Organic Electronic Devices Research Articles

Optoelectronic conversion and polarization hysteresis in organic MISM and MISIM devices with DA-type single-component molecules.

Organic electronic devices offer various advantages, such as low cost and tunability. However, the organic semiconductors used in these devices have significant drawbacks, including instability in air and low carrier mobility. To address these challenges, we recently introduced organic MISM and MISIM (M = metal, I = insulator, S = semiconductor) devices, which effectively generate photo-induced displacement current and exhibit ferroelectric behavior. In previous studies, the S layer consisted of an organic donor-acceptor (DA) bilayer. In the present research, we fabricated MISM and MISIM devices using DA-type single-component molecules as the S layer and examined their photocurrent and polarization hysteresis. While the performance of these devices does not surpass that of DA bilayer devices, we discovered that DA-type single-component molecules can be utilized for photoelectric conversion and polarization trapping.

Conjugated polymers with near-infrared (NIR) optical absorption: structural design considerations and applications in organic electronics

This review highlights key strategies in structural engineering for achieving near-IR (NIR) optical absorption with conjugated polymers (NIR-CPs), and it details their utility in various organic electronic device applications.

Advancements in π-conjugated polymers: harnessing cycloalkyl straps for high-performance π-conjugated materials.

Pendant alkyl chains are widely used to successfully obtain a wide variety of soluble linear 1D π-conjugated polymers. Over the past several decades, a wide variety of π-conjugated polymers have been synthesized to realize the desired properties and improve the performance of organic electronic devices. However, this strategy is not suitable for generating soluble 2D-π-conjugated materials, including ladder polymers, nanoribbons, and 2D-π-conjugated polymers, due to strong van der Waals interactions between the ribbons and sheets. The drive to synthesize higher dimensional polymers and to enhance polymers' properties has spurred the exploration of a novel direction in materials chemistry-the synthesis of unconventional monomers and polymers. The Gavvalapalli research group has developed and used cycloalkyl straps containing aryl building blocks for the synthesis of conjugated polymers. These cycloalkyl straps, positioned either above or below the π-conjugation plane, have been shown to directly control the π-π interactions between the polymer chains. We have demonstrated that π-face masking cycloalkyl straps hinder interchain π-π interactions. The first part of this review article highlights the use of cycloalkyl straps for the synthesis of higher dimensional π-conjugated polymers. In this section, we discuss the synthesis of 2D-H-mers, dispersible hyperbranched π-conjugated polymers, and conjugated porous polymers without the pendant solubilizing chains. The second part of the feature article highlights how the cycloalkyl straps can be used to gain control over polymer-acceptor interactions, including the interaction strength and the location of the acceptor along the polymer backbone. We conclude the article with the future outlook on cycloalkyl strap-containing building blocks in the world of conjugated polymers.

Carrier behavior of a carbon material assisted TIPS-pentacene composite film for improvement of electrical conductivity.

Organic semiconductor devices have a lower intrinsic carrier density than inorganic semiconductors, and improving their electrical conductivity is important for organic electronic devices. Further theoretical investigations and understanding the properties of these electronic devices are necessary to improve the electrical conductivity of organic devices. In this study, we demonstrate how two carbon-material-assisted organic semiconductor devices affect the electrical conductivity and charge mechanism by using electrical measurements (i.e., I-V and C-V measurements, and numerical simulations). To clearly demonstrate the enhancement of the charge injection into TIPS (6,13-bis(triisopropylsilylethynyl)-pentacene), we studied the blending effect of carbon materials (carbon nanotube and fullerene) in TIPS and discussed injection, transport and charge accumulation of hole and electron in relation to trapped charge. This study will be helpful for understanding charge mechanisms in composite organic semiconductor devices.

Structure-Property Relationships for the Electronic Applications of Bis-Adduct Isomers of Phenyl-C61 Butyric Acid Methyl Ester.

Higher adducts of a fullerene, such as the bis-adduct of PCBM (bis-PCBM), can be used to achieve shallower molecular orbital energy levels than, for example, PCBM or C60. Substituting the bis-adduct for the parent fullerene is useful to increase the open-circuit voltage of organic solar cells or achieve better energy alignment as electron transport layers in, for example, perovskite solar cells. However, bis-PCBM is usually synthesized as a mixture of structural isomers, which can lead to both energetic and morphological disorder, negatively affecting device performance. Here, we present a comprehensive study on the molecular properties of 19 pure bis-isomers of PCBM using a variety of characterization methods, including ultraviolet photoelectron spectroscopy, thermal gravimetric analysis, differential scanning calorimetry, single crystal structure, and (time-dependent) density functional theory calculation. We find that the lowest unoccupied molecular orbital of such bis-isomers can be tuned to be up to 170 meV shallower than PCBM and up to 100 meV shallower than the mixture of unseparated isomers. The isolated bis-isomers also show an electron mobility in organic field-effect transistors of up to 4.5 × 10-2 cm2/(V s), which is an order of magnitude higher than that of the mixture of bis-isomers. These properties enable the fabrication of the highest performing bis-PCBM organic solar cell to date, with the best device showing a power conversion efficiency of 7.2%. Interestingly, we find that the crystallinity of bis-isomers correlates negatively with electron mobility and organic solar cell device performance, which we relate to their molecular symmetry, with a lower symmetry leading to more amorphous bis-isomers, less energetic disorder, and higher dimensional electron transport. This work demonstrates the potential of side chain engineering for optimizing the performance of fullerene-based organic electronic devices.

Ground-state electron transfer in all-polymer donor:acceptor blends enables aqueous processing of water-insoluble conjugated polymers

Water-based conductive inks are vital for the sustainable manufacturing and widespread adoption of organic electronic devices. Traditional methods to produce waterborne conductive polymers involve modifying their backbone with hydrophilic side chains or using surfactants to form and stabilize aqueous nanoparticle dispersions. However, these chemical approaches are not always feasible and can lead to poor material/device performance. Here, we demonstrate that ground-state electron transfer (GSET) between donor and acceptor polymers allows the processing of water-insoluble polymers from water. This approach enables macromolecular charge-transfer salts with 10,000× higher electrical conductivities than pristine polymers, low work function, and excellent thermal/solvent stability. These waterborne conductive films have technological implications for realizing high-performance organic solar cells, with efficiency and stability superior to conventional metal oxide electron transport layers, and organic electrochemical neurons with biorealistic firing frequency. Our findings demonstrate that GSET offers a promising avenue to develop water-based conductive inks for various applications in organic electronics.

Polarity-Induced Morphological Transformation with Tunable Optical Output of Terpyridine-Phenanthro[9,10-d]imidazole-Based Ligand and Its Zn(II) Complexes with I-V Characteristics.

Self-assembled nanostructures obtained from various functional π-conjugated organic molecules have been able to draw substantial interest due to their inherent optical properties, which are imperative for developing optoelectronic devices, multiple-color-emitting devices with color-tunable displays, and optical sensors. These π-conjugated molecules have proven their potential employment in various organic electronic applications. Therefore, the stimuli-responsive fabrication of these π-conjugated systems into a well-ordered assembly is extremely crucial to tuning their inherent optical properties for improved performance in organic electronic applications. To this end, herein, we have designed and synthesized a functional π-conjugated molecule (TP) having phenanthro[9,10-d]imidazole with terpyridine substitution at the 2 position and its corresponding metal complexes (TPZn and (TP)2Zn). By varying the polarity of the self-assembly medium, TP, TPZn, and (TP)2Zn are fabricated into well-ordered superstructures with morphological individualities. However, this medium polarity-induced self-assembly can tune the inherent optical properties of TP, TPZn, and (TP)2Zn and generate multiple fluorescence colors. Particularly, this property makes them useful for organic electronic applications, which require adjustable luminescence output. More importantly, in 10% aqueous-THF medium, TPZn exhibited H-type aggregation-induced white light emission and behaved as a single-component white light emitter. The experimentally obtained results of the solvent polarity-induced variation in optical properties as well as self-assembly patterns were further confirmed by theoretical investigation using density functional theory calculations. Furthermore, we investigated the I-V characteristics, both vertical and horizontal, using ITO and glass surfaces coated with TP, TPZn, and (TP)2Zn, respectively, and displayed maximum current density for the TPZn-coated surface with the order of measured current density TPZn > TP > (TP)2Zn. This observed order of current density measurements was also supported by a direct band gap calculation associated with the frontier molecular orbitals using the Tauc plot. Hence, solvent polarity-induced self-assembly behavior with adjustable luminescence output and superior I-V characteristics of TPZn make it an exceptional candidate for organic electronic applications and electronic device fabrication.

Aromatic systems with two and three pyridine-2,6-dicarbazolyl-3,5-dicarbonitrile fragments as electron-transporting organic semiconductors exhibiting long-lived emissions.

The pyridine-3,5-dicarbonitrile moiety has gained significant attention in the field of materials chemistry, particularly in the development of heavy-metal-free pure organic light-emitting diodes (OLEDs). Extensive research on organic compounds exhibiting thermally activated delayed fluorescence (TADF) has led to numerous patents and research articles. This study focuses on the synthesis and investigation of the semiconducting properties of polyaromatic π-systems containing two and three fragments of pyridine-2,6-dicarbazolyl-3,5-dicarbonitrile. The compounds are synthesized by Sonogashira coupling reactions and characterized by steady-state and time-resolved luminescence spectroscopy. The compounds show efficient intramolecular charge transfer (ICT) from the donor to the acceptor. The photoluminescence (PL) spectra of the solutions of the compounds showed non-structured emission peaks in the visible region, which are attributed to ICT emission. The PL intensities of the solutions of the compounds are enhanced after deoxygenation, which is indicative of TADF. The photoluminescence quantum yields and TADF properties of the compounds are sensitive to the medium. Cyclic voltammetry measurements indicate good hole-blocking and electron-injecting properties due to their high ionization potentials. Photoelectron spectroscopy and time-of-flight measurements reveal good electron-transporting properties for one of the compounds. In general, polyaromatic π-systems with pyridine-3,5-dicarbonitrile fragments demonstrate promising potential for use in organic electronic devices, such as OLEDs.

Molecular Engineering of Rylene Diimides via Sila-Annulation Toward High-Mobility Organic Semiconductors.

The continuous innovation of captivating new organic semiconducting materials remains pivotal in the development of high-performance organic electronic devices. Herein, a molecular engineering by combining sila-annulation with the vertical extension of rylene diimides (RDIs) toward high-mobility organic semiconductors is presented. The unilateral and bilateral sila-annulated quaterrylene diimides (Si-QDI and 2Si-QDI) are designed and synthesized. In particular, the symmetrical bilateral 2Si-QDI exhibits a compact, 1D slipped π-π stacking arrangement through the synergistic combination of a sizable π-conjugated core and intercalating alkyl chains. Combining the appreciable elevated HOMO levels and reduced energy gaps, the single-crystalline organic field-effect transistors (SC-OFETs) based on 2Si-QDI demonstrate exceptional ambipolar transport characteristics with an impressive hole mobility of 3.0 cm2 V-1 s-1 and an electron mobility of 0.03 cm2 V-1 s-1, representing the best ampibolar SC-OFETs based on RDIs. Detailed theoretical calculations rationalize that the larger transfer integral along the π-π stacking direction is responsible for the achievement of the superior charge transport. This study showcases the remarkable potential of sila-annulation in optimizing carrier transport performances of polycyclic aromatic hydrocarbons (PAHs).

Dual Clay Nanobrick Wall Thin Films with High Oxygen Barrier at High Humidity

AbstractThin polymer‐based coatings with high oxygen barrier at elevated humidity are needed for the protection of food and organic electronic devices. Polyelectrolyte‐based thin films (deposited via layer‐by‐layer assembly) perform well at ambient humidity, but their performance typically dwindles as humidity increases due to their hydrophilic nature. Retention of their high barrier can be achieved through the addition of chemical crosslinkers or the introduction of inorganic platelets that create a nanobrick wall structure. In this study, a nanobrick wall barrier prepared with two types of clay, with a thickness less than 200 nm, is shown to reduce the oxygen transmission rate (OTR) of 179 µm polyethylene terephthalate to less than 0.016 cm3 m−2 day−1 atm−1. At 90% relative humidity (RH), a quadlayer barrier consisting of polyethylenimine, boehmite clay, poly(acrylic acid), and vermiculite clay maintains nearly 90% of its barrier performance at 0% RH (OTR = 0.019 cm3 m−2 day−1 atm−1). This study demonstrates the potential of dual clay thin film nanocomposites to protect various consumer goods at high humidity.

Hydrophilic Conjugated Polymers for Sustainable Fabrication of Deep‐Red Light‐Emitting Electrochemical Cells

AbstractIt is crucial to develop functional electronic materials that can be processed from green solvents to achieve environmentally sustainable and cost‐efficient printing fabrication of organic electronic devices. Here, the design and cost‐efficient synthesis of two hydrophilic and emissive conjugated polymers, TQ‐OEG and TQ2F‐OEG, are presented, which are rendered hydrophilic through the grafting of oligo(ethylene glycol) (OEG) solubilizing groups onto the thiophene‐quinoxaline conjugated backbone and thereby can be processed from a water:ethanol solvent mixture. The results show that the introduction of the OEG groups enables for a direct dissolution of salts by the neat polymer for the attainment of solid‐state ion mobility. These properties are utilized for the design and development of light‐emitting electrochemical cells (LECs), the active materials of which can be solution cast from a water:ethanol‐based ink. It is specifically shown that such an LEC device, comprising an optimized blend of the TQ2F‐OEG emitter and a Li salt as the active material positioned between two air‐stabile electrodes, delivers deep‐red emission (peak wavelength = 670 nm) with a radiance of 185 µW m−2 at a low drive voltage of 2.3 V. This study contributes relevant information as to how polymers and LEC devices can be designed and fabricated to combine functionality with sustainability.

Floating Film Transfer: A Facile and Cost-Effective Approach Towards Uniform Large Area Oriented Thin Films for Organic Electronic Devices

Floating Film Transfer: A Facile and Cost-Effective Approach Towards Uniform Large Area Oriented Thin Films for Organic Electronic Devices

High-Performance n-Type Polymeric Mixed Ionic-Electronic Conductors: The Impacts of Halogen Functionalization.

Developing high-performance n-type polymer mixed ionic-electronic conductors (PMIECs) is a grand challenge, which largely determines their applications in vaious organic electronic devices, such as organic electrochemical transistors (OECTs) and organic thermoelectrics (OTEs). Herein, two halogen-functionalized PMIECs f-BTI2g-TVTF and f-BTI2g-TVTCl built from fused bithiophene imide dimer (f-BTI2) as the acceptor unit and halogenated thienylene-vinylene-thienylene (TVT) as the donor co-unit are reported. Compared to the control polymer f-BTI2g-TVT, the fluorinated f-BTI2g-TVTF shows lower-positioned lowest unoccupied molecular orbital (LUMO), improved charge transport property, and greater ion uptake capacity. Consequently, f-BTI2g-TVTF delivers a state-of-the-artµC* of 90.2 F cm-1 V-1 s-1 with a remarkable electron mobility of 0.41 cm2 V-1 s-1 in OECTs and an excellent power factor of 64.2 µW m-1 K-2 in OTEs. An OECT-based inverter amplifier is further demonstrated with voltage gain up to 148V V-1 , which is among the highest values for OECT inverters. Such results shed light on the impacts of halogen atoms on developing high-performing n-type PMIECs.

Pyrazino[2,3-g]quinoxaline core-based organic liquid crystalline semiconductor: Proficient hole transporting material for optoelectronic devices

Hole transport materials (HTMs) have a significant impact on the effectiveness of organic electronic devices; therefore, we present a molecular architecture of pyrazino[2,3-g]quinoxaline (PQ10)-based room-temperature organic liquid crystalline semiconductor (OLCS) as an alternative HTM. The PQ10 compound exhibits three different rectangular columnar (Colr) phases offering an impressive hole mobility of 8.8 × 10−3 cm2V−1s−1 which is found to be dexterous than most of existing polymeric hole transport materials. The charge transport mechanism is governed by the hole polarons hopping through H-aggregates of the PQ10 molecules and the hole mobility remains nearly constant throughout the mesophase range, but it decreases with increasing applied electric field. The current-voltage characteristics of the PQ10 have also been investigated in all three Colr phases and explained via the Poole-Frenkel conduction mechanism. The dielectric spectroscopy has been eventually carried out to understand the nature of dielectric permittivity and conductivity as a function of temperature and a correlation is established between the molecular architecture of the Colr phases and aforementioned physical properties. Solar cell simulation has been additionally performed to demonstrate that the PQ10 material can be a better choice as HTM for organic electronics and photovoltaic applications.

Solvent Impact on Langmuir and Langmuir–Schaefer Films of Soluble Main‐Chain Poly(fullerene)s Based on C60

Understanding the morphology and electronic properties of poly(fullerene)s is crucial for the development of new organic devices. This work addresses the fabrication and characterization of Langmuir–Schaefer (LS) films of poly(fullerene)s based on C60 with short (HSS8) and long (HSS16) sidechains, solubilized in chloroform or xylene. In addition, density functional theory (DFT) calculations are used to optimize the molecular geometries, determine energies, and investigate the influence of solvent applied. Depending on the organic solvent, floating material isotherms indicate the formation of disordered aggregates in the aqueous subphase. The influence of solvent in LS films is also evidenced by way of atomic force microscopy (AFM), UV‐vis, and cyclic voltammetry (CV) measurements. From DFT calculations, the arms of the poly(fullerene)s start to extend from an initial position of surrounding the fullerene sphere. In AFM measurements, depending on the organic solvent, the roughness significantly reduces, while the homogeneity is much higher. In UV‐vis and CV measurements, the propensity to form aggregates depends mainly on the polarization of the solvent and is directly related to the maximum absorption, oxidation, and reduction peaks. From the optical bandgap energy values, the poly(fullerene)s studied here present high potential for application in organic electronic devices.

Extremely Stable Perylene Bisimide-Bridged Regioisomeric Diradicals and Their Redox Properties.

Excellent stability is an essential premise for organic diradicals to be used in organic electronic and spintronic devices. We have attached two tris(2,4,6-trichlorophenyl)methyl (TTM) radical building blocks to the two sides of perylene bisimide (PBI) bridges and obtained two regioisomeric diradicals (1,6-TTM-PBI and 1,7-TTM-PBI). Both of the isomers show super stability rather than the monomeric TTM under ambient conditions, due to the increased conjugation and the electron-withdrawing effects of the PBI bridges. The diradicals show distinct and reversible multistep redox processes, and a spectro-electrochemistry investigation revealed the generation of organic mixed-valence (MV) species during reduction processes. The two diradicals have singlet ground states, very small singlet-triplet energy gaps (ΔES-T ) and a pure open-shell character (with diradical character y0 =0.966 for 1,6-TTM-PBI and 0.967 for 1,7-TTM-PBI). This work opens a window to developing very stable diradicals and offers the opportunity of their further application in optical, electronic and magnetic devices.

Zinc phthalocyanine compound-based photo-electric organic shock-proof disposable flexible sensors

This research study introduces a multifunctional photo-electric sensor that utilises a semiconductor composite material and is implemented on a cellulose substrate. The flex electronic devices were manufactured using a rubbing-in technique that does not require energy. The investigation focused on using a compound consisting of zinc phthalocyanine and multi-walled carbon nanotubes (MWCNTs) as an active layer. However, aluminium top electrodes were utilized for photo-electric characterization, respectively. The surface type symmetry was designed to achieve disposable organic, shock-proof, and vibration-free electronic devices. They are then analyzed and characterized for their morphological and electrical parameters. The material structural analysis was performed with x-ray diffraction of materials, UV–Vis, photo luminance, Fourier-transform infrared spectroscopy, and for electrical characterization, the capacitance and impedance at varying ultra-violet (0–1300 W/cm), infrared (0–1580 W/m2), and frequency (0.1–200 kHz) were performed. Each parameter's influence is broken out in detail to illuminate the underlying physics of the results further. The results show that when Infrared intensity rises, impedance falls, whereas UV intensity increases. In the context of capacitance, it is observed that exposure to ultraviolet radiation leads to a decrease or increase in capacitance, while intensification of infrared light also results in a corresponding change in capacitance.Moreover, it can be observed that the sensitivity of electronic equipment exhibits a reduction when the frequency is increased. These devices have a wide range of applications, such as their use in food supply chains to safeguard food from the detrimental impact of high ultraviolet and infrared radiation on public health. They can also be employed in the medical industry for optical physiotherapy treatments and in universities for research purposes in countries that fall below the international poverty line, owing to their cost-effective fabrication technique.

Potential Application of Organic Electronics in Electrical Sensing of Insects and Integrated Pest Management towards Developing Ecofriendly Replacements for Chemical Insecticides.

Synthetic insecticides are widely used against plant pest insects to protect the crops. However, many insecticides have poor selectivity and are toxic also to beneficial insects, animals, and humans. In addition, insecticide residues can remain on fruits for many days, jeopardizing food safety. For these reasons, a reusable, low-cost electronic trap that can attract, detect, and identify, but attack only the pest while leaving beneficial insects unharmed could provide a sustainable, nature-friendly replacement. Here, for the first time, research results are presented suggesting the great potential and compatibility of organic electronic devices and technologies with pest management. Electrical characterizations confirm that an insect's body has relatively high dielectric permittivity. Adaptive memcapacitor circuits can track the impedance change for insect detection. Other experiments show that printed polymer piezoelectric transducers on a plastic substrate can collect information about the weight and activity of insects for identification. The breakdown voltage of most insects´ integument is measured to be <200V. Long channel organic transistors easily work at such high voltages while being safe to touch for humans thanks to their inherent low current. This feasibility study paves the way for the future development of organic electronics for physical pest control and biodiversity protection.

Recent Insights about the Role of Gels in Organic Photonics and Electronics.

This review article provides an in-depth exploration of the role of gels in the fields of organic electronics and photonics, focusing on their unique properties and applications. Despite their remarkable potential, gel-based innovations remain relatively uncharted in these domains. This brief review aims to bridge the knowledge gap by shedding light on the diverse roles that gels can fulfil in the enhancement of organic electronic and photonic devices. From flexible electronics to light-emitting materials, we delve into specific examples of gel applications, highlighting their versatility and promising outcomes. This work serves as an indispensable resource for researchers interested in harnessing the transformative power of gels within these cutting-edge fields. The objective of this review is to raise awareness about the overlooked research potential of gels in optoelectronic materials, which have somewhat diminished in recent years.

Progress of Polycyclic Boron-Doped Molecular Carbons

Molecular carbons, namely molecular cutout of carbon materials, are of importance for understanding accurate structures of carbon allotropes and developing functional π-electron materials. Doping the boron atoms into π-conjugated skeletons of molecular carbons enables the construction of boron-doped molecular carbons (BMCs), further leading to new chemistry and attractive material systems, which are distinct from carbon-based and other heteroatom-doped molecular carbons. Herein, the bottom-up organic synthesis methodologies have been employed to synthesize BMCs that feature the boron atoms at the edge or in the center of π-skeletons. They have not only amazing topological structures and good stability but also intriguing photophysical and electronic properties. Moreover, they have sufficient Lewis acidity and can coordinate with Lewis bases to form Lewis acid–base complexes, which exhibit stimuli-responsive functions. Notably, some of these BMCs can be utilized in the fields of organic reactions, optical and electronic devices, as well as supramolecular chemistry and photothermal materials. In this short review, we aim to highlight the design and synthetic strategies of polycyclic BMCs, and their unique physical properties and practical applications.