Development Of Organic Electronic Devices Research Articles

Poly(4‐methoxyaniline) composites: Investigating structure–property relationship towards semiconducting applications

ABSTRACTConjugated polymers are essential materials for the organic optoelectronic industry, serving a pivotal role in cutting‐edge technologies. In this study, we conducted an integrated characterization approach, including spectroscopic techniques coupled with X‐ray diffraction analysis to explore the structure–property relationship of poly(4‐methoxyaniline), commonly referred to as poly(p‐anisidine) or PPA, along with two distinct ceramic composites: PPA/α‐Al2O3 and PPA/Eu2O3. From powder X‐ray diffraction analysis, a triclinic unit cell in space group P1 is proposed, after the whole powder pattern decomposition (WPPD) refinement is employed for the semicrystalline regions of the polymeric phases. Fractal‐like structures are observed, following analysis of small‐angle X‐ray scattering (SAXS) data and scanning electron microscopy (SEM) from which we could infer the approximate sizes of the fractal clusters. Pure PPA displays a glass transition temperature (Tg) of approximately 80°C and an electrical conductivity slightly above 10−5 S/cm. In contrast, the composite materials do not exhibit a glass transition temperature but perform better in terms of crystallinity and thermal stability. PPA/Eu2O3 present conductivity enhancement exceeding tenfold, surpassing 10−4 S/cm. These findings provide the baseline for further explorations on the development of organic electronic devices and sensors.

Accurate Description of Coulombic Interactions in Organic Field‐Effect Transistors Enabled by Efficient 3D Poisson's Equation Solver with Mixed Boundary Conditions

AbstractThe rational development of organic electronic devices can greatly benefit from a molecular‐level description, where an accurate description of the Coulombic interactions among charge carriers holds paramount importance. However, the molecular‐level organic field‐effect transistor (OFET) simulations do not fully include the short‐range charge‐carrier Coulombic interactions, thus limiting their accuracy. Here, an efficient solution is demonstrated to the 3D Poisson's equation with mixed boundary conditions, optimized for integration into the simulations of organic electronic devices. It leverages the finite difference method for discretization, the Krylov subspace iterative methods for solving the linear system, the algebraic multigrid algorithm for preconditioning, and OpenMP and CUDA parallelization for acceleration. For the organic field‐effect transistors of micrometer sizes or smaller dimensions, obtaining the electric potential within the device takes less than 0.1 s, which is sufficiently efficient for molecular‐level modeling. As a result, both short‐ and long‐range electrostatic interactions are successfully incorporated in the molecular‐level modeling of OFET devices. This integration significantly enhances the robustness of OFET modeling for future applications.

Tuning Dielectric Constant of P3HT by Ultrasound-Induced Aggregation

Poly(3-hexylthiophene) (P3HT), a semiconducting polymer, is integral to the development of organic electronic devices. Its optoelectronic properties are significantly influenced by the nature of its intermolecular interactions, predominantly classified as J-type and H-type couplings. This study investigates the effect of sonication on the dielectric properties of P3HT, focusing on the transition from J-type (or less prominent H-type) to H-type intermolecular interactions, accompanied by disorder-order transformation. The research determined that sonication leads to a significant change in the dielectric properties of P3HT by forming distinct ordered regions interspersed within disordered or quasi-ordered areas. Specifically, there is an observable transition from J-type to H-type aggregation, which has profound effects on the material's electronic structure and optoelectronic performance. This transition was confirmed by changes in the absorption and photoluminescence spectra, indicating a more localized electronic character and the formation of non-emissive excitons in the case of H-aggregates. Increased dielectric constant after sonication is attributed to interface polarization, especially the Maxwell-Wagner-Sillars polarization. This effect is likely because new interfaces are created between the ordered regions and disordered/quasi-ordered regions within the P3HT material, where charges can accumulate as a result of disorder-order transformation. Our research contributes to the broader understanding of polymer physics and the development of organic electronic devices by showing how the manipulation of microstructural environments can control material properties.

Recent Research Progress of Organic Small-Molecule Semiconductors with High Electron Mobilities.

Organic electronics has made great progress in the past decades, which is inseparable from the innovative development of organic electronic devices and the diversity of organic semiconductor materials. It is worth mentioning that both of these great advances are inextricably linked to the development of organic high-performance semiconductor materials, especially the representative n-type organic small-molecule semiconductor materials with high electron mobilities. The n-type organic small molecules have the advantages of simple synthesis process, strong intermolecular stacking, tunable molecular structure, and easy to functionalize structures. Furthermore, the n-type semiconductor is a remarkable and important component for constructing complementary logic circuits and p-n heterojunction structures. Therefore, n-type organic semiconductors play an extremely important role in the field of organic electronic materials and are the basis for the industrialization of organic electronic functional devices. This review focuses on the modification strategies of organic small molecules with high electron mobility at molecular level, and discusses in detail the applications of n-type small-molecule semiconductor materials with high mobility in organic field-effect transistors, organic light-emitting transistors, organic photodetectors, and gas sensors.

Redox-Active Hydrocarbons: Isolation and Structural Determination of Cationic States toward Advanced Response Systems.

Invited for this month's cover is the group of Prof. Yusuke Ishigaki at Hokkaido University, Japan. The cover picture shows a cyclic voltammogram drawn in the style of an ink painting, along with the structures of cationic species composed of pure hydrocarbons. The sunrise, a metaphor for X-rays irradiated on cations, is reminiscent of the dawn of redox chemistry of hydrocarbons. Elucidation of their redox properties should provide important insights into the development of organic electronic devices. The cover was designed by YAP Co., Ltd. More information can be found in the Review by T. Harimoto and Y. Ishigaki.

Front Cover: Redox‐Active Hydrocarbons: Isolation and Structural Determination of Cationic States toward Advanced Response Systems (ChemPlusChem 8/2022)

The cover picture illustrates a cyclic voltammogram drawn in the style of an ink painting. The sunrise, a metaphor for X-rays irradiated on cations, is reminiscent of the dawn of redox chemistry of pure hydrocarbons. Elucidation of their redox properties should provide important insights into the development of organic electronic devices. More information can be found in the Review by T. Harimoto and Y. Ishigaki.

Cover Feature: Multi‐Redox Active Carbons and Hydrocarbons: Control of their Redox Properties and Potential Applications (Chem. Rec. 9/2021)

The cover feature shows the structures of some multi-redox active CxHy molecules (x ≥1, y ≥0) and a representative cyclic voltammogram, and possible applications of such molecules. If controlled, the redox properties of such carbon and hydrocarbon molecules make them attractive candidates for organic batteries, multielectrochromic devices, and information storage devices. In all, 185 multi-redox active CxHy molecules mainly reported in the last decade are classified based on their chemical structures, and their redox properties as solutes and adsorbed species, which underpin the development of organic electronic devices, are summarized. See the Personal Account by H. Ueda and S. Yoshimoto (DOI: 10.1002/tcr.202100088).

Self-assembly of ClAlPc molecules on moiré-patterned graphene grown on Pt(111)

Phthalocyanines are promising molecules for the development of organic electronic devices, for instance, molecular heterojunctions in organic solar cells or organic field-effect transistors. For an optimum performance of these devices, the molecular ordering on the substrate and the molecular electronic level alignment have been shown as crucial factors. In this work, the self-assembled structure and the electronic structure of chloroaluminum phthalocyanines (ClAlPc) on graphene grown on Pt(111) surfaces have been studied by scanning tunneling microscopy (STM) under ultrahigh vacuum (UHV) and low-temperature conditions. Graphene grown on Pt(111) exhibits multiple moiré patterns with different periodicities, offering a benchmark to investigate the influence of the graphene and the moiré patterns in the ClAlPc ordering. This surface allows to extend previous works performed on graphite and graphene on Cu(100), where no moiré patterns are found. Well-ordered molecular islands exhibiting rotational domains have been observed in the submonolayer regime. The orientation of individual ClAlPc molecules within the structure unit cell has been characterized pointing out to a Cl-Up configuration adopted by the molecules. Our measurements show a correlation between the molecular lattice orientation and the graphene directions, whereas no influence of the underlying moiré patterns has been found. Finally, the ClAlPc electronic structure has been characterized indicating a weak graphene-molecule interaction.

Temperature-Modulated Doping at Polymer Semiconductor Interfaces

Understanding doping in polymer semiconductors has important implications for the development of organic electronic devices. This study reports a detailed investigation of the doping of the poly(3-hexylthiophene) (P3HT)/Nafion bilayer interfaces commonly used in organic biosensors. A combination of UV–visible spectroscopy, dynamic secondary ion mass spectrometry (d-SIMS), dynamic mechanical thermal analysis, and electrical device characterization reveals that the doping of P3HT increases with annealing temperature, and this increase is associated with thermally activated interdiffusion of the P3HT and Nafion. First-principles modeling of d-SIMS depth profiling data demonstrates that the diffusivity coefficient is a strong function of the molar concentration, resulting in a discrete intermixed region at the P3HT/Nafion interface that grows with increasing annealing temperature. Correlating the electrical conductance measurements with the diffusion model provides a detailed model for the temperature-modulated doping that occurs in P3HT/Nafion bilayers. Point-of-care testing has created a market for low-cost sensor technology, with printed organic electronic sensors well positioned to meet this demand, and this article constitutes a detailed study of the doping mechanism underlying such future platforms for the development of sensing technologies based on organic semiconductors.

P‐169: Towards Fully Integrated 3D Master Equation — Kinetic Monte Carlo Predictive Device Simulations

In the past decade, the discovery of organic semiconductor materials and the development of organic electronic devices has occurred mostly by experimental trial‐and‐error. In the past years, rational design based on predictive modeling has started playing a larger role in accelerating research and development of organic semiconductor devices. To make this transition possible, we developed and validated advanced predictive simulation software, Bumblebee, based on 3D kinetic Monte Carlo (KMC) and 3D master equation (ME) methods for simulating state‐of‐the art multilayer organic light emitting diode (OLED) stacks. While the 3D‐KMC engine is optimized for high voltages, the 3D‐ME engine is especially suitable for the low voltage regime, making these two engines complementary to each other for efficient simulation of OLED device performance in different operation regimes. To demonstrate the power of predictive modelling, we show several examples of device simulation results obtained with Bumblebee for different OLED stacks. Particular focus will be given to the low current/low voltage range where the impact of traps and energetic disorder on device turn‐on/turn‐off is most important.

Polydiacetylene ribbons formed using the controlled evaporative self-assembly (CESA) method

Abstract

Modeling of Actual‐Size Organic Electronic Devices from Efficient Molecular‐Scale Simulations

AbstractRational development of organic electronic devices requires a molecular insight into the structure–performance relationships that can be established for the organic active layers. However, the current molecular‐scale simulations of these devices are limited to nanometer sizes, well below the micrometer‐sized systems that are needed in order to consider actual‐scale morphologies and to reliably model low dopant concentrations and trap densities. Here, by enabling descriptions of both the short‐range and the long‐range electrostatic interactions in master equation simulations, it is demonstrated that reliable molecular‐scale simulations can be applied to systems 100 times larger than those previously accessible. This quantum leap in the modeling capability allows us to uncover large inhomogeneities in the charge‐carrier distributions. Furthermore, in the case of a blend morphology, charge transport in an actual‐scale device is found to behave differently as a function of applied voltage, compared to the case of a uniform film. By including these features in realistic‐scale descriptions, this methodology represents a major step into a deeper understanding of the operation of organic electronic devices.

Use of Microdischarge Lithography for Development of Organic Electronic Devices over Large Areas

The concept of 'displays everywhere', which may be extended to wearable sensors, signal tags or energy devices, implies ubiquity of electronic devices not only in walls or appliances but integrated in all kind of domestic objects, such as clothes, bags or wrappings, and is expected to preside over our daily lives in the near future. For this expectation to succeed, Electronics industry must face compatibility with three new paradigms: flexible substrates -to be adapted to different surfaces and geometries-, large areas (eventually up to square meters), and lightness. In any case, this revolution can only take place from a drastic reduction of the production costs. As it is well known, these paradigms are difficult to access solely for conventional microelectronics technology based on silicon or other crystalline materials, and many alternatives based in new materials and procedures have been proposed. Thus, a manufacturing facility based in the roll-to-roll (R2R) technology is considered a suitable candidate to achieve high yield over large areas in a cost effective way. In consequence, those patterning techniques compatible with R2R production lines are receiving enhanced attention. In this contribution, we exploit the possibilities of a dry and subtractive lithography based on electrical microdischarges to pattern both electrodes, cathode and anode, of organic devices, particularly displays based in organic light emitting diodes (Fig. 1). Using a homemade prototype rated at technology readiness level 4, we demonstrate that electrical discharge lithography may overcome many obstacles such as tilt correction and relocation after processing, avoiding the use of masks and many of the photolithographic steps. This is thanks to the electrical monitoring during operation as well as a precise electronic control of the position, with 1 µm reproducibility. Since sparks are very fast processes (range of few µs or less) features may be performed at speeds of tens mm/s, ensuring scalability to large areas (cms), and hence compatibility with high throughput manufacturing lines. Of particular interest results patterning of graphene as electrode, due to the practical absence of residues under electrical discharges. Other advantages and drawbacks will be discussed, as well as physical aspects involved. Figure 1

In-Situ GISAXS Study of Supramolecular Nanofibers having Ultrafast Humidity Sensitivity

Self assembled nanofibers derived from donor-acceptor (D-A) pair of dodecyl methyl viologen (DMV) and potassium salt of coronene tetracarboxylate (CS) is an excellent material for the development of organic electronic devices particularly for ultrafast response to relative humidity (RH). Here we have presented the results of in-situ grazing incidence small angle x-ray scattering (GISAXS) measurements to understand aridity dependent self reorganization of the nanofibers. The instantaneous changes in the organization of the nanofibers was monitored with different equilibrium RH conditions. Additionally formation of nanofibers during drying was studied by GISAXS technique – the results show two distinct stages of structural arrangements, first the formation of a lamellar mesophase and then, the evolution of a distorted hexagonal lattice. The RH dependent GISAXS results revealed a high degree of swelling in the lattice of the micelles and reduction in the distortion of the hexagonal structure with increase in RH. In high RH condition, the nanofibers show elliptical distortion but could not break into lamellar phase as observed during formation through drying. This observed structural deformation gives insight into nanoscopic structural changes of the micelles with change in RH around it and in turn explains ultrafast sensitivity in its conductivity for RH variation.

TH-CD-201-12: Preliminary Evaluation of Organic Field Effect Transistors as Radiation Detectors

Purpose: To fabricate organic field effect transistors (OFETs) and evaluate their performance before and after exposure to ionizing radiation. To determine if OFETs have potential to function as radiation dosimeters. Methods: OFETs were fabricated on both Si/SiO2 wafers and flexible polymer substrates using standard processing techniques. Pentacene was used as the organic semiconductor material and the devices were fabricated in a bottom gate configuration. Devices were irradiated using an orthovoltage treatment unit (120 kVp x-rays). Threshold voltage values were measured with the devices in saturation mode and quantified as a function of cumulative dose. Current-voltage characteristics of the devices were measured using a Keithley 2614 SourceMeter SMU Instrument. The devices were connected to the reader but unpowered during irradiations. Results: Devices fabricated on Si/SiO2 wafers demonstrated excellent linearity (R2 > 0.997) with threshold voltages that ranged between 15 and 36 V. Devices fabricated on a flexible polymer substrate had substantially smaller threshold voltages (∼ 4 – 8 V) and slightly worse linearity (R2 > 0.98). The devices demonstrated excellent stability in I–V characteristics over a large number (>2000) cycles. Conclusion: OFETs have demonstrated excellent potential in radiation dosimetry applications. A key advantage of these devices is their composition, which can be substantially more tissue-equivalent at low photon energies relative to many other types of radiation detector. In addition, fabrication of organic electronics can employ techniques that are faster, simpler and cheaper than conventional silicon-based devices. These results support further development of organic electronic devices for radiation detection purposes. Funding Support, Disclosures, and Conflict of Interest: This work was funded by the Natural Sciences and Engineering Research Council of Canada.

Epitaxial Growth of an Organic p-n Heterojunction: C60 on Single-Crystal Pentacene.

Designing molecular p-n heterojunction structures, i.e., electron donor-acceptor contacts, is one of the central challenges for further development of organic electronic devices. In the present study, a well-defined p-n heterojunction of two representative molecular semiconductors, pentacene and C60, formed on the single-crystal surface of pentacene is precisely investigated in terms of its growth behavior and crystallographic structure. C60 assembles into a (111)-oriented face-centered-cubic crystal structure with a specific epitaxial orientation on the (001) surface of the pentacene single crystal. The present experimental findings provide molecular scale insights into the formation mechanisms of the organic p-n heterojunction through an accurate structural analysis of the single-crystalline molecular contact.

A biphenyl containing two electron-donating and two electron-accepting moieties: a rigid and small donor-acceptor-donor ladder system.

Ladder π-conjugated materials and also push-pull systems belong to important classes of compounds for the development of organic electronic devices. In this communication, a novel π-conjugated material that unifies the properties of both of these classes is presented. The material comprises a rigid biphenyl framework, which bears two bridging electron-accepting phosphine oxide moieties as well as two electron-donating amino groups. The structure and photophysical properties of this compound are discussed and compared with those of a related system lacking the second P-moiety.

Relationship between Mobility and Lattice Strain in Electrochemically Doped Poly(3-hexylthiophene).

Conjugated semiconducting polymers, such as poly(3-hexylthiophene) (P3HT), are poised to play an integral role in the development of organic electronic devices; however, their performance is governed by factors that are intrinsically coupled: dopant concentration, carrier mobility, crystal structure, and mesoscale morphology. We utilize synchrotron X-ray scattering and electrochemical impedance spectroscopy to probe the crystal structure and electronic properties of P3HT in situ during electrochemical doping. We show that doping strains the crystalline domains, coincident with an exponential increase in hole mobility. We believe these observations provide guidance for the development of improved theoretical models for charge transport in semiconducting polymers.

Recently Advanced Polymer Materials Containing Dithieno[3,2‐b:2′,3′‐d]phosphole Oxide for Efficient Charge Transfer in High‐Performance Solar Cells

Two novel semiconducting polymers based on benzodithiophene and dithienophosphole oxide (DTP) units are designed and synthesized. A novel electron‐deficient DTP moiety is developed. Surprisingly, the introduction of DTP units brings highly polarizable characteristics, which is beneficial for the photocurrent in solar cells. Thus, the donor–acceptor type of conjugated polymers based on this novel acceptor has superior charge transfer properties and highly efficient PL quenching efficiencies. As a result, polymer solar cells (PSCs) with high power conversion efficiencies of 6.10% and 7.08% are obtained from poly(3,5‐didodecyl‐4‐phenylphospholo[3,2‐b:4,5‐b']dithiophene–4‐oxide‐alt‐4,8‐bis(5‐decylthiophen‐2‐yl)benzo[1,2‐b:4,5‐b']dithiophene) (PDTP–BDTT) and PDTP–4‐oxide‐alt‐4,8‐bis(5‐decylselenophen‐2‐yl)benzo[1,2‐b:4,5‐b']dithiophene) (PDTP–BDTSe), respectively, when the photoactive layer is processed with the 1,8‐octanedithiol (ODT) additive. The PDTP–BDTSe copolymer is now the best performing DTP‐based material for PSCs. Using the polarizable unit strategy determined in this study for the molecular design of conjugated polymers is expected to greatly advance the development of organic electronic devices.

Characteristics of Vertical Type Polymer Light Emitting Transistor Using Dimethyldicyanoquinonediimine as a <I>N</I>-Type Buffer Layer

Contact resistance between a metal electrode and an organic active layer is one of the most critical issues in the research and development of organic electronic devices. In the present work, we have fabricated vertical type organic light emitting transistor (OLET) using P3HT as a organic active semiconductor and DMDCNQI as a charge transfer material. The device configuration is ITO/PEDOT:PSS/P3HT/Al gate/P3HT/DMDCNQI/Al. The characteristics of OLET were investigated from the measurement of current-radiance voltage characteristics The needle form of highly conducting DMDCNQI-Al charge transfer complex was obtained, which resulted in the improvement of device performance due to the low organic-metal contact resistance and the high electron transport ability.