Application In Organic Devices Research Articles

C1 symmetric dual-carboxyl-functionalized BODIPY dye: Synthesis, photophysical properties, and self-assembly behavior via hydrogen bonding

A BODIPY derivatives 3 with phenylethynyl bridging two carboxyl groups was synthesized via Sonogashira cross-coupling reaction. The structure was characterized by 1HNMR and HRMS. Its photophysical properties and aggregation behavior in solution were studied by UV–Vis absorption and fluorescence spectroscopy. The compound 3 displays strong absorption and high fluorescence quantum yield. The investigations of UV–Vis and emission also revealed the formation of self-assembled structures in the solid state or liquid/state with translationally slipped π-stacks of BODIPY units driven by hydrogen bonding between the carboxyl groups. The thermodynamic properties of the BODIPY derivative were carried out by DSC and TGA, indicating it possesses high thermal stability. In addition, the self-assembly of the BODIPY derivative functionalized with two carboxyl groups was explicitly investigated by using scanning tunneling microscopy (STM). The highly ordered supramolecular self-assembly monolayers endow the novel carboxyl functionalized BODIPY with good potential for application in organic devices.

Oxygen-Induced Lattice Strain for High-Performance Organic Transistors with Enhanced Stability.

Integrating the merits of low cost, flexibility, and large-area processing, organic semiconductors (OSCs) are promising candidates for the next-generation electronic materials.The mobility and stability are the key figures of merit for its practical application. However, it is greatly challenging to improve the mobility and stability simultaneously owing to the weak interactions and poor electronic coupling between OSCs molecules. Here, an oxygen-induced lattice strain (OILS) strategy is developed to achieve OSCs with both high mobility and high stability. Utilizing the strategy, the maximum mobility of dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) organic field-effect transistor (OFET) rises to 15.3cm2 V-1 s-1 and the contact resistance lowers to 25.5Ωcm. Remarkably, the thermal stability of DNTT is much improved, and a record saturated power density of ≈3.4×104 Wcm-2 is obtained. Both the experiments and theoretical calculations demonstrate that the lattice compressive strain induced by oxygen is responsible for their high performance and stability. Furthermore, the universality of the strategy is manifested in both n-type and p-type small OSCs. This work provides a novel strategy to improve both the mobility and the stability of OSCs, paving the way for the practical applications of organic devices.

Bio Medical Applications of Organic Devices

Bio Medical Applications of Organic Devices

Orientation in large-area semiconducting 2-amino-anthracene thin films fabricated by dynamic floating film transfer method

In organic electronics, fabrication of stable, soluble, and uniform thin films of large surface area is highly important for a wide range of organic device applications. However, these objectives are difficult to achieve when using organic liquid crystalline molecules. This work focuses on a molecular organic material synthesized in our lab which was used to fabricate large-area thin films by applying the recently developed ribbon-shaped floating film transfer method (FTM). After establishing the most optimal casting parameters, organic molecule thin films of large surface area (up to 15 cm in length and 2 cm in width) were obtained. Subsequent polarized optical microscopy and atomic force microscopy investigations confirmed that film morphology and texture was uniform. Further, UV spectroscopy measurements using a polarizer were performed to study the π-π conjugation, indicating that the films exhibited optical anisotropy, as a Dichroic Ratio (DR) of 3.8 was obtained, with a 10 nm redshift in parallel FTM relative to the spin-coating method.

High‐Resolution Electronic Excitation and Emission Spectra of Pentacene and 6,13‐Diazapentacene Monomers and Weakly Bound Dimers by Matrix‐Isolation Spectroscopy

N‐Heteropolycycles are among the most promising candidates for applications in organic devices. For this purpose, a profound understanding of the low‐energy electronic absorbance and emission characteristics is of crucial importance. Herein, we report high‐resolution absorbance and fluorescence spectra of pentacene (PEN) and 6,13‐diazapentacene (DAP) in solid neon obtained using the matrix‐isolation technique. Accompanying DFT calculations allow the assignment of specific vibrationally resolved signals to corresponding modes. Furthermore, we present for the first time evidence for the formation of van der Waals dimers of both substances. These dimers exhibit significantly different optical characteristics resulting from the change of electronic properties evoked by the incorporation of sp2 nitrogen into the molecular backbone.

Highly Stable Contact Doping in Organic Field Effect Transistors by Dopant-Blockade Method.

In organic device applications, a high contact resistance between metal electrodes and organic semiconductors prevents an efficient charge injection and extraction, which fundamentally limits the device performance. Recently, various contact doping methods have been reported as an effective way to resolve the contact resistance problem. However, the contact doping has not been explored extensively in organic field effect transistors (OFETs) due to dopant diffusion problem, which significantly degrades the device stability by damaging the ON/OFF switching performance. Here, the stability of a contact doping method is improved by incorporating "dopant-blockade molecules" in the poly(2,5-bis(3-hexadecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT) film in order to suppress the diffusion of the dopant molecules. By carefully selecting the dopant-blockade molecules for effectively blocking the dopant diffusion paths, the ON/OFF ratio of PBTTT OFETs can be maintained over 2 months. This work will maximize the potential of OFETs by employing the contact doping method as a promising route toward resolving the contact resistance problem.

Synthesis of Phenanthro[9,10‐d]imidazoles and their Potential Applications in Solution Processable Bottom‐Gated OFETs

AbstractPhenanthro[9,10‐d]imidazole is synthesized by employing Radziszewski method and further functionalized through palladium catalyzed Suzuki cross‐coupling reaction. Solution processable organic field‐effect transistors (OFETs) are assembled in bottom gate‐top contact architecture. A binary solvent system comprising of chloroform/toluene in the ratio of 1/1 is preferred for the deposition of active semiconducting layer. The fabricated devices demonstrated excellent p‐type characteristics with a good mobility, high ON/OFF ratio of 109 and a minimum threshold voltage of −4.5 V. Computational investigations indicted proper charge separation of the energy levels for the phenanthro[9,10‐d]imidazole containing nitro group. Frontier molecular orbitals and the packing patterns obtained from computational studies suggest an efficient band gap for better device operation. The ordered morphologies of the molecules obtained from SEM analysis prove to be beneficial in the OFET performance. The photophysical, electrochemical and thermal properties of the molecules are studied in detail. The research work majorly emphasized on structural designing of the phenanthro[9,10‐d]imidazoles for potential applications in organic devices.

Study of Dactylopius opuntiae and its electrical properties as thin film for application in organic devices

In this work, we perform morphological and physicochemical studies of Dactylopius opuntiae (cochineal) with electron microscopy and explore their use as a transporting layer for organic electronic devices. The charge transport properties of this pigment were investigated through current-voltage measurements. The current-voltage characteristics have shown that the cochineal can be used as a hole-transporting layer (HTL) with mobility of 5.30 ± 0.03 × 10−4cm2V−1 s−1. Different analyses were realized on this pigment and the results were compared with other HTL organic compounds, as Poly(3,4-ethylene dioxy thiophene): poly(styrene sulfonate) (PEDOT:PSS). The results show that the cochineal pigment does not produce luminescence and has a band gap of 2.6 ± 0.2 eV with optical absorption in the visible range. The roughness of cochineal thin films was measured after filtering the solution with a value of 11.8 ± 0.2 nm. Cochineal and PEDOT:PSS were successfully used as HTL in the fabrication of a [Ir(fliq)2acac] based PHOLED. The results show an increase in the electroluminescent color purity emission due to the filtering action of the natural pigment when compared with the PEDOT:PSS based in this device.

Organic Semiconductors: Fast‐Response, Highly Air‐Stable, and Water‐Resistant Organic Photodetectors Based on a Single‐Crystal Pt Complex (Adv. Mater. 2/2020)

The success of any organic device ultimately relies on two factors: mobility and stability under ambient and extreme conditions. Toward this goal, in article number 1904634, Norman Lu, Xiaosheng Fang, Jr-Hau He, and co-workers develop a Pt-complex-based organic semiconductor with high mobility and stability, as an active channel and/or photoabsorption layer for high-performance organic device applications. The device displays the highest combined efficiency and stability reported to date for an organic semiconductor.

Feasibility of a low-power, low-voltage complementary organic thin film transistor buskeeper physical unclonable function

This paper demonstrates an implementation of physical unclonable function (PUF) using complementary organic transistors operating at low-voltage. PUF is an essential security element, and is important for various applications of organic devices. We implement a simple buskeeper PUF, which consists of two inverters. We confirm that the PUF bit values on the test chip can be read at a standard voltage for electronic circuits (3.3 V) via a standardized circuit board interface. We observed a low static current consumption (11.8 μA/90 bits) for the PUF chip. The PUF performance, chip-to-board interface performance, and requirements for the board interface in an organic transistor chip are discussed based on the measurement results of the test chip.

Solution-processed electrical doping of organic semiconductors and their application for organic devices

An economically expedient and simple method to improve charge injection and transport through organic semiconductors via solution processed low concentration doping is suggested Two organic species Pyronin B PyB and Acridine Orange AO dissolved in butanone have been used as dopants for a conjugated polymer Ultraviolet photoelectron spectroscopy UPS and UV vis NIR absorption spectroscopy studies confirmed that charge transfer between the organic semiconductor and dopants took place successfully It should also be noted that the doping efficiency of the dopants is strongly dependent on the intrinsic properties of the conjugated polymers

Synthesis and Properties of a Highly Congested Tri(9-anthryl)methyl Radical.

The synthesis of persistent, neutral organic radicals is challenging because of their inherent reactivities. Herein, we report the synthesis and characterization of a highly congested mesityl-substituted tri(9-anthryl)methyl (TAntM) radical (1). The scaffold was successfully synthesized by circumventing the steric hindrance imposed by the bulky groups surrounding the central methyl carbon atom. The radical has a threefold propeller structure, and the unpaired electron is mainly localized on the central carbon atom. Owing to its congested structure, 1 is remarkably stable, which facilitated handling under ambient conditions. Evaluation of the dynamic behavior of the TAntM scaffold indicated that the stability is due to the bulky anthryl units and the mesityl substituents. Because of its high persistence, wide-range absorption, and good reversible redox properties, 1 has promising applications in organic devices.

Enhancing the electrical and thermal stability of organic thin‐film transistors by utilizing fluorinated polyimide and silicon dioxide bilayer gate dielectric

ABSTRACTThe grand vision of next generation electronics is expected to realize via the wholescale industrialization of organic devices. However, one serious obstacle hindering the practical application for organic devices is their instability regardless of it induced by high temperatures or sustained gate bias stress. Herein, pentacene‐based thin‐film transistors (TFTs) with both good heat resistance and high electrical stability were realized. The TFTs, where fluorinated polyimide (ODA–6FDA PI) and a silicon dioxide (SiO2) bilayer are used as gate dielectric, exhibit superior electrical stability under protracted gate bias stress for 150 min (ΔVth ~1 V with voltage range of 30 to −60 V) and are extremely less susceptible to annealing treatment for temperatures up to 150 °C (Δμ/μ0 ~2.9%), as compared to counterparts with a single dielectric layer. We demonstrated that the excellent bias‐stress stability arises from the higher activation energy of defects of fluorinated PI surface based on exponential barrier distribution model and the suppression of charge injection and back‐channel effect via bilayer. Also, the superior thermal stability is ascribed to the restraint of film cracks and phase transformation of pentacene at high temperatures induced by the better match between the thermal expansion coefficients of semiconductor and dielectric. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47013.

Linear and nonlinear optical properties of nano-spherical Perylenetetracarboxylic dianhydride/ITO as a new optical system

In the current work, the thermal evaporation method was used to deposit the Perylenetetracarboxylic dianhydride (PTCDA) into conductive glass titled (ITO glass) as a new trend in the optical spectroscopy nowadays. X-Ray Diffraction (XRD) was evidenced that the PTCDA/ITO thin film has had a nanostructural characteristic, and the crystalline part of the film oriented with (1 0 2) plane. Atomic Force Microscopes (AFM) was definite that the morphology containing nano-spherical particles. The absorption spectra were examined in the UV–Vis-NIR regions and determined the significant parameters such as molar extinction coefficient εmolar, oscillator strength ƒ, electric dipole strength q2 and optical energy gap. The linear optical constant; extinction coefficient, (k), and refractive index (n) were measured using spectrophotometric measurements in the wavelength range 300–2500 nm. The real part and imaginary parts of the dielectric constant and optical conductivity were evaluated and discussed. The third order non-linear susceptibility, χ(3) and nonlinear refractive n(2) were estimated based on generalized Miller's rule and linear refractive index at photon energy from 0.5 to 4 eV. All possible linear and nonlinear parameters are reported for using this material in OLED devices. PTCDA is a promising organic semiconductor for wide-scale application in organic devices and engineering.

Enhancing the Thermal Stability of Organic Field-Effect Transistors by Electrostatically Interlocked 2D Molecular Packing

Thermal instability is one of the major obstacles for the application of organic devices. We report herein for

Synthesis and characterization of two new TiO2-containing benzothiazole-based imine composites for organic device applications.

The effect of the presence of titanium dioxide in two new imines, (E,E)-(butane-1,4-diyl)bis(oxybutane-4,1-diyl) bis(4-{[(benzo[d][1,3]thiazol-2-yl)methylidene]amino}benzoate) (SP1) and (E)-N-[(benzo[d][1,3]thiazol-2-yl)methylidene]-4-dodecylaniline (SP2), on the properties and stability of imine:TiO2 composites for organic device applications were examined. The investigated titanium dioxide (in anatase form, obtained via the sol–gel method) exhibited a surface area of 59.5 m2/g according to Brunauer–Emmett–Teller theory, and its structure is a combination of both meso- and microporous. The average pore diameter calculated by the Barrett–Joyner–Halenda method was 6.2 nm and the cumulative volume of pores was 0.117 m3/g. The imine SP1 exhibited columnar organization (Col), while SP2 revealed a hexagonal columnar crystalline phase (Colhk). The imine:TiO2 mixtures in various weight ratio (3:0, 3:1, 3:2, 3:3) showed a lower energy gap and HOMO–LUMO energy levels compared to pure TiO2. This implies that TiO2 provides not only a larger surface area for sensitizer adsorption and good electron collection, but also causes a shift of the imine energy levels resulting from intermolecular interaction. Also the temperature of the phase transition was slightly affected with the increase of TiO2 concentration in imine-based composites. The changes observed in the Fourier transform middle-infrared absorption (FT-MIR) spectra confirmed the significant influence of TiO2 on structural properties of both investigated imines. Similar interactions of oxygen vacancies existing on the TiO2 surface with SP1 and SP2 were observed. The imine:TiO2 mixtures showed good air stability and reusability, which demonstrates its potential for organic device applications.

Improvement of Cochineal Extract (Dactylopius coccus Costa) Properties Based on the Green Synthesis of Silver Nanoparticles for Application in Organic Devices

The UV-Vis absorption and conductivity properties of the organic sample cochineal (Dactylopius coccus Costa) were modified by using it as a reducing agent in the biosynthesis of silver nanoparticles. This was done in a straightforward way in order to allow its possible application in organic devices. The biosynthesized solution exhibited a hybrid material with a UV-Vis absorbance range from 205 to 650 nm. The sizes of silver nanoparticles of the hybrid material were between 5 and 10 nm. X-ray diffraction (XRD) revealed silver structures, when samples were dried at 100°C. At 40°C, the structures detected were chlorargyrite (AgCl) and silver oxide (Ag2O). The nucleation and subsequent growth of the hybrid thin film on the substrates indicated an increase of clusters and roughness in comparison to thin films made solely from cochineal. The thin films of hybrid materials showed an improvement of 40% in their electrical potential. The stability at room temperature demonstrated that the hybrid material could be useful as a potential candidate for photoactive thin films in organic devices.

In situ one step synthesis of Fe inserted octaethylporphyrin/polyindole: A multifunctional hybrid material with improved electrochemical and electrical properties

We report a facile and novel methodology for synthesis of Fe(II)-octaethylporphyrin/polyindole (Fe-OEP/PIn) hybrid material for electronic and electrochemical applications. The novelty of the work lies in coordination of iron in the OEP cavity and polymerization of indole monomer in a single step at room temperature. The ferric chloride used as oxidizing agent for polymerization of indole and the reduced Fe(II) ions are allowed to occupy the OEP cavity due to strong attraction of Fe(II) state towards porphyrinic cavity. The as synthesised hybrid materials are characterized and further used for fabrication of Schottky diode using a sandwiched structure Al/Fe-OEP-PIn/ITO which shows 0.21 cm2/Vs mobility, 2.1 ideality factor, and 0.60 eV barrier height. The improvement in electrochemical and electronic properties is discussed taking into account of outcome of various characterizations. Our study demonstrates the facile and novel synthesis of Fe-OEP/PIn hybrid material and its electrochemical and organic device applications.

Electronic structure, transport, and collective effects in molecular layered systems.

The great potential of organic heterostructures for organic device applications is exemplified by the targeted engineering of the electronic properties of phthalocyanine-based systems. The transport properties of two different phthalocyanine systems, a pure copper phthalocyanine (CoPc) and a flourinated copper phthalocyanine–manganese phthalocyanine (F16CoPc/MnPc) heterostructure, are investigated by means of density functional theory (DFT) and the non-equilibrium Green’s function (NEGF) approach. Furthermore, a master-equation-based approach is used to include electronic correlations beyond the mean-field-type approximation of DFT. We describe the essential theoretical tools to obtain the parameters needed for the master equation from DFT results. Finally, an interacting molecular monolayer is considered within a master-equation approach.

Adsorption of Phenacenes on a Metallic Substrate: Revisited

Phenacenes represent a class of simple hydrocarbons with appealing physical properties ranging from high charge mobility to superconductivity in combination with chemical robustness that are easily modified to serve as versatile building blocks for tailored structures. As a promising candidate for applications in organic devices, phenacenes are the focus of recent investigations. Thereby, the initial growth behavior starting from a single molecule is controversial. Here, we address the growth of [7]phenacene and [9]phenacene on a Ag(111) surface, studying the details of the initial stage of growth by scanning tunneling microscopy. According to our results, a previously introduced model involving a coverage-dependent phase change with the out-of-plane rotation of molecules in the initial growth stage can be disregarded. Instead, we find evidence for the formation of a new phase on top of an in-plane wetting layer during the initial stage of growth.