Organic Light-emitting Field-effect Transistors Research Articles

Estimation of the Charge Mobility of Phenanthroline derivatives with the view of Density Functional Theory: Reorganization Energy and Charge Transfer Integral are in play

Molecular arrangement and noncovalent interactions in organic materials greatly influence the charge mobility in organic light-emitting diodes (OLEDs), organic photovoltaics (OPVs), and organic field-effect transistors (OFETs). In the light of the this argument, we examined the electronic properties of the phenanthroline derivatives by considering the charge mobility with the combination of density functional theory and Marcus Charge Transfer Theory. The drift electron mobility of the molecule 1 and 2 were determined to 21.13 cm2 V-1 s-1 and 18.00 cm2 V-1 s-1, respectively through J type π⋯π stacking interactions created by small perpendicular distances between the adjacent rings. The effective charge pathways of the molecules were generated with strong π⋯π stacking interactions consolidated by noncovalent interactions in their solid phases. The electron reorganization energy for both molecules were determined smaller than that of holes which means they have n-type semiconductor properties. The charge transfer integrals were calculated with the optimization of molecules’ dimer configurations that the theoretical results demonstrate the charge transfer integral depends on the distance between the stacking rings. High charge transfer integral and small reorganization energy give the high charge mobility fort he semiconductor molecules. Beside the mobility, energy band gap, ionization potential, electron and hole injection barriers of the molecules were interpreted to further understand their electronic properties. Due to the small LUMO values which provide n-type molecule and small electron injection barrier. From the our work both molecules can be effective n type organic semiconductor devices with the high mobility and can be modified for more efficient charge transport in phenanthroline derivatives.

Sequential in-situ growth of layered conjugated polymers for optoelectronics under electrochemical control.

Layered optoelectronic devices are manufactured using multistep procedures that require high precision in the spatial positioning of individual materials. Current technology uses costly and tedious procedures and instrumentation. In this work instead, we propose an approach which exploits the fundamental properties of the substrate to direct the growth of the next layer, here controlled by an electrochemical potential. We have electrochemically synthesized and characterized a series of polymeric materials that are most commonly used in the field. The films produced show gradient monomer ratios embedded in the polymeric film as a function of the distance from the working electrode. Under the optimized conditions, reproducible construction of simple electronic elements, e.g., rectifying diodes, is achieved. We argue that the sequential in situ method leads to gradient composition of polymer chains and the film resulting in the rectification of electric current. We discuss how this system can open new avenues in advanced optoelectronic applications, such as organic light-emitting diodes (OLEDs) or field-effect transistors (OFETs).

Improved Performance of Organic Light-Emitting Transistors Enabled by Polyurethane Gate Dielectric.

Organic light-emitting transistors (OLETs) are multifunctional optoelectronic devices that combine in a single structure the advantages of organic light-emitting diodes (OLEDs) and organic field-effect transistors (OFETs). However, low charge mobility and high threshold voltage are critical hurdles to practical OLET implementation. This work reports on the improvements obtained by using polyurethane films as a dielectric layer material in place of the standard poly(methyl methacrylate) (PMMA) in OLET devices. It was found that polyurethane drastically reduces the number of traps in the device, thereby improving electrical and optoelectronic device parameters. In addition, a model was developed to rationalize an anomalous behavior at the pinch-off voltage. Our findings represent a step forward to overcome the limiting factors of OLETs that prevent their use in commercial electronics by providing a simple route for low-bias device operation.

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.

Microminiature Pressure Sensors Based on Diode Structures

The paper analyzes modern microminiature pressure sensors made on various diode structures, in particular on organic light-emitting diodes, field-effect transistors, photovoltaic elements and multi-circuit piezoresistive sensors. The possible areas of application of such sensors, their main advantages and disadvantages are shown. The study of 4 groups of samples of diode heterostructures based on CdS / ZnS / CuS / CdTe was carried out and the perspective of using pressure sensors based on these materials as an analogue of existing semiconductor devices was shown. On the basis of experimental studies with the application of pressure, twisting and illumination, it is substantiated that these structures are piezoelectric. The complete technological process of the step-by-step creation of these structures is presented. The obtained structures were analyzed: structural diagrams, current-voltage and piezoelectric characteristics in comparison with the characteristics of other piezoelectric materials are given. Possible areas of application of such structures are described. The provided design schemes and parameters of the obtained diode structures may be of interest to a wide range of specialists in the field of sensor technology and automation of various technological processes of microelectronic equipment manufacturing. It is shown that by changing the sensor manufacturing technologies and the concentration of chemical elements in the obtained films, it is possible to change the sensitivity of the sensor and the dynamic range of its operation, adapting the sensor parameters to the field of its application in the relevant measuring electronic equipment and pressure control systems.

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.

Simultaneously improving the quality factor and outcoupling efficiency of organic light-emitting field-effect transistors with planar microcavity.

Organic light-emitting field-effect transistors (OLEFETs) are regarded as an ideal device platform to achieve electrically pumped organic semiconductor lasers (OSLs). However, the incorporation of a high-quality resonator into OLEFETs is still challenging since the process usually induces irreparable deterioration to the electric-related emission performance of the device. We here propose a dual distributed Bragg reflector (DBR)-based planar microcavity, which is verified to be highly compatible with the OLEFETs. The dual DBR planar microcavity shows the great advantage of simultaneously promoting the quality (Q) factor and outcoupling efficiency of the device due to the reduced optical loss. As a result, a moderately high Q factor of ∼160, corresponding to EL spectrum linewidth as narrow as 3.2 nm, concomitantly with high outcoupling efficiency (∼7.1%) has been successfully obtained. Our results manifest that the dual DBR-based planar microcavity is a promising type of resonator, which might find potential applications in improving the spectra and efficiency performance of OLEFETs as well as in OLEFET-based electrically pumped OSLs.

Theoretical Study of the Structural, Optoelectronic, and Reactivity Properties of N-[5′-Methyl-3′-Isoxasolyl]-N-[(E)-1-(-2-)]Methylidene] Amine and Some of Its Fe2+, Co2+, Ni2+, Cu2+, and Zn2+ Complexes for OLED and OFET Applications

Herein, we report the structural, electronic, and charge transfer properties of N-[5′-methyl-3′-isoxasolyl]-N-[(E)-1-(-2-thiophene)] methylidene] amine (L) and its Fe2+, Co2+, Ni2+, Cu2+, and Zn2+ complexes (dubbed A, B, C, D, and E, respectively) using the density functional theory (DFT). All molecules investigated were optimized at the BP86/def2-TZVP/RI level of theory. Single point energy calculations were carried out at the M06-D3ZERO/def2-TZVP/RIJCOSX level of theory. Reorganization energies of the hole and electron (λh and λe) and the charge transfer mobilities of the electron and hole (μe and μh) have been computed and reported. The λe and λh values vary in the order D > E > A > B > C > L and E > A > D > L > C > B, respectively, while μe and μh vary in the order B > C > L > A > E > D and C > B > A > L > E > D, respectively. μh of B (39.5401 cm2·V−1S−1) and C (366.4740 cm2·V−1s−1) is remarkably large, suggesting their application in organic light-emitting diode (OLED) and organic field-effect transistor (OFET) technologies. Electron excitation analysis based on time-dependent (TD)-DFT calculations revealed that charge transfer excitations may significantly affect charge transfer mobilities. Based on charge transfer mobility results, B and C are outstanding and are promising molecules for the manufacture of electron and hole-transport precursor materials for the construction of OLED and OFET devices as compared to L. The results also show that L and all its complexes interestingly have higher third-order NLO activity than those of para-nitroaniline, a prototypical NLO molecule.

Multifunctional Heteropentalenes: From Synthesis to Optoelectronic Applications.

In the broad family of heteropentalenes, the combination of two five-membered heterocyclic rings fused in the [3,2-b] mode has attracted the most significant attention. The relatively straightforward access to these structures, being a consequence of the advances in the last two decades, combined with their physicochemical properties which match the requirements associated with many applications has led to an explosion of applied research. In this Perspective, we will discuss the recent progress of heteropentalenes’ usefulness as an active element of organic light-emitting diodes and organic field-effect transistors. Among the myriad of possible combinations for the different heteroatoms, thieno[3,2-b]thiophenes and 1,4-dihydropyrrolo[3,2-b]pyrroles are subject to the most intense studies. Together they comprise a potent optoelectronics tool resulting from the combination of appreciable photophysical properties, chemical reactivity, and straightforward synthesis.

Remove the water-induced traps toward improved performance in organic solar cells

Clusters of water molecules have low ionization energies because of stabilization of charge from the dipole moment of surrounding molecules, and thus can form potential traps resulting in the undesirable photovoltaic performance in organic solar cells (OSCs). Herein, we demonstrated a solvent-water evaporation (SWE) strategy, which can effectively remove the water-induced traps that are omnipresent in photoactive layers, leading to a significant improvement in device performance. A higher power conversion efficiency of 17.10% and a better device photostability are achieved by using this SWE method, as compared with the untreated binary PM6:Y6 system (15.83%). We highlight the water-related traps as a limiting factor for carrier transport and extraction properties, and further reveal the good universality of the SWE strategy applied into OSCs. In addition, organic light-emitting diodes and organic field-effect transistors are investigated to demonstrate the applicability of this SWE approach. This strategy presents a major step forward for advancing the field of organic electronics.

Large Area Emission in p-Type Polymer-Based Light-Emitting Field-Effect Transistors by Incorporating Charge Injection Interlayers.

Organic light-emitting field-effect transistors (LEFETs) provide the possibility of simplifying the display pixilation design as they integrate the drive-transistor and the light emission in a single architecture. However, in p-type LEFETs, simultaneously achieving higher external quantum efficiency (EQE) at higher brightness, larger and stable emission area, and high switching speed are the limiting factors for to realise their applications. Herein, we present a p-type polymer heterostructure-based LEFET architecture with electron and hole injection interlayers to improve the charge injection into the light-emitting layer, which leads to better recombination. This device structure provides access to hole mobility of ~2.1 cm2 V−1 s−1 and EQE of 1.6% at a luminance of 2600 cd m−2. Most importantly, we observed a large area emission under the entire drain electrode, which was spatially stable (emission area is not dependent on the gate voltage and current density). These results show an important advancement in polymer-based LEFET technology toward realizing new digital display applications.

Insight into the structures and dynamics of organic semiconductors through solid-state NMR spectroscopy

Organic semiconductors (OSCs) are of fundamental and technological interest, owing to their properties and functions in a range of optoelectronic devices, including organic light-emitting diodes, organic photovoltaics and organic field-effect transistors, as well as emerging technologies, such as bioelectronic devices. The solid-state organization of the subunits in OSC materials, whether molecular or polymeric, determines the properties relevant to device performance. Nevertheless, the systematic relationships between composition, structure and processing conditions are rarely fully understood, owing to the complexity of the organic architectures and the resulting solid-state structures. Characterization over different length scales and timescales is essential, especially for semi-ordered or amorphous regions, for which solid-state NMR (ssNMR) spectroscopy yields nanoscale insight that can be correlated with scattering measurements and macroscopic property analyses. In this Review, we assess recent results, challenges and opportunities in the application of ssNMR to OSCs, highlighting its role in state-of-the-art materials design and characterization. We illustrate how insight is obtained on local order and composition, interfacial structures, dynamics, interactions and how this information can be used to establish structure–property relationships. Finally, we provide our perspective on applying ssNMR to the next generation of OSCs and the development of new ssNMR methods. The structure of organic semiconductor thin films influences their performance in optoelectronic devices. This Review highlights how solid-state NMR techniques can be used to investigate the structure, composition and dynamics of organic semiconductors and, thus, establish structure–property relationships.

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.

Thermal-annealing effects on energy level alignment at organic heterojunctions and corresponding voltage losses in all-polymer solar cells

Abstract Matched energy level alignment is a key requirement for efficient organic devices such as organic light-emitting diodes, photovoltaics, and field-effect transistors. The effect of thermal stress/annealing on energy level alignment and related properties of the devices are less discussed compared to the extensively explored effect on morphology and corresponding device performance. Here all polymer solar cells (all-PSCs) are employed to study thermal annealing effects on energy level alignment and the corresponding effect on the device properties of the all-PSCs. It is found that optimized energy level alignment can be achieved by thermal annealing. An interface dipole layer at the donor/acceptor interface is introduced by energy level realignment that assists charge generation by reducing geminate recombination so that the voltage loss is dramatically reduced, improving the performance of the all-PSCs.

Vertical Organic Tunnel Field-Effect Transistors

Doping organic semiconductors has become a key technology to increase the performance of organic light-emitting diodes, solar cells, or field-effect transistors (OFETs). However, doping can be used...

Separation in the Roles of Carrier Transport and Light Emission in Light-Emitting Organic Transistors with a Bilayer Configuration.

To develop high-performance organic light-emitting organic field-effect transistors (LE-OFETs), a fundamental problem in organic semiconductors is to compromise light luminescent efficiency for high carrier mobility and vice versa. Therefore, LE-OFETs can avoid this problem by separating the light-emission and carrier-transport functions. Here, a bilayer LE-OFET composed of a tetracene crystal as a carrier transporter (bottom crystal) and a 4-(dicyanomethylene)-2-methyl-6-( p-dimethylaminostyryl)-4 H-pyran (DCM1)-doped tetracene crystal as a light emitter (top crystal) was fabricated. Red light-emission color, which is distinct from the green emission color of tetracene, was detected in the top crystal. Light emission from the top layer was prohibited when an insulating thin film was inserted between the two crystals. These observations indicate that excitons are formed in the bottom crystal and transferred to the top crystal, emitting reddish light. Bilayer LE-OFETs have the advantage of providing both high current density and a bright emission for high-performance light-emitting FETs.

Light-Emitting Field-Effect Transistors Based on Composite Films of Polyfluorene and CsPbBr3 Nanocrystals

Light-emitting organic field-effect transistors (LE-FETs) on the basis of composite films that consist of perovskite nanocrystals (CsPbBr3) embedded in a matrix of conjugated polymer—polyfluorene (PFO)—have been obtained, and their electrical and optical properties have been investigated. Output and transfer current-voltage characteristics (I-Vs) of FETs based on PFO : CsPbBr3 films (component ratio 1 : 1) have a slight hysteresis at temperatures of 100–300 K and are characteristic of hole transport. The hole mobility is ∼3.3 and ∼1.9 cm2/(V s) at the modes of the saturation and low fields, respectively, at 250 K and reaches ∼5 cm2/(V s) at 100 K. It has been shown that the application of pulsed voltage to LE-FETs based on PFO : CsPbBr3 can reduce the ionic conductivity and provide electroluminescence in this structure at 300 K.

Светоизлучающие полевые транзисторы на основе композитных пленок полифлуорена и нанокристаллов CsPbBr-=SUB=-3-=/SUB=-

Abstract—Light-emitting organic field-effect transistors (LE-FETs) on the basis of composite films that consist of perovskite nanocrystals (CsPbBr_3) embedded in a matrix of conjugated polymer—polyfluorene (PFO)—have been obtained, and their electrical and optical properties have been investigated. Output and transfer current-voltage characteristics (I-Vs) of FETs based on PFO : CsPbBr_3 films (component ratio 1 : 1) have a slight hysteresis at temperatures of 100–300 K and are characteristic of hole transport. The hole mobility is ∼3.3 and ∼1.9 cm^2/(V s) at the modes of the saturation and low fields, respectively, at 250 K and reaches ∼5 cm^2/(V s) at 100 K. It has been shown that the application of pulsed voltage to LE-FETs based on PFO : CsPbBr_3 can reduce the ionic conductivity and provide electroluminescence in this structure at 300 K.

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...

Nanocage-Confined Synthesis of Fluorescent Polycyclic Aromatic Hydrocarbons in Zeolite.

Polycyclic aromatic hydrocarbons (PAHs) attract much attention for applications to organic light-emitting diodes, field-effect transistors, and photovoltaic cells. The current synthetic approaches to PAHs involve high-temperature flash pyrolysis or complicated step-by-step organic reactions, which lead to low yields of PAHs. Herein, we report a facile and scalable synthesis of PAHs, which is carried out simply by flowing acetylene gas into zeolite under mild heating, typically at 400 °C and generates the products of 0.30 g g-1 zeolite. PAHs are synthesized via acetylene polymerization inside Ca2+-ion-exchanged Linde type A (LTA) zeolite, of which the α-cage puts a limit on the product molecular size as a confined-space nanoreactor. The resultant product after the removal of the zeolite framework exhibits brilliant white fluorescence emission in N-methylpyrrolidone solution. The product is separated into four different color emitters (violet, blue, green, and orange) by column chromatography. Detailed characterizations of the products by means of various spectroscopic methods and mainly mass spectrometric analyses indicate that coronene (C24H12) is the main component of the blue emitter, while the green emitter is a mixture of planar and curved PAHs. The orange can be attributed to curved PAHs larger than ovalene, and the violet to smaller molecules than coronene. The PAH growth mechanism inside Ca2+-exchanged LTA zeolite is proposed on the basis of mass spectral analyses and density functional theory calculations.