarize the recent important work on MHP-FETs and propose solutions in terms of the development bottleneck of perovskite-based transistors, in an attempt to boost the research of MHP transistors further. First, the advantages and potential applications of MHP-FETs are briefly introduced, which is followed by a detailed description of the MHP crystalline structure and various material fabrication techniques. Afterward, MHP-FETs are discussed, including transistors based on hybrid organic-inorganic perovskites, all-inorganic perovskites, and lead-free perovskites., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We report the development of low operating voltages in inorganic-organic hybrid light-emitting transistors (HLETs) based on a solution-processed ZrO x gate dielectric and a hybrid multilayer channel consisting of the heterojunction In 2 O 3 /ZnO and the organic polymer "Super Yellow" acting as n- and p-channel/emissive layers, respectively. Resulting HLETs operate at the lowest voltages reported to-date (<10 V) and combine high electron mobility (22 cm 2 /(V s)) with appreciable current on/off ratios (≈10 3 ) and an external quantum efficiency of 2 × 10 -2 % at 700 cd/m 2 . The charge injection, transport, and recombination mechanisms within this HLET architecture are discussed, and prospects for further performance enhancement are considered.

Following the unprecedented rise in photovoltaic power conversion efficiencies during the past five years, metal-halide perovskites (MHPs) have emerged as a new and highly promising class of solar-energy materials. Their extraordinary electrical and optical properties combined with the abundance of the raw materials, the simplicity of synthetic routes, and processing versatility make MHPs ideal for cost-efficient, large-volume manufacturing of a plethora of optoelectronic devices that span far beyond photovoltaics. Herein looks beyond current applications in the field of energy, to the area of large-area electronics using MHPs as the semiconductor material. A comprehensive overview of the relevant fundamental material properties of MHPs, including crystal structure, electronic states, and charge transport, is provided first. Thereafter, recent demonstrations of MHP-based thin-film transistors and their application in logic circuits, as well as bi-functional devices such as light-sensing and light-emitting transistors, are discussed. Finally, the challenges and opportunities in the area of MHPs-based electronics, with particular emphasis on manufacturing, stability, and health and environmental concerns, are highlighted., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Area emission is realized in all-solution-processed hybrid light-emitting transistors (HLETs). A new HLET design is presented with increased aperture ratio, and optical and electrical characteristics are shown., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)